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This study presents a method for evaluating plastic properties and equi-biaxial residual stress (RS) simultaneously using the images of generated imprints in indentation tests and an artificial neural network (ANN). The ANN model is trained with data from finite element analysis (FEA) for establishing the relationship between material properties and the radial (ur) and vertical (uz) displacements resulting from indentation tests. To deal with the inherent noise in experimental data, an artificial random noise was added to the FEA data used for training the ANN model. By inputting parameters with artificial errors into the ANN model, the robustness of predicted values against potential testing errors was examined. Also, the accuracy of the predicted residual stresses and material properties from ANN are validated using tensile tests and indentation tests on the stress-induced specimens.

In this work, a double hollow cylinder with a joint region, representative of nozzles, pipe systems, valves, or pressure regulators, was chosen to measure and simulate its 3D residual stress (RS) distribution. The part was printed by Laser-Powder Bed Fusion (L-PBF) using commercial 316L steel powders, and a mapping of residual stress along the joint cross-section was measured at three geometrical sample directions. The distribution of RS in the printed part was not homogeneous, showing important gradients of about ±1200 με from the inner to the outer surface of the wall, as well as along the building direction, translated into an equivalent Von Mises stress gradient up to 400 MPa towards the inner surface. After heat treatment only axial strains are significantly affected and relieved 200 με in average, but not necessarily in a homogeneous manner. The comparison of the Von Mises equivalent stress against available simulation tools based on mechanical and thermomechanical models concluded that although these models succeeded in the benchmarking of total macroscopic distortion of components, they do not capture the asymmetric distribution of RS within the bulk in end-use complex geometries and/or joints and those should be implemented from the microstructural level.

[Display omitted] • TiC-based self-healing coatings was prepared on AISI 321 stainless steel by plasma spraying. • The resistances to oxidation and thermal shock of 321 steel could be improved by the prepared self-healing coating. • An improved thermal shock life model based on the Paris law crack propagation model was developed. • The coating failure was mainly attributed to the increasing internal residual stress caused by thickening of TGO. The AISI 321 steels of structural components serviced at high temperature are usually subjected to oxidation and thermal shock damage during service. Therefore, to improve their high-temperature oxidation and thermal shock resistance, the self-healing coating consisting of Al 2 O 3 -13 %TiO 2 layer, TiC layer and NiCrAlY layer was prepared for 321 steels in this work. The experimental and microstructural characterization results showed that the thermal shock resistance of such self-healing coating was remarkably improved as compared to the counterpart double-AT13 coating. This is because the volume increment resulting from the oxidation reaction between the TiC and oxygen decreased the porosity of the self-healing coating and retarded crack growth, which also led to the improved high-temperature oxidation resistance. Further, a thermal shock life model based on the crack growth model of Paris formula were developed. The modeling results not only agreed well with the experimental results but also indicated that thickening of thermal grown oxide (TGO) is the main cause of crack initiation and growth. [ABSTRACT FROM AUTHOR]

The Powder Bed Fusion-Laser Beam/Metals (PBF-LB/M) is a promising additive manufacturing process that can be used to directly produce functional components with a complex shape for a wide variety of applications. However, the layer-by-layer scanning and high cooling rates result in a high thermal gradient and thus, in thermally induced stresses. The stresses developed during the additive process could lead to undesirable cracking and delamination phenomena that can seriously affect the performance of the final component. The alloy composition can exacerbate crack and delamination formation, however, the need to expand the portfolio of high-strength materials processable for PBF-LB/M makes the resolution of these undesirable phenomena a primary challenge in the additive manufacturing field. This works aims to systematically investigate some strategies to make processable non-standard compositions. As no standard compositions, the promising pre-alloyed AlSi10Cu8Mg composition was chosen for the present work. Based on the results obtained from a condition of severe delamination, the synergetic use of appropriate process parameters and support structures can lead to crack-free and fully dense specimens also when platform heating is not allowed. The developed approach could also be applied to adapt other cracking-sensitive alloys for PBF-LB/M production.

[Display omitted] • Propose a Cryogenic Minimum Quantity Lubrication and Ultrasonic Rolling Strengthening hybrid process for blade. • Reveal the formation mechanism of grain refinement on the TC4 blade surface. • Form a 2.1 mm nanocrystalline layer and a 3.7 mm reinforced layer on the blade surface. This study proposes a hybrid process method based on Cryogenic Minimum Quantity Lubrication and Ultrasonic Rolling Strengthening Process (CMQL-URSP) to improve the surface integrity and enhance the mechanical properties of blade surface. First, the principle of the CMQL-URSP hybrid process was described. Second, the TEM experiments were conducted to clarify the influence of the CMQL-URSP hybrid process on aircraft engine blades. Finally, the blade processing experiments were performed to demonstrate the effectiveness of the CMQL-URSP hybrid process on the blade surface micro-morphology, micro-hardness and residual stress. The results indicate that the CMQL-URSP hybrid process effectively overcomes the limitations inherent to the solitary application of URSP. The CMQL process inhibits work hardening, thereby allowing the URSP to achieve better low-plastic surface improvement. Grain refinement governed by the continuous dynamic recrystallization mechanism leads to the formation of nanocrystals, which significantly improves mechanical properties of blade surface. The CMQL-URSP hybrid process results in a reduction in surface roughness from Ra 2.644 μm to Ra 0.055 μm, an increase in surface residual compressive stress from 321 MPa to 657 MPa, and the formation of a reinforced layer with a depth of 3.7 mm on the blade, thereby enhancing the surface integrity of the blade. [ABSTRACT FROM AUTHOR]

[Display omitted] • FSPed steel surfaces are alloyed with WC tool constituent elements and strengthened via solid solution and grain refinement hardening. • Compressive residual stresses are applied and peak at Ms of 150 °C on the alloyed steel surfaces. • Retained austenite formed by lowering Ms below 150 °C results in the application of tensile residual stresses. • Deformation-induced martensitic transformation of retained austenite improves tensile and fatigue properties. Friction stir processing (FSP) effectively improves the fatigue strength of arc-welded joints; however, wear of tools is inevitable in case of high-strength materials. Notably, a new benefit has been discovered: compressive residual stress is applied on the FSPed steel surface, alloyed with the WC tool constituent elements, contrasting with the tensile residual stress typically applied via conventional FSP. To elucidate the mechanism of compressive residual stress application, FSP was performed on a low-carbon steel plate at various rotational speeds. The alloyed topmost layers in the stir zone comprised martensite structures with a small amount of retained austenite grains, resulting in a hardness increase owing to the tool constituent elements. The residual stresses on the stir zone surface were influenced by the alloying contents and the corresponding martensite start temperature (Ms). Compressive residual stresses were maximized at an Ms of approximately 150 °C owing to martensitic transformation expansion near room temperature. Lowering the Ms below approximately 150 °C led to tensile residual stresses and an increased volume fraction of the retained austenite, suggesting that martensitic transformation expansion is insufficient to apply compressive residual stress. Conversely, the retained austenite can resist plastic deformation and crack propagation through deformation-induced martensitic transformation, thereby enhancing fatigue properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • The existence of a textured heterogeneous microstructure at the millimetric scale of a WAAM material is observed via optical observations and Electron BackScatter Diffraction. • The existence of deformation field heterogeneities under uniaxial tension in the plastic domain of a WAAM material is observed via Digital Image Correlation. • The existence of stress field heterogeneities under uniaxial tension in the elastic domain of a WAAM material is observed via Thermoelastic Stress Analysis. • The observed mechanical field heterogeneities are compared and linked to the microstructural heterogeneities. Wire and Arc Additive Manufacturing (WAAM) is particularly well suited to the fabrication of large-scale structural components. Its use for the deposition of Duplex Stainless Steel (DSS) structures is especially sought upon by the naval industry. Although additively manufactured materials usually come with heterogeneous microstructure, residual stresses, internal and surface defects that must not jeopardize the structural integrity of components. In this context, the present study aims to analyse the as-deposited microstructure of a WAAM DSS and its influence on the mechanical behaviour via mechanical field measurement using both Digital Image Correlation (DIC) and Thermoelastic Stress Analysis (TSA). [ABSTRACT FROM AUTHOR]

