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This study explores the evolution of solidification microstructure of a laser powder bed fusion (L-PBF) martensitic stainless steel during solution annealing and aging. Quasi in-situ experiments using electron backscatter diffraction (EBSD) revealed that the finer, more equiaxed microstructure below the melt pool was susceptible to recrystallization and grain growth during solution annealing. The two distinct solidification microstructures below and inside the melt pool converged into a uniform grain morphology after solution annealing and aging processes. [ABSTRACT FROM AUTHOR]

In this study, the effects of microstructural modifications induced by tuning the laser-powder bed fusion (L-PBD) process parameters on electrochemical stability of the L-PBF-AlSi10Mg alloy are investigated. Three groups of L-PBF-AlSi10Mg samples were fabricated utilizing combinations of L-PBF process parameters for their Upskin layers. The implemented process parameters modifications were found to be not only effective in reducing the as-printed surface roughness of the components, but also led to the formation of cyclic small-large melt pools (MPs) in Upskin layers of the fabricated samples. Such consecutive modification in the size of MPs led to the increased inhomogeneity of the microstructure, contributing to the formation of a coarser intercellular eutectic-Si network, larger grain size, and lower density of low angle grain boundaries. Among all fabricated samples, the sample that experienced the fastest cooling during solidification was found to reveal the highest corrosion resistance and the best passive film stability on its Upskin surface both in naturally-aerated and deaerated 3.5 wt.% NaCl electrolyte, owing to the finer Al-Si eutectic structure that forms along its large MP-boundaries. The as-printed microstructure of the L-PBF-AlSi10Mg was found a dominant factor in determining the necessity of applying post-printing surface polishing procedures to attain better corrosion properties. [ABSTRACT FROM AUTHOR]

Direct metal laser sintering (DMLS) is an additive manufacturing technique that creates near-net-shape functional components by selectively melting metal powders in two dimensions layer by layer using a high power laser as a heat source. This technique offers to create parts with complex net-shape structures at an affordable cost with the least lead time. The main purpose of this study is to investigate the corrosion behavior and microstructure of AlSi10Mg_200C manufactured using DMLS compared with its die cast counterpart (A360.1 die cast Al alloy). The impact of the alloy’s surface finish, i.e . as-printed surface versus as-ground one, on the corrosion performance was also investigated. Several AlSi10Mg_200C cube samples were additively manufactured through DMLS technique. In addition, the same size cubes were cut from an aluminum A360.1 die cast ingot. The corrosion behavior of the two alloys was analyzed utilizing potentiodynamic polarization testing and electrochemical impedance spectroscopy in aerated 3.5 wt.% NaCl solution to mimic sea water environment at 25 °C. Further, the microstructures and composition of the samples before and after corrosion testing were investigated using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) spectroscopy. The results confirmed that the corrosion resistance of the alloy processed through DMLS was significantly better than the cast counterpart. This was attributed to the fine microstructure produced by DMLS, uniform distribution of the fine Si particles without formation of any intermetallic, due to the extremely rapid cooling and solidification rate during DMLS process and slightly lower Fe and Cu concentration of the AlSi10Mg alloy. In contrast, the A360.1 cast Al alloy samples experienced severe localized corrosion of the Al matrix in the periphery of the Fe containing IMC and Si flakes. The results also highlighted improved corrosion resistance of the as-printed DMLS sample compared with that of the as-ground one. [ABSTRACT FROM AUTHOR]

In the present paper, the microstructural evolution and tensile properties of additively manufactured stainless steel CX were investigated. Using scanning electron microscope (SEM), several powder particle morphologies were identified in the stainless s steel CX feedstock powder where the spherical morphology was found to be the dominant one. In addition, X-ray diffraction (XRD) technique detected austenite and martensite phases in both stainless steel CX powder and as-built sample, whereas no carbide peak appeared on the XRD patterns. Moreover, lath or needle-like martensite phase was observed in the microstructure of the as-built sample. The level of porosity was very low in the as-built sample, indicating the manufacturing of a nearly fully dense sample. Furthermore, a high ultimate tensile strength together with a good elongation to fracture was obtained for the horizontally-built stainless steel CX sample. Finally, examination of the fracture surfaces after tensile tests confirmed the ductile failure mode of the samples, in which the pull-out of the scan tracks and coalescence of the voids resulted in the tear and final rupture. This study demonstrates the successful additive manufacturing of stainless steel CX with outstanding tensile properties. [ABSTRACT FROM AUTHOR]

