Improvement In Yield Strength Research Articles

Synthesis of a356 alloy-variable particle sized boron carbide composites: investigations on mechanical behaviour and tensile fractography

Lightweight metal matrix composites made of aluminium are now essential in several fields, including aerospace and automotive. An important factor determining the quality and properties of the composite material is the ease or difficulty of evenly dispersing the reinforcement throughout the matrix. The goal of this research is to find out the impact of 40 and 90 µm varying- sized boron carbide (B4C) particles in A356 alloy composites. Using the liquid stir casting technique and K2TiF6 as the wetting flux, A356 alloy with 9 wt.% of B4C composites were prepared. SEM and EDS images were used to study the material’s microstructure. ASTM-approved methods were used to measure the material’s mechanical properties. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) confirmed that B4C particles were evenly distributed throughout the A356 alloy. The addition of B4C reinforcement to the A356 alloy matrix increased the hardness, ultimate, yield, compression, and impact strength of composites with a reinforcement size of 40 μm. The hardness of A356 alloy was enhanced by 40.7% and 34.6%, respectively, when 9 wt. % of 40 and 90 μm B4C were added. Similarly, there was a 34% increase in ultimate strength and a 31% improvement in yield strength. Both cases showed a little decrease in the ductility of the composites. Scanning electron micrographs were used to examine the morphologies of tensile fractured surfaces.

High-strength titanium alloy with hierarchical-microstructure design via in-situ refinement-splitting strategy in additive manufacturing

Microstructure design of high-strength materials based on single-principal-microstructure advantage can hardly meet the increasingly strict service requirements of modern aviation and aerospace industries. Compared with conventional forming methods, additive manufacturing (AM) technology introduces more regulatory variables, making it possible to gain multiple microstructure advantages simultaneously for critical components. This study introduces a universal process strategy in laser-powder bed fusion (L-PBF) to achieve hierarchical-microstructure optimization for titanium alloys. Specifically, a higher energy density can refine (R) martensite lath, and an appropriate scanning strategy can split (S) both coarse prior-β grains and α’-colony. For L-PBF-fabricated Ti-6Al-4 V (Ti64) alloy, the proposed refinement-splitting (R & S) optimization strategy improved yield strength (up to ∼1.3 gigapascals) by 30% and the total elongation increase by about 1.9 times compared to the alloy samples with a conventional rich α’-colony microstructure. The split prior-β grains also help with the complex service environment by reducing the anisotropy-induced deterioration of mechanical properties. The R&S approach is, in principle, applicable also to other titanium alloys beyond Ti64.

Unique Yttria Nanoparticle Strengthening in an Inconel 718 Superalloy Fabricated by Additive Manufacturing

AbstractOxide dispersion strengthened (ODS) nickel (Ni)‐based superalloys are advanced materials known for their outstanding tensile and creep performance at temperatures exceeding 1000 °C. Nevertheless, their conventional synthesis presents a longstanding challenge in cost‐effectively producing intricate components for critical applications. In this work, electrostatic self‐assembly (ESA) of powders with the laser powder bed fusion (LPBF) process are successfully combined to produce yttria ODS Inconel 718 (IN718) alloy for the first time. This approach demonstrates a significant contribution of yttria to the strength of IN718 after the solid solution heat treatment, as evidenced by ≈50% improvement in room temperature yield strength with a 0.5 wt.% yttria addition. The addition of yttria by this process leads to a heterogeneous microstructure. This heterogeneous microstructure comprises two distinct grain areas with varying amounts of yttria nanoparticles and dislocation storage. The results show that the yield strength increase can be predicted by the combination of both Y2O3 dispersion strengthening and dislocation strengthening mechanisms. These findings offer an effective approach to tailor heterogeneous microstructures, unlocking new opportunities for cost‐effectively producing high‐performance ODS Ni‐based superalloy products with excellent mechanical properties.

Effective Platform Heating for Laser Powder Bed Fusion of an Al-Mn-Sc-Based Alloy.

