Aspect Ratio Of Grains Research Articles

Synergistic optimization of microstructure and mechanical properties of AISI 430 ferritic stainless steel via dual-phase zone annealing process

This study systematically evaluated the impact of dual-phase zone annealing on the microstructure and mechanical properties of cold-rolled 430 Ferritic Stainless Steel (FSS), focusing on the phase transformation process from ferrite to austenite and the dissolution and precipitation behavior of the M23C6 phase. The annealing process significantly affects the microstructural characteristics of ferrite and martensite, including grain size, the distribution of grains of various sizes, aspect ratio, and phase content. The amount of martensite first increased and then decreased with rising annealing temperatures. The sample annealed at 1050 °C exhibited the highest martensite content of 29.5%. The variation in martensite content reflects the complex interplay between phase transformation kinetics and thermodynamic equilibrium. As the annealing time increased or temperature rose, the M23C6 phase at ferrite grain boundaries gradually dissolved and re-precipitated at higher temperatures. At lower temperatures, the M23C6 phase precipitated within martensite, but as the temperature increased, the precipitated phase diminished until it disappeared. Temperature changes affect the solubility of precipitates, atomic diffusion rates, and the uniform distribution of atoms across different phases. Appropriately increasing annealing temperature or extending annealing duration enhances the strength and hardness of 430 FSS. However, excessively high annealing temperatures lead to a decline in mechanical properties. The sample annealed at 1000 °C demonstrated the best mechanical properties, achieving a tensile strength of 783 MPa and an elongation of 16.0%. Furthermore, the analysis of fracture morphology and yield behavior in stress-strain curves further elucidated the macroscopic mechanical performance of the material.

The effect of inhomogeneous microstructures on strength and stress corrosion cracking of 7085 aluminum alloy thick plate

Inhomogeneous microstructures and alloy chemistry along the thickness direction can greatly affect the mechanical and corrosion properties of new generation 7xxx aluminum alloy thick plates. The inhomogeneous microstructure, stress corrosion cracking (SCC) resistance and strength of AA7085 thick plate (160 mm) at T/2, T/4, and surface position using mechanical tests, double cantilever beam (DCB) crack extension tests and electron microscopy experiments. The results show that the ultimate tensile strength, yield strength and elongation of the T/2 position are slightly lower than those of the surface position, but the SCC resistance of the T/2 position is significantly higher than that of the surface position. The reason is that larger discontinuously quench-induced grain boundary precipitates (Q-GBPs), and lower Zn and Mg elemental content of GBPs (including Q-GBPs and age-induced GBPs (A-GBPs)) and grain boundaries (GBs). Furthermore, it is newly found that the mechanical effects of larger-sized low aspect ratio unrecrystallized grains contribute significantly to the excellent SCC resistance of the T/2 position. The large size grain structure makes short-range SCC cracks along the large-angle GB more tortuous at T/2, improving the stress intensity required for sustained crack extension. In addition, the high GB triple junction deflection angle resulting from a low aspect ratio grain structure at T/2 improves the average driving force required for crack extension and drive force reduction after localized crack growth.

Influence of solid solution treatment on fatigue crack propagation behavior in the thickness direction of 2519A aluminum alloy thick plates

2519A aluminum alloy thick plates have excellent applications in the military industry due to their superior ballistic resistance and fatigue properties. However, the delamination cracking along the thickness direction of this alloy hinders its further utilization. To address this issue and enhance the fatigue properties of this alloy, the effect of single-stage solid solution treatment (SST) and two-stage solid solution treatment (DST) on the fatigue crack propagation (FCP) behavior in the thickness direction of the alloy was investigated. Compared to the optimum SST, the volume fraction of the secondary phase of the alloy was reduced by 28.6% after DST. The precipitated phases were finer with more uniform distribution, and the volume fraction and number density of the precipitation increased by 47% and 30%, respectively. The DST resulted in a lower fatigue crack growth rate (FCGR) and an increase of 2.92% in the critical stress intensity factor value (ΔKcr). The crack propagation mode of the alloy after SST was inter/transgranular crack propagation, while it was transgranular after DST. The aspect ratio of grain and the number of secondary phases in the alloy decrease after DST. Meanwhile, the grain boundary (GB) precipitation phase spacing, the precipitation-free zone (PFZ) width, and the spacing between the secondary phases increase. These changes result in decreased crack sources in the alloy and reduced the bridging effect of secondary phases on fatigue cracks, thus improving the fatigue performance of the alloy.