A unit cell model based on the interaction between the fibre and a matrix at the micromechanics scale for a long fibre reinforced composite is developed. An interphase zone is defined to describe the load transfer between the fibre and matrix. The interphase zone has functionally graded properties, and occupies a region including the physical boundary between the fibre and matrix. Material paring constants k and l are introduced to define the size of the interphase zone, independent of the volume fraction of reinforcement for a given set of materials. This model allows the prediction of the average stress in the composite as well as the constituents. [ABSTRACT FROM AUTHOR]

• Friction stir processing (FSP) eliminated the L-PBF induced porosities in AlSi10Mg alloy. • Grain refinement and uniform silicon particles distribution were detected after FSP. • FSPed L-PBF AlSi10Mg alloy showed improved corrosion performance. • Formation of a more stable and thicker passive film was noticed after FSP. • Donor density in the passive layer decreased after FSP. The solid-state structural modification technique friction-stir-processing (FSP) was applied on the surface of a laser-powder-bed-fusion fabricated AlSi10Mg alloy to locally modify the microstructure and enhance the corrosion properties of the alloy. A uniform microstructure was formed after FSP, comprised of a homogenous distribution of the Si-particles embedded in an Al-matrix with an ultrafine-grained structure containing a low fraction of subgrains, and reduced porosity level. This structure offers improved corrosion properties, ascribed to the formation of a thicker passive layer with a lower donor density on the FSPed regions as compared to the as-fabricated metal. [ABSTRACT FROM AUTHOR]

The application of soft and hard recoater-blades is studied on the mechanical properties and microstructure of additively manufactured maraging steels. The soft recoater-blade leads to unmelted powders as an initial site for premature fracture. Lower retained austenite fraction ends up with lower phase transformation, strain hardening and ductility. [ABSTRACT FROM AUTHOR]

This research explores the sintering behavior and microstructure of ZrB 2 -based materials containing graphene nano-platelets (GNPs) and SiC whiskers (SiC w). Spark plasma sintering (SPS) process at 1900 °C was implemented to sinter the specimen, leading to a composite with 100% relative density. High-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), field emission-electron probe microanalyzer (FE-EPMA), and high-resolution X-ray diffractometry (HRXRD) were employed to study the SPSed sample, along with the thermodynamics predictions. According to the HRXRD result and microstructural observations, the sintering process was non-reactive, which was endorsed with the XPS analysis. Furthermore, graphene presented a beneficial role for eradicating the oxide impurities in the sample during the sintering. Such oxide impurities were reduced to the original phases of SiC and ZrB 2 , contributing to porosity removal. Nanostructural investigations revealed the formation of ultrathin amorphous interfaces (~10 nm) between ZrB 2 /graphene phases, disordered atomic planes in graphene platelets, and dislocations in ZrB 2 grains. One reason for generating crystalline defects in the microstructure was found out to be the mismatches amongst the elastic properties of the available compounds in the system. [ABSTRACT FROM AUTHOR]

A TiB 2 –Ti 3 AlC 2 ceramic was manufactured by spark plasma sintering at 1900 °C temperature for 7 min soaking time under 30 MPa biaxial pressure. The role of Ti 3 AlC 2 additive on the microstructure development, densification behavior, phase evolution, and hardness of the ceramic composite were studied. The phase characterization and microstructural investigations unveiled that the Ti 3 AlC 2 MAX phase decomposes at the initial stages of the sintering. The in-situ formed phases, induced by the decomposition of Ti 3 AlC 2 additive, were identified and scrutinized by XRD and FESEM/EDS techniques as well as thermodynamics principles. The sintered TiB 2 –Ti 3 AlC 2 ceramic approached a near full density of ~99% and a hardness of ~28 GPa. The densification mechanism and sintering phenomena were discussed and graphically illustrated. [ABSTRACT FROM AUTHOR]