[Display omitted] • Production of graded microstructures by laser powder bed fusion. • Texture and residual stress control by scan strategy variation. • Characterization of the microstructure gradient at scan strategy interfaces. • Alignment of residual stress and scan direction for 90° interlayer rotation. • 67° interlayer rotation promotes formation of a transverse isotropic stress state. Additive manufacturing techniques, such as laser powder bed fusion (PBF-LB), are well known for their exceptional freedom in part design. However, these techniques are also characterized by the development of large thermal gradients during production and thus residual stress (RS) formation in produced parts. In this context, neutron diffraction enables the non-destructive characterization of the bulk RS distribution. By control of the thermal gradients in the powder-bed plane by scan strategy variation we study the impact of in-process scan strategy variations on the microstructure and the three-dimensional distribution of RS. Microstructural analysis by means of electron backscatter diffraction reveals sharp microstructure transitions at the interfaces ranging from 100-200 µm. The components of the RS tensor are determined by means of neutron diffraction and the principal stress directions and magnitudes are determined by eigenvalue decomposition. We find that the distribution of RS in the powder-bed plane corresponds to the underlying scan strategy. When the alternating scan vectors align with the x- and y sample coordinate axes, the principal stress directions co-align. In the present geometry, nearly transverse isotropic stress states develop when the scan vectors are either aligned 45° between x and y or continuously rotated by 67° between each layer. [ABSTRACT FROM AUTHOR]

Direct comparisons are made between the crystallographic texture and residual stress distribution within two otherwise identical Inconel cubes produced by Selective Laser Melting (SLM) and Electron Beam Melting (EBM) additive manufacturing processes. In both respects, significant differences were observed; the SLM process produced a sample with high residual stress and cubic texture, while the EBM process generated negligible residual stress and a fibre texture. In the case of the SLM sample, the paper continues on to examine two different approaches to modelling the residual stress field; 1. a simplistic version based on an assumed radially symmetric isotropic eigenstrain, and 2. a layer-by-layer combined thermo-mechanical approach based on finite element modelling. Both models were able to capture the important overall features of the residual stress distribution, however the layer-by-layer approach showed more fidelity in the finer details. • Residual stress and crystallographic texture from two 3D printing processes for inconel-718 samples are compared (SLM vs EBM). • Significant residual stresses up to yield are observed from SLM while EBM produced no detectable residual stress. • SLM and EBM produced very different texture; 'Goss' texture in the SLM sample, fibre texture in the EBM sample. • Two residual stress modelling approaches were compared; 1. An empirical model, and 2. A mechanistic layer-by-layer approach. • Both models captured the overall distribution of stress; the layer-by-layer showed more fidelity to small details. [ABSTRACT FROM AUTHOR]

[Display omitted] • Utilizes machine learning models to subtly enhance the automation and optimization of laser shock peening parameters for nickel-aluminium bronze surfaces. • Achieves a distribution of residual compressive stress in areas prone to residual stress holes. • Achieves compressive stresses up to 472 MPa, significantly reducing design iterations. • Offers a novel method for the efficient design of complex residual stress fields in LSP model. Laser Shock Peening (LSP) is an advanced technique for enhancing surface properties, drawing significant interest for its ability to induce beneficial residual stresses in materials. Traditional LSP design processes, reliant on manual parameter selection, often result in imprecise control over the stress distribution, necessitating multiple iterations and high costs. This study introduces a machine learning (ML)-based approach, utilizing the Random Forest (RF) algorithm, to automate and optimize the design of LSP parameters for nickel-aluminium bronze surfaces. Our findings demonstrate the RF model's capability to accurately predict and optimize residual stress distributions, achieving compressive stresses up to 472 MPa with a notable reduction in design iterations. The model forecasts both uniform and non-uniform stress patterns, particularly identifying areas susceptible to Residual Stress Holes (RSH) with improved precision. With an Absolute Percentage Error (APE) of only 6.2 %, our approach significantly outperforms traditional ML algorithms, offering a novel method for efficiently designing complex residual stress fields in LSP applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • The solid-state transformation of yttria stabilized zirconia in the brazed joint was induced by the decreasing temperature and its caused residual stress. • The addition of yttria stabilized zirconia in the brazed joint contributed to the change of reaction layer from single structure to composite structure. • The yttria stabilized zirconia particles obviously reduced the residual stress in the joint by controlling the thermal mismatch and absorbing stress energy. Residual stress is the main hindrance to achieve a robust ceramic/metal brazed joint. In this study, yttria stabilized zirconia (YSZ) particles was fabricated into solid-state transformation composite filler, which was proposed as a new strategy to strengthen Ti 3 SiC 2 /Cu brazed joint. After detailed characterization conducted on YSZ particles and brazed joint, the abnormal expansion properties of YSZ and its strengthening brazed joint mechanism were clarified. The content of Y 2 O 3 in YSZ had significant effects on the phase transformation of ZrO 2 from tetragonal to monoclinic. When 3 mol.% Y 2 O 3 was added, the maximum phase transformation occurred at about 500 ◦C, half of brazing temperature, during the cooling process. The phase transformation of ZrO 2 effectively released residual stress in the joint, which was induced by both temperature changes and residual stress. The abnormal volume expansion during phase transformation decreased the thermal mismatch of brazed joint further to strengthen brazed joint. [ABSTRACT FROM AUTHOR]

Process parameters in laser-based powder bed fusion (LBPF) play a vital role in the part quality. In the current study, the influence of different novel scan strategies on residual stress, porosities, microstructure, and crystallographic texture has been investigated for complex L-shape parts made from nickel-based superalloy Inconel 718 (IN718). Four different novel scanning strategies representing total fill, re-melting, and two different sectional scanning strategies, were investigated using neutron diffraction, neutron imaging, and scanning electron microscopy techniques. These results were compared with the corresponding results for an L-shape sample printed with the conventional strategy used for achieving high density and more uniform crystallographic texture. Among these investigated novel strategies, the re-melting strategy yielded approximately a 25% reduction in surface residual stress in comparison to the reference sample. The other two sectional scanning strategies revealed porosities at the interfaces of the sections and due to these lower levels of residual stress were also observed. Also, variation in crystallographic texture was observed with different scan strategies.

