Strengthening Contributions Research Articles

Achieving excellent properties in high-speed steel by hot isostatic pressing and heat treatment using PREP and EIGA powders

The powder metallurgy T15 high-speed steels (PM T15 HSS) with the powders of plasma rotating electrode process (PREP) and electrode induction-melting inert gas atomisation (EIGA) were successfully prepared by hot isostatic pressing (HIP) at 960°C (960-EIGA), 1130°C (1130-EIGA, 1130-PREP) and 1200°C (1200-EIGA), respectively, and the effect of heat treatment (HT) including quenching and tempering on PM HSS has been studied. The microstructures including the average size, sphericity and volume fraction of the carbides, the mechanical properties and wear properties were visibly modified after HT. The hardness of more than HRC67, the fracture toughness of exceeding 25 MPa·m1/2, the wear depth of 0.644 μm, the width of 0.455 μm and the wear rate of 0.98 × 10−6 mm3·N−1·m−1 were achieved in PM HSS after HT. Mechanisms about microstructure evolution and strengthening were discussed. The total strengthening contributions of 613 MPa for grain boundary strengthening of ∼173 MPa, carbides strengthening of ∼244 MPa and solute strengthening of ∼196 MPa were calculated for 1130-EIGA. The current study offers ideas for the high performance of HIP and HT samples can be implemented equally by high-quality PREP and EIGA powders.

Effect of purity on the tensile mechanical behavior of pure iron

The current work systematically investigated the microstructures, mechanical properties, textures, dislocation density and dislocation substructures of 3N2, 4N2 and 5N2 pure irons (3N2, 4N2 and 5N2 pure irons represent that the content of Fe are 99.9264 wt%, 99.9925 wt% and 99.9992 wt%, respectively) using SEM, EBSD, XRD and TEM. The results indicated that the recrystallization temperature decreased with increasing purity, and higher purity accelerated grain growth. 4N2 and 5N2 pure irons both presented equiaxed ferrite grains, while the microstructure of 3N2 pure iron was consisted of irregular polygonal ferrites and equiaxed ferrite grains. Low-density LAGBs were observed in annealed pure irons. The fraction of LAGBs increased significantly after deformation, and the LAGBs density decreased as the purity increased. The dislocation substructures of 3N2 and 4N2 pure irons were dominated by sub-grain boundaries with high dislocation densities and dislocation tangles, whilst 5N2 pure iron primarily consisted of fewer sub-grain boundaries and random dislocations. Work hardening was the primary strengthening contribution of pure irons. As the purity decreased, the capacity of work hardening increased, which resulted from the effective obstacles to dislocations by higher fraction of LAGBs, sub-grain boundaries with high dislocation densities and dislocation tangles. Therefore, the improved mechanical properties may be attributed to the increase of work hardening ability with the decrease of purity. 3N2 pure iron presented discontinuous yielding behavior, while 4N2 and 5N2 pure irons exhibited continuous yielding behaviors. The continuous yielding was attributed to the minimal interstitial atoms rarely segregated on mobile dislocations to form Cottrell atmosphere.

Designing a new ultra-high strength steel with multicomponent precipitates under material genetic design

Ultra-high strength steels with excellent strength, ductility and toughness have become one of indispensable high-performance structural materials. The development of ultra-high strength steels with higher performance has been widely concerned to break the strength-ductility trade-off. This study proposes a material inverse design strategy that combines material genetic design with thermodynamic calculation to search for new alloys with desirable microstructure and optimal strengthening contributions. Based on the advancement of the 'Pareto Front', a new steel with superior properties was successfully screened from 390,625 candidate individuals, which was verified by experiments. The experimental results show that a new steel Fe-0.25C-14.8Ni-17.0Co-2.54Mo-1.56Cr-0.53Al-1.06Cu-0.38V (wt. %) has been successfully developed. After quenching-cryogenic-aging process, the new steel achieved a superior combination of strength, ductility and toughness, with a yield strength of 2.2 GPa, an elongation-to-failure of 10% and a V-notch impact energy of 15 J. Multi-scale microstructure characterization indicates that such superior property synergy arises from the unique microstructure: lath martensite matrix with high-density dislocations and interstitial solid soluble carbon atoms, embedded fine M2C, NiAl and Cu-rich nanoprecipitates. We present an in-depth discussion on the origins of superior strength/ductility/toughness combinations of the new steel to validate the design strategy and provide an accessible pathway exploiting high-performance ultra-high strength steels.