The effects of adding graphene nano-platelets (6 wt%) on the microstructure and thermal diffusivity and conductivity of TiN-based ceramics were investigated. Two samples, a monolithic TiN, and a graphene-added TiN ceramics were fabricated using spark plasma sintering technique at 1900 °C for 7 min under 40 MPa. The microstructure of the polished and fractured surfaces of both samples was analyzed by scanning electron microscopy. Adding graphene resulted in a 2% reduction in the relative density, but led to obtaining a fine-grained microstructure. The consumption of graphene nano-additive during the sintering, through the reduction of surface oxide layers of TiN matrix (TiO 2), and consequently, the formation of titanium carbonitride (TiN 0 · 8 C 0.2) were disclosed by X-ray diffraction analysis. The measurement of the thermal diffusivity was done using the laser flash technique. The TiN–6 wt% graphene sample obtained lower thermal conductivity compared to the monolithic TiN, which can be attributed to the smaller grain size of the graphene-added sample. [ABSTRACT FROM AUTHOR]

Introducing the SiC additive resulted in a noticeable enhancement in the sintering behavior of the ZrB 2 –hBN composite, profiting from the SiC involvement in the surface oxide removal. This research intended to compare two ceramics of ZrB 2 –hBN and ZrB 2 –SiC–hBN in terms of sinterability, microstructure, and mechanical features. Both samples were spark plasma sintered at 2000 °C for 5 min under 30 MPa. The SiC-free specimen reached a relative density of lower than 95%, while incorporating SiC improved this value up to 99.3%, resulting in near fully dense material. The role of SiC on oxide removal was found to be the chief cause in enhancing the sinterability of the ZrB 2 –SiC–hBN sample compared to ZrB 2 –hBN. According to the field emission scanning electron microscopy (FESEM), field emission-electron probe microanalyzer (FE-EPMA), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS) studies, both systems were unreactive, and no major in-situ phase could be produced over the sintering process. The ZrB 2 –SiC–hBN composite reached an elastic modulus of 374 GPa and a Vickers hardness of 19 GPa. [ABSTRACT FROM AUTHOR]

The microstructure, mechanical properties, and oxidation behavior of a ZrB 2 –20 vol% SiC–5 vol% B 4 C composite hot-pressed at the temperature of 1850 °C for 1 h under 40 MPa were investigated. A highly dense ceramic with a density of 99.4% containing ZrB 2 , SiC, and B 4 C phases in the final sintered sample, was obtained. The fractography revealed the existence of few oxide impurities in cauliflower-like morphologies. The mechanical properties investigations showed that the composite possessed a Vickers hardness of 20.1± 1.2 GPa, a flexural strength of 275 ± 21 MPa, and a fracture toughness of 4.0 ± 0.2 MPa m1/2. An oxidation activation energy of 275.2 kJ/mol was estimated by studying the behavior of the oxidation process at the temperatures of 1000, 1400, and 1700 °C for 1, 4, and 10 h. Moreover, different layers formed during the specimen's oxidation process: a ZrO 2 /SiO 2 /B 2 O 3 layer, a ZrB 2 /SiC–depleted intermediate layer, and an unaffected substrate. It was found that the released carbon monoxide has the tendency to move toward the outer oxidized layer in order to leave the bulk structure. [ABSTRACT FROM AUTHOR]