[Display omitted] • Significant improvement in fatigue is observed after applying both aging and shot peening treatments on 17-4PH MEX. • For as-sintered 17-4PH, Al 2 O 3 dominates at high cycle, while other surface inhomogeneities dominate at low cycle regimes. • For unpeened 17-4PH, aging increases tensile strength and hardness, but does not affect fatigue properties. Material extrusion additive manufacturing (MEX) gains increasing interest due to its cost-effectiveness. However, concerns arise regarding inherent MEX characteristics potentially affecting mechanical properties. This study investigates the effects of shot peening and heat treatment on MEX 17-4PH stainless steel. After shot peening, surface nanocrystalline and compressive residual stress are induced. Aging results in higher hardness and tensile strength with lower elongation, while shot peening results in higher surface hardness with minimal change in elongation. For fatigue properties of as-sintered specimens, Al 2 O 3 particle contamination dominates at high cycle regimes, while other MEX surface inhomogeneities dominate at low cycle regimes. Furthermore, as-aged properties are dominated by all surface inhomogeneities, resulting in the non-improvement of fatigue performance compared to the as-sintered specimens. However, shot peening on the as-sintered specimens significantly enhances fatigue properties through the formation of surface nanocrystalline structures and the induction of compressive residual stress, albeit with the occurrence of wrapped corners acting as fatigue crack initiation sites. Remarkably, the combination of aging and shot peening yields the most improvement in fatigue performance, exhibiting behaviours akin to as-sintered specimens with shot peening but without the generation of wrapped corners. Instead, fatigue crack initiation sites shift to subsurface region's inhomogeneities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Machine learning coupled with infrared modality is a practical approach to detecting heat accumulation in real time. • Heat accumulates at thermal concentration spots around interior features and at thin walls. • A scan strategy with optimum stripe angle and scan vector lengths can mitigate local hot spots. • Considering the design features in the execution of a laser scanning strategy can significantly improve thermal uniformity. • Local heat accumulation is linked to porosity formation at part edges. Metal additive manufacturing is associated with thermal cycles of high rates of heating, melting, cooling, and solidification. Some areas within the build experience thermal cycles that depend on the paths of the energy source. Additionally, geometrical features, such as thin walls and overhangs, can lead to heat accumulation, potentially affecting the microstructure, fatigue life, and induced residual stresses that may lead to dimensional distortion and cracking. The identification of significant heat accumulation can be used for part quality monitoring to inform the design process, enhance the quality of printed parts, and optimize the process parameters. This study aims to efficiently identify heat accumulation with affordable in-situ infrared imaging for further characterization and mitigation to enhance the quality of printed parts. A computational framework employing machine learning is developed to identify zones of local heat accumulation in real time. The effectiveness of this approach is demonstrated by experiments conducted on a build with a wide variety of geometrical features. In addition, characterization and detailed analyses of detected local heat accumulation zones are provided. [ABSTRACT FROM AUTHOR]

[Display omitted] • Quasi-static compressions of Ti6Al4V novel 2D auxetic lattices fabricated by PBF-EB. • ATC and TLR structures outperformed double DAH lattice structures in SEA. • Residual stresses are in the order of DAH > TLR > ATC, inversely correlating with SEAs. • TLR fabricated at high-speed scan exhibited small fluctuations in SEA. The metal-based 2D auxetic lattice structures hold the potential for multifunctional tasks in aerospace applications. However, the compression response of those manufactured by powder bed fusion process is underexplored. This study proposes a comprehensive comparison of in-plane quasi-static compression performance of 2D auxetic lattice structures, utilizing three designs (anti-tetrachiral (ATC), double arrow-headed (DAH), and tree-like re-entrant (TLR)), manufactured with stiff Ti6Al4V by the electron beam powder bed fusion process (PBF-EB) with various manufacturing speeds. The results revealed unique failure patterns and superior energy absorptions among 2D lattice structures in the literature. TLR design enhanced energy absorption by overcoming failures between DAH columns and exhibited the lowest standard deviations in specific energy absorption (SEA) values (9.75 %–12.62 %). Besides, Kernel average misorientation (KAM) values followed the order of DAH, TLR, and ATC, and inversely correlated with SEA values. ATC structures with the lowest KAM outperformed DAH and TLR by 47.5 % and 6.44 %, respectively. Scan speed variations affected SEA and porosity values differently for each lattice design while exhibiting similar microstructure characteristics. The findings in this study propose a significant contribution to the development of aerospace sandwich structures where harsh environments exist and employment of 2D topologies are required. [ABSTRACT FROM AUTHOR]

This paper proposes a strategy to optimize the design of the substrate structures used in Additive Manufacturing (AM) by Directed Energy Deposition (DED) to minimize the residual stresses induced by this fabrication process. To this end, several numerical analyses were performed to analyse different substrate designs in order: (i) to reduce the sensitivity to the initial non-steady stage when the first layers of material are deposited, (ii) to optimize the heat flux through the substrate to reduce the Maximum Temperature Gradients (MTG) and, (iii) to modify the substrate stiffness and its mechanical constraining to the thermal deformations during the building process and the cooling phase. To ensure the reliability of the numerical simulations, an in-house software is calibrated to allow for an accurate analysis of DED. Thus, an experimental setting is undergone to feed the numerical model with suitable values of both material and process parameters through temperature and displacement measurements and numerical fitting. Once calibrated, the software is used to evaluate the performance of several substrate designs to mitigate the residual stresses induced by the DED process. A thin-walled rectangular part selected as industrial demonstrator showed a significant reduction (up to 62%) of the maximum tensile stresses.

Superlattice (SL) thin films composed of refractory ceramics unite extremely high hardness and enhanced fracture toughness; a material combination which is often mutually exclusive. While the hardness enhancement is well described by existing models based on dislocation mobility, the underlying mechanisms behind the increase in fracture toughness are yet to be unraveled. Here, we provide a model based on linear elasticity theory to predict the fracture toughness in (semi-)epitaxial nanolayers. As representative of cubic transition metal nitrides, a TiN/CrN superlattice structure on MgO (100) is studied. The density of misfit dislocations is estimated by minimizing the overall strain energy, each time a new layer is added on the nanolayered stack. The partly relaxed coherency stresses are then used to calculate the apparent fracture toughness (Kapp) by applying the weight function method. The results show that Kapp increases steeply with increasing bilayer period for very thin SLs, before the values decline more gently along with the formation of misfit dislocations. The characteristic Kapp vs. bilayer-period-dependence nicely matches experimental trends. Importantly, all critical stress intensity values of the SLs clearly exceed the intrinsic fracture toughness of the layer materials, evincing the importance of coherency stresses for increasing the crack growth resistance.

Orthotropic steel decks (OSD's) are susceptible to fatigue failure due to cyclic loading. Often fatigue cracks are found in the joint between the deck plate and the trough. Due to the welding process, residual stresses are present in and around the joint. In this paper, the effect of residual stresses on the fatigue crack propagation rate has been evaluated. First, a FE model has been made to predict and validate the residual stress field of the OSD due to welding. The validation of residual stresses is made comparing measured data at the surface of the OSD and over the thickness of the deck flange. The residual stresses are used to subsequently model for a crack propagation analysis based on extended finite element method (XFEM). The fatigue crack simulation including residual stress field shows good correlation compared to the experimental data, while the simulation without residual stress field shows less correlation. The effects of the residual stresses are relatively large as the tensile transversal residual stresses increase the crack propagation, while the tensile longitudinal residual stresses decrease the crack propagation rate. The optimal modelling of the component of residual stresses is investigated.

Alloy 718 is a nickel-based superalloy that is widely used as a structural material for high-temperature applications. One concern that arises when Alloy 718 is manufactured using powder bed fusion (PBF) is that residual stresses appear due to the high thermal gradients. These residual stresses can be detrimental as they can degrade mechanical properties and distort components. In this work, residual stresses in PBF built Alloy 718, using both electron and laser energy sources, were measured by neutron diffraction. The effects of process parameters and thermal post-treatments were studied. The results show that thermal post-treatments effectively reduce the residual stresses present in the material. Moreover, the material built with laser based PBF showed a higher residual stress compared to the material built with electron-beam based PBF. The scanning strategy with the lower amount of residual stresses in case of laser based PBF was the chessboard strategy compared to the bi-directional raster strategy. In addition, the influence of measured and calculated lattice spacing (d0) on the evaluated residual stresses was investigated.

