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In this study, multifunction cavitation (MFC) was performed on low‐alloy steel (AISI 4140 steel) rods with different hardnesses to increase their fatigue limit. It was found that a high compressive residual stress was generated on the surface of steel rods by MFC and that the magnitude of the compressive residual stress tended to increase with increasing specimen hardness, which resulted in a higher fatigue limit. However, fatigue cracks are known to be initiated from the pits and red rust that form on the surface during MFC treatment in water. Furthermore, relaxation of the compressive residual stress was also investigated during the fatigue test to elucidate the mechanism for improving the fatigue properties. The results showed that the fatigue limit for MFC‐treated steel rods was accurately estimated by considering residual stress relaxation, hardness, and pit formation. Validation of the fatigue limit estimation was also conducted through comparison with Murakami's equation. Highlights: MFC generated compressive residual stress on the surface of steel rods.MFC increased the fatigue limit for steel rods.The fatigue limit of MFC‐treated steel rods with different hardnesses was estimated.Fatigue cracks were initiated at surface pits formed by MFC. [ABSTRACT FROM AUTHOR]

Residual stress of a welding joint based on finite element simulation was predicted to gain popularity in the process equipment industry. As for the nuclear power industry, the weldment located in a primary coolant system should be evaluated to verify the boundary integrity. The weld residual stress is an important load for leaks before break or fatigue crack growth estimation. Heat input is a key factor to accurately simulate the weld's residual stress. Hence, heat transfer activities of weld beads, based on the theoretical volume heat generation rate of the weld element, were simulated using finite element analysis. The traditional method of controlling heat input in finite element method simulation of the welding process is achieved by setting the temperature monitoring point. When the melting temperature is reached, the calculation for weld bead melting is terminated. However, it does not comply with the real welding process because too many assumptions are involved. Therefore, a novel heat input function to modify the temperature differences of weld beads and weld layers was proposed to predict the temperature and residual stress field. Four simulations based on the modified heat input methods and traditional approaches were performed to predict the weld residual stress field of a butt-welded joint for thick-walled pipe and were compared with experimental data. Results show that more accurate thermal fields and weld residual stress fields were achieved using the proposed heat input approach. [ABSTRACT FROM AUTHOR]

The investigation carried out in the current study illustrates the dissimilar gas tungsten arc welding (GTAW) between Inconel 718 (IN 718) and austenitic stainless steel (ASS 304L) utilizing three different filler materials. This study utilizes Ni-based fillers (ERNiCrCoMo-1 (IN 617) and ERNiFeCr-2 (IN 718)), and austenitic filler ASS 304L and characterizes the relationship among microstructural and mechanical characteristics using identical weld parameters. The obtained dissimilar weld joint using Ni-based filler materials depicts no weld solidification cracking, whereas austenitic filler causes the weld solidification cracks. The microstructural characterizations were examined using optical and FESEM revealing the occurrence of columnar, cellular, and equiaxed dendritic structures in all three weld metals. FESEM/EDS analysis illustrates the occurrence of Mo and Cr-rich phases (M23C6 and Mo6C) in ERNiCrCoMo-1 weld metal, NbC, Mo/Ti–rich, and laves phases in ERNiFeCr- 2 weld metal and Cr- rich carbides in ASS 304L weld metals. EBSD assessment shows the improved texture of the weld metals through IPF and PF maps. The Vickers microhardness demonstrates the highest hardness value (271 HV5) for the ERNiFeCr- 2 weld metal due to the existence of the brittle intermetallic phases, and minimum in the case of ASS 304L weld metals (156 HV5). The ambient temperature tensile test exhibits the maximum (649 MPa) and minimum (404 MPa) UTS corresponding to ERNiCrCoMo-1 and ASS 304L weld metals respectively. The tensile specimens for all the weld metals experience fracture from the weld metals. The Charpy toughness values of the weld metals show lower values (ERNiCrCoMo-1 (70 J), ERNiFeCr-2 (56 J) and ASS 304L (32 J)) than the BMs (IN 718 (135 J) and ASS 304L (228 J). Residual stress analysis was conducted employing the deep hole drilling (DHD) technique, indicating that the highest residual stress occurs 2 mm below the top weld face, classified as tensile stress for all three used filler materials. [ABSTRACT FROM AUTHOR]

Double‐layer thermal barrier coatings are one of the development directions of thermal barrier coatings technology. LaYbZr2O7 (LYZO) has high toughness and low thermal conductivity, making it promising for use as a high‐temperature thermal barrier coating. However, its relatively poor mechanical properties, especially low fracture toughness, limit its further application. Therefore, we prepared a double‐layer coating of LYZO and Y2O3 partially stabilized ZrO2 (YSZ) using atmospheric plasma spraying, with the inner layer being YSZ and the outer layer being LYZO. The results showed that after spraying, LYZO was in the metastable fluorite phase, while YSZ was in the tetragonal phase. LYZO and YSZ had good chemical compatibility, and an interaction layer formed at the interface between them, with its thickness increasing with the sintering time. Eventually, after 100 h of heat treatment, the thickness reached 12 µm. The hardness of the LYZO/YSZ interface increased with the sintering time, reaching a maximum value after sintering at 1300°C for 10 h. When evaluating the interfacial bonding strength using indentation method, the length of cracks caused by indentation significantly decreased with the increase of sintering time. The increase in bonding strength can be attributed to the formation of a reaction layer and the reduction of thermal residual stresses. Raman spectroscopy was used to measure the thermal residual strain at the LYZO/YSZ interface. Unbalanced distribution of thermal residual stress and M phase was observed near the interface. As the sintering time increased, both thermal residual stress and M phase content decreased. In summary, the double‐layer thermal barrier coating of LYZO/YSZ has good potential for development. [ABSTRACT FROM AUTHOR]

The key to understanding the shear failure mechanism of prestressed concrete girders lies in how to properly deal with the combined effects of the applied load, the support reaction, as well as the prestressing force. This paper firstly conceptualizes a combined stress field model, which integrates these effects by manifesting several subfields to disclose the potential failure patterns at different locations in the short shear span. Then, shear tests of four full-scale pretensioned concrete T-girders with a height of 1.6 m and two kinds of shear-span-to-depth ratios were carried out. The test results showed that all the specimens failed in a web-crushing pattern near the support accompanied by a bond-slip of the deflected strands. By analyzing the deviated compression subfields in the highly stressed webs and introducing a failure criterion for cracked concrete, the ultimate shear strength of pretensioned concrete girders was formulated. Finally, the shear strength evaluated by the proposed formula and by some other design codes were compared, and it was proved that the results of the proposed model were closer to the test. [ABSTRACT FROM AUTHOR]