The impact of Si 3 N 4 and SiC additives incorporation in the microstructure and sintering behavior of TiB 2 -based composites were studied. Three ceramic composites including TiB 2 –Si 3 N 4 , TiB 2 –SiC, and TiB 2 –SiC–Si 3 N 4 were manufactured by spark plasma sintering (SPS) at 1950 °C for 8 min under 35 MPa. The acquired ceramics were analyzed by X-ray diffractometry and scanning electron microscopy. In addition, the sintering thermodynamic was investigated using the HSC Chemistry package. X-ray diffraction patterns of the prepared ceramics revealed the in-situ formation of graphite and boron nitride in the final composites initiated from SiC and Si 3 N 4 , respectively. The thermodynamic assessments proved the role of liquid phase sintering on the sinterability enhancement of all composite samples. Field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy verified the in-situ formation of both BN and graphite components in the sample containing SiC and Si 3 N 4 additives. Finally, the fractographical investigations clarified the transgranular breakage as the main fracture mode in the TiB 2 -based ceramics. [ABSTRACT FROM AUTHOR]

Three near fully dense TiB 2 –SiC composites were achieved, benefiting from the coaddition of SiC and a nitride compound (Si 3 N 4 , h-BN or TiN). All composites were produced by spark plasma sintering (SPS) at 1900 °C. The in-situ formed TiC phase was identified in the all three composites due to occurring a chemical reaction between TiO 2 oxide and SiC reinforcement. Although h-BN additive remained intact in the final microstructure of TiB 2 –SiC composites, Si 3 N 4 additive participated in some chemical interaction with B 2 O 3 and TiO 2 surface contaminations, leading to the in-situ generation of h-BN, TiB 2 , and SiO 2 phases. In contrast, TiN additive reacted with the in-situ formed TiC, producing the TiC x N 1-x compound during the sintering process. Liquid phase sintering was also identified as one of the involved mechanisms, enhancing the sinterability of the prepared composites. [ABSTRACT FROM AUTHOR]

The present research aims to investigate the influences of SiC reinforcement and h-BN additive on the relative density, microstructure, and thermodynamic aspects of TiB 2 -based ceramics. Three different specimens, including monolithic TiB 2 , TiB 2 –SiC, and TiB 2 -SiC-BN were fabricated using spark plasma sintering (SPS) at 1900 °C. A dwelling time of 7 min and an external pressure of 40 MPa were applied as the sintering conditions. The characteristics of SPSed monolithic TiB 2 and the prepared composites were studied using X-ray diffractometry, thermodynamic inspections, and scanning electron microscopy. These assessments unveiled the in-situ formation of TiC and graphitized carbon in the TiB 2 –SiC preparation process, whereas no carbon was detected in the composite doped with h-BN. Introducing SiC had immense impact on the relative density of both composites, yielding near fully dense ceramics. The intergranular type was the dominant fracture mode in the all three TiB 2 -based ceramics. Moreover, the addition of secondary phase substantially refined the microstructure of TiB 2 , reaching ceramics with finer grains than the undoped ceramic. [ABSTRACT FROM AUTHOR]

Abstract Rod shaped samples of AlSi10Mg alloy were additively manufactured in vertical and horizontal directions using direct metal laser sintering technique and subjected to dynamic loading using Split Hopkinson Pressure Bar apparatus at a strain rate of 1400 s−1. Despite employing the same process parameters to fabricate the samples in two directions, the as-built samples possessed different microstructures, where columnar and equiaxed microstructures were developed in the vertical and horizontal samples, respectively. Moreover, fine and coherent Si precipitates were observed in the vertical sample while coarse and semi-coherent ones were developed in the horizontal sample. In addition, changing the building direction from horizontal to vertical led to a three-fold increase in dislocation density. After applying the compressive impact loads on the vertical and horizontal samples, it was found that the dynamic loading behavior of the two samples was almost similar despite the crucial differences in the initial microstructures. The microstructural analysis of the deformed samples revealed entangled networks of dislocations. In addition, over some locations, low angle grain boundaries developed due to partial dynamic recovery. The strengthening behaviors of the two samples additively manufactured in vertical and horizontal directions were investigated using the fundamentals of alloy hardening to unveil the similarities. Graphical abstract Unlabelled Image Highlights • Rod samples of AlSi10Mg additively manufactured in horizontal and vertical directions through DMLS using same parameters • Microstructure of as-built samples were different in terms of cell structure, pre-existing dislocations and Si precipitates • The samples were subjected to high strain rate compressive deformation using Split Hopkinson Pressure Bar apparatus • Deformed microstructure consisted entangled dislocation networks along with low angle grain boundaries due to partial DRV • Strengthening behavior of the samples was analyzed considering Orowan, Hall-Petch and dislocation hardening mechanisms [ABSTRACT FROM AUTHOR]