Inductive surface hardening processes are widely used in the manufacturing of automotive parts. They combine short process times with high economic and energy efficiency. Because of their high surface hardness, induction hardened steel parts feature beneficial wear resistance and also good fatigue properties due to the induced compressive residual stresses in the surface. Considering the positive effects on the mechanical properties by creating a bainitic-martensitic microstructure, outlined by severel authors, this study includes the implementation of a temperature controlled inductive surface hardening process on a conventional hardening machine. Therefore an innovative inductor design, which allows a controlled sample cooling is presented. Supported by dilatometric studies as well as different heat treatment strategies, limitations are identified to gain a profund process understanding. Hereby an accelerated bainite formation after short time austenitization is detected. By using different heat treatment strategies, the fraction of the bainitic phase can be adjusted in the surface of the part made of AISI 4140. The results of this innovative heat treatment method are compared to short time inductive hardening and tempering processes regarding microstructure, hardness and residual stresses. The generated surface layer states, including mixed microstructures, show promising properties resulting in a possible enhancement of the fatigue strength of induction hardened parts.

The current study investigates the effects of a wide range of process parameters on three part properties; density, surface roughness, and surface residual stresses simultaneously for selective laser melting of Inconel 718. In addition to the lack of investigations on surface roughness and residual stresses in selective laser melting of Inconel 718, process maps were developed for the selection of the best process parameters to achieve the desired values for the three parameters combined. Five laser powers, six scan speeds and three hatch spacings were chosen from the stable single tracks tests. Based on each property, a 99.5% density or a 2 μm surface roughness or the least surface tensile residual stress of 248 MPa were possible. However, no single process parameter combination was able to achieve good values for all three parameters. Prioritizing density and surface roughness, being crack initiators, over residual stresses for their effect on fatigue failure, it was found that 99.2% density and relatively low roughness of 3.5 μm are feasible at 320 W, 600 mm/s and 0.12 mm hatch spacing. Finally, opposite to the commonly observed columnar grain in Inconel 718, mixed grain structure was obtained at 600 mm/s and 1000 mm/s, indicating reduced anisotropy.

[Display omitted] • The synergistic enhancement of multiple reinforcing mechanisms makes the composites have excellent properties. • The interface structure is regulated and optimized. • The impact of residual stress on composite materials is elucidated. This paper presents a new fabrication method utilizing lost foam casting as a processing technique to synthesize high-strength and ultra-wear-resistant particle reinforced iron matrix composites. The composite material incorporates large-sized WC-11Co reinforcement. The composite exhibits a multiphase microstructure composed of WC-11Co, α-Fe, and carbide precipitates that extend at different length scales. The precipitation of large-sized M3W3C (M = Fe, Co) type carbides at the WC-11Co/matrix interface is well controlled. A favorable reaction layer is formed between WC-11Co and the matrix. Nano-precipitates are pinned within the reaction layer, exhibiting a high degree of coherence with the iron matrix. The stress field at the interface is complex due to thermal stress, phase transformation stress, and microstress. The stress state between WC-11Co and the matrix consists of compressive residual stress-tensile residual stress-compressive residual stress, with compressive residual stress far exceeding tensile residual stress. The WC-11Co/Fe0.35C5CrMn composite exhibits outstanding compressive strength of 2.18 GPa and a fracture strain of approximately 24.6 %. Moreover, the composite demonstrates excellent wear resistance, with a threefold improvement compared to the matrix under severe wear conditions. The following mechanisms contribute to the enhanced mechanical properties: multiphase material system, coherent multiscale interfaces, grain refinement, dislocation strengthening, and residual stress strengthening. [ABSTRACT FROM AUTHOR]

[Display omitted] • An indentation technique is proposed for the simultaneous evaluation of material properties and residual stresses. • The indentation horizontal displacement field, indentation depth, and imprint size are used as inverse parameters. • The range for in-plane displacement field ensuring the identifiability of inverse solution is suggested via identifiability analysis. • The ANN model evaluating the material properties is constructed using data from indentation FEA. • The evaluated material properties from ANN are verified by comparing them with those from a tensile test. This study presents a method for evaluating plastic properties and equi-biaxial residual stress (RS) simultaneously using the images of generated imprints in indentation tests and an artificial neural network (ANN). The ANN model is trained with data from finite element analysis (FEA) for establishing the relationship between material properties and the radial (u r) and vertical (u z) displacements resulting from indentation tests. To deal with the inherent noise in experimental data, an artificial random noise was added to the FEA data used for training the ANN model. By inputting parameters with artificial errors into the ANN model, the robustness of predicted values against potential testing errors was examined. Also, the accuracy of the predicted residual stresses and material properties from ANN are validated using tensile tests and indentation tests on the stress-induced specimens. [ABSTRACT FROM AUTHOR]