• Flexoelectricity and surface effect on piezoelectric nanolaminates were reported. • Analytical solution of bending deformation and vibration were obtained. • Effects of residual surface stress and the flexoelectric coefficient were examined. • Effects of aspect ratio and plate thickness on bending behavior were examined. In this paper, a model of double-layer rectangular piezoelectric nanolaminates with different upper and lower surface properties is established. The bending and vibration behavior of the piezoelectric nanolaminates are evaluated and analyzed, taking into consideration the flexoelectric and surface effects. Utilizing the surface piezoelectric model, flexoelectric theory, and Kirchhoff plate theory, this study provides analytical solutions for the bending deflection and natural frequency of rectangular piezoelectric nanolamination materials under various boundary conditions. The results indicate that the effects of flexoelectric and surface influences on piezoelectric nanolaminates are associated with residual surface stress and flexoelectric coefficients. These effects can enhance the bending stiffness and decrease the natural frequency of the piezoelectric nanolaminates. Furthermore, altering the residual stress on the upper and lower surfaces of the laminates separately will result in different trends in bending deflection, while causing a consistent trend in natural frequency change. When the electric potential direction of piezoelectric nanolaminates is different, the bending deflection of piezoelectric nanolaminates will change accordingly. The natural frequency of piezoelectric nanolaminates is determined by the absolute value of the flexoelectric coefficients, and is independent of their positive or negative values. Both the surface effect and the flexoelectric effect are influenced by size-dependent behaviors. When the thickness of the laminates is sufficiently large, both the surface effect and flexoelectric effect can be disregarded. This paper's research methods and results provide theoretical models and analytical methods for the microstructure design, multi-physical field characterization, and bending deformation behavior of intelligent components containing rectangular piezoelectric nanolaminates. [ABSTRACT FROM AUTHOR]

Achieving high‐performance perovskite solar cells hinges on the precise management of interfacial properties. However, the current research predominantly concentrates on addressing individual interfaces, often overlooking the potential synergies between the upper and lower interfaces crucial for efficient carrier transfer. Herein, an effective interfacial strategy is introduced, which combines 2‐aminoterephthalic acid (2‐AA) pre‐processing with post‐processing techniques to prepare superior mixed tin‐lead perovskite films suitable for both single‐junction and all‐perovskite tandem solar cells. Incorporating 2‐AA at both the upper and lower interfaces of the perovskite films serves to regulate interfacial defects, alleviate interface residual stress, and improve film crystallinity. In addition, the 2‐AA molecule acts as an interface protective layer, anchoring tin and lead atoms, facilitating band energy alignment, and improving film and device stability. As a result, mixed tin‐lead perovskite solar cells achieved an improved open‐circuit voltage of 0.87 V and PCE of 21.57%. Furthermore, the integration of these optimized tin‐lead perovskite subcells into four‐terminal all‐perovskite tandem solar cells yielded an impressive efficiency of 27.46%. This work thus offers an effective strategy for comprehensive interfacial engineering and stress relief, paving the way for the production of high‐performance perovskite solar cells (PSCs). [ABSTRACT FROM AUTHOR]

Fused Filament Fabrication (FFF) is one of the most popular extrusion based metal Additive Manufacturing (AM) Technologies, which has unique advantages in the rapid prototyping of thermoplastic materials, enabling the fabrication of metal parts with low mechanical anisotropy and no residual stress. However, the mechanical properties and dimensional accuracy of FFF printed parts are susceptible to changes in various printing parameters, which affects the FFF application in large-scale manufacturing. This study experimentally studied the effect of various printing parameters namely layer thickness (0.1, 0.2, 0.3, and 0.4 mm), raster angle (0°, 90°, + 45°/−45°, and 0°/90°), raster width (0.3, 0.35, 0.4, and 0.45 mm), and infill density (70, 80, 90, and 100%) on mechanical properties and dimensional accuracy of 316L stainless steel fabricated by FFF. The results showed that the infill density was the most important factor affecting the mechanical properties, followed by the layer thickness, and it was found that higher values of infill density and lower layer thickness result in better tensile strength. Layer thickness was also the main factor affecting the dimensional accuracy, which increased with the decrease in the layer thickness. [ABSTRACT FROM AUTHOR]

This paper investigated the evolution of residual stress of 7050 aluminum alloy during solid solution, uphill quenching and aging treatments through finite element simulation method (FEM) and experiments. The effects of residual stress on processing deformation and tensile properties were explored. The results showed that overall residual stress amplitude of the sample was increased with the decrease in cryogenic temperature, which was independent of the cooling rate. The combination of uphill quenching and aging treatment can release the quenching residual stress by 55%. The mechanism of uphill quenching was related to the temperature difference between the surface and core of the sample. With the increase in temperature difference, the direction of residual stress caused by heating was consistent with quenching residual stress, which resulted in stress superposition and consequently released the residual stress through plastic deformation. With the decrease in temperature difference, the direction was opposite to the quenching residual stress, and they interacted with each other to induce the release of residual stress. Original residual stress with low amplitude and uniform distribution after combined uphill quenching and aging treatment made contribution to improve the dimensional accuracy of aluminum alloy components after machining without no obvious deterioration in tensile strength. [ABSTRACT FROM AUTHOR]

The present study proposes machining Ti-6Al-4V with graphite nanopowder mixed electric discharge machining (NPMEDM) process using deionized water (6 gm/L) as the dielectric. A comparative analysis is performed with conventional electric discharge machining (EDM) and NPMEDM processes with peak current (IP), pulse on time (TON), and gap voltage (GV) as input parameters. Surface integrity, recast layer thickness (RLT), material removal rate (MRR), chemical analysis, and residual stress are investigated by different characterization techniques such as field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD). FESEM study reveals that the addition of nano graphite powder leads to a glossy surface finish, lesser micro-cracks, and micro-holes. Recast layer thickness (RLT) improved drastically by 69% with the addition of graphite powder. The investigation also revealed an improvement in surface roughness by 74.75% in NPMEDM compared to conventional EDM. Further, the induced residual stress is investigated by XRD analysis. Obtained results reveal substantial improvement in residual stress from (340.5 ± 12.6) to (239.9 ± 62) MPa, which diminishes the chance of failure of the component. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM)'s ability to produce customized products with reduced material wastage and other advantages helped the technology to gain popularity in many industries. However, its poor surface integrity is its weak side, and to overcome this, additional post-processes are essential. Slide diamond burnishing, known for its enhancement of surface roughness, residual stress, microhardness, and other properties, was combined with grinding in this research after 3D printing of MetcoAdd 17-4PH-A to mitigate the mentioned shortcomings. This study aimed to analyze the effects of each process on surface roughness, residual stress (both on the surface and in-depth), and microhardness. Workpieces were ground with the same parameters and burnished with four levels of force, feed, and number of passes. The L16 Taguchi experimental design was used to optimize the process parameters and to study their effects. For surface roughness, the optimum parameters were found to be 60 N force, 0.02 m/min feed rate, and three passes. The longitudinal surface residual stress has optimal values at 80 N force, 0.02 m/min feed rate, and four passes. In the case of transverse surface residual stress, the optimal values were 60 N force, 0.17 m/min feed rate, and three passes. Microhardness was maximized with 60 N force, 0.02 m/min feed rate, and one pass. Additionally, the in-depth residual stress for selected surfaces was investigated, and 100 N force showed a deep burnishing effect. Further multi-objective optimization using desirability function analysis found that the optimal parameters for all responses were achieved at the fourth burnishing force level (100 N), the first tool feed level (0.02 m/min), and the fourth number of passes level (four passes). Ultimately, both grinding and burnishing processes exhibited significant enhancements in the measured parameters. [ABSTRACT FROM AUTHOR]