Platform heating is one of the effective strategies used in laser powder bed fusion (LPBF) to avoid cracking during manufacturing, especially when building relatively large-size components, as it removes significant process-induced residual strains. In this work, we propose a novel and simple method to spare the elaborate post-processing heat treatment typically needed for LPBF Al-Sc alloys without compromising the mechanical properties. We systematically investigated the effects of LPBF platform heating at 200 °C on the residual stress relief, microstructure, and mechanical performance of a high-strength Al-Mn-Sc alloy. The results reveal that LPBF platform heating at 200 °C is sufficient to largely relieve the process-induced residual stresses compared to parts built on an unheated 35 °C platform. Meanwhile, the platform heating triggered the dynamic precipitation of uniformly dispersed (1.5-2 nm) Sc-rich nano-clusters. Their formation in a high number density (1.75 × 1024 m-3) resulted in a ~20% improvement in tensile yield strength (522 MPa) compared to the build on the unheated platform, without sacrificing the ductility (up to 18%). The improved mechanical properties imply that platform heating at 200 °C can strengthen the LPBF-synthesised Sc-containing Al alloys via in situ aging, which is further justified by an in situ measurement study revealing that the developing temperatures in the LPBF part are within the aging temperature range of Al-Sc alloys. Without any post-LPBF treatments, these mechanical properties have proven better than those of most Al-Sc alloys through long-time post-LPBF heat treatment.

Achieving high strength-ductility in TiBw-GNPs/Ti6Al4V composites via 3D interface configuration

Strong interface bonding is critical to achieve the graphene nanoplates reinforced titanium matrix composites (GNPs/TMCs) with excellent strength and ductility. In this study, the TiBw-GNPs/Ti6Al4V composites with three-dimensional (3D) interface configuration are fabricated through the combination of vibration milling and the spark plasma sintering (SPS). The 3D interface configuration is constructed by the in-situ generated TiB whiskers (TiBw) together with the sandwiched TiC-GNPs-TiC, in which TiBw grow epitaxially into the adjacent Ti6Al4V grains and immobilize TiC-GNPs-TiC. As a result, 1.5 wt%TiBw-GNPs/Ti6Al4V composite exhibit simultaneously improved yield strength, ultimate strength and ductility, manifesting marked increments of 26.5%, 26.4% and 30.1% compared to GNPs/Ti6Al4V composite, respectively. The strengthening enhancement of TiBw-GNPs/Ti6Al4V composites can be mainly attributed to the constructed 3D interface microstructure, which boosts the interface bonding and promotes grain refinement as well as load transfer. Moreover, the equiaxed α-Ti phase and the deformation compatibility gifted from the tailored interface endow the TiBw-GNPs/Ti6Al4V composites with excellent ductility. This strategy of tailoring 3D interface configuration could pave a promising way to obtain robust interfacial bonding and break through the strength-ductility trade-off in graphene reinforced titanium matrix composites.

Evading the strength-ductility compromise in medium manganese steel by a novel low temperature warm rolling treatment

Strength-ductility trade-off is an enduring problem in a wide range of metals and alloys including the advanced high-strength steels. In this work, we propose a novel non-isothermal low-temperature warm rolling (WR) treatment which was applied after the conventional intercritical annealing (IA) in order to overcome the strength-ductility compromise in a medium manganese steel, Fe-5.1Mn-0.22C-0.85Si-0.42Al (composition in wt%). IA + WR treatment yielded a simultaneous improvement in tensile properties, wherein yield strength (YS), ultimate tensile strength (UTS), and ductility improved by 32%, 12%, and 6% respectively, compared to the conventional IA treatment. Despite an increase in the yield point elongation (2%) and Lüders strain (3%) in the IA + WR specimen, the ductility of the same improved as compared to the IA specimen. Microstructure of the IA + WR specimen was tailored by introducing a significantly higher dislocation density in the constituent ferrite and retained austenite (RA) phases along with a relatively higher density of planar defects (stacking faults and nano-twins) in the RA phase. X-ray line profile analysis quantified the increased dislocation density (order ∼1015 vs 1014 m−2) and twin fault probability (∼1.35% vs ∼0.12%) in the RA phase of the IA + WR compared to the IA specimen. The improvement in YS was primarily due to the increase in the dislocation density of the constituent phases in the IA + WR specimen. Introduction of a high density of lattice defects in the RA phase during the WR treatment above the Md30 temperature enhanced the mechanical stability of the RA phase, leading to a decreased rate of TRIP effect and formation of hierarchical twins during tensile deformation. The near-ubiquitous strength-ductility trade-off was overcome via a tailored microstructure consisting of regulated austenite stability leading to discontinuous TRIP effect, hierarchical twinning in RA phase, and favorable texture in the constituent phases. The present study provides a pathway to tailor the microstructure for escaping the strength-ductility paradox in different metastable FCC alloys such as stainless steel, HEAs, TWIP steels etc.