Reduced order model for hard magnetic films

In the pursuit of rare earth-lean permanent magnets for green technologies, microstructural optimisation offers a promising strategy to enhance coercivity while minimising critical element content. For this approach, the combination of experimental work on hard magnetic films and numerical investigations is necessary. However, computational limitations restrict micromagnetics to small systems, motivating the development of a reduced order model for investigating large multigrain systems. The model is based on the embedded Stoner-Wohlfarth method and is used to investigate the influence of a nonmagnetic grain boundary phase thickness and the aspect ratio of the magnetic grains on the overall coercivity. It is possible to simulate large NdFeB multigrain structures which can be compared to hard magnetic films. We derive design recommendations to increase coercivity by increasing the grain boundary phase thickness and the aspect ratio of the grains in hard magnetic materials.

Characterization of Fe-6Si Soft Magnetic Alloy Produced by Laser-Directed Energy Deposition Additive Manufacturing

Commercial electrical steels, Fe-Si alloys with < 4 wt.% Si, are inexpensive and efficient materials for electrical power conversion. Further efficiency improvements require increasing the silicon concentration to 6 wt.%, at which point the material becomes brittle and difficult to form by conventional rolling and sheet fabrication methods. Additive manufacturing stands to overcome challenges with commercial manufacturing techniques by leveraging near-net-shape fabrication. The wide array of process conditions provides additive manufacturing with increased flexibility, enabling control over the microstructure and mechanical properties. This work explores the microstructures and magnetic properties of ring-shaped Fe-Si alloys produced using concentric and cross-hatch tool paths on a laser-directed energy deposition additive manufacturing system. Concentric-built samples exhibit elongated grain structures while cross-hatch-built samples comprise lower aspect ratio grain structures. Thermal finite element analysis simulations model the stress conditions produced by the different scan path geometries. Microhardness measurements probe the mechanical properties as a function of anneal temperature, providing a qualitative understanding of the intergranular defect density. Soft magnetic properties measured under quasistatic and AC conditions show frequency- and microstructure-dependent coercivity and permeability. Finally, analysis of the core loss quantifies how the build strategies and thermal treatments influence efficiency in electrical power conversion applications. Understanding the influences of scan path geometry and thermal treatment provides a pathway towards application of additively manufactured soft magnetic materials.

Exploring the creep and oxidation behaviors of four types of FeCrAl alloys through small punch test at 600 °C: Experiments and simulations

Four types of iron-chromium-aluminum (FeCrAl) alloys, composed of different elements, were used to investigate the creep performance and high-temperature oxidation resistance. The microstructures in the undeformed regions after the small punch creep test (SPCT) remained consistent with the as-received (AR) FeCrAl alloys, while the grain aspect ratio (GAR) decreased and grains elongated in the deformed regions. Amongst the four alloys, Q1 exhibited the worst oxidation resistance, whereas Q4 showed superior oxidation resistance due to the addition of Si. Precipitates were observed in the deformed regions after SPCT but not in undeformed regions, indicating that deformation had a positive effect on element segregation. Creep models including Norton power law, Monkman-Grant relationship, Larson-Miller Parameters, and Fracture-Time law were obtained. Calculation results from these creep models revealed that under low loads Q4 had lower minimum creep rate δm and longer creep fracture time tr compared to other alloys; however, Q3 demonstrated better performance in terms of δm and tr under high loads. This suggests a strong correlation between creep performance and loads. Additionally, finite element method (FEM) was employed to explore the effects of minor variation (±0.005 mm) in specimen thickness on SPT curves and SPCT curves. FEM results indicated that this slight variation alone did not account for discrepancies observed in load-deflection curves; deviations of ±6.1% for δm and ±6.3% for tr were found corresponding to specimens with 0.5 ± 0.005 mm thickness.