During the milling process of aramid honeycomb, residual stresses arise, which will affect the surface quality of the honeycomb. Studies have shown that reasonable processing techniques can reduce residual stresses, indicating a close relationship between residual processing stresses and the processing parameters, such as technique. By investigating the changes in residual stresses after the processing of aramid honeycomb materials, the influence of processing techniques on these changes is analyzed. Leveraging the correlation between residual stresses and surface quality, this study proposes the use of residual stress as an indicator for evaluating processing techniques. The longitudinal–torsional ultrasonic vibration milling method is applied to the processing of aramid honeycombs. A single-factor experimental approach is adopted, utilizing ABAQUS 2020 software to mimic the longitudinal–torsional ultrasonic milling process. This study explores the influence patterns of various process parameters on the residual stresses generated during the milling of honeycombs. The simulation results indicate that within the selected range, the residual stress decreases as the tool rotation speed increases, while it increases with the increase in feed rate. The influence of milling depth on residual stress can be negligible. Furthermore, experiments were conducted based on the proposed correlation between residual stress and surface quality. The experimental results show good agreement with the simulation results, indicating that under reasonable process parameters, the residual stress values decrease, thereby improving the milling surface quality of aramid honeycomb materials. Therefore, measuring residual stress can serve as an effective method for evaluating the processing technique. [ABSTRACT FROM AUTHOR]

The welding process adopted for nuclear vessels is important from temperature and residual stress. In, this study stainless steels material was used to simulate the weldability with respect to reaching the melting at the Fusion zone with respect to the weld input power and process time. Static thermoelastic process simulation was done using 3D-Finite Element Analysis using ANSYS. For a representative 3 mm plate butt welding process, isotherms in the transverse weld bead area were used to identify melting and solid to solid phase change points in Fusion and HAZ. The distributions evaluated at Fusion, HAZ and in base material along the longitudinal direction, transverse and along the thickness. The residual stress evaluated along the transverse direction is compared with yield strength to evaluate weldability. Also, the transverse analysis leads to an understanding of structural stability. A single-pass weld process limit was obtained for a feasible time and power source and the thermoelastic distributions studied. [ABSTRACT FROM AUTHOR]

The article presents a study on the effects of ultrasonic treatment on residual welding stresses (RWS). Ultrasonic treatment was administered from three orientations: external, internal, and bilateral. Six samples, each with a thickness of 8 mm and composed of steel grade 09G2S, were prepared. The welding of these samples was executed using semi-automatic equipment and adhered to regulatory and technical guidelines. The magneto anisotropic technique, foundational to the operation of the Stress Vision Lab device, was employed to measure residual stresses. Given that this device quantifies residual stress values in arbitrary units, a calibration table was devised to translate these measurements into megapascals (MPA). This calibration was established by correlating values obtained from the ZW-100 testing machine with those measured by the Stress Vision Lab, necessitating the preparation of three additional samples of the same steel grade. Experimental investigations revealed that ultrasonic treatment applied internally to the samples facilitated the most significant reduction in residual (tensile) stresses, with reductions of 37.5% from external application and 27% from internal application. Leveraging the data acquired, a device has been developed to mitigate residual welding stresses within the inner wall of the near-seam zone of pipelines. [ABSTRACT FROM AUTHOR]

This study investigates the reduction in thermal residual stress during the powder bed fusion (PBF) process in a non-standardized shape generated by topology optimization method in lightweight automotive part of brake caliper. While the caliper of the braking system for reducing the CO2 consumption in vehicle systems undergoes a redesign to increased strength and reduced weight, challenges arise due to biased melting area ratios in the topologically optimized design, causing the thermal deformation. To address this, our research proposes an efficient PBF scan strategy aimed at minimizing anisotropy and residual stress—a critical consideration for successful manufacturing. The effectiveness of the laser scan strategy is validated through testing on a brake dynamometer, following the JASO C406 test procedure, an authorized standard for commercial brake calipers. Furthermore, a comparative analysis between the conventional product and the proposed brake caliper highlights superior performance, particularly under lightweight conditions. This comprehensive approach contributes valuable insights to the field, offering a potential solution for overcoming manufacturing challenges associated with topologically optimized designs in automotive components. [ABSTRACT FROM AUTHOR]

Internal state variable models are well suited to predict the effects of an evolving microstructure as a result of metal-based additive manufacturing (MBAM) processes in components with complex features. As advanced manufacturing techniques such as MBAM become increasingly employed, accurate methods for predicting residual stresses are critical for insight into component performance. To this end, the evolving microstructural model of inelasticity (EMMI) is suited to modeling these residual stresses due to its ability to capture the evolution of rate- and temperature-dependent material hardening as a result of the rapid thermal cycling present in MBAM processes. The current effort contrasts the efficacy of using EMMI with an elastic–perfectly plastic (EPP) material model to predict the residual stresses for an Inconel 718 component produced via laser powder bed fusion (L-PBF). Both constitutive models are used within a thermo-mechanical finite element framework and are validated by published neutron diffraction measurements to demonstrate the need for higher-fidelity models to predict residual stresses in complex components. Both EPP and EMMI can qualitatively predict the residual stresses trends induced by the L-PBF local raster scanning effects on the component, but the influence of the temperature-dependent yield and lack of plastic strain hardening allowed EPP to perform similar to EMMI away from free surfaces. EMMI offered the most insight at the free surfaces and around critical component features, but this work also highlights EMMI as a process–property-dependent model that needs be calibrated to specimens produced with a similar reference structure for microstructure evolution effects to be accurately predicted. [ABSTRACT FROM AUTHOR]