Fabrication of iron-based amorphous reinforced CoCrNi medium-entropy alloys by selective laser melting: Enhancement of mechanical properties and improvement of corrosion resistance

Due to their exceptional mechanical characteristics and corrosion resistance, CoCrNi medium-entropy alloys have been the subject of increasing interest in recent years. In this study, CoCrNi medium entropy alloys strengthened with iron-based amorphous materials were fabricated using Selective Laser Melting (SLM) technology, with established gradients at 0, 3, 5, and 7 wt%. At room temperature, the yield strength and hardness of the CoCrNi-5MG specimen showed marked improvements of 27.5 % and 34.7 % respectively, compared to its pure CoCrNi counterpart, while still preserving a considerable fracture elongation of 24 %. Under low-temperature conditions, all samples prepared via Selective Laser Melting (SLM) demonstrated significant improvements in yield strength and fracture plasticity. Furthermore, the CoCrNi samples doped with iron-based amorphous material exhibited superior low-temperature performance, with the increase in plasticity exceeding that of the Pure CoCrNi samples compared to room temperature conditions. Importantly, an increase in the content of iron-based amorphous material resulted in a decrease in the corrosion current density, thereby noticeably enhancing corrosion resistance. Our study proposes an innovative approach to enhancing the strength and corrosion resistance of CoCrNi medium-entropy alloys. This is achieved by incorporating iron-based amorphous materials during the SLM preparation process, thereby providing a new avenue for optimizing its properties.

Laser printed amorphous magnesium alloy: Microstructure, mechanical properties and degradation behavior

Amorphous magnesium (Mg) alloy, especially Mg–Zn–Ca series, has been receiving continuous attention in biomedical field, because of its favorable corrosion resistance, suitable modulus and biocompatibility. In this work, laser powder bed fusing (LPBF) with unique characteristics of rapid solidification and layer-by-layer fashion was used to fabricate bulk Mg–Zn–Ca and Mg–Zn–Ca–Y amorphous parts. It was revealed that the as-built parts contained amorphous structure, since the molten pool experienced an extremely high cooling rate that suppressed ordered arrangement of atoms. A few of nanocrystals (α-Mg and Ca2Mg5Zn13) were obtained due to repeated heat accumulation in heat-affected zones. More significantly, Y alloying altered the glass forming ability and stimulated in-situ formation of quasicrystal I-phase with high hardness and elastic modulus, which not only acted as reinforced particles, but also retarded the propagation of shear bond and thereby excited the emergence of secondary shear bands and vein patterns. Thus, Mg–Zn–Ca–Y part exhibited simultaneously improved yield strength and plasticity. Despite the micro galvanic corrosion induced by crystalline phases, it exhibited a moderate corrosion rate. Furthermore, in vitro cell tests proved its favorable biocompatibility. Our work highlighted the feasibility to prepare amorphous Mg alloy with controllable performance.