In present research, the effect of building orientation on microstructure, texture and mechanical properties of a low carbon maraging steel processed by selective laser melting (SLM) technique is studied. The microstructural characterization and grain structure observations of the fabricated samples are conducted using electron microscopies and electron backscatter diffraction. It is observed that by altering the building orientation from vertical to horizontal, the morphology of the grains changes from columnar-dendritic to equiaxed. In addition, a higher volume fraction of austenite is retained in the horizontal sample compared with the vertically printed sample due to a faster cooling rate, higher degree of micro-segregation, and smaller prior austenite grains. Consequently, a higher strength and better ductility are achieved in the horizontally printed sample. The Taylor factorshows that different obtained tensile properties are not related to the crystallographic texture but are affected by grain size, retained austenite, and stress concentration conditions. • Samples of new maraging stainless steels were additively manufactured using the SLM process in different orientations. • Evolution of microstructure and micro-texture is elucidated. • A higher fraction of austenite is retained in the horizontal sample's microstructure than the vertically printed sample. • Higher strength and better ductility are achieved in the horizontally printed sample. [ABSTRACT FROM AUTHOR]

• Ti64 samples were fabricated through L-PBF and EBM techniques. • The microstructure of the samples was analyzed using EBSD technique. • The micromechanical properties of the samples were evaluated using nanoindentation. • The microstructure of L-PBF-Ti64 was one order of magnitude finer than EBM-Ti64. • The micromechanical strength of L-PBF-Ti64 was higher than EBM-Ti64. Employing a depth-sensing indentation testing technique, the room temperature mechanical properties of Ti-6Al-4V (Ti64) alloy fabricated through laser powder-bed fusion (L-PBF) and electron beam melting (EBM) additive manufacturing processes were studied. Mechanical properties including nano-hardness (in GPa), reduced elastic modulus, yield pressure, elastic recovery, and wear resistance were extracted. The microstructure of the fabricated materials was correlated with the indentation-derived characteristics. It was observed that the nano-hardness and reduced elastic modulus values were 3.66 ± 0.06 GPa and 118 ± 3 GPa, for the L-PBF, and 3.43 ± 0.22 GPa and 136 ± 4 GPa, for the EBM materials, respectively. The higher strength of the L-PBF alloy is due to the finer microstructure of this alloy. While α laths with an average width of 3.61 ± 0.92 μm developed in the EBM-Ti64, the microstructure of L-PBF-Ti64 consisted of α′ martensite with an average width of 0.37 ± 0.10 μm. [ABSTRACT FROM AUTHOR]

To restore defected AA2618 alloy molds, remanufacturing of the damaged areas using AlSi10Mg alloy through laser powder bed fusion (L-PBF) technique is proposed. This study in particular focuses on the corrosion characteristics of the fabricated L -PBF AlSi10Mg / cast AA2618 bimetal structure in aerated 3.5 wt.% NaCl electrolyte with respect to the individual alloys. The L -PBF AlSi10Mg side of the bimetal sample was characterized with a superior corrosion response and the highest passive film stability compared with the cast AA2618 side and the dissimilar sample (prepared from the interface region), ascribed to its homogeneous microstructure, containing a very fine network of eutectic Si embedded in a fine grained and supersaturated α-Al matrix. The overall corrosion performance of the dissimilar sample was found to be between the cast AA2618 and L -PBF AlSi10Mg part, with no sign of macro-galvanic corrosion effect between the dissimilar alloys. The heavily precipitated microstructure of the cast AA2618 alloy, particularly the anodic Al 2 CuMg phase and cathodic Fe-containing intermetallics versus the Al-matrix, dictated the inferior corrosion properties of the cast sample and the cast side of the dissimilar sample. [ABSTRACT FROM AUTHOR]