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Aluminum 6061-T6 sheets with a Ti–6Al–4V titanium alloy interlayer were investigated using friction stir welding (FSW) to achieve strong bonding. The influence of welding parameters on welding quality and strength was assessed by varying rotational speeds and traverse speeds, the optimal welding conditions. Welded samples with a cross section of 28 mm and excellent surface smoothness were prepared and analyzed to measure the residual stress using X-ray diffraction (XRD) techniques. This study investigated the effect of tool geometry and type on residual stresses in welded specimens and highlighted the importance of choosing the appropriate tool geometry and type to minimize residual stresses. Furthermore, finite element simulation of the FSW process was conducted using a thermal modeling approach to calculate the heat generated and predict residual stresses using ABAQUS software. Comparison of the residual stress values obtained from numerical simulations with experimental measurements demonstrated the model's ability to predict residual stresses in FSW adequately. The experimental and numerical results revealed that an increase in rotational speed and tool feeding led to higher stresses in the welded region due to an increased thermal gradient. Examination of the microstructure shows that during the welding process, the weld cross-section has become smaller than the base metal. The ultimate tensile strength and microhardness obtained in optimal conditions were 245 MPa and 108.2 HV, respectively. Examining the fracture surfaces from the tensile tests showed the soft fracture type, which is characterized by the presence of holes and depressions in the three-layer sheet. [ABSTRACT FROM AUTHOR]

Welding residual stresses significantly influence the mechanical behavior of hollow section joints, especially in the pivotal connection zones of steel structures employed in construction. The research object of this study is the Q355 steel square tube–plate Y-joint welded using Gas Metal Arc Welding (GMAW) with CO2 Shielding. The thermodynamic sequence coupling method was employed to simulate the temperature field, microstructure distribution, and welding residual stresses in square tube–plate Y-joints. Based on the monitored temperature field data and the cross-sectional dimensions of the weld pool, this study calibrated the finite element model. Subsequently, the calibrated finite element model was employed to analyze the influence of microstructural phase transformations and welding sequences on the welding residual stresses in square tube–plate Y-joints. The research findings indicate that the peak transverse welding residual stresses in the branch pipes of the four joint zones were lower when considering the phase transformation effect than when not accounting for it in the calculations. There was no significant difference in the transverse and longitudinal welding residual stresses on the surface of branch pipes under the three welding sequences. However, there were certain differences in the microstructural content of the weld zones under the three welding sequences, with the martensite content in the third welding sequence being significantly lower than that in the other two sequences. [ABSTRACT FROM AUTHOR]

(1) Background: Dental glass–ceramics shrink during crystallization, complicating restoration manufacturing. Thermo-pressure molding was introduced to address this, with lithium disilicate crystals providing high strength. Residual tensile stresses can influence the chipping strength of single tooth crowns. (2) Methods: Insync dentine was layered onto three lithia-based disilicate core ceramics (Amber Press, IPS e.max Press) for microtensile bond strength tests. The Vickers test assessed the residual tensile stress and interfacial bonding. Porcelain-veneered posterior ceramic crowns were fabricated and subjected to axial loading, measuring fracture loads (three per group). (3) Results: A chemical bonding layer formed at the interface, which was thicker in the Insync-IPS e.max Press and increased with more firings. The ultimate tensile bond strength was 28.5 MPa for the four-times-fired Insync-Amber Press, similar to the twice-fired Insync-IPS e.max Press. No residual tensile stress was found in the Insync-Amber Press; the Insync-IPS e.max Press showed crack growth within 250 μm of the bonded interface. The average fracture resistance was twice as high for the Insync-Amber Press. (4) Conclusions: The Insync-Amber Press exhibited better thermal harmony with no crack growth, while the IPS e.max Press showed crack growth due to residual tensile stress. Insync-Amber Press posterior ceramic crowns had significantly greater fracture resistance than Insync-IPS e.max Press crowns. [ABSTRACT FROM AUTHOR]

The pulsed current electrodeposition method was employed for the first time to achieve tungsten coating with a thickness of 433.72 μm on a CuCrZr alloy from Na2WO4-WO3-KCl-NaF molten salt. The microstructure of the coating was observed and the coating density, porosity, hardness, bonding strength, residual stress and oxygen content were tested. The results revealed that the tungsten coating exhibited desirable characteristics such as high density, absence of impurities, excellent adhesion to the matrix (53.16 MPa), residual compressive stress as surface stress, and good stability and durability. Moreover, this thick tungsten coating possesses high density and hardness, low oxygen content and porosity. This offers a novel solution to solve the challenging issue of the connection between tungsten material and heat sink material. [ABSTRACT FROM AUTHOR]

This study presents new results on the practical adhesion behavior of a boride layer formed on Monel 400 alloy, developed using the powder-pack boriding (PPBP) at 1223 K for 2, 4, and 6 h of exposure times, obtaining layer thicknesses from approximately 7.9 to 23.8 µm. The nickel boride layers were characterized using optical microscopy, Berkovich nanoindentation, X-ray diffraction (XRD), and scanning electron microscopy (SEM) to determine microstructure, hardness distribution, and failure mechanisms over the worn tracks. Scratch tests were conducted on the borided Monel 400 alloy according to the ASTM C-1624 standard, applying a progressively increasing normal load from 1 to 85 N using a Rockwell-C diamond indenter, revealing that critical loads (LC1, LC2, and LC3) increased with layer thickness. The tests monitored the coefficient of friction and residual stress in real time. Critical loads were determined based on the correlation between the normal force and visual inspection of the worn surface, identifying cracks (cohesive failure) or detachment (adhesive failure). The results exposed those cohesive failures that appeared as Hertzian cracks, while adhesive failures were chipping and delamination, with critical loads reaching up to 49.0 N for the 6 h borided samples. Also, the results indicated that critical loads increased with greater layer thickness. The boride layer hardness was approximately 12 ± 0.3 GPa, ~4.0 times greater than the substrate, and Young's modulus reached 268 ± 15 GPa. These findings underscore that PPBP significantly enhances surface mechanical properties, demonstrating the potential for applications demanding high wear resistance and strong layer adhesion. [ABSTRACT FROM AUTHOR]