Establishment of a facile technique to fabricate bulk AA6061/CNT composite with improved mechanical properties using combined stir-casting and squeeze-casting

Three dispersion techniques were investigated for fabricating AA6061–0.5 wt% CNT composites by combined stir-casting and squeeze-casting - direct drop of CNT (DD), mixed Al and CNT pellet drop (PD), and direct drop of ultrasonicated CNT (USDD). Al-20Mg alloy was added to enhance CNT wettability. The PD samples resulted in the highest retention of CNTs in the matrix along with a uniform distribution, confirmed by detailed transmission electron microscope analysis. The selected area electron diffraction pattern and X-ray diffraction confirmed the formation of Mg2Si. The hardness of all composite samples increased significantly over AA6061, predominantly due to a reduction in crystallite size and an increase in dislocation density. The best combination of tensile properties was achieved in the PD composite, yielding an improvement of ultimate tensile strength and yield strength by 40% and 33%, respectively, compared to as-cast AA6061 without sacrificing the ductility. Well-developed serrations were observed in the stress-strain plots of the samples, which have been attributed to the pinning-unpinning action of mobile dislocations by the Mg solute atoms. The fracture surface of the PD composite displays features of ductile fracture along with CNT bridging and rupture, confirming the presence of a strong interface and effective load transfer strengthening.

A Comparative Study on Microstructure, Segregation, and Mechanical Properties of Al-Si-Mg Alloy Parts Processed by GISS-HPDC and SEED-HPDC.

There are multiple routes to prepare semi-solid slurries with a globular microstructure for semi-solid forming. The variations in the microstructure of semi-solid slurries prepared using different routes may lead to significant differences in the flow behavior and mechanical properties of rheo-diecasting parts. Therefore, it is crucial to have a comprehensive understanding of the microstructure evolution associated with different slurry preparation routes and their resulting effects. In this study, the gas-induced semi-solid process (GISS) and the swirl enthalpy equilibrium device (SEED) routes were employed to prepare semi-solid Al-Si-Mg slurries for their simplicity and productivity in potential industrial applications. The prepared slurries were then injected into the shoot sleeves of a high-pressure die casting (HPDC) machine to produce tensile test bars. Subsequently, the bars underwent T6 treatment to enhance their mechanical properties. The microstructure, segregation, and mechanical properties of the samples were investigated and compared with those of conventional HPDC. The results indicated that the GISS and SEED can produce semi-solid slurries containing a spherical α-Al primary phase, as opposed to the dendritic structure commonly found in conventional castings. The liquid fraction had a significant effect on the flow behavior, resulting in variations in liquid segregation and mechanical properties. It was observed that a higher solid fraction (>75%) had a suppressing effect on surface liquid segregation. In addition, the tendency for liquid segregation gradually increased along the filling direction due to the special flow behavior of the semi-solid slurry with a low solid fraction. Furthermore, under the same die-casting process parameters, the conventional HPDC samples exhibit higher yield stress (139 ± 3 MPa) compared to SEED-HPDC and GISS-HPDC samples, which may be attributed to the small grain size and the distribution of eutectic phases. After undergoing the T6 treatment, both SEED-HPDC and GISS-HPDC samples showed a significant improvement in yield and tensile strength. These improvements are a result of solution and precipitation strengthening effects as well as the spheroidization of the eutectic Si phase. Moreover, the heat-treated SEED-HPDC samples demonstrate higher ultimate strength (336 ± 5 MPa) and elongation (13.7 ± 0.3%) in comparison to the GISS-HPDC samples (307 ± 4 MPa, 8.8 ± 0.2%) after heat treatment, mainly due to their low porosity density. These findings suggest that both GISS-HPDC and SEED-HPDC processes can be utilized to produce parts with favorable mechanical properties by implementing appropriate heat treatments. However, further investigation is required to control the porosities of GISS-HPDC samples during heat treatment.

The strengthening effect of high-energy ultrasound treatment on the additively manufactured ZL114A aluminum alloy

Wire - arc additive manufacturing (WAAM) is a promising technology for rapid manufacturing of large aluminum alloy complex structures. However, the coarse grain structure and low mechanical properties of deposited aluminum alloy limit its further application. In this study, high-energy ultrasound treatment was used to enhance the mechanical properties of WAAM-processed aluminum alloy ZL114A. Compared with as-deposited samples, significant grain refinement and improved yield strength and tensile strength of up to 177 MPa and 266 MPa, respectively, were achieved after high-energy ultrasound treatment during and after deposition. These findings provide new insights for the better utilization of high-energy ultrasound to enhance the mechanical properties of arc additively manufactured aluminum alloy products.