Process window for electron beam melting of Ti–42Nb wt.%

Pre-alloyed β-phase Ti˗42Nb alloy was successfully produced for the first time by E-PBF. The study focuses on the determination of the processing parameter window by varying the beam current, beam speed, layer thickness, and line offset to achieve the defect-free manufacturing of new material with desired properties. Overall, 49 regimes were investigated. The Ti˗42Nb powder were characterized using the DSC/TG, XRD, and SEM/EDX analyses to evaluate its suitability for E-PBF manufacturing. The alloys with the best-built quality fall into the narrow zone between the line energies of 0.30 and 0.34 J/mm. The predicted optimal process parameters were I = 4 mA, v = 700–800 mm/s, h = 100 μm, U = 60 kV, and t = 100 μm. Detailed microstructural characterization was carried out to gain insights into the fundamental mechanisms that govern the behavior of the studied alloys. TEM identified the α'' martensitic phase nucleation occurred preferentially at the β grain boundaries. Un-melted ellipsoidal NbC (∼10 μm) particles were detected with no preferential segregation sites. EBSD revealed coarse microstructures and <001> fiber texture, as well as epitaxial grain growth of columnar grains of about 300 μm. The optimal regime demonstrated a texture composed of a high amount of low aspect ratio grains (50%), which yielded a microindentation hardness of 3.0 GPa and a low elastic modulus of 68 GPa. Hence, these results provide opportunities to design novel alloys to be of interest for biomedical applications. Moreover, this study extends the scope of AM by establishing the process parameter window that yields a material with favorable mechanical properties.

Enhanced thermal conductivity of Si3N4 ceramics through pyrolytic carbon prepared by gel casting using DMAA

To reduce the lattice oxygen content of Si3N4 green bodies, samples were prepared using an N,N-dimethylacrylamide (DMAA) system. The endothermic and exothermic peaks are related to the decomposition of organic matter and the reaction between pyrolytic carbon and impurity oxides in the sintering process. Multi-step heat preservation during the thermal degreasing process reduced the carbon content and defects. The α→β phase transformation and aspect ratio of grains changed from 89.2% to 4.84:1 at 1640 °C to 96.3% and 7.80:1 at 1700 °C, respectively. The relative density, hardness, fracture toughness, and thermal conductivity of the Si3N4 samples reached 98.5%, 1353 HV, 8.51 MPa·m1/2, and 97.1 W·m−1·K−1, respectively. Pyrolytic carbon can react with SiO2, which reduces the content of the glass phase in the green body and affects the dissolution and precipitation process and lattice oxygen content. In the structure of the Si3N4 sample, carbon particles with sizes of 100–500 nm and near-spherical shapes were observed. Intergranular-phase YMgSi2O5N was formed during the sintering process, which was conducive to improving the thermal conductivity. This article uses lower temperature and no pressure conditions to prepare Si3N4 ceramics, which can provide reference for batch and low-cost production.

Texture in silicon carbide via aqueous suspension material extrusion and seeded grain growth

Textured SiC with anisotropic crystallographic texture is proposed as a material with improved mechanical properties. Textured SiC was created via alignment of platelet seed particles during aqueous suspension material extrusion, also known as direct ink writing, and subsequent pressureless liquid phase sintering and annealing. The microstructure and texture of the SiC fabricated with and without 5 vol% platelet seeds, and with and without annealing at 2050 °C and 2150 °C was explored via SEM, XRD, and EBSD. All samples fabricated had over 95% theoretical density. Annealing leads to the development of large, high aspect ratio plate-shaped grains among a matrix of many finer, low aspect ratio grains. Higher annealing temperatures and addition of platelet seeds both increased the size of the large grains. Samples were found to be textured regardless of having platelet seeds. Via XRD and EBSD, unseeded SiC was found to have texture where the crystallographic direction [0001] had a preferred orientation perpendicular to the normal direction. This occurred for both direct ink written and cast SiC, so the texture development must have occurred during sintering, though the mechanism is unknown. For seeded SiC, platelet seeds aligned in direct ink writing seeded the grain growth to develop crystallographic texture. The texture was mainly influenced by the alignment of platelet seed particles via shear stresses in the print nozzle, causing a one-dimensional texture where [0001] is perpendicular to the printing direction. However, it was found that the texture was not the expected concentric alignment of platelet particles in direct ink writing, so the shear stresses in the nozzle are not solely responsible for the texture developed.