Effect of ECAP and aging on microstructure of an Al-Cu-Mg-Si alloy

The effect of equal-channel-angular pressing (ECAP) on the microstructure and precipitation of an Al-4.7Cu-0.74 Mg-0.51Si-0.48Mn-0.10Cr-0.09Ti-0.02Fe (all wt%) has been studied using aberration-corrected scanning transmission electron microscopy. The ECAP followed by a short-term aging provides a superior combination of strength and ductility in the present alloy. The ECAPed alloy shows a substantially different precipitation behavior in the deformation bands (DBs) compared to extended regions (ERs) during aging. The relatively coarse particles of the equilibrium θ (Al2Cu) and β (Mg2Si) phases were found to form along deformation-induced grain/subgrain boundaries within the DBs after short-term aging. In the present alloy after ECAP and aging, the phases continuously decorating dislocation lines or forming the discrete particles in the ERs are similar to those in the bulk matrix after conventional aging. The macroscopic strengths have been estimated for the ERs and DBs in the samples after ECAP and aging. The former, i.e., ERs, with predominant strengthening contributions originating from solid solution, precipitation and dislocations, is likely have a higher YS than the latter with the relatively coarse equilibrium particles and mainly strengthened by only grain boundaries and dislocations.

On the Origin of Enhanced Tempering Resistance of the Laser Additively Manufactured Hot Work Tool Steel in the As-Built Condition

In laser additive manufacturing (AM) of hot work tool steels, direct tempering (DT) of the tool from as-built (AB) condition without prior conventional austenitization and quenching results in enhanced tempering resistance. To date, intercellular retained austenite (RA) decomposition, leading to a shift in secondary hardening peak temperature, and finer martensite substructure are reported to be responsible for such a behavior. In this work, authors aimed at studying the strengthening contributions by performing isothermal tempering tests for long times (up to 40 hours) at elevated temperatures (up to 650 °C) on DT and quenched and tempered (QT) specimens. The thermal softening kinetics and the microstructural evolution were evaluated with the support of computational thermodynamics. The results suggest that the main contributor to enhanced temper resistance in DT condition is the larger fraction of thermally stable and extremely fine (~ 20 nm) secondary (tempering) V(C,N) compared with QT. This could be explained by the reduction of available V and C in austenitized and quenched martensite for a later secondary V(C,N) precipitation during tempering, because of equilibrium precipitation of relatively large (up to 500 nm) vanadium-rich carbonitrides during the austenitization process. A complementary effect of the substructure refinement (i.e., martensite block width) in rapidly solidified highly supersaturated martensite was also quantified in terms of Hall–Petch strengthening mechanism. The significant effect of secondary V(C,N) was successfully validated by assessing a laser AM processed vanadium-free hot work tool steel in QT and DT condition, where no significant differences in strength and temper resistance between the two conditions were evident.Graphical

Evolution of mechanical properties and microstructure of selective laser melted AlSi10MgMn alloy with different post heat treatments

This study investigated the effects of various post heat treatments on the mechanical properties and microstructure evolution of an AlSi10MgMn alloy containing 0.5 wt% Mn produced by the selective laser melting process for the first time. The microstructures under different conditions were analyzed using optical microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. In the as-manufactured (F) condition, the alloy exhibited an ultimate tensile strength (UTS) of 486 MPa, a yield strength (YS) of 299 MPa, and an elongation of 10.3 %. After a T5 treatment, the UTS and YS increased to 532 MPa and 386 MPa, respectively, resulting in a remarkable 30 % improvement in YS compared to the F state. The tensile properties achieved by the new alloy were considerably higher than those reported for conventional AlSi10Mg alloys in the F, T5, and T6 conditions. The T5 treatment promoted the precipitation of a large fraction of Si-rich nanoparticles and MgSi-based precipitates without disrupting the Si-rich network. After a T6 treatment, the Si-rich network completely disappeared, and the main strengthening phase was MgSi-based precipitates accompanied by α-Al(Mn,Fe)Si dispersoids induced by the Mn addition. Using microstructure-based constitutive models, the strengthening contributions of various microstructural components to mechanical strength in different processing conditions were analyzed.