Tailoring the enhanced mechanical behavior of 6061Al composites via nano SiCp and micron B4Cp addition

In this work, the hybrid micron B4C particles (m-B4Cp) and nano SiC particles (n-SiCp) reinforced 6061Al matrix composites were prepared by powder metallurgy. The synergistic effects of hybrid m-B4Cp and n-SiCp were investigated. The results showed that m-B4Cp were well dispersed in the matrix, while n-SiCp were uniformly distributed inside the grains as well as at the grain boundaries. The coupled addition of n-SiCp and m-B4Cp significantly refined the grain size of matrix from 3.60 μm to 0.91 μm. The synchrotron X-ray computed tomography (SR-CT) revealed that the volume of pores increased with increase of particle content. Compared with the composites reinforced with only one type of particle, the 6061Al composites reinforced with micro and nano dual-size particles possessed higher tensile strength, while maintaining reasonable plasticity. The strengthening contributions to the yield strength improvement of 6010Al matrix composites reinforced with micro and nano dual-size particles are resulted from thermal expansion mismatch strengthening, fine grain strengthening and Orowan strengthening caused by n-SiCp.

A quasi-in-situ EBSD study on the formation and development of η-fiber in 0.15 mm ultra-thin Fe-4.5 wt. % Si sheet

Texture evolution of 0.15 mm ultra-thin Fe-4.5 wt. % Si sheet with strong η-fiber produced by two-stage rolling and final annealing was investigated using ex-situ and quasi-in situ electron backscatter diffraction (EBSD). The Goss grain of the hot-rolled plate was rotated to γ-fiber (<111>//ND) dominated by {111}<112> during one stage of moderate warm rolling reduction and then formed strong Goss after intermediate annealing. When the rolling reduction was slightly increased, the annealed strong Goss rotated to near {111}<112> and then formed strong {120}<001> after final annealing. The quasi-in-situ EBSD characterization of the intermediate and final recrystallization process indicated that the recrystallized Goss, {120}<001> and {111}<112> grains were nucleated and grown within the shear bands of deformed {111}<112>, near {111}<112>({223}<362>), and {111}<110> matrices respectively. The recrystallized strong η-fiber textures dominated by {120}<001> were dependent on the coarser Goss grains and suitable rolling reduction and could remain unchanged after considerable grain growth. The 0.15 mm specimen with superior magnetic properties and high strength achieved an iron loss (P10/400 =7.82 W/kg) improvement of 17 %, magnetic induction (B50 =1.65 T) improvement of 0.04 T, and yield strength (474 MPa) improvement of 61 MPa compared to commercial products with the same thickness.

Enhancing Microstructural, Textural, and Mechanical Properties of Al-Ti Dissimilar Joints via Static Shoulder Friction Stir Welding

Abstract The present study explores the application of static shoulder friction stir welding (SSFSW) to address the challenges of poor mechanical properties in conventional Al-Ti dissimilar friction stir joints, which arise due to significant material mixing and the formation of thick intermetallic layers. The results show that SSFSW inhibited material mixing and the mutual diffusion of Al and Ti were suppressed due to lower heat input. Mutual interdiffusion of Al and Ti was directed by an exothermic chemical reaction, forming an Al5Ti2 – Al3Ti sequence due to sluggish diffusion of Al in Ti at a temperature of 512°C achieved in this study. The microstructure at stir zone (SZ) comprised equiaxed grains with Ti particles acting as dispersoids for nucleation, whereas the presence of large Ti blocks at SZ of Conventional FSW (CFSW) resisted plastic deformation, resulting in non-homogeneous concentration of dislocations near its interface. A significant decrease in grain size at all the critical zones of weldment was due to rearrangement of dislocations through slip-and-climb mechanism, as evidenced by the occurrence of dynamic recrystallization. Emergence of γ-fiber and basal fiber texture increased the tensile strength of SSFSW to 289 MPa, which is about 11.2% higher than CFSW, with joint efficiency of about 88%. The study also analysed the contribution of various strengthening mechanisms to the yield strength improvement of SSFSW weldments in detail of SSFSW weldments in detail, and the results showed that grain boundary strengthening contributed the most to strength improvement in SSFSW.