A new approach has been developed and implemented to determine the main components of residual stresses that arise as a result of the contact interaction of a spherical indenter and a flat surface of composite plate made. The experimental technique includes drilling a probe hole and measuring the increments of the diameters of this hole in the direction of the principal residual deformations by speckle interferometry. The high-quality interference fringe patterns essential for the implementation of this procedure are visualized both inside and outside the contact dimple. Data from interference measurements of in-plane displacement components are used to determine the principal components of residual stresses based on the unequivocally solution to the properly posed inverse problem. This procedure provides minimal possible errors inherent in a determination of residual stress components by measurements of local deformation response to small hole drilling in orthotropic plate. The presented studies were carried out both for static and dynamic application of contact indentation of a spherical indenter into a flat surface of samples made of laminated carbon fiber material with cross-ply stacking sequence. It is shown that the values of residual stresses, unlike indirect parameters, are a parameter that can be used to establish a correlation between the results of residual strength tests and the quantitative characteristics of the residual stress field in the vicinity of the contact dimple

To inhibit cracking and improve performance, Ni60 alloy layers were deposited on the 38CrMoAl steel substrate using an inductive preheating-assisted high-speed laser-directed energy deposition technique (IP-HS-LDED). The effects of the preheating temperature on the crack, element distribution, microstructure, and performance of the deposited layers were systematically investigated via experiment, finite element simulation, and theoretical analysis. The results revealed that substrate preheating reduced the residual stresses and amount of brittle and hard Cr7C3 particles in the deposited layers, thereby eliminating cracks. The deposited layers were primarily composed of γ-Ni, Ni3B, Cr7C3, CrB, and ferrite. Compared with the deposited layer preheated to 500 °C, the size and content of Cr7C3-type carbides in the deposited layer preheated to 400 °C increased, thus the load transfer and dislocation strengthening effects were enhanced, and the hardness of the deposited layers increased by 72.6 HV. Because preheating to 400 °C produced aggregated and coarse Cr7C3 carbides, the significant mechanical property difference between the carbides and the substrate caused a large stress concentration between them during friction wear, easily leading to crack formation and the further development of spalling and weakening of friction performance. Abrasive wear was the main wear mechanism of the deposited layers.

Finite element models of the burnishing process for galvanized Advanced High-Strength Steels (AHSS) sheets were developed. To reduce the number of points that describe a real surface profile, optimization algorithms were implemented, considering three sequential stages: (1) surface profile filter, (2) mean line determination and, (3) eight roughness parameters validation. The finite element models developed accurately reproduce the experimental roughness profile, obtained with different burnishing forces. Also, the effect of the real surface roughness on the residual stress distribution was numerically investigated by considering the interaction between the coating layer present on the steel. The simulation showed that considering the real surface strongly influences the residual stress profile on the surface and to a certain depth.

As a novel coating spray technique, the aerosol deposition method is applied for the fabrication of dense, nanostructured ceramic coatings at room temperature via an impact consolidation mechanism. It is widely recognized that the successful deposition of coatings is strongly dependent on processing parameters during the deposition process. In this study, a brush‐type aerosol generator was employed to enhance the continuity and stability of the aerosol supply. The uniformity of powder consumption at different packing densities was evaluated; an optimal loading density of 33% was identified for the alumina powders used in this study. Both simulation and experimental studies were performed to investigate the influence of gas flow rate and standoff distance (SoD) on coating fabrication and properties. The predicted particle impact velocity increased with increasing gas flow intensity and SoD, resulting in enhanced mechanical properties of the coatings, including adhesive strength and hardness. The maximum compressive residual stress value of 389 MPa was determined for an alumina coating fabricated at a gas flow rate of 20 L/min. [ABSTRACT FROM AUTHOR]

Progressive-intermittent cutting using controlled eccentricity to the rotation of grinding wheel, referred to as "eccentric sleeve grinding", is projected as one of the promising methodologies for minimising damages while machining Fibre Reinforced Polymer Composites (FRPs). This paper unveils the micromechanics of eccentric sleeve grinding through a detailed investigation of the progressive interaction of abrasive cutting edges with a fibre-matrix system. The theoretical model in this paper provides a comprehensive understanding of the contact/cutting behaviour of abrasive grains located on a wheel that rotates with fine eccentricity during its interaction with the matrix as well as fibres embedded in the matrix. A seven-grit experimental analogy of progressive cutting with the assessment of elastic and brittle modes of material removal, supplemented with the analysis of grinding force and surface micrographs, is a unique contribution to the work. Defect volume estimation using X-ray tomography, residual stress measurement using Raman Spectroscopy, and the hypothesis of skin level defects have also been discussed to provide a deeper insight into the micro mechanism of eccentric sleeve grinding. [Display omitted] [ABSTRACT FROM AUTHOR]

The Battery Thermal Management System rely heavily on cold plates. Manufacturing cost effective, highly productive cold plates having integrated channels is promising solution for thermal management. Friction Stir Channeling is a newly developed and promising manufacturing process for the formation of integrated functional channels on metal blocks for cold plate applications. This research presents the solution to control over channel surface roughness, catering to thermal management system requirements, and shows that it is achievable by manipulating factors like heat input, plasticization effect, and process pitch (v /ω). The study establishes the correlations between important channel features and secondary parameters like pseudo heat index (PHI), flow stress (σ f), and changes in thermal history. Notably, the study highlights the pivotal role of channel roughness as a key determinant of corrosion initiation within the channel through an electrochemical corrosion test. Additionally, the FSC process is found to impart lower compressive residual stresses adding to the advantages of the process. [ABSTRACT FROM AUTHOR]

In this study, the Gaussian heat flux source was used for thermal analysis to estimate the effect of heat input in the C-276 weldments. The L4 design of experiments was used for both simulation and experimentation; the experiments were carried out using the CO2 laser beam welding process. In thermal analysis, the maximum temperature at the fusion zone, and the resulting residual stresses were verified with experimentation. The weld joints were found to be free from defects verified with optical and scanning electron microscopy. The micro-segregation occurring in the joints was investigated using energy-dispersive X-ray spectroscopy (EDS). Factor of safety was more than 1.0 in all the samples compared to the base material tensile strength. Tensile tests confirmed that the strength of the weld zone is higher than that of the parent metals. [ABSTRACT FROM AUTHOR]

In the production of transition metal nitride hard coatings under specific deposition conditions, the resulting residual stresses play a critical role in determining the mechanical properties, adhesion, and overall performance of the coatings. In this work, an artificial neural network (ANN) that utilizes feed-forward architecture is used to predict the average residual stress in titanium nitride (TiN) coatings with different coating thickness. These coatings are manufactured under varying bias voltages and temperature on substrate. The impact of variations in coating thickness, bias voltage, and temperature on development of internal residual stresses and changes in microstructure within sputtered coatings have been gathered from existing literature. The data collected is within the context of fibrous (zone I) and mix columnar and fibrous structure (combined zone) as defined by an existing structure zone model. The model is trained with experimental data from literature. The model is trained with experimental data from literature. The validation of the ANN model is carried out by comparing the predictions with experimental results. X-ray diffraction is used to analyze the residual stresses, preferred orientation, and the structure (zone I and combined zone) of produced coatings under different sputtering parameters. The regression and performance curves are used to assess the efficacy of ANN model. The coefficient of determination of trained model and mean square error are 0.9918 and 0.35, respectively. The predicted results show good agreement with experimental and subsequently AFM grain morphology analysis captures the growth mechanisms involved in the residual stresses evolution.

