Synchronous enhancement of the strength and ductility in a metastable β-Ti alloy by a new refined α phase mechanism

Grain refinement is a fascinating method to improve both strength and plasticity of metallic materials. In particular, grains below the micrometer scale can produce significant strengthening effects while avoiding progressive stress localization and early failure of the alloy and then improving the plasticity. A new α grain refinement mechanism, FCC phase-stress delocalization, is found in hot-rolled metastable β titanium alloys. The fragmentation process of α phases followed the formation of FCC phase → accumulation of dislocation and stress localization on the α/β phase interfaces → FCC phase as a site to release the stress concentration and promote the formation of grooves → the final refinement completed via developing grooves. At the same time, it is researched by TEM that the orientation relationship (OR) between the α and the FCC phase is P-type and B-type, and the variant selection of the FCC phase occurs. Furthermore, the highest ultimate tensile strength (UTS) ~1210.3 MPa and excellent elongation (EL) ~22.5% were obtained under the R90 sample. Such significant performance breakthroughs are attributed to the occurrence of ultra-fine α grain and the FCC phase, which breaks the trade-off between strength and ductility.