Zhixiong Zhang

Developing cost-effective Fe-based alloys that combine high strength and ductility at low temperatures remains a major challenge for structural applications. In this work, we designed a series of Fe50.9Ni34Cr6Al6Ti3-xNbxB0.1 (x = 0, 2, 3 at.%) medium-entropy alloys (MEAs) strengthened by coherent L12-type nanoprecipitates to reveal how Ti-to-Nb substitution regulates precipitate coarsening, grain-boundary evolution, grain growth, and cryogenic deformation. Aging experiments at 700 ℃ decouple composition-dependent thermal stability: The TiNb2 alloy exhibited the finest L1₂ nanoprecipitates and the lowest apparent coarsening rate constant, whereas the Nb3 alloy showed the slowest grain growth despite faster intragranular precipitate coarsening. The alloys also exhibited favorable cryogenic tensile properties; in particular, the Nb3 alloy achieved a yield strength of ~901 MPa, an ultimate tensile strength of ~1524 MPa, and an elongation of ~35% at -196 ℃. Strengthening analysis indicates that the room-temperature yield-strength increment is mainly governed by ordering strengthening associated with shearing of coherent L1₂ nanoprecipitates in weak-pair coupling mode, while cryogenic deformation involves stacking-fault-mediated planar slip, dislocation storage, and Lomer–Cottrell lock formation. These results demonstrate that Ti/Nb substitution provides an effective route to separately tune precipitate coarsening resistance, grain-growth resistance, and cryogenic mechanical performance in cost-effective, high-strength Fe-rich structural alloys.

The heterogeneous deformation of Ti‐6Al‐4V alloy during multidirectional isothermal forging and its effect on microstructure, microtexture, and related mechanical properties are investigated here. It is found that lowering the deformation temperature, combined with increasing the number of forging times, accelerates the grain refinement and recrystallization process in the as‐received billet, especially in the surface section rather than the inner of the billet. Finally, a heterogeneous lamellar structure is formed after annealing the billet with a fourth step of forging. The heterogeneous lamella structure enables a better synergy of strength and ductility when compared to its equiaxed counterpart, achieving a high tensile strength of 1194 MPa and an elongation of 13.1%. During the deformation, a high proportion of back stress to total flow stress, ranging from 64–67%, denotes that back stress strengthening is one of the main reasons for the better synergy of strength and ductility. This study guides a low‐cost and convenient way for the regulation of microstructure and mechanical properties of titanium alloy with good performance.

TiAl alloy is a high temperature structural material with excellent comprehensive properties in the range of 750–900 °C. However, its engineering application is limited by its poor plasticity and hot working properties at room temperature. Based on the above background, a novel three-phase Ti-40Al-6V-1Cr-0.3Ni (at.%) alloy was designed and fabricated in the present study. The as-cast ingot was subjected to near-isothermal forging, and the thermoplastic deformation behavior, microstructure evolution and mechanical properties were systematically studied. Near-isothermal forging shows excellent forming capability, and the forging disk is flawless without cracking. The core of the forging disk shows the greatest degree of deformation, and the microstructure is composed of fine equiaxed grains and residual (α2/γ) lamellae. The hardness of the B2 phase and the hardness difference between the B2 phase and γ phase are reduced by the Cr and V elements added in the alloy. The wrought alloy exhibits excellent mechanical properties at room temperature and elevated temperature, respectively. The uniform fine microstructure, low nanohardness of the B2 and γ phase and the property matching of each phase can be accounted for the excellent mechanical properties.