Gradient microstructure and strength-ductility synergy improvement of 2319 aluminum alloys by hybrid additive manufacturing

Wire-arc additive manufacturing (WAAM) technology has been considered as a suitable method for manufacturing large components of aluminum alloys due to its high deposition rate and material utilization. However, the coarse grain size, high porosity and poor mechanical properties of as-deposited aluminum alloys have limited their further development. In this study, a novel hybrid additive manufacturing (HAM) technology combining WAAM and friction stir processing (FSP) has been developed, and a gradient microstructure 2319 aluminum alloy with ultrafine grains-equiaxed grains-columnar grains was successfully fabricated. The microstructure evolution and mechanical properties also have been investigated in this study. The grain size distribution, texture analysis, and the percentage of recrystallized grains were characterized by electron backscatter diffraction (EBSD). The experimental results demonstrated that the hybrid additive manufacturing can achieve a substantial grain refinement (87.09%) and increase the dynamic recrystallization content to 62% due to alternating mechanical and thermal effects. Meanwhile, compared with WAAM specimens, the hybrid-manufactured 2319 aluminum alloy has improved yield strength (YS) by 32.22%, ultimate tensile strength (UTS) by 8.75%, and elongation (EL) by 20%. The dominant mechanism of the significant strength-ductility synergy improvement also has been revealed.

Simultaneous enhancement of strength and ductility by combining heterogeneous microstructure and nanoprecipitates

Developing advanced metallic materials with high strength and ductility is an eternal theme, however, the strength and ductility are generally considered to be conflicted to each other. Here, a simultaneous enhancement of strength and ductility is achieved in a commercial Al6061 alloy by combining the heterogeneous microstructure (composed of recovered zones and partially recrystallized zones) and nanoprecipitates. This unique microstructure is produced by the cold-drawing (∼61%) and pre-torsion (∼360°) followed by low-temperature ageing treatments. When the ageing temperature decreases from ∼300 °C to ∼150 °C, the nanoprecipitates changes from the coexistence of the needle-like β′ and rod-shaped β′′ to exclusive granular β′′ with refined size and increased volume fraction, which leads to the remarkable improvement of yield strength from σy∼176.0 MPa to σy∼340.2 MPa. Concurrently, the evading of precipitate-free zones (PFZs), the suppression of the grain-boundary precipitates and the formation of extremely fine nanoprecipitates (<5 nm) contribute to the unexpected enhanced uniform elongation (from εu∼5.3–5.6%). Furthermore, the hetero-deformation induced (HDI) strengthening and work hardening by the heterogeneous microstructure are also beneficial for the synergistic enhancement of the strength and ductility.

Microstructure evolution, mechanical properties, and wear behavior of in-situ TiCx/TC4 composites

In this work, In-situ TiCx/TC4 composites were fabricated using Ti3AlC2 as a precursor via vacuum hot-pressing sintering. The effect of Ti3AlC2 content on the microstructure, mechanical properties, and wear behavior of TC4 matrix composites was investigated. The results indicate that the TiCx phase formed from the reaction between Ti3AlC2 and Ti during sintering. The in-situ formation of the TiCx phase could refine the size of the prior β grain and alter the microstructures of the matrix from the Widmanstatten structure of neat TC4 to an equiaxed structure. The TC4 matrix composites with different amounts of Ti3AlC2 exhibited higher hardness, yield strength, and tensile strength than neat TC4. When the volume fraction of Ti3AlC2 was 2.5%, the yield strength and tensile strength of composites were 951.2 MPa and 1033 MPa, respectively, which increased by 16.5% and 9.4% compared to neat TC4, respectively. Moreover, the elongation of the composites was 12.8% with substantially maintained plasticity. The improvement of yield strength in the composites is attributed to grain refinement strengthening and load transfer strengthening. The wear behavior of in-situ TiCx/TC4 composites was enhanced significantly. Abrasive wear and adhesive wear are the dominant wear mechanism in the TiCx/TC4 composites.