Effective medium method in solution of the elastic and thermo-elastic homogenization problems for polycrystals with spheroidal transverse isotropic grains

Self-consistent effective medium method is used for determination of the effective elastic and thermo-elastic properties of polycrystalline materials with spheroidal transverse isotropic grains. The grains with arbitrary aspect ratios including very oblate (disks) and very prolate (fibers) spheroids are considered. The function of the Owens-March type is used for description of distribution of grains over orientations. The equations for the effective elastic stiffness tensor and the tensor of effective coefficients of thermo-expansion of polycrystals are derived using integral equations for elastic and thermo-elastic fields in heterogeneous media and the hypotheses of the effective medium method. The numerical algorithm of the method is described in detail. Numerical examples are presented for polycrystalline clay rock materials with strongly anisotropic grains and for polycrystalline zinc. Graphs of the dependences of the effective elastic constants and effective coefficients of thermo-expansion of the polycrystals on the parameters of the orientation distribution function and aspect ratios of grains are presented.

Could effective fracture toughness of polycrystalline aggregates exceed inner grain fracture toughness by adjusting toughness of grain boundary?

Obtaining intergranular and transgranular fractures through grain boundary engineering has been considered an efficient technique that improves the effective fracture toughness of polycrystalline aggregates. In this paper, the idealized hexagonal microstructure, random microstructures, and microstructures of grains with large aspect ratios are analyzed through a semi-analytical approach and the cohesive finite element method. The results indicate that when the aspect ratio of grains is not too large, the crack paths consisting of intergranular and transgranular fractures are approximately Mode I fracture morphologies among these microstructures. As the ratio of toughness between grain boundaries and grains varies, the effective fracture toughness of the microstructure can be increased more than the grain boundary fracture toughness but cannot exceed the inner grain fracture toughness.In contrast, the microstructure of grains with a large aspect ratio leads to deflected crack paths that are unexpectedly obtained, which implies that the approximate Mode-I intergranular fracture along transverse direction is almost impossible. The results demonstrate that the projected energy dissipation rate along the direction perpendicular to the loading axis can be significantly improved beyond the inner grain fracture toughness by enlarging the aspect ratio of the grains. Nevertheless, the mixed-mode effective fracture toughness is still limited to the grain fracture toughness. Corresponding experiments are also carried out to qualitatively verify the numerical results. The underlying mechanism for this deflection of fracture path is due to the strong anisotropy of fracture toughness. The higher the grain aspect ratio, the greater the anisotropy of the macroscopic effective fracture toughness. The energy favored fracture path is determined by the largest ratio between the driving force and the toughness of fracture over all directions. Therefore, cracks cannot propagate in the direction of the maximum fracture toughness when the aspect ratio of the grain is sufficiently large. The fracture diagrams that vary with the aspect ratio of grain and the ratio of fracture toughness between the grain and grain boundary are provided. The results can provide valuable guidance for designing microstructures and improving fracture toughness in materials.

Characterization of cryo-rolled low carbon steel using ferrite-martensite starting microstructure

Cryo-rolling, a technique of severe plastic deformation (SPD) performed at cryogenic temperatures, has proven to be a promising technique for improving the microstructure and mechanical properties of low-carbon steels. Low carbon steel with a two-phase ferrite-martensite starting microstructure was subjected to cryogenic rolling at liquid nitrogen temperature to produce sheets with different deformation rates: 50%, 70%, and 90%. The microstructure, mechanical properties, and corrosion resistance were investigated. The results show that cryo-rolling effectively refines the microstructure and leads to a higher dislocation density and smaller grain size as the deformation rate increases. The cryorolled sample deformed at 90% has the highest grain aspect ratio (35.5), the smallest crystallite size (13.70 nm), the highest lattice strain (74.6 x 10-3), and the highest dislocation density compared to the samples deformed at 50% and 70%. This refined microstructure significantly improves the mechanical properties, with the cryo-rolled sample deformed at 90% exhibiting the highest hardness (152 HV), tensile strength (1020 MPa), and yield strength (950 MPa), corresponding to an increase of 175.6%, 344.0%, and 466.5%, respectively. In addition, cryo-rolling at 90% showed a decrease in corrosion resistance, with the lowest corrosion rate observed at 90% deformation (5.97 mm/year).

