Heterostructure evolution and strengthen-toughness synergic mechanism of a powder metallurgic chemical gradient Ti–Mo alloy during hot deformation

Strength-toughness synergy for metallic materials is always a direction of committed development for metallic materials. In this work, a facile strategy using spark plasma sintering (SPS) combined with hot diffusion and rolling was employed to design a chemical gradient Ti-Mo alloy with a gradient coupling grain (GCG) heterostructure. Key microstructural parameters of the GCG heterostructure, including β phase fraction, heterogeneity parameter, texture intensity, grain size distribution, and region width, were systematically analyzed and found to strongly depend on processing temperature. Tensile property variations with temperature were also investigated. After rolling at 500 °C, the specimen with an optimized GCG heterostructure exhibited outstanding mechanical properties (yield strength of 1192 ± 13 MPa, ultimate tensile strength of 1307 ± 8 MPa, and elongation of 10 ± 0.9%). Below 700 °C, the strength decreased but elongation increased with increasing rolling temperature. The primary strengthening mechanism is attributed to fine grain strengthening and dislocation strengthening. However, processing at 800 °C induced a significant reversal in mechanical behavior: an unexpected increase in strength coupled with a decline in elongation. This abrupt reversal was primarily driven by precipitation of hard ω phase, texture evolution, and microstructural heterogeneity. This work demonstrates a viable strategy to achieve exceptional strength-toughness synergy via GCG heterostructures in chemical gradient Ti-Mo alloys. It also deepens the fundamental understanding of heterostructure formation and associated strengthening-toughness mechanisms, offering insights into the design of heterogeneous alloys with excellent mechanical properties.