Microstructure, interfacial reaction behavior, and mechanical properties of Ti3AlC2 reinforced Al6061 composites

The interfacial reaction behavior of Al and Ti3AlC2 at different pouring temperatures and its effect on the microstructure and mechanical properties of the composites were investigated. The results show that the addition of 3.0 wt.% Ti3AlC2 refines the average grain size of α(Al) in the composite by 50.1% compared to Al6061 alloy. Morphological analyses indicate that an in-situ Al3Ti transition layer of ~180 nm in thickness is generated around the edge of Ti3AlC2 at 720 °C, forming a well-bonded Al−Al3Ti interface. At this processing temperature, the ultimate tensile strength of Al6061−3.0 wt.%Ti3AlC2 composite is 199.2 MPa, an improvement of 41.5% over the Al6061 matrix. Mechanism analyses further elucidate that 720 °C is favourable for forming the nano-sized transition layer at the Ti3AlC2 edges. And, the thermal mismatch strengthening plays a dominant role in this state, with a strengthening contribution of about 74.8%.

Simultaneously improving the strength and ductility of an oxide dispersion-strengthened high-entropy alloy by employing innovative precursors for oxide formation

The engineering of a composite microstructure, achieved by coupling heterogeneous grain distribution with oxide dispersion, has been demonstrated as an effective strategy for enhancing the strength-ductility synergy of alloys at both room and elevated temperatures. The effectiveness of this approach is strongly correlated with the micro-features of dispersed oxides. In this study, we selected the Ni38Co20Cr20Fe18Ti4 high-entropy alloy (HEA) as the base material, which could achieve the desired composite structure through preparation using mechanical alloying and spark plasma sintering methods. Our primary objective was to investigate the effects of incorporating Y2O3 or utilizing hydrides (TiH2 and YH3) as alternative precursors on the modification of oxide precipitates, evolution of a bimodal grain microstructure, and alteration in mechanical properties for the oxide dispersion strengthened (ODS) HEA. The results show that the incorporation of Y2O3 promotes the formation of ultrafine and semi-coherent Y2Ti2O7 ternary oxide particles, in addition to the pre-existing coarse binary TiO in the HEA matrix. Moreover, this leads to a significant increase in the fraction and a decrease in the average size of ultrafine grains (UFGs) within the bimodal microstructure. Notably, utilizing Ti- and Y-hydrides instead of Y2O3 and Ti as oxide-forming precursors within an equivalent composition remarkably amplifies the precipitation proportion of Y2Ti2O7 among dispersoids while further refining UFGs. The ODS-HEA synthesized using hydrides exhibits a simultaneous enhancement of 12 % in yield strength and 13 % in elongation to fracture, compared to that prepared from Ti and Y2O3. This intriguing phenomenon primarily arises from the heightened strengthening and toughening contributions, facilitated by the increased precipitation of advantageous Y2Ti2O7 nanoparticles.

Inhomogeneous deformation in the radial direction of the cold radial forged 30SiMn2MoVA steel tube

In this paper, the inhomogeneous deformation in the radial direction of the cold radial forged 30SiMn2MoVA steel tube was studied by finite element method, analyzing the microstructure and mechanical tests. The simulated result shows that the inhomogeneous deformation mainly distributed from the inner layer to the middle layer. In this region, the equivalent plastic strain rapidly decreases. The change from the middle to the outer is not significant. The distribution of microstructure and the results of mechanical properties also follow this pattern. The inner layer has the most refined grain size and the highest dislocation density. The strongest {110}<110> texture component has also been formed in the inner layer. The strength value of the inner layer is the highest, and the elongation is the lowest. There is not much difference in these indicators between the middle and outer regions. By calculating the strengthening contributions of solid solutions, dislocation density, and grain boundaries to yield strength, it was found that dislocation density is the main contributor. The calculated yield strength value is consistent with the experimental value.