The heterogeneity of dynamic recrystallization and texture evolution in stirring zone of Al-Mg-Sc alloy

Friction stir processing (FSP) is a potential way to improve the mechanical properties of alloys. However, compared with the dynamic recrystallization (DRX) of pin, the effect of shoulder is not deliberately distinguished. In this study, the grinding stirring processing (GSP) was applied to Al-2.7 Mg-0.24 Sc alloy to isolate the effect of shoulder. The tool of GSP had the same features as FSP except that it had no pin. The shoulder in GSP formed the discontinuous DRX (DDRX) cores and the deformation bands throughout the processing zone. On the basis of this result, ten observed objects in stirring zone of FSP were selected to analyze the gradient of DRX and orientation. By the characteristics of the recrystallized grains, we found that the frequency with the aspect ratio of grains >1.8 was positively correlated with the frequency of DDRX. The distribution of aspect ratio revealed that although DDRX could not be ignored, continuous DRX (CDRX) was dominant, and the frequency of CDRX increased with the distance from the top increased. Finally, the analysis of texture showed that Goss texture was favorable to the CDRX. • Applying grinding stirring processing (GSP) to compare shoulder-effect and pin-effect systematically. • Clearly proved that the shoulder would participate in dynamic recrystallization (DRX), mainly discontinuous DRX. • Detailed analysis of grain boundary characteristics semi-quantified DDRX variation. • Evolution of texture revealed Goss texture was favorable to the continuous DRX.

Effect of ζ‐Ta4C3−xon the mechanical properties of tantalum carbide at elevated temperatures

AbstractTantalum carbide ceramics containing at least 75‐wt% ζ‐Ta4C3−xwere synthesized and densified to ∼99% of the theoretical density. Flexural strength in four‐point bending was measured from room temperature up to 1600°C, achieving strengths of 710 ± 36.5 MPa at room temperature and decreasing to 180 ± 19.7 MPa at 1600°C. Fracture toughness was measured via the chevron notch method from room temperature up to 1600°C, with a toughness of 10.2 ± 0.4 MPa m1/2at room temperature and decreasing to 4.7 ± 0.1 MPa m1/2at 1600°C. At 1600°C, ductile behavior was observed during testing, and mixed mode fracture was observed on all fracture surfaces. Vickers indentations were used at room temperature to damage the surface of specimens and shed some light on damage mechanisms in the material. Kinking and delamination were observed around the indentations. At elevated temperatures, these deformation mechanisms may activate more often, causing a decrease in strength and resulting in ductility between 1400 and 1600°C. The Griffith analysis was also used to identify critical flaws. The long axis of high aspect ratio grains appears to be the critical flaw from room temperature up to 1400°C, prior to any ductile behavior. Overall, the nanolaminate microstructures, and the kinking and delamination deformation mechanisms that result from it, are reminiscent of MAX phase and kinking nonlinear elastic materials.

Mechanical anisotropy of laser powder bed fusion fabricated Ti-41Nb alloy using pre-alloyed powder: Roles played by grain morphology and crystallographic orientation

This work investigated the influence of the grain morphology and crystallographic orientation on the mechanical anisotropy of a laser powder bed fusion produced (L-PBFed) Ti-41 Nb alloy using pre-alloyed alloy for dental implants. The microstructure of L-PBFed Ti-41Nb alloy consists of columnar grains of a high aspect ratio with a strong< 001 > preferred orientation along the building direction (BD). To evaluate the mechanical anisotropy of L-PBFed Ti-41 Nb alloy, the external loading was compressed either perpendicular or parallel to BD (i.e., horizontal and vertical samples, respectively). Compression results show that the compressive yield strength (CYS) of horizontal samples is significantly higher than that of vertical samples. At the early stage of deformation, obvious {332}< 113 > mechanical twins are preferentially detected in the nearly< 001 > orientated grains along the compression axis. The dominant reasons for the lower CYS of vertical samples can be attributed to the easier activation of {332}〈113〉 mechanical twins in the typical columnar grains with strong< 001 > crystallographic orientation. It is suggested that the anisotropy of the L-PBFed alloy can be utilized through simple position control such as adjustment of the BD and reasonable structural design.