[Display omitted] Additive manufacturing experiments using the laser powder bed fusion (LPBF) method reveal that changing the build direction can stimulate morphological transitions in the solidification microstructure. As a result, the final texture and material properties can be altered. In this work, we conduct numerical investigations to explore the effect of building direction on the microstructure evolution of dilute Al-Si alloy produced by the LPBF process. A finite element thermal model is developed to incorporate the effect of build direction on the thermal characteristics of the melt pool for a vertically and horizontally printed Al-Si powder layer. We then utilize a multi-order parameter phase-field model to probe the microstructure evolution of LPBF Al-Si alloy in the dilute limit under the aforementioned thermal conditions for horizontal and vertical printing strategies. The phase-field model described here can self-consistently emulate spontaneous formation of nuclei from inoculant particles and simulate morphological transitions. The accuracy of the phase-field model is validated through the numerical examination of morphological transitions under directional solidification conditions of a dilute Al-Si alloy and compared to the predictions of the analytical CET theory of Hunt [1]. The phase-field simulations and subsequent grain analysis of the microstructure under transient thermal conditions reveal that the nucleation rate and hence equiaxed to columnar microstructure ratio is notably higher in the horizontally built samples. These results are in consistence with experimental observations. [ABSTRACT FROM AUTHOR]

• L-PBF process led to the formation of a hierarchical microstructure in the l -PBF components. • After heat treatment, the microstructure of l -PBF samples is free of sub-grains and austenite. • The microstructure of heat-treated SS 420 is composed of coarse grains, a high fraction of austenite and Cr-rich carbides. • Low corrosion performance of heat-treated wrought sample is attributed to the formation of Cr-rich carbides and austenite phase. • The adverse impact of nano-scale inclusions and β-NiAl precipitates on corrosion performance is lower than carbide precipitates and austenite. The corrosion resistance of heat-treated additively manufactured (AM) precipitation hardening martensitic stainless steel (SS) CX and wrought components of AISI 420-SS with lower Ni content, were compared. The microstructure of heat-treated AM-CX comprised of a martensitic matrix and a few nano-scale particles, while the wrought AISI 420-SS contained approximately 8% of austenite and Cr-rich carbides in a martensitic matrix. Superior corrosion resistance was detected for the AM-CX part as compared to the AISI 420-SS ascribed to nearly absence of Cr-rich carbides and martensite-retained austenite interfaces in the AM-CX SS, while their presence in the AISI 420-SS destabilized the passive film. [ABSTRACT FROM AUTHOR]

• L-PBF was used to fabricate a modified A205 alloy with TiB 2 nanoparticles nucleants. • An isotropic microstructure, containing TiB 2 and Al 2 Cu secondary phases, was formed. • Ultrafine texture-free grained structure of the alloy led to its improved passivity. • Microstructural homogeneity of the alloy led to its isotropic corrosion response. • TiB 2 agglomerates-Al matrix interface was susceptible to localized corrosion attack. Herein, a newly developed laser-powder-bed-fusion (L-PBF) fabricated Al-Cu-Mg-Ag-Ti-B alloy, known as A205 alloy, is introduced with exceptionally refined, uniform, and texture-free microstructure comprised of an ultrafine-grained Al-matrix reinforced with eutectic-Al 2 Cu precipitates and TiB 2 particles/agglomerates. Preliminary electrochemical characterization of the fabricated samples on planes parallel and perpendicular to the part's building direction revealed a similar polarization response characterized by a clear passive window for both samples. The corrosion morphology assessment of both samples showed the susceptibility of Al-matrix adjacent to TiB 2 agglomerates to localized corrosion attack. The electrochemical impedance spectroscopy (EIS) results also confirmed similar integrity and protectiveness for the passive layer on both samples, further affirming the obtained isotropic corrosion response of the L-PBF-A205 alloy. [ABSTRACT FROM AUTHOR]