Highlights This study investigates the effect of the annealing treatment for carbon fiber reinforced Polyether‐ketone‐ketone (CF/PEKK) composite structures under flexural and compressive loadings through reference, pre‐damaged, and annealed sample sets. Significant recovery of pre‐existing damage is observed after the annealing process, following both flexural and compressive loading. Acoustic emission (AE) inspection is employed to monitor the failure behavior and assess the impact of pre‐damage and annealing on CF/PEKK composite. Initially, AE inspection reveals that the reference CF/PEKK material exhibits a notable fiber‐related failure with 85% of cumulative AE counts under flexural load, whereas matrix‐related failures are more pronounced with 92% cumulative AE counts under compressive load. Pre‐damages in the matrix alter the cumulative count percentages and initiation time that are related to matrix, interface, and fiber‐related failures, under flexural and compressive loadings. After annealing, each cumulative AE count percentages are comparable to reference sample values, due to changes in microstructure and relieving of residual stresses. The annealing effect is further validated through dynamic scanning calorimetry (DSC) analysis results with increased glass transition temperature (Tg) and degree of crystallization (Xc). Overall, these findings indicate that annealing treatment effectively restores structural integrity and improves the mechanical performance of CF/PEKK composites. Annealing aims for damage recovery in CF/PEKK under flexural and compressive loads. Significant damage recovery in CF/PEKK is seen after annealing. Annealing raises Tg and crystallinity, and enhances CF/PEKK structural integrity. [ABSTRACT FROM AUTHOR]

Residual stresses existing on the surface of a structural component can be accurately and non-destructively assessed using the instrumented indentation technique, which is crucial for the safety assessment of in-situ structures. In this study, a novel instrumented spherical indentation model based on the equivalent material assumption and the principle of energy density equivalence is proposed for determining the equi-biaxial residual stresses of isotropic power-law hardening metallic materials. The model establishes the correlations between equi-biaxial residual stresses, total work of indentation, and constitutive parameters. Finite element analysis is utilised to determine the model constants by calculating the total work of indentation. Furthermore, the equi-biaxial residual stresses predicted by the model are close to the reference equi-biaxial residual stresses provided by finite element simulations under various equi-biaxial residual stress states for multiple power-law hardening materials. Subsequently, the instrumented spherical indentation experiments are conducted on specimens without equi-biaxial residual stress and on bending cross-shaped specimens with multilayer equi-biaxial residual stresses for six types of metallic materials. The equi-biaxial residual stresses applied by the tests agree well with those predicted by the novel indentation model. [ABSTRACT FROM AUTHOR]

Remarkable casting properties and superior mechanical characteristics of cast iron make it an ideal material for a wide range of industrial applications. However, the production of cast iron components may result in the formation of cracks and defects, posing a significant threat to their structural integrity. Repair welding is a promising solution to resolve cast iron production defects. However, repair welding cast iron components poses unique challenges that stem from residual stress (RS) formation and the possibility of cracking during the repair process. Moreover, research on cast iron repair is scarce. To overcome these challenges, this paper presents a thermo-mechanical model validated by experiments to reduce RS in cast iron repair welding through the optimization of welding parameters and weld sequences as well as the geometry of the repair area. An experimental bead-on-plate weld is set up in order to validate the developed thermo-mechanical model. The temperature distribution in the weld is measured using thermocouples placed around the weld line. An X-ray diffraction technique is used to measure the axial and transverse RS at different points around the weld line. The developed finite element model is employed to simulate the repair welding process and analyze the effect of inter-pass temperature, the number of welding passes, welding sequences, and groove geometry on the RS. The numerical approach applied in this study provides a framework for repair welding optimization of cast iron and other materials, fostering the development of more efficient and reliable repair methods for industrial applications. [ABSTRACT FROM AUTHOR]

Nickel alloys are widely used in aerospace and defense industries due to their excellent high-temperature characteristics. In order to increase fatigue resistance and oxidation corrosion resistance, aerospace curved surface parts always need to be strengthened using laser shock peening technology on five-axis machines. However, it is easy to generate dense laser spots in certain regions during the process, which might lead to an uneven distribution of residual stress on surfaces of the component. To address this issue, the study investigates the problem of excessive spot overlap rate at large curvature positions caused by a mismatch between the surface curvature of curved components and the dynamic performance of equipment, then proposes an optimization algorithm for motion control based on linear interpolation principles. By analyzing the relationship between the feed rate of the program segment and the actual feed rate, the speed of each axis of the machine tool is confirmed and adjusted, and the control flow of the optimization algorithm is established. The feasibility of the algorithm is preliminarily verified by comparing the changing trend of feed rate before and after optimization through simulation. In actual laser shock peening experiments on nickel alloy spherical shell elements, the laser spot distribution on the surface of the component is uniform, and the relative error range between the actual overlap ratio and the theoretical value can be controlled within 5%, demonstrating the correctness of the optimization algorithm. This study can significantly improve the surface machining quality of curved components and have practical applications. [ABSTRACT FROM AUTHOR]

