Rengeng Li

Wire drawing is a key processing method for producing ultrahigh-strength stainless steel wires. In metastable austenitic steels, the strain-induced martensitic transformation is known to govern strain hardening. However, the transformation mechanism and kinetics behavior under wire drawing remain unclear due to the distinct deformation conditions compared to those of conventional loading modes. In this work, the microstructural evolution, transformation kinetics and strengthening behavior of the 304 stainless steel during cold wire drawing are systematically analyzed. The results show that the transformation is dominated by the austenite → twin→ α′-martensite pathway, with the ε-martensite effectively suppressed. The martensite fraction follows a sigmoidal evolution with the equivalent drawing strain and could be well described by the Olson–Cohen model. The yield strength is increased from 320 MPa to 2 GPa and exhibits a linear relationship with the martensite fraction, indicating a dominant composite strengthening mechanism. These findings clarify the deformation-mode-dependent transformation mechanism and its role in governing mechanical properties during wire drawing.

Laser-directed energy deposition (LDED)-fabricated TiAl alloys tend to develop coarse columnar microstructures, exhibit strong anisotropy, and consequently suffer from limited mechanical properties. The present study investigated the effect of Er2O3 nanoparticle addition on the microstructural evolution and mechanical performance of a Ti–48Al–2Cr–2Nb alloy produced by LDED. The addition of Er2O3 transformed the solidification microstructure from coarse columnar grains into a refined equiaxed lamellar colonies. As a result, the average colonies size decreased markedly from 183 to 38.7 μm. Moreover, the γ{111} texture intensity decreased from 17.34 to 8.86, indicating a pronounced weakening of the preferred crystallographic orientation. These microstructural changes lead to a clear improvement in mechanical performance. At 750 °C, the ultimate tensile strength is increased by 12.2%, from 615.1 MPa to 689.9 MPa, accompanied by a 16.7% increase in elongation, from 8.23% to 9.88%. In addition, the room-temperature ultimate compressive strength increased by 38.1%, from 1964.9 MPa to 2714.5 MPa. The enhanced mechanical performance is mainly associated with the synergistic effects of refined lamellar microstructure, effective particle-dislocation interactions, twin-assisted strain accommodation, and enhanced resistance to crack propagation. This work provides an effective strategy for improving the performance of LDED-fabricated TiAl alloys for high-temperature structural applications.

This study systematically investigates the influence of key process parameters—layer thickness and substrate preheating—on solidification cracking in K418 nickel-based superalloy fabricated by laser powder bed fusion (LPBF). For a 30 μm layer, preheating to 350 °C combined with a volumetric energy density (VED) of 60–80 J/mm³ effectively suppressed hot cracking while achieving a relative density > 99%. Preheating to 200 °C showed limited effectiveness. Without preheating, increasing the layer thickness to 60 μm reduced cracking compared to 30 μm, yet preheating became counterproductive under this thicker condition due to excessive thermal accumulation and increased shrinkage stress. Microscopic analysis revealed that cracks propagated along high-angle grain boundaries accompanied by the segregation of low-melting-point elements (O, B, Si, C), with cracking attributed to thermal stress and grain boundary weakening during rapid solidification. This work establishes 350 °C preheating with moderate VED as an effective strategy for manufacturing high-density, crack-minimized K418 alloy components via LPBF.

GH2097, a Fe-Ni-Co-based superalloy extensively employed in high-temperature critical components such as aircraft engines, was investigated to elucidate the influence of Si content on its precipitation behavior and mechanical properties. By systematically adjusting Si concentrations, it was demonstrated that Si significantly modulates the size, distribution, and stability of γ′ phase (Ni₃TiNb). As Si content increases, γ′ phase coarsening (mean size: 30.1→40.3 nm) results in a marginal increase in volume fraction of 2%. Mechanical testing revealed a direct correlation between Si content and yield strength enhancement, achieving a maximum increment of 97.1 MPa. Post solution-aging treatment, γ′ strengthening dominated the strengthening mechanisms in GH2097, contributing over 50% to the overall strength. Microstructural characterization (SEM/TEM) further confirmed that optimal Si addition balances precipitation kinetics and grain boundary stabilization without inducing detrimental phases. Therefore, it is important to consider the role of the Si element in the microstructure control of GH2907 alloy.

Thermomechanical processing by applying deformation-induced ferrite transformation (DIFT) is an effective method of producing ultrafine-grained (UFG) ferritic steels, which usually present high yield strength but low strain hardening. In this study, we explored the concept of DIFT in the processing of UFG dual-phase (DP) steel, in order to improve its strain hardening capability and thus its ductility. The processing temperature was reduced to enhance the dislocation storage in austenite. It was found that the warm deformation of austenite induced a dramatic occurrence of DIFT, resulting in the formation of UFG-DP microstructures along the whole thickness of the specimen. In the UFG-DP microstructure, the average ferrite grain size was 1.2 μm and the ferrite volume fraction was 44 vol.%. The observation of twinned martensite suggests the occurrence of carbon partitioning during the DIFT process. The UFG-DP microstructure exhibited a good combination of strength and ductility, which was enabled by the synergy of the ultrafine ferrite grains and the efficient composite effect. The outcome of this study provides a novel pathway to develop advanced hot-rolled steels with a UFG-DP microstructure and which are associated with the advantages of their readiness to be scaled up and low costs.

Magnesium and its rare-earth alloys are extensively studied for their lightweight properties and high specific strength, making them attractive for aerospace, automotive, and biomedical applications. However, their hexagonal close-packed structure leads to a strong basal texture, limiting plasticity and formability at room temperature. Considerable research has been devoted to texture control strategies, including alloying, thermomechanical processing, and recrystallization mechanisms, yet a comprehensive understanding of their effects remains an ongoing research focus. This review summarizes recent advances in texture regulation of rare-earth magnesium alloys, focusing on the role of RE elements (Gd, Y, Nd, Ce) and non-RE elements (Zn, Ca) in modifying basal texture and enhancing mechanical properties. The influence of key processing techniques, such as extrusion, rolling, equal channel angular pressing, and rotary shear extrusion, is discussed in relation to their effects on recrystallization behavior. Additionally, the mechanisms governing texture evolution, including continuous dynamic recrystallization, discontinuous dynamic recrystallization (DDRX), and particle-stimulated nucleation, are critically examined. By integrating recent findings, this review provides a systematic perspective on alloying strategies, processing conditions, and recrystallization pathways, offering valuable insights for the development of high-performance magnesium alloys with improved formability and mechanical properties.

This study investigates the influence of friction stir processing (FSP) on the microstructure, microhardness, and tribological properties of cold-sprayed AlSi10Mg+TiB₂ composite coatings on Al substrates. Due to the limitation of particle deformation during cold spraying, there were still some porosities and poorly bonded regions in the as-deposited AlSi10Mg+TiB₂ composite coating, which decreased the mechanical performance. Applying FSP to the composite coating significantly reduced the porosity and improved metallurgical bonding. Further, the FSP process induced severe plastic deformation, leading to a more uniform distribution of TiB₂ particles and a homogenized microstructure in the composite coating. The microhardness decreases progressively from the unaffected region through the heat-affected zone and thermomechanical-affected zone, and ultimately reaches its lowest value in the stir zone. The decreased microhardness is primarily attributed to the removal of the work-hardening effect. The FSP treatment seems to have little impact on the wear performance for both the pure AlSi10Mg and AlSi10Mg+TiB₂ composite samples, as the coefficient of friction values and wear rates remain essentially unchanged after the FSP treatments.