This examination intended to evaluate the synergic influence of graphene nano-platelets (GNPs) and AlN on the microstructure and consolidation behavior of TiC. The spark plasma sintering (SPS) method was employed as the manufacturing process under the sintering circumstances of 40 MPa, 10 min, and 1900 °C. The simultaneous incorporation of AlN and GNPs could improve the relative density of TiC more than 4%, reaching a fully dense ceramic. According to the X-ray diffraction (XRD) spectrum, thermodynamic study, as well as the microstructural assessments, i.e., scanning electron microscopy (SEM), Electron probe micro-analyzer (EPMA), scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM), the TiN and Al 2 OC ingredients were produced over the SPS process as the in-situ phases. Although Al 2 OC remained in the microstructure as an amorphous-like phase, the in-situ produced TiN dissolved into the TiC matrix, creating a Ti(C,N) solid solution. A chemical reaction between AlN and the surface oxide of TiC, namely TiO 2 , was found to be responsible for the in-situ generation of the TiN compound. Thanks to the formation of the solid solution, strong interfaces were created amongst the matrix grains, promoting the transgranular fracture mode. Moreover, some dislocations and distorted atomic planes were seen in the microstructure, derived from the thermal expansion coefficients' inconsistency between the different phases over the cooling stage. • Synergic effect of graphene and AlN on microstructure of TiC ceramics was studied. • TiN and Al 2 OC phases were in-situ formed during the SPS process at 1900 °C. • Al 2 OC remained in the ceramic, but TiN dissolved into TiC to form solid solution. • Many dislocations and distorted atomic planes were detected in the microstructure. [ABSTRACT FROM AUTHOR]

This examination is aimed to study the various densification mechanisms in the ZrB 2 -SiC system at different sintering temperatures. For such an objective, hot-pressing process was implemented to fabricate three ceramics at sintering temperatures of 1650, 1850, and 2050 °C under 10 MPa for 1 h. According to the results, particle rearrangement and fragmentation were the predominant densification mechanisms at the lowest sintering temperature. Additionally, it was found that the activation of the liquid phase sintering mechanism was advantageous in the particle rearrangement at low temperatures. However, rising the sintering temperature to 1850 °C changed the dominant mechanism to the plastic deformation. Such a phenomenon was accompanied by the creation of many dislocations in both ZrB 2 and SiC grains. Implementing a higher sintering temperature (2050 °C) activated another consolidation mechanism called diffusion. This occurrence, together with the evaporation of the majority of the liquid phase at elevated temperatures, resulted in emerging transgranular fracture mode in the sample. • Various densification mechanisms in hot-pressed ZrB 2 -SiC composites were studied. • Sintering processes were implemented at temperatures of 1650, 1850, and 2050 °C. • Particle rearrangement/fragmentation were the dominant mechanisms at 1650 °C. • The dominant densification mechanism was plastic deformation at 1850 °C. • At the highest hot-pressing temperature of 2050 °C, diffusion was the dominant one. [ABSTRACT FROM AUTHOR]