[Display omitted] • The negative linear correlation between phase transition temperature and grain size of t-ZrO 2 was established. • t-ZrO 2 achieves phase stability, which cannot occur martensitic transformation when grain size below the critical size. • The dislocation tangle and interfacial cohesion enhance the stability of t-ZrO 2. In this work, the trade-off between transformation toughening of ZrO 2 /TiO 2 ceramic coatings and low temperature (293.15 K∼203.15 K) was achieved by adjusting the grain size of t-ZrO 2 (d t - Z r O 2 ). A negative correlation between d t - Z r O 2 and phase transition temperature (M s) was also established based on strain energy and chemical free energy in ZrO 2 /TiO 2 ceramic coatings. Interestingly, t-ZrO 2 grains lost toughening effects when the d t - Z r O 2 reaches the critical size (20 nm) even under cooling and stress. This is attributed to the number of dislocations per unit volume increases 1.5 times with the d t - Z r O 2 decreases from 40 nm to 20 nm, which aggravates the lattice distortion and dislocation tangle and leads to the fracture toughness increases by 32.5% at 203.15 K. Therefore, the interfacial cohesion of the semi-coherent interface between (0 1 1) t-ZrO 2 and (1 1 0) TiO 2 was enhanced and t-ZrO 2 was completely stabilized when d t - Z r O 2 reaches critical size. This work elucidates the effect of size effect on M s and provides a reference for transformation toughening of ceramic coatings at cryogenic temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • A hybrid finite element model of the arc-based directed energy (ADED) deposition hybrid inter-layer hammering is constructed for the first time. • Studying the reduction of two kinds of hammering strategies on residual stress in cross-structure. • Compared to the cross-structure constructed by ADED alone, the residual stress reduction of the cross-structure is 76.2 % (from 164 Mpa to 39 Mpa) under the intervention of inter-layer hammering. • Described the phenomenon of "stress self-relief" and explained its mechanism based on the evolution of stress and strain. Using arc-directed energy deposition (ADED) to manufacture parts with cross-structures is common in the aviation field. Inter-layer hammering with lower load demand has proved to be a promising technology to improve the microstructure and mechanical properties. At present, the residual stress (RS) evolution mechanism during inter-layer hammering hybrid ADED of the crosse-structures is not clear. In this study, a finite element model for inter-layer hammering hybrid ADED is developed to simulate two distinct hybrid manufacturing strategies for cross-structure: Alternating Inter-layer Hammering (AIH) and Complete Inter-layer Hammering (CIH). The accuracy of the hybrid model has been validated through assessments of thermal history, residual stress (RS), and warping. The hammering-introduced tensile plastic strain mitigates the compressive plastic strain caused by the cross-structure shrinkage during the deposition process and then reduces the tensile stress. The "Stress self-relief" helps to reduce the magnitude of stress under the CIH. Compared to the cross-structure manufactured by ADED alone, the stress at the cross-position is reduced to 79 Mpa and 39 Mpa under AIH and CIH strategies, respectively, from an initial 164 Mpa. Additionally, both of the two hammering strategies eliminate warping in the crosse-structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • The stress-free d 0 was determined utilizing the RS measurement itself. • The maximum compressive RS was obtained as the phases composed by α′-bcc and γ-fcc with the same fraction of 50%. • The compressive RS was attributed to the type II intergranular RS. • The compressive RS arose from the α′-bcc formed directly from the γ-fcc matrix. The strain-induced martensitic transformation (α′-martensite) and residual stress (RS) introduction in the gradient nanostructured (GNS) austenitic stainless steel have been extensively reported in the last three decades, however, their correlation is still unclear. Here, the XRD, EBSD, ECCI and TEM were used to study the RS distribution and martensite behaviors in a GNS SS304 fabricated by ultrasonic surface nanocrystallization modification. We found the non-linear relationship between the magnitude of RS and the fraction of α′-martensite due to the role of α′-martensite in the development of type II intergranular RS. The maximum compressive RS of about 1,244 MPa was obtained as the γ-austenite and α′-martensite phases were each at approximately 50 %. Otherwise, the RS would decrease with the second phase fraction. The developed maximum compressive RS arises from the α′-martensite that formed directly from the γ-austenite. By contrast, the RS from other deformation structures, i.e., α′-martensite produced by γ → ε → α′, ε-martensite, nanotwin and dislocations, is relatively low. The current study classified the correlation of RS and the role of martensite for the first time, which may inspire new approaches for improving the fatigue properties of materials by controlling the phase fraction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Steel-nickel bimetallic component was fabricated by using wire-arc directed energy deposition using criss-crossed path. • The crack easily occurred at the bimetallic interface near nickel side due to stress concentration and microstructural evolution. • The carbide precipitation could induce high dislocation density that is related to crack initiation. Steel-nickel bimetallic structures exhibit attractive site-specific properties, but it is challenging to fabricate large a monolithic component while maintaining the dense regular interface that enable their properties. This study proposed a criss-crossed interface in steel (316L stainless steel) – nickel (IN 718 alloy) bimetallic component, with in-situ microstructure interlocking and improved mechanical response. A difference in physical properties between these two materials creates cracks at their interface where were fully explored using metallographic examination and numerical simulation. It is found cracks easily occur at their interface near nickel side due to alternate thermal cycles that lead to a variation in residual stress and microstructure, including grain orientation, texture strength, dislocation density and Schmid factors. The research outcomes enable better understanding of crack initiation mechanism in bimetallic structures printed by arc-based metal additive manufacturing and may advance the design and fabrication of advanced structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 316L near-net-shape double hollow cylinder with a joint region component was fabricated by Laser Powder Bed Fusion. • Gradients of residual stresses in the printed part were compared to mechanical and thermo-mechanical model simulations. • The evolution of microstructure and residual stress distribution was studied after printing and 2 h/700 °C of heat treatment. In this work, a double hollow cylinder with a joint region, representative of nozzles, pipe systems, valves, or pressure regulators, was chosen to measure and simulate its 3D residual stress (RS) distribution. The part was printed by Laser-Powder Bed Fusion (L-PBF) using commercial 316L steel powders, and a mapping of residual stress along the joint cross-section was measured at three geometrical sample directions. The distribution of RS in the printed part was not homogeneous, showing important gradients of about ±1200 με from the inner to the outer surface of the wall, as well as along the building direction, translated into an equivalent Von Mises stress gradient up to 400 MPa towards the inner surface. After heat treatment only axial strains are significantly affected and relieved 200 με in average, but not necessarily in a homogeneous manner. The comparison of the Von Mises equivalent stress against available simulation tools based on mechanical and thermomechanical models concluded that although these models succeeded in the benchmarking of total macroscopic distortion of components, they do not capture the asymmetric distribution of RS within the bulk in end-use complex geometries and/or joints and those should be implemented from the microstructural level. [ABSTRACT FROM AUTHOR]

Abstract Laser deposition strategies can have significant effect on the temperature distribution for multi-bead multi-layered additive manufacturing. Its influence on thermal field will affect the induced residual stress and distortion. In this paper, a computationally efficient numerical model for Laser Aided Additive Manufacturing (LAAM) process was developed for evaluating deposition strategies and understanding how their dynamic temperature evolution can cause significant differences in the residual stress and distortion. The numerical model was calibrated with experimental clad bead dimensions and process parameters for depositing multi-bead SS316L onto the substrate of the same material. The numerical model was validated with experimental results for depositing a rectangular clad layer on a 3 mm thick substrate using Zigzag strategies along the width (x-axis) and length (y-axis) directions. Temperature field measurements using infrared camera and X-ray diffraction residual stress field measurements agreed well with numerical results. The predicted residual stress field showed that the approximately 2.3 times larger distortion along the y-axis direction in width-wise Zigzag scanning is caused by non-uniform stress distribution in the y-axis direction. However, width-wise Zigzag scanning leads to more homogeneous stress distribution in the x-axis and therefore lower distortion in the x-axis direction compared to length-wise Zigzag scanning. Graphical abstract Unlabelled Image Highlights • A computationally efficient method was developed to consider influence of scanning patterns in LAAM process. • A continuous computational domain and material property activation scheme was developed to simulate deposition. • Effects of scanning patterns on thermo-mechanical distribution and distortion were demonstrated. • Correlation between residual stress and distortion magnitudes for different scanning patterns were established. [ABSTRACT FROM AUTHOR]

Path pattern is one of the most significant parameters in the additive manufacturing (AM) process because it influences the specimen's final shape and residual stress distribution. Generally, the optimal path pattern is a computationally expensive, high-dimensional, and black-box permutation optimization problem. In this paper, we propose a combinatorial radial basis function surrogate-assisted genetic algorithm (CRBF-GA) to effectively generate the optimal path pattern by integrating the combinatorial radial basis function surrogate model (CRBF) with the genetic algorithm (GA). To demonstrate the effectiveness of the proposed CRBF-GA, a Ti-6Al-4V thin rod, a component of lattice, is chosen as the research object. Through numerical simulation, experimental verification, and error comparison analysis, the RBF-GA pattern is demonstrated to be the best path pattern among the random forest-assisted evolutionary algorithm (RF-EA), GA, spiral, and zigzag patterns, and it excels in achieving a more precise rod shape compared to the other patterns examined. • Proposed irregular discretization enhances the fitting accuracy of structural boundaries. • Developed combinatorial surrogate-assisted genetic algorithm solves the expensive permutation optimization problem. • Results affirm the accuracy of the proposed method in forming Ti-6Al-4V thin rods. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fracture behaviour of BaTiO3 thin film attached to different substrates were studied using microcantilever facture experiments. • These experiments revealed a significant effect of the substrate elastic modulus on the fracture toughness of the films. • Increase in fracture toughness of the bi-layered system was found as the crack tip approach the film-substrate interface. • Presence of ductile interface shielded the crack tip and changed the crack trajectory. • These measurements provide a template for design of thin films with increased fracture resistance. Damage tolerance of a thin film attached to a substrate is dependent on several parameters such as film thickness, film orientation, residual stresses, nature of interfaces, microstructure and defects present. Here we study the fracture resistance and crack growth trajectory in BaTiO 3 thin films attached to elasticially stiff substrates using micromechanical experiments and finite element modeling. Microcantilever fracture tests are carried out on bi-layered systems of BaTiO 3 film on Pt-Si and SrTiO 3 substrates to study the effect of interfaces, texture and elastic mismatch on fracture toughness. The substrates in the bi-layers are chosen to force the crack to experience a shielding effect in terms of a decrease in the crack driving force. Experiments revealed an unexpectedly large increase in fracture toughness when the crack tip is closer to a stiffer substrate, qualitatively matching the predictions from the numerical model. The bi-layered films attached to the substrate showed 125% (on Pt-Si) and 160% (on SrTiO 3) increase in fracture toughness compared to the free-standing films, for the first time, revealing the significant effect of elastic modulus of the substrate on improving the fracture resistance at such micrometer length scales. [ABSTRACT FROM AUTHOR]