Efficient lubrication and cooling are crucial in machining operations to enhance tool life and workpiece quality. Sustainable methods like minimum quantity lubrication (MQL) and dry cutting often face limitations in cooling efficiency and chip evacuation, especially under high-speed conditions or when machining difficult-to-cut materials such as stainless steel. This study introduces the novel pressurized injection lubrication (PIL) technique designed to address these challenges by optimizing lubrication, cooling, and chip evacuation during the turning operations of stainless steel 304. Using flaxseed oil as the lubricant, the PIL system employs a 0.26 mm stream diameter at a pressure of 16 bar to provide the necessary cooling and lubrication to the cutting zone. Cutting temperature and surface roughness were selected as the primary responses. Experimental runs were designed using the Taguchi L9 method. Analysis of variance showed that the lubrication method significantly affected the cutting temperature, with a contribution percentage approaching 94%. The experimental results demonstrated that PIL reduced the cutting temperature by up to 55%, while MQL reduced it by about 48%, both compared to dry cutting at the highest utilized speed. The lubrication method was also found to be the most significant factor affecting surface roughness, with a contribution percentage of 72.8%. Experimentally, PIL improved surface roughness by a maximum of 16.2% compared to MQL. Additionally, PIL maintained low oil consumption (0.9 l/h) and energy usage (< 0.017 kWh). The cost-effective PIL setup, priced under 65 USD, underscores its potential as a sustainable and efficient alternative for machining processes. The system's components are readily available, facilitating easy integration into existing metal-cutting machines. Finite element analysis (FEA) modeling was used to predict residual stresses under different lubrication methods. The FEA model indicated that PIL and MQL reduced residual stresses by about 81.2% and 76.6%, respectively, compared to dry cutting at a speed of 500 rpm. These findings suggest that PIL can significantly enhance machining performance and sustainability, offering a viable solution to modern manufacturing challenges. [ABSTRACT FROM AUTHOR]

The surface residual stress of the parts has an important influence on their performance. The generation mechanism of surface residual stress in ultrasonic vibration-assisted grinding (UVAG) of bearing steel was investigated, and the correlation between processing parameters and residual stresses was obtained. Based on the ultrasonic vibration-assisted grinding force and thermal model and the flow stress model considering the initial material microstructure, the mechanical and thermal stresses of the material were calculated. Finally, the theoretical model of residual stress is established based on the yield theory and experimentally verified. High-speed ultrasonic aerostatic spindle for ultrasonic vibration-assisted grinding, change the inlet pressure to realize the ultrasonic amplitude and frequency adjustment, the experimental results show that the cutting direction and the vertical cutting direction of the residual stress test results and the model prediction results of the average relative error of 11.4% and 11.7%, and the rule of change is more consistent. Based on the experimental results, the influence pattern of process parameters on the experimental results was analyzed. The results show that the residual compressive stress on the surface of ultrasonic vibration-assisted grinding is directly proportional to the grinding depth, feed rate, and inlet pressure of pneumatic ultrasonic wave and inversely proportional to the linear speed of the grinding wheel. This study provides a theoretical basis for the analysis of UVAG residual stress and optimization of UVAG process parameters. [ABSTRACT FROM AUTHOR]

Currently, there is a significant need for affordable coatings that are both authentic and ecofriendly, with the goal of reducing pollution. In order to mitigate frictional loss, researchers have produced hybrid coating based on carbon through the utilization of the high‐velocity oxygen fuel (HVOF) spray technique. The results showed that the coefficients of friction (COFs) varied in the range of 0.1–0.5, and the wear rates ranged from 40 to 115 μm. The experiments were performed under different situations, encompassing temperatures ranging from 50°C to 200°C, loads ranging from 40 to 55 N, and sliding speeds ranging from 0.3 to 1.2 m/s. The corrosion tests showed a decrease in mass loss from 0.15 to 0.02 g after 1 h of immersion and from 0.20 to 0.04 g after 5 h of immersion. The tribological testing revealed significant improvements in various properties. The microhardness increased by 78.7%, residual stress decreased by 78%, mass loss due to corrosion decreased by 60% after 1 h and 62.5% after 5 h, coefficient of friction decreased by 76.9%, and wear rate reduced by 62.5%. [ABSTRACT FROM AUTHOR]

In this investigation, Taguchi's grey relational analysis (GRA) is utilized to optimize parameters in an orthotropic steel deck section subjected to thermo‐mechanical tensioning. In this study, it is aimed to determine optimal values for deck thickness, welding sequence, and welding speed, which are evaluated through finite‐element analysis based on outputs such as longitudinal stress, transverse stress, and deflection. In this study, a previously validated numerical simulation model is extended by conducting a parametric analysis to investigate the influence of varying parameters on the model's behavior. An analysis of variance is conducted to identify the most significant variable affecting the input parameters. Additionally, a confirmatory test is also performed to validate the characteristics of the Grey Relational Grade. In the results, it is indicated that faster welding speeds result in increased deflection of the deck plate. Furthermore, the transition from compressive to tensile longitudinal stress is more abrupt in thinner decks (9–10 mm) compared to thicker decks (11–12 mm). This redistribution of residual stresses is attributed to the increasing thickness of the deck plate. Optimal input levels (A2–B1–C1: 10 mm deck thickness, welding sequence case 1, and 0.005 m s−1 welding speed) are determined using GRA. Welding speed contributes the maximum to the optimization results among the evaluated variables. [ABSTRACT FROM AUTHOR]

The effect of plastic deformation on the hydrogen embrittlement behavior of high-strength martensitic steels was investigated using a U-bend test. The hydrogen embrittlement susceptibility appeared to be enhanced with increasing plastic strain. Based on fractographic and stress-strain analyses, the maximum principal stress dominated the hydrogen embrittlement fracture. Although an apparent enhancement with increasing plastic deformation was observed, the origin of this enhancement was increased residual stress arising from the evolution of graded plastic strain during U-bending. We conclude that residual stress, rather than plastic strain induced by plastic deformation strongly affects hydrogen embrittlement susceptibility in deformed high-strength steel components. • Hydrogen embrittlement susceptibility of U-bend specimens was independent of plastic strain. • Maximum principal stress was the primary criterion for the hydrogen embrittlement susceptibility. • The apparent decrease in hydrogen embrittlement resistance with reduced bending radii was due to increased residual stress. [ABSTRACT FROM AUTHOR]

Mechanical behavior of B 4 C - HfB 2 particulate ceramic composite doped with CrB + Cr 3 B 4 chromium boride compounds were studied by nanoindentation. Hardness, Young's modulus, and indentation stress - indentation strain behavior of B 4 C and HfB 2 phases was computed. It was found that hardness and Young's modulus of B 4 C matrix phase in B 4 C - HfB 2 doped with Cr - B was increased as compared to those hardness and Young's modulus of pure B 4 C. It was also found that indentation stress was relieved by "pop-in" events in some of the B 4 C grains, however, the "pop-in" discontinuous events were always observed upon indentation of HfB 2 grains, that lead to a decrease in hardness of HfB 2 from 40 to 50 GPa before "pop-ins" to 28–32 GPa after "pop-ins". The obtained results can be further used in calculations of thermal residual stresses in B 4 C and HfB 2 phases of B 4 C - HfB 2 particulate ceramic composite. [ABSTRACT FROM AUTHOR]