Additive manufacturing of a low carbon Fe–Cr–Ni–Al maraging stainless steel (with the brand name CX) through the laser-powder bed fusion (LPBF) process is studied. Since the strength of this material is enhanced through precipitation hardening, the effect of different heat treatment cycles on the hardness and microstructure is assessed. The LPBF-CX is heat treated through a standard heat treatment procedure consisted of austenitization at 900 °C for 1 h followed by air cooling and aging at 530 °C for 3 h. Moreover, the effect of aging treatment (with no austenitization) on the as-built sample is studied. The microstructure of the as-built, austenitized-aged, and aged samples is studied using multiscale electron microscopy techniques. The as-built LPBF-CX consists of the typical lath martensitic structure and minor retained austenite. The martensite laths are featured by high dislocation density, with no evidence of precipitates. Austenitization-aging treatment shows a detrimental effect on the strength of LPBF-CX, due to martensite laths growth and retardation of precipitates evolution. Aging of the as-built LPBF-CX results in strength enhancement due to the evolution of nanometric and coherent β-NiAl precipitates, and martensite laths refinement. Moreover, the pre-existing dislocation networks play a key role in the strength of the aged material. The strength enhancement of the aged LPBF-CX is investigated through the fundamentals of alloy hardening. [ABSTRACT FROM AUTHOR]

In this work, the effect of built direction on the small-scale mechanical properties and microstructure of a novel maraging stainless steel (SS-CX) manufactured through the selective laser melting (SLM) process was studied. Advanced electron microscopy and nanoindentation techniques were utilized to evaluate retained austenite fraction and micro-mechanical properties, respectively. Different thermal histories caused by the change of the built direction resulted in microstructures with different volume fractions of retained austenite and grain morphology. Furthermore, the slower cooling rates in the vertically built sample was found to result in the formation of large elongated grains and lower hardness values during the nanoindentation experiments. • The building direction changes the microstructure of selective laser melting product. • Changing the building direction resulted in different volume fractions of retained austenite. • The thermal history of the product depends on the printing orientation. • The laser scan path changes the static and dynamic recovery processes. [ABSTRACT FROM AUTHOR]

This study aims to achieve a clear understanding of relationships between the anisotropy in the microstructure and corrosion behavior in a newly developed maraging stainless steel (Corrax® or SS CX) fabricated by the laser-powder bed fusion (L-PBF) technique. The focus was to compare the properties of the planes parallel (side) and perpendicular (top) to the building direction of the fabricated sample. Various electrochemical testing and multiscale electron microscopy techniques were used to investigate the microstructure and corrosion behavior of both planes. The results indicated that different thermal histories experienced on the top versus the side planes during the L-PBF lead to microstructural variations between the planes. A slight increase in the laths size, and the lower fractions of dislocation density and low angle grain boundaries, and plausibly the lower level of residual stresses on the side plane were found to contribute to the improved corrosion response of the side plane as compared to the top plane. • Martensite packets with a slight content of retained austenite were observed in L-PBF SS CX. • Nanometric round regions of inclusions containing Al and O were detected in L-PBF SS CX. • Anisotropic corrosion resistance of L-PBF SS CX was related to the differences in the level of residual stresses and the LAGBs density. • The plane parallel to building direction with larger grain size revealed higher corrosion resistance. [ABSTRACT FROM AUTHOR]

In this paper, a comprehensive study on the microstructure and mechanical properties of an additively manufactured 18Ni-300 maraging steel (with the brand name MS1), fabricated through the laser-powder bed fusion (LPBF) technique is presented. The influence of powder layer thickness and the characteristics of feedstock powder as the input in the LPBF process is investigated on the microstructure and mechanical properties of solid cubes and cylindrical rods. Relative density and hardness are measured through the depth of the manufactured cubes. The study of porosity and hardness through the depth of LPBF-MS1 cubes proves homogeneous properties in the core of the material in comparison with more heterogeneous properties closer to the subsurface layers. X-ray diffraction techniques both on the powder and the as-built samples are then performed to identify phases in the fabricated samples. A correlation between lower austenite content and higher strength is observed for the tensile samples manufactured with lower powder layer thickness. Texture analysis shows a directional grain growth along the building direction resulting in a weak texture, while the material induces a stronger texture with an increased amount of austenite after the deformation. Studying the effects of powder layer thickness shows slightly lower strength and ductility for the samples manufactured with higher powder layer thickness, while the energy consumption, as well as the manufacturing time, are reduced. [ABSTRACT FROM AUTHOR]