[Display omitted] • This review comprehensively summarizes the advances in additive friction stir deposition processes, as well as the microstructure and properties of the final part. • The implications of the experimental and modeling research findings on additive friction stir deposition are discussed in detail. • The fundamental difference between additive friction stir deposition and fusion-based metallic additive manufacturing are summarized. • The existing problems and possible future research directions for additive friction stir deposition are stated in this paper. Additive friction stir deposition (AFSD) is a relatively new additive manufacturing technique to fabricate parts in solid state below the melting temperature. Due to the solid-state nature, AFSD benefits from lower residual stresses as well as significantly lower susceptibility to porosity, hot-cracking, and other defects compared to conventional fusion-based metallic additive manufacturing. These unique features make AFSD a promising alternative to conventional forging for fabricating large structures for aerospace, naval, nuclear, and automotive applications. This review comprehensively summarizes the advances in AFSD, as well as the microstructure and properties of the final part. Given the rapidly growing research in AFSD, we focus on fundamental questions and issues, with a particular emphasis on the underlying relationship between AFSD-based processing, microstructure, and mechanical properties. The implications of the experimental and modeling research in AFSD will be discussed in detail. Unlike the columnar structure in fusion-based additive manufacturing, fully dense material with a fine, fully-equiaxed microstructure can be fabricated in AFSD. The as-wrought structure brings the as-printed parts with comparable properties to wrought parts. The fundamental difference between AFSD and fusion-based metallic additive manufacturing will be summarized. Furthermore, the existing challenges and possible future research directions are explored. [ABSTRACT FROM AUTHOR]

[Display omitted] • A correlation was found among surface residual stress, crack length, and the relaxation of residual stress fields. • The proposed assessment method achieved accurate prediction of fatigue crack growth rates. The compressive residual stress field (CRSF) relaxes during the fatigue crack growth (FCG) process, and the pattern of this relaxation remains unclear. Residual stress (RS) relaxation leads to a change in residual stress intensity factor (RSIF), which significantly affects the fatigue crack growth rate (FCGR) and thus affects the assessment of fatigue crack growth rate. To this end, this work designed a series of experiments to explore the FCG behaviour in compressive residual stress fields (CRSFs) by considering RS relaxation. Firstly, shot peening(SP) treatments were conducted on the specimens. Then, residual stress fields (RSFs) at different crack propagation stages were measured to analyse the relationship between surface RS and inner RSF distribution. The derived weight function and the real-time RSF are combined to calculate the RSIF with/without considering RS relaxation. Finally, the effect of RS relaxation on the accuracy of FCGR assessment was investigated. The results show that the positive effect of CRS on the fatigue performance of the peened specimens is primarily embodied in the early stage of the FCG process. With the continuous relaxation of the CRSF, the difference in FCGR between the peened and unpeened specimens gradually decreases and tends to disappear. When the applied SIFs are large enough, the CRS would completely relax, and the inhibiting effect of CRSF on FCGR would fail. The proposed method in this work can effectively predict the FCGR of the peened specimen when considering the RS relaxation. This work could provide some meaningful insights for the assessment method of FCGR prediction in CRSF induced by surface strengthening treatment. [ABSTRACT FROM AUTHOR]

Abstract Ultra-high temperature ceramic matrix composites (UHTCMCs) based on ZrB 2 -matrix reinforced with 45 vol% of unidirectional continuous carbon fibers are studied through the thermal mechanical hysteresis in order to investigate the thermal damage accumulation. The analysis carried out allowed to extrapolate the Young's modulus of the matrix from thermal expansion measures. It was found that the initial matrix Young's modulus of 195 GPa steadily decreases by thermal cycling the samples between RT and 1300 °C as a consequence of matrix cracking. On the other hand, the analysis suggested that carbon fibers keep their Young's modulus constant at 780 GPa. Finally, the residual stresses due to the different coefficient of thermal expansion between matrix and carbon fibers are discussed and let to justify the Young's modulus of 230 GPa, which cannot be explained with the so-called "rule of mixtures" generally valid and widely used in the composite science. Graphical abstract Unlabelled Image Highlights • Thermal cycles induce matrix cracking which decreases the Young's modulus of the ZrB 2 -based matrix from 195 GPa to 24 GPa. • The longitudinal thermal dilatation of the composites decreases by thermal cycling and approaches that of bare carbon fibers. • Contrary to linear elasticity the composite Young's modulus is affected by residual stresses even in absence of micro-damage. • A new equation is proposed to account for residual stresses effect and damage frequency on Young's modulus. [ABSTRACT FROM AUTHOR]

Abstract Amorphous diamond-like carbon coating (DLC) of 2 μm in thickness was deposited over the aluminum alloy substrate using magnetron sputtering deposition technique. In order to understand the efficacy of coating deposition, coated specimens were subjected to rotating bending fatigue in air and methanol environments respectively. Raman spectroscopy was used in conjunction with grazing incidence X-diffraction technique to obtain depth-resolved residual stress gradients of coated-aluminum substrate. The residual stress generated due to coating deposition was calculated using Raman spectroscopy and it was −1.13 ± 0.16 GPa (compressive in nature). Furthermore, Raman spectroscopy was utilized for the quantification of stress relaxation upon fatigue loading in air and methanol environments. It was observed that the irrespective of the testing environment, good correlation exists between the stress relaxation magnitude and number of cycles endured before failure. Graphical abstract Unlabelled Image Highlights • Diamond-like amorphous carbon was coated over the aluminum alloy substrate using magnetron sputtering technique. • Residual stress profile of coated substrates up to 3 μm in depth measured using non-destructive techniques. • Role of chemical environment revealed through poor fatigue performances of specimens tested in methanol environment. • Good correlations exist between residual stress relaxation upon fatigue loading and the fatigue properties of the material. [ABSTRACT FROM AUTHOR]