Experimental assessment of FRP repairing in concrete cylinders exposed high temperatures

This study presents an experimental evaluation of fiber-reinforced polymer (FRP) strengthening in concrete specimens damaged by exposure to high temperatures. For this purpose, sixty cylindrical concrete specimens were produced. Specimens exposed to temperatures of 200 °C, 400 °C, and 600 °C were strengthened using carbon and glass FRP fabrics in two or three layers. Compression tests were conducted to assess the strength of the specimens. The impact of temperature, fabric type, and the number of fabric layers on the concrete's strength was thoroughly investigated. Digital microscopy was employed to explore the formation of cracks due to temperature changes, followed by Scanning Electron Microscopy (SEM) analyses to examine the microscopic structural changes in the concrete samples. The study highlights the importance of considering changes in both strength and behavior models together when evaluating the strengthening contributions provided by FRP. The results indicate that FRP applications on fire-damaged concrete structures can provide effective strengthening up to 400 °C but may be insufficient at temperatures of 600 °C and above. Although an effective increase in strength was achieved at 600 °C, low levels of ductility were observed, which is undesirable for an engineering structure. Therefore, it has been determined that FRP-strengthening applications may not be effective in reinforced concrete (RC) structural elements exposed to temperatures of 600°C and higher.

Eliminating metallurgical defects and achieving strength-ductility combination in selective laser melted martensitic stainless steel through high-pressure annealing

Due to high difficulty in fabricating and processing high-strength metals, additive manufacturing has been considered to have broad prospects compared to the traditional casting means. However, unavoidable metallurgical defects and strength–ductility trade-off dilemma have become Achilles' heels for their practical applications. In this work, one high-pressure annealing (HPA) strategy was introduced to process the selective laser melted (SLM) martensitic stainless steel. The microstructures and mechanical properties of as-built, high temperature annealing and HPA and as-rolled SLM samples were systematically investigated. It was found that the HPA treatment makes the stainless steel achieve the significant yield strength of 1828 MPa and the comparable plastic strain of 36.2% compared to other samples. The pores and laminar structures from the SLM process were eliminated by HPA. What is more, the HPA treatment results in uniform carbide precipitation, grain refinement and nanoscale heterogeneous structure comprising a series of coarse and fine grains. The physical mechanism for nanoscale heterogeneous structure induced by HPA was discussed from the perspective of the cooperative effect of temperature and pressure. Additionally, the strengthening contributions from grain refinement, carbide precipitation, dislocation hardening, heterogeneous structure and pore closure were quantitatively determined. The current study not only reveals the comprehensive effect of temperature and pressure on microstructure and mechanical properties, but also establishes HPA as an effective method to evade the strength-ductility trade-off in alloys fabricated by additive manufacturing.

Predicting tensile behavior and fatigue life of laser shock peened titanium alloy by crystal plasticity model

Laser shock peening (LSP) could improve fatigue resistance of metals, but the complex surface microstructures created by LSP make it extremely challenging to predict the mechanical behavior. Here, we present a crystal-plasticity (CP) modeling framework to predict the tensile behavior and fatigue life of LSPed titanium alloy, in which LSP induced three strengthening mechanisms (i.e., residual stress, grain-size gradient, and dislocation) are fully involved. The fatigue life is evaluated by incorporating CP finite-element results and a modified Tanaka–Mura model. The three strengthening mechanisms of LSP and their individual contribution to the tensile and fatigue properties are quantitatively clarified. The predicted tensile behavior and fatigue life of LSPed titanium alloys are demonstrated to agree well with experimental results. In terms of tensile property, the major strengthening contribution is ascribed to the LSP induced grain-size gradient, followed by dislocation and residual stress. As for fatigue life, all predictions are within the ±2 times error band. It is found that balancing residual stress with grain size and dislocation is crucial for improving fatigue life. This work provides a predictive approach for evaluating tensile and fatigue performance of LSPed alloys, and is insightful for fatigue life enhancement by LSPed microstructure engineering.