3D printing with recycled ABS resin: Effect of blending and printing temperature

Recycled acrylonitrile butadiene styrene (RABS) has undesirable thermal properties that cause the material to shrink and not adhere to the printing bed during three-dimensional (3D) printing. In order to address this issue, virgin acrylonitrile butadiene styrene (VABS) of varying weight proportions (i.e., 10–50%) is blended with RABS to fabricate parts at various printing temperatures (i.e., 230 °C, 240 °C, and 250 °C). The study emphasizes to achieve proper inter-layer bonding and enhancing the physical and mechanical characteristics of the final product made from RABS. It was found that blending of VABS up to 40% in RABS with components fabricated at 240 °C resulted in the highest improvement in physical and mechanical properties. The 60% RABS/40%VABS sample printed at 240 °C exhibits improvements in Young's modulus (E), yield strength (σy), and ultimate tensile strength (UTS) by 13.69%, 13.37%, and 15.64%, respectively. Moreover, the RABS sample blended with 20% VABS exhibited comparable flexural results to the 100% VABS samples as blending VABS enhances molecular chain bonding and provides better elasticity to the material.

Effect of nitrogen content on mechanical properties of 316L(N) austenitic stainless steel

Increasing the yield strength of 316L(N) stainless steel is both scientifically and commercially crucial. In this study, five 316L(N) stainless steels with different nitrogen contents were melted and specimens with grain size from 5 μm to 320 μm were obtained by cold rolling and heat treatment. The yield strength was examined through tensile tests. The microstructure was investigated using electron-backscatter diffraction, transmission electron microscopy, and X-ray diffraction. The fracture morphology was studied by scanning electron microscopy. Nitrogen improved the coefficient in the Hall–Petch equation. As the nitrogen content increased from 0.008 wt% to 0.34 wt%, the coefficient K increased from 363 MPa μm0.5–1895 MPa μm0.5 and the coefficient σ0 increased from 168 MPa to 331 MPa, resulting in an improvement of yield strength from 249 MPa to 757 MPa (grain size of 20 μm). Planar slips and stacking faults were found in deformation structures of 316L(N) steel with higher nitrogen content, which is underlying factors for the significant improvement of yield strength. Strain-induced martensite near the fracture surface contributed to the plasticity of 316L(N) steel. This study discusses the contribution of nitrogen, including solution strengthening, stacking fault energy, and short-range ordered structure to strength enhancement. It provides a valuable reference for developing new austenitic stainless steel with an optimal strength–plasticity combination.

Microstructure, mechanical and soft magnetic properties of in-situ TiC reinforced Fe27.5Ni27.5Co45-based medium entropy composites

The insufficient mechanical properties of conventional soft magnetic materials (SMMs) hinder their widespread applications, and unfortunately, traditional strengthening mechanisms could dramatically deteriorate their soft magnetic properties without adjusting the alloy composition. Here, we developed TiC/Fe27.5Ni27.5Co45 medium-entropy composites (MECs) possessing multi-scale microstructure consisting of ultrafine and micron-sized grains by introducing in-situ formed TiC nano particles during the spark plasma sintering (SPS) process. Compared with the precipitate-free Fe27.5Ni27.5Co45 medium-entropy alloy, TiC/Fe27.5Ni27.5Co45 MEC with ∼ 8.7 vol% TiC (noted as Ti5-MEC) demonstrated a significant improvement in compressive yield strength (from 459 MPa to 1114 MPa), attributing to the grain-boundary strengthening and dispersive precipitation strengthening, as well as hetero-deformation induced (HDI) strengthening. Meanwhile, the Ti5-MEC exhibits a high saturation magnetization (Ms) of 153.1 emu/g and a low coercivity (Hc) of ∼ 8.2 Oe, indicating excellent soft magnetic properties, primarily due to the multi-scale microstructure. Our work has demonstrated that engineering multi-scale microstructures in MECs is an effective strategy to achieve desirable combinations of soft magnetic and mechanical properties.