Abstract We have used optical and electron microscopy and Raman spectroscopy to study the structural changes and residual stress induced by typical industrial machining and laboratory polishing of a synthetic graphite. An abrasion layer of up to 35 nm in thickness formed on both machined and polished surfaces, giving the same I D /I G ratios evidencing graphite crystal refinement from an L a of ~110 nm down to an average of 21 nm, but with different residual compression levels. For the as-polished sample, structural change was limited to the near surface region. Underneath the as-machined surface, large pores were filled with crushed material; graphite crystals were split into multi-layered graphene units that were rearranged through kinking. Graphite crystal refinement in the sub-surface region, measured by L a , showed an exponential relationship with depth (z) to a depth of 35–40 μm. The positive shift of the G band in the Raman spectrum indicates a residual compression accompanied by refinement with the highest average of ~2.5 GPa on top, followed by an exponential decay inside the refined region; beyond that depth, the compression decreased linearly down to a depth of ~200 μm. Mechanisms for the refinement and residual compression are discussed with the support of atomistic modelling. Graphical abstract Unlabelled Image Highlights • Typical machining of highly graphitised iso-graphite leads to a plastically deformed surface with refined crystallites. • The plastic deformation in graphite is evidenced by HRTEM images showing split and/or bent graphene layers. • The C-C σ bonds in the plastic/elastic deformation region are highly stressed with a maximum net compression >2.5 GPa. • MD modelling of plastic deformation in graphite by means of indentation shows splitting and bending of graphene layers. [ABSTRACT FROM AUTHOR]

Abstract The design of a product component may require complex processing steps such as metal forming followed by a thermal treatment. The thermal treatment may improve the functional performance of the material itself, but may result in rather unwanted changes in the shape of the product. Here it is shown that Finite Element modeling of the various processes can assist in the design of a robust and accurate production process. The modeling approach presented allows a coupling between various complex material models, in such a way that full cold forming and thermal treatment processes are calculated. This coupling of material models is key for the design and concerns the novelty of the proposed approach. Cold forming by deep drawing is calculated whereby planar anisotropy is implemented. The thermal hardening treatment consists of three contributions: creep, thermal expansion and phase transformation. All models are based on experimental data, acquired from tensile and dilatometer tests, and are implemented into the material model either directly or by a simple fit. It is shown that the effects of a complete forming and heat treatment of a cup could be successfully calculated. The predicted cup shape change was compared to experiments, and shows excellent agreement. Graphical abstract Unlabelled Image Highlights • The predictability and accuracy of the shape changes in the product design • Coupling between forming and thermal treatment • Processing steps of forming and thermal treatment are successfully implemented in the Finite Element computer code. [ABSTRACT FROM AUTHOR]

A new approach is proposed to achieve an in-depth understanding of crystallisation, residual stress and adhesion in epitaxial splats obtained by Combustion Flame Spray. Modelling of the fundamental process mechanisms is achieved with the help of experimental observations providing details with a sub-micrometre spatial resolution. At this scope, High Angular Resolution Electron Backscatter Diffraction and Transmission Electron Microscopy analysis are employed to provide insights into crystallisation and residual stress levels, while FIB-milled microcantilever beam bending is used for fracture strength measurements in the case of single splats. A comparison to fully-developed coatings is achieved by employing the X-ray Diffraction sin 2 ψ technique and pull-off methods for residual stress and fracture strength, respectively. The methodology is applied to metallic CoNiCrAlY material sprayed onto a Ni-based superalloy substrate. The establishment of different crystallisation regions: epitaxial and polycrystalline, is the result of variations in the heat flux direction at the solidification front. Significant dislocation density is also reported, indicating the relevance of impact dynamics and plastic deformation mechanisms. The comparison with fully-developed coatings suggests a reduction in inter-splat bonding at splat overlapping. [ABSTRACT FROM AUTHOR]

Additively manufactured intersections have the theoretical risk to contain hydrostatic tensile residual stresses, which eventually cannot be thermally stress relieved. The stresses in Ti-6Al-4V wire + arc additively manufactured (WAAM) intersections are lower compared to single pass walls and stresses in continuous walls are larger compared to discontinuous walls with otherwise identical geometry. Thermal stress relief was found to virtually eliminate them. Inter-pass rolling can yield the desired grain refinement, without having any noteworthy influence on the development of residual stresses. The strain measurement itself by neutron diffraction is facilitated by the refined microstructure, because the otherwise textured microstructure produces anisotropic peak intensity, not allowing Pawley refinement. Without rolling, the 10 1 ¯ 1 and 10 1 ¯ 3 family of hcp planes are the only ones that diffract consistently in the three principal directions. [ABSTRACT FROM AUTHOR]

Despite the application of aluminum melt filtration with ceramic foam filters since the 1960s the process is not fully understood. Outstanding issues are for example the influence of the wetting behavior and filter chemistry on the filtration efficiencies. Contact angle measurements by the sessile drop method coupled with non-contact heating and capillary purification technique were conducted at 730 °C with AlSi7Mg alloy on the substrates of four different oxides (Al 2 O 3 , MgAl 2 O 4 , 3Al 2 O 3 ·2SiO 2 and TiO 2 ). The highest contact angle was measured on 3Al 2 O 3 ·2SiO 2 , followed by MgAl 2 O 4 , Al 2 O 3 and TiO 2 . Experimental values of contact angles were correlated with the evaluated filtration efficiencies of filtration trials performed at Constellium. They show a good correlation for inclusions smaller than 110 μm - the larger the contact angle the higher is the filtration efficiency. The adhesion forces of alumina inclusions on the four filter materials were experimentally estimated with an AFM in water based model system. The highest adhesion forces were measured on the Al 2 O 3 substrate, followed by the 3Al 2 O 3 ·2SiO 2 , the MgAl 2 O 4 and the TiO 2 substrate. For inclusions >70 μm, both the measured filtration efficiencies for >70 μm and the adhesion forces increase by the following order of coatings: TiO 2 , 3Al 2 O 3 ·2SiO 2 , MgAl 2 O 4 , Al 2 O 3 . [ABSTRACT FROM AUTHOR]

Although several works have been published in literature on agave fibers and their biocomposites, accurate information about the choice of both the fibers and the manufacturing processes that allow the user to optimize the biocomposites properties in terms of strength and stiffness are not yet available; also, no theoretical models that can be used for an accurate evaluation of the mechanical properties of these biocomposites, are reported. To this aim, the present work intends to give a contribution by considering green epoxy biocomposites reinforced by both short and discontinuous sisal agave fibers arranged in proper MAT-type fabrics. In particular, an optimized manufacturing process that allows to obtain good quality biocomposites, is proposed. A detailed analysis of the experimental results, obtained through preliminary pull-out and tensile tests carried out, along with an accurate analysis of the damage process performed by SEM micrographs, have allowed to develop reliable theoretical models that permit the mechanical properties evaluation of the analyzed biocomposites. Finally, the comparison with the most performing short/discontinuous fiber biocomposites reported in literature has shown how the implemented biocomposites exhibit comparable tensile strength and significantly higher stiffness, also respect to biocomposites reinforced by more stiff and more expensive fibers (flax, hemp, etc.). [ABSTRACT FROM AUTHOR]

Multicomponent carbide thin films of (CrNbTaTiW)C (30–40 at.% C) with different metal contents were deposited at different temperatures using non-reactive DC magnetron sputtering. The lattice distortion for the metal lattice was estimated to vary from about 3 to 5%. Most films crystallized in the cubic B1 structure but Ta/W-rich films deposited at 600 °C exhibited a tetragonal distortion. X-ray diffraction results show that near-equimolar films exhibited a strong (111) texture. In contrast, Ta/W-rich films exhibited a shift from (111) to (100) texture at 450 °C. The in-plane relationship was determined to MC(111)[-12-1]//Al 2 O 3 (001)[110] with a lattice mismatch of about 11% along the Al 2 O 3 [110] direction. A segregation of Cr to the grain boundaries was observed in all films. The microstructure was found to be the most important factor for high hardness. Less dense Nb-rich and near-equimolar films deposited at low temperatures exhibited the lowest hardness (12 GPa), while very dense Ta/W-rich high temperature films were found to be the hardest (36 GPa). No correlation was found between the lattice distortion and the hardness. Corrosion studies revealed that the multicomponent films exhibited excellent corrosion resistance, superior to that of a reference hyper-duplex stainless steel, in 1.0 M HCl. [ABSTRACT FROM AUTHOR]