Assessing the factors underlying the high yield strength of laser powder bed fusion processed niobium

The present study focuses on the factors underlying the substantially higher yield strength (YS) and ultimate tensile strength (UTS) in laser powder bed fusion (LPBF) processed niobium, as compared to electron beam additive manufacturing (EBAM) or conventionally processed Nb. LPBF builds of pure Nb, with a relative density of 98 %, exhibited an YS of 490 MPa, UTS of 609 MPa, and ductility of 9 % with appreciable strain hardenability. Detailed electron backscatter diffraction analysis revealed a high density of sub-boundaries within the BCC Nb grains. Additionally, the LPBF Nb sample contained ∼1200 ppm of oxygen and ∼380 ppm of nitrogen, part of which segregated to the grain boundaries, as revealed by atom probe tomography (APT). The individual strengthening contributions from grain boundaries, dislocations, and oxygen and nitrogen interstitials have been quantitatively estimated, giving an overall computed YS of 506 MPa, in close agreement with the experimentally measured value of 490 MPa. This quantitative assessment also revealed that solid solution strengthening from oxygen and nitrogen can be of the same order of magnitude as strengthening from dislocations and sub-boundaries in LPBF processed Nb.

Crystal plasticity quantification of anisotropic tensile and fatigue properties in laser powder bed fused Inconel 718 superalloy

The high thermal gradients during the laser powder bed fusion (LPBF) process induce an inhomogeneous microstructure with anisotropic mechanical properties. This study developed a dislocation-based strain-gradient crystal plasticity finite element (CPFE) model to reveal the microstructure-based deformation mechanisms and quantify their strengthening contributions to the mechanical property anisotropy of LPBF-ed Inconel 718 (IN718) superalloy. The analyzed microstructural attributes included 1- crystallographic orientations/misorientations, 2- solid solutions (SS), 3- grain size and morphologies, and 4- dislocation dynamics, such as statistically stored dislocations (SSDs) and geometrically necessary dislocations (GNDs). The investigated mechanical properties contained tensile strength, fatigue resistance, fracture mechanisms, and their anisotropy under loading towards building (BD) and transverse (TD) directions. The experimentally obtained microstructural features of the as-LPBF-ed IN718 were synthesized into the crystal plasticity representative volume elements (CPRVE) to model the deformation behavior using a user-defined material subroutine (UMAT) in the ABAQUS solver. The energy-based fatigue indicator parameter (FIP) captured the fatigue properties and failure mechanisms. The main slip-strengthening contributions stemmed from SSDs, grain size, SS, and GNDs. in TD. The corresponding order in BD was SSDs, SS, GNDs, and grain size because the grain dimensions were larger in BD than in TD. The grain-size effect had the highest contribution to the tensile property anisotropy, followed by SSDs, GNDs, and SS. Aside from their strengthening effects, crystal texture and grain size induced mechanical property heterogeneity and fatigue sensitivity at grain boundaries, reducing their contributions to fatigue strength relative to tensile. In contrast to the previous findings, local accumulations of SSDs and GNDs at softer sides of grain boundaries during cyclic loading reduced the strength heterogeneity in these areas, improving fatigue properties. The highest slip-strengthening effect for fatigue resistance and anisotropy was under SSDs, followed by GNDs, SS, and grain size.

A novel cast Co68Al18.2Fe6.5V4.75Cr2.55 dual-phase medium entropy alloy with superior high-temperature performance