The high residual stress and low toughness of ceramic matrix composite/metallic brazed joints poses severe challenges for the stable operation of high-speed aircraft under harsh conditions. This article innovatively tackles this issue with electrophoretic deposition (EPD), creating a CNT covered Cu foam composite interlayer for brazing C f /SiC and Nb with an Ag–Cu–Ti alloy filler. A layer of mass ratio-controllable and percolated CNTs was physically adsorbed on the surface of the Cu foam substrate. EPD time was systematically investigated for its impact on the microstructure and mechanical properties of the joints. Results indicate that during brazing, the CNTs reacted with the active Ti element, transforming into ultrafine TiC grains with particle sizes ranging from 6 to 16 nm. These were dispersed evenly in the Ag solid solution. The elastic recovery rate of the cluster regions showed an increase of 123 % compared to the Ag solid solution, showing improved toughness of the seam. When the EPD time was 80 min, the shear strength of the joint produced with the composite interlayer reached 128.6 MPa, a 69 % increase over the directly brazed joint. Moreover, the fracture location of the joint shifted from the brazed seam towards the interior of the bulk C f /SiC. Additionally, finite element analysis was utilized to confirm a significant decrease in residual stresses within the joint, and verified the findings. [ABSTRACT FROM AUTHOR]

In order to study the influence of the lifting force arrangement on the mechanical performance of the long-span steel-concrete composite girder which using the lifting-composing construction method, based on the Qinhe grand bridge along the Taihang expressway, the effects of different first and secondary lifting force, the number and distance of lifting points on the stress, deformation, stability, and bridge deck compressive stress reserve of the steel-concrete composite girder were studied by using the Midas-Civil finite element software and a control variable method. The sensitivity of different factors on the steel-concrete composite girder was analyzed through variable normalization, moreover, the optimal scheme was selected, and the implementation effect was monitored on site. The results show that the stress of upper flange of the steel girder, bridge deck, and bridge deflection are most sensitive to the secondary lifting force, with sensitivities of 0.61, 1.95, and 0.16, respectively. The stress of lower flange of the steel girder is most sensitive to the number of lifting points, with a sensitivity of 0.20. The theoretical optimal pre-bending of Qinhe grand bridge is 78%, the final scheme arranges 5 groups of lifting points with distance of 11 m, and the first and the secondary lifting forces are 1 500 kN and 6 500 kN, respectively. The on-site monitoring results show that the construction effect of the scheme is consistent with the theoretical analysis results, and the on-site lifting force is reasonably arranged. The on-site monitoring results show that the implementation effect of the scheme is consistent with the theoretical analysis, and the lifting force is reasonably arranged. The research results can provide reference for similar projects. [ABSTRACT FROM AUTHOR]

This study investigates the effects of film thickness and substrate bias on the microstructure and stress state of tungsten (W) films prepared by arc ion plating (AIP) on substrates including 304 stainless steel (SS), tungsten (W), and Si (100). The microstructure of the films was characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Residual stress was analyzed using substrate curvature techniques combined with Stoney's formula and Huseh's formula. The results indicate that the W films are single-phase, predominantly comprising the pure α-phase. The film surfaces are dense and smooth, with the absence of large particles. The films consist of closely packed columnar grains, and no microcracks, voids, or delamination were observed at the film-substrate interface, indicating strong adhesion. As the film thickness increased, the curvature of the W/SS system and the compressive stress in the film both increased, which closely matched the fitted curves. As the substrate bias increased, the curvature of the W/SS system decreased, and the compressive stress in the W film increased. At higher substrate biases, deposition temperatures are higher, and growth stress remains nearly constant across a range of continuous bias variations, with the increase in residual stress primarily due to thermal stress. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the effects of toolpath patterns, geometry types, and layering effects on the mechanical properties of parts manufactured by direct energy deposition (DED) additive manufacturing using data analysis and machine learning methods. A total of twelve case studies were conducted, involving four distinct geometries, each paired with three different toolpath patterns based on finite element method (FEM) simulations. These simulations focused on residual stresses, strains, and maximum principal stresses at various nodes. A comprehensive analysis was performed using a linear mixed-effects (LME) model, principal component analysis (PCA), and self-organizing map (SOM) clustering. The LME model quantified the contributions of geometry, toolpath, and layer number to mechanical properties, while PCA identified key variables with high variance. SOM clustering was used to classify the data, revealing patterns related to stress and strain distributions across different geometries and toolpaths. In conclusion, LME, PCA, and SOM offer valuable insights into the final mechanical properties of DED-fabricated parts. [ABSTRACT FROM AUTHOR]

This work systematically investigated the effect of dual shot peening (DSP) and conventional shot peening (CSP) on the microstructure, residual stress and wear performance of the CNT/Al-Cu-Mg composites. The results indicated that compared with CSP, DSP effectively reduced surface roughness (Rz) from 31.30 to 12.04 μm. In parallel, DSP introduced a smaller domain size (33.1 nm) and more dislocations, higher levels compressive residual stress and a stiffer deformation layer with deeper affected zones. Moreover, DSP effectively improved the uniformity of the surface layer's microstructure and residual stress distribution. The improvement is mainly due to secondary impact deformation by microshots and fine grain strengthening. In addition, the transformation of the hard second phases such as Al4C3 and CNT and its effects on improving the surface strength and deformation uniformity were discussed. Significantly, DSP improved the wear resistance by 31.8% under the load of 6 N, which is attributed to the synergistic influence of factors including hardness, compressive residual stress, surface roughness, and grain size. In summary, it can be concluded that DSP is an effective strategy to promote the surface layer characteristics for CNT/Al-Cu-Mg composites. [ABSTRACT FROM AUTHOR]

Friction stir welding has been extensively applied for the high-quality bonding of Mg alloys. The welding temperature caused by friction and plastic deformation is essential for determining the joint characteristics, especially the residual stress and weld microstructure. In this work, a modified moving heat source model was proposed by considering the variations in heat generation caused by friction shear stress at both the side and bottom surfaces of the tool. The application of this model was further extended to the entire welding process, especially in the plunging stage. The relative errors between the experimental and simulated peak temperatures at characteristic points were small, with a maximum of 10%, thereby validating the model for accurate temperature prediction. Furthermore, the influence of welding and rotational speed on temperature fields was systematically investigated. At relatively low welding and rotational speeds, the welding temperature increased significantly with either an increase in rotational speed or a decrease in welding speed. However, this effect gradually diminished at higher welding and rotational speeds. These results provide some valuable guidelines for controlling heat generation to improve the quality of Mg alloy welds. [ABSTRACT FROM AUTHOR]