Titanium porous cellular microstructures are commonly used in bone mimetic implants. The orientations of the internal strut architectures of these microstructures affect the mechanical performance under various loads; however, poor architectural designs may result in their failure. Three-dimensional (3D) finite element models of cubic, diamond, and body-centered cubic (BCC) geometries were constructed with 1 – 4 numbers of unit cells and 4–10-mm unit cell size. Mechanical testing of the finite models of the cubic, diamond, and BCC structures with porosities of 20–90% was performed under compression, bending, and torsional loads. The BCC structure showed moderate and relatively isotropic mechanical properties compared with those of the diamond and cubic structures. A design space for a BCC porous structure with a porosity of 40–65% was estimated to model a complete porous stem to mimic the bone properties. Furthermore, the stems with the determined porous mechanical properties of the BCC microstructures with 20–90% porosities were tested under physiological loading conditions. It was found that a porosity of 47.3% of the BCC structure exhibits the closest stiffness (469 N/mm) to an intact bone (422 N/mm). This was predicted by our suggested design space of the porosity. [ABSTRACT FROM AUTHOR]

Residual stresses play a crucial role in determining material properties and behaviour, in terms of structural integrity under monotonic and cyclic loading, and for functional performance, in terms of capacitance, conductivity, band gap, and other characteristics. The methods for experimental residual stress analysis at the macro- and micro-scales are well established, but residual stress evaluation at the nanoscale faces major challenges, e.g. the need for sample sectioning to prepare thin lamellae, by its very nature introducing major modifications to the quantity being evaluated. Residual stress analysis by micro-ring core Focused Ion Beam milling directly at sample surface offers lateral resolution better than 1 μm, and encodes information about residual stress depth variation. We report a new method for residual stress depth profiling at the resolution better than 50 nm by the application of a mathematically straightforward and robust approach based on the concept of eigenstrain. The results are validated by direct comparison with measurements by nano-focus synchrotron X-ray diffraction. [ABSTRACT FROM AUTHOR]

Residual stresses in materials affect their resistance to the initiation of fracture and to subsequent crack growth. Using full-field strain measurements and finite element analysis we demonstrate that the effect of residual stress on a material's crack growth resistance curve can be understood using elastic-plastic fracture mechanics. It is shown that Lei's modified J -integral formulation ( J mod ) is a good predictor of the load vs crack extension behaviour of an elastic-plastic material containing residual stresses. [ABSTRACT FROM AUTHOR]

The candidacy of ninth earth abundant material, titanium is supreme when it comes to the higher strength to weight ratio, and higher corrosive resistance. Next generation of jet engines for aerospace industry clearly depends on the manufacturability and improved ability of titanium alloys that can withstand the high temperatures. However, the primary sheets, plates, billets, ingots, or rods are of limited sizes that need to be either machined or welded in order to produce a desired structure with optimal the buy-to-fly ratio. This article primarily summarizes the research in the field of joining of titanium sheets with a direct focus on friction stir welding (FSW). The industrial requirements, whether to weld similar or dissimilar titanium alloys, or of different thicknesses, or even with composites, are often challenged by the selection of the tool, position of the alloying sheets, cooling of the weld nugget, material composition, complex material flow in the wake of the rotating, and traversing tool etc. This article provides a review of FSW of similar and dissimilar titanium alloys focusing on surface, and subsurface properties, such as microstructural, and mechanical properties, texture evolution, current challenges summarizing a possible remedy, encompassing the recent development and research in the field. [ABSTRACT FROM AUTHOR]

Through a localized nanocrystallization process using surface mechanical attrition treatment (SMAT), a new method is proposed to build bistable and multistable metallic shells. The impacts from randomly fast-moving balls during the nanocrystallization process accumulate plastic deformations, which induce nanotwins and mesh grains into nanoscales significantly increasing elastic behavior range of the treated shells. The in-plane self-equilibrium residual stress field, which is induced from the stretching plastic deformations in the treated region under the constraint of the untreated region, renders nanostructured shells bistable characteristics. An effective numerical modelling is carried out to analyze the bistable behavior and predict their stable configurations. A flat plate with multiple nanostructured regions is manufactured and numerically studied, which is capable of holding multiple stable configurations. In addition, the developed bistable and multistable shells can be further mechanically processed to modify their stable configurations. [ABSTRACT FROM AUTHOR]

Polyether-ether-ketone (PEEK) has high mechanical strength, thermal performance, and biocompatibility, and is widely used in biomedical and chemical engineering applications. However, to date there are no guidelines for the building of a 3D printer for highly viscous materials, e.g., PEEK. In this paper, a screw extrusion method was developed to overcome the existing problems of the filament-feeding method. Excellent flow stability (< 3% variation) and high printing speed (up to 370 mm/s) for PEEK printing were achieved. Highly reproducible mechanical tests of the printing products were demonstrated with 96% of the bulk material strength for the first time. Furthermore, an exchangeable printing head was built to cover both line- and plane-printing needs to widen its applications and improve printing surface quality (up to 0.945 nm in Ra). All printed material had a more brittle character in comparison with the bulk material and the post annealing process was found to have no significant effect on the mechanical strength. Additionally, porous artificial intervertebral cages with controllable size and distribution were manufactured to demonstrate potential applications. [ABSTRACT FROM AUTHOR]

Protection of the molten pool from gaseous contamination has always been of prime importance in welding of titanium alloys. A vacuum environment in electron beam welding serves this purpose and eliminates the use of shielding gas during the joining process. However, this may lead to variation in microstructure, mechanical properties, residual stress distribution and distortions compared to the widely used laser and TIG welding operations. In the present work, EBW was used to weld Ti-5Al-2.5Sn alloy sheet with welding current ranging from 14 mA to 20 mA. Owing to vacuum environment, oxygen contents in the fusion zone were very low for all the welding currents. However, welding current had a significant influence on the weld pool width, micro-hardness and grain size in the FZ. A complete martensitic transformation was not observed in the FZ at any of the welding currents used. Furthermore, maximum residual stresses upto 280 MPa (compressive) and 320 MPa (tensile) were found in the longitudinal direction near the weld centerline. The measured high residual stresses, distortions and partial martensitic transformations in FZ were attributed to a reduced cooling rate due to the absence of shielding gas in electron beam welding. [ABSTRACT FROM AUTHOR]

Modelling the mechanical mixing occurring at the interface of a linear friction weld (LFW) is complex, making it difficult to study the development of residual stresses within real engineering workpieces. To address this, a sequentially-coupled numerical model of a Ti-6Al-4V LFW was developed, bypassing the modelling of the oscillations by applying the heat at the weld interface and sequentially removing rows of elements to account for the burn-off. Increasing the rubbing velocity was found to numerically increase the peak of residual stress while narrowing the distribution. Only small changes arose from increasing the applied pressure or changing the oscillation direction. Predictions suggested a strong correlation between the phase 3 temperature profile and the residual stress field subsequently created. Validation against neutron diffraction and contour method are also presented. This approach provides a computationally efficient technique to study the residual stress development within large 3D structures. [ABSTRACT FROM AUTHOR]