The effects of interfaces stability on mechanical properties, thermal conductivity and helium irradiation of V/Cu nano-multilayer composite

Interface engineering is a significant strategy to develop structural materials with good properties. In this study, bulk V/Cu nano-multilayers with different layer thicknesses were fabricated by cross accumulative roll bonding (CARB). Interface stability of V/Cu nano-multilayers with different layer thicknesses and their effects on thermal conductivity and helium irradiation have been explored. The microstructure analysis, tensile and hardness tests result show that V/Cu nano-multilayers maintain high mechanical properties and good thermal stability after annealing at 500 °C for 1 h. However, the strength drastically degrades after higher-temperature annealing because of microstructure instability, which is closely related to the aspect ratio of grains. Furthermore, spheroidization occurring in multilayer during the annealing process promotes efficient electron transportation and weakens electron scattering, which benefits the increase of thermal conductivity. The irradiation response of V/Cu nano-multilayers was explored by helium bombardment with a fluence of 1 × 1017 ions/cm2 at room temperature and 500 °C, respectively. Helium bubbles transform to gas cavities with increasing irradiated temperature, and different morphology of cavities at heterointerface, newly formed grain boundaries and triple junctions is attributed to the defect diffusion preference combined with thermal-induced interfaces migration.

Особенности формирования микроструктуры и механических свойств алюминиевой бронзы при различном тепловложении во время электронно-лучевой аддитивной печати

Microstructure and mechanical characteristics of aluminum bronze fabricated using electron beam additive manufacturing (EBAM) under adjusting the heat input as a function of the sample’s height have been investigated. It was shown that such an adjustment of the heat input had effect on the dendrite grain size and morphology as well as mechanical characteristics. Columnar high aspect ratio grains were formed during deposition at maximum heat input values. The columnar grain width in section parallel to the deposition direction was increasing in EBAM conducted at lower heat input. Tensile static testing showed that the tensile strength values were improving from 435 to 483 MPa in the process. Some moderate degree of anisotropy has been revealed between samples oriented by their tensile axes parallel and perpendicular to the deposition direction. Samples with tensile axes parallel to the deposition direction showed higher tensile strength and less plasticity as compared to those of samples with perpendicular orientations of their tensile axes. In addition, the heat input adjustment had no effect on the mean width of columnar grains measured in a section perpendicular to the deposition direction.

PGE distribution in Merensky wide-reef facies of the Bushveld Complex, South Africa: Evidence for localized hydromagmatic control

ABSTRACT The wide-reef facies of the Merensky Reef in the eastern part of the western lobe of the Bushveld Complex was sampled in order to better resolve otherwise spatially constrained variation in highly siderophile elements across this geological unit. The platinum group element mineralogy and whole-rock highly siderophile element concentrations were measured across two vertical sections in close proximity. In one section, the Merensky Reef unit was bound by top and bottom platinum group elements-enriched horizons (reefs) with a well-developed pegmatoidal phase in the top third of the intrareef pyroxenite, but with neither a top nor a bottom chromitite present. The other drill core section featured a thin (&amp;lt;1 cm thick) chromitite layer associated with the highest platinum group element concentrations of any rock in this study as the bottom reef, but with a chromitite-absent top reef, and very poor development of the pegmatoid. Primitive mantle-normalized profiles of the main lithological units show relatively flat, primitive mantle-like highly siderophile element abundances (Cr, V, Co, Ni, platinum group elements, Au and Cu) in the Merensky pyroxenite, with modest depletion in Ir-affiliated platinum group elements. The platinum group element-rich top and bottom reefs, and the pegmatoidal upper pyroxenites, display characteristic enrichment in the Pt-affiliated platinum group elements and undepleted Ir-affiliated platinum group elements. The leuconoritic hanging wall and footwall rocks show comparable highly siderophile element profiles, distinguished from one another by relative depletion in the Pt-affiliated platinum group elements of the footwall samples. The vertical variation in highly siderophile element abundances through both sections is characterized by low platinum group element abundances through the lower reef pyroxenite, with platinum group element, Au, and Cu ± Ni concentrations increasing through the upper pegmatoidal pyroxenite, and main enrichment peaks at the top and bottom reefs. Significant localized (centimeter-scale) zones of chalcophile metal depletion are present immediately above the top reef and below the bottom reef. In addition, a wider zone of Pt-affiliated platinum group elements (with Pd more depleted than Pt)-depletion was identified within the pegmatoidal pyroxenite around one meter below the top reef. The platinum group element mineralogy of the bottom reef consists mainly of platinum group element sulfides, with minor arsenides and antimonides. In contrast, the platinum group element mineralogy of the top reef, and the small amount of data from the intrareef pyroxenite, mainly consist of Pt-affiliated platinum group elements-Bi-tellurides. The Pt-sulfides are mainly equant, relatively coarse crystals (many grains between 50 to 100 μm2 area), contrasting with the Pt-affiliated platinum group elements-Sb-As and -Bi-Te minerals that tend be high aspect-ratio grains, occurring in veinlets or as rims on earlier-forming platinum group element phases. These Te-As-Bi-Sb compounds are closely associated with chlorite, actinolite, quartz, and chalcopyrite, consistent with secondary deposition at lower temperatures and association with aqueous fluids. A model is proposed involving the emplacement of the Merensky unit as a magma pulse into at least semi-crystallized host rock, followed by aqueous fluid saturation and local migration, combined with concentration of late magmatic fluids around the top and bottom contacts of the magma pulse. Late remobilization of Pt-affiliated platinum group elements from the zones immediately (centimeter-scale) above the top reef, and from the underlying meter or two of pyroxenite, and from the centimeters underlying the bottom reef, have added additional platinum group elements to the reefs as late platinum group elements-Te-As-Bi-Sb minerals, independent of whether or not chromite is present in the reef initially.