A newly-designed Co68Al18.2Fe6.5V4.75Cr2.55 medium entropy alloy (MEA) with FCC + B2 structure exhibits not only an excellent strength-ductility combination at room temperature, but also an outstanding high-temperature mechanical properties in particular. The phase formation, microstructure and deformation mechanism of this designed dual-phase MEA at room and high temperatures were investigated and discussed in detail. Based on experimental results (XRD, SEM and TEM) and theoretical analysis (calculated diagram and empirical thermodynamic parameters), it is demonstrated that this newly-designed MEA consists of a dual-phase structure of a face-centered-cubic (FCC) phase (70.3 vol %) plus chemically ordered body-centered cubic phase (B2) (29.7 vol %). Meanwhile, the FCC phase is enriched with Co, Fe and Cr elements, while the B2 phase is enriched with Al and Co elements. Furthermore, compared with some HEAs/MEAs and commercial alloys, this newly-designed dual-phase MEA exhibits excellent strength-ductility combination with a high compressive yield strength of ∼1254 MPa, a fracture strength of ∼2657 MPa and a large compressive plasticity of ∼34.6 % at room temperature. In particular, the studied MEA also shows an outstanding high-temperature performance with an ultrahigh yield strength of ∼1213 MPa at 600 °C and ∼626 MPa at 800 °C, respectively. The excellent comprehensive mechanical properties of this designed dual-phase MEA at both room and temperatures mainly originate from synergy effect of alternate FCC + B2 structure and strengthening contributions of B2 phase. These important findings not only reveal the deformation and strengthening mechanisms of the newly-designed dual-phase MEA, but also provides an effective alloy design strategy for developing advanced structural materials serving as a wide range of temperature.

Natural and artificial aging behaviour of Al-Cu-Mg-Ag-Ti-B (A205) alloy processed by laser powder bed fusion: Strengthening mechanisms and failure analysis

The Al-Cu-Mg-Ag-Ti-B (A205) alloy has gained success in the additive manufacturing domain due to its good processibility. It is a precipitation hardening alloy, and because of this, its mechanical properties are greatly influenced by post-processing treatments. In the present work, A205 samples processed by laser powder bed fusion were first solution treated and then aged by: (i) natural aging (NA) and (ii) artificial aging (AA). The effects of different aging treatments on the microstructure and mechanical behaviour were evaluated. Both NA and AA heat treatments improved the mechanical behaviour of as-built A205 alloy. Peak hardness was achieved in 20 days (≈ 137 HV) for the NA specimen, whereas it took 4 h at 190 °C (≈ 144 HV) for the AA specimen. The average yield strength, ultimate tensile strength and elongation to fracture for NA and AA were, 276 MPa, 434 MPa, 20% and 397 MPa, 463 MPa, 11%, respectively. The structure-property corelation was analysed by evaluating various strengthening factors. Considerable grain boundary strengthening was observed in both NA and AA specimen. The major strengthening contributions in the NA specimen were due to the disordered Ag-Mg co-clusters and solid solution strengthening by Cu. In AA instead, strengthening due to the precipitation of plate-type Ω/θ’- Al2Cu phase was dominant. In the end, failure mechanisms in the NA and AA conditions were also briefly discussed. The laser powder fused A205 alloy demonstrated a significant response to the NA and possessed a high-ductility and good-strength combination.

Microstructure evolution and strengthening mechanism of FeCo-1.5V0.5Nb0.4 W soft magnetic alloy rolled strip with high yield strength and low coercivity

The low strength of soft magnetic alloy limits the ability to operate high speed rotors in aero-generators. Strengthening of soft magnetic alloys remains a challenge, as most methods that enhance strength lead to the deterioration of magnetic properties. In this work, a rolled strip of FeCo-1.5V0.5Nb0.4W (wt.%) alloy with high yield strength and low coercivity was developed. We demonstrated that minor additions of Nb and W has a little effect on the magnetic properties. Due to the microalloying has a negligible effect on magnetocrystalline anisotropy, and low content of the secondary phase. Additionally, solute atoms are enriched at the grain boundaries, which reduces the grain boundary energy and promotes the nucleation and growth of Laves-Co2Nb phase at the grain boundary by grain boundary diffusion. These lead to almost stagnation of grain growth during isothermal annealing at 1123 K for 3 h and stabilization at ∼6 μm. Therefore, based on the reduction of dislocation density by high-temperature annealing to restore the magnetic properties of the alloy, fine-grain strengthening coupled with solid solution strengthening, and a certain amount of Orowan bypass effect and dislocation strengthening contribution, provide for the high strength of the alloy. The yield strength of the rolled strip reached 742 MPa under the conditions of no significant decrease in the saturation magnetization of 2.39 T and an extremely low coercivity of 152 A/m. These results are of great significance for understanding the relationship between the strengthening mechanisms of metallic materials and further developing high-performance FeCo-based soft magnetic alloys.