Formability study of bake hardening steel and its correlation with microstructure

In the present study, the bake hardening (BH 240) steel sheet’s formability behavior is studied experimentally based on the Nakajima test method. A forming limit diagram is successfully constructed using universal sheet metal forming machine by offline measuring the strains of deformed specimens. In-process strain measurement based on a digital image correlation technique is also performed for a few selected samples to compare the results with manual strain measurement techniques. All the deformed specimens are also characterized to correlate the sample geometries with hardness values and microstructure. It is observed that the hardness value gradually decreases with an increase in sample width for all the deformed specimens up to the width of 150 mm, except for full-width sample of 200 mm. Microstructural analysis reveals that the morphology of ferrite grains changes with the sample geometry in all the deformed specimens. Microstructural characterization at the top surface of the specimen demonstrates that the aspect ratio of grains is maximum for a 25 mm width sample due to uni-axial stretching. It is also noted that grain’s aspect ratio is close to one (minimum) for a 200 mm width sample due to almost equi-biaxial elongation in grains. It is also observed that the aspect ratio of grains obtained from specimen cross-section indicates that the ratio increases gradually from 25 to 200 mm width samples.

On the effect of rapid annealing on the microstructure and mechanical behavior of additively manufactured stainless steel by Laser Powder Bed Fusion

This work presents an investigation on the effect of rapid annealing on the microstructure evolution and mechanical performance of stainless steel 316L (SS316L) fabricated by Laser Powder Bed Fusion. In this process, it is well documented that the intensive thermal gradient in the heat flux direction leaves remarkable residual stress and promotes strong texture along the building direction (BD). In the current research, to swiftly reduce residual stresses, a short-term heat treatment at 1300 °C for different holding times of 10–120 s was designed and studied. Microstructural observation through the optical microscopy and scanning electron microscopy, as well as the X-ray diffraction analysis, revealed that rapid annealing longer than 30 s resulted in the gradual annihilation of the cell walls which are indeed the sub-grain boundaries (SGBs). In addition, electron backscatter diffraction outputs demonstrated that rapid annealing significantly reduced the low angle grain boundaries and attenuated the texture developed along the BD. Moreover, the analysis of grains size and shape illustrated that annealing up to 30 s recovered the structure. In contrast, longer annealing resulted in increasing the aspect ratio of grains along the direction with maximum residual strain (i.e. BD) due to activation of the strain induced grain boundary migration (SIGBM) mechanism. After the rapid annealing, the mechanical performance of the samples also indicated that annealing up to 30 s would not reduce the compressive and tensile strength more than 6%. In comparison, longer annealing resulted in 24% reduction in mechanical properties along with coarsening of dimples in the fracture surface of the samples.