Ultrastrong Nanocrystalline Inconel 718 Fabricated by Powder High‐Pressure Torsion and Annealing

In this study, bulk nanocrystalline material is fabricated from Inconel 718 powder through a process of powder high‐pressure torsion (HPT) and subsequent annealing heat treatment. Numerous dislocations generated during the powder HPT process successfully produced bulk Inconel 718 with nanocrystalline grains during the post‐annealing treatment. In addition, the Inconel 718 exhibited additional strengthening contributions such as dislocation strengthening by high pre‐existing dislocation density and precipitation strengthening from randomly distributed precipitates. As a result of these strengthening effects, the Inconel 718 showed ultrastrong yield strength of 1.40 GPa and ultimate tensile strength of 1.53 GPa. Although the elongation of 12.0% did not indicate good ductility, the proposed Inconel 718 boasted improved mechanical properties compared to previous studies of Inconel 718 fabricated by various processing methods. The prepared Inconel 718 and its fabrication technique suggest the potential for manufacturing ultrahigh‐strength bulk nanocrystalline materials not only for Inconel 718 but also for various metallic materials using powder metallurgy.

Optimization of Mechanical and Thermoelectric Properties of SnTe-Based Semiconductors by Mn Alloying Modulated Precipitation Evolution.

Multiscale defects engineering offers a promising strategy for synergistically enhancing the thermoelectric and mechanical properties of thermoelectric semiconductors. However, the specific impact of individual defects, in particular precipitation, on mechanical properties remains ambiguous. In this work, the mechanical and thermoelectric properties of Sn1.03- xMnxTe (x = 0-0.30) semiconductors are systematically studied. Mn-alloying induces dense dislocations and Mn nano-precipitates, resulting in an enhanced compressive strength with x increased to 0.15. Quantitative calculations are performed to assess the strengthening contributions including grain boundary, solid solution, dislocation, and precipitation strengthening. Due to the dominant contribution of precipitation strengthening, the yield strength of the x = 0.10 sample is improved by ≈74.5% in comparison to the Mn-free Sn1.03Te. For x ≥ 0.15, numerous MnTe precipitates lead to a synergistic enhancement of strength-ductility. In addition, multiscale defects induced by Mn alloying can scatter phonons over a wide frequency spectrum. The peak figure of merit ZT of ≈1.3 and an ultralow lattice thermal conductivity of ≈0.35Wm-1K-1 are obtained at 873 K for x = 0.10 and x = 0.30 samples respectively. This work reveals thaprecipitation evolution optimizes the mechanical and thermoelectric properties of Sn1.03- xMnxTe semiconductors, which may hold potential implications for other thermoelectric systems.

Evolution of microstructure and deformation mechanisms in a metastable Fe42Mn28Co10Cr15Si5 high entropy alloy: A combined in-situ synchrotron X-ray diffraction and EBSD analysis

In this work, a combination of in-situ high synchrotron X-ray diffraction and electron backscattered diffraction were used to systematically investigate the activation and evolution of the deformation mechanisms in an as-cast Fe42Mn28Co10Cr15Si5 metastable high entropy alloy deformed until fracture at room temperature. This work unveils the critical role of the dual-phase γ-f.c.c. / ε-h.c.p. microstructure on the deformation response of the alloy. The different deformation modes, i.e., slip, transformation induced plasticity (TRIP) and transformation induced twinning (TWIP), were seen to initiate at different loading stresses and then to overlap. Quantitative microstructural characterization, which included the evolution of the phase fraction, stress partitioning, dislocation density, c/a ratio and lattice strain for different planes, was performed to elucidate the role of each phase on the macroscopic mechanical response of the metastable high entropy alloy. Furthermore, the magnitude of the different strengthening contributions has been quantified for the first time.