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 alpha grain refinement mechanism, FCC phase-stress delocalization, is found in hot-rolled metastable beta titanium alloys. The fragmentation process of alpha phases followed the formation of FCC phase -> accumulation of dislocation and stress localization on the alpha/beta 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 a 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) similar to 1210.3 MPa and excellent elongation (EL) similar to 22.5% were obtained under the R90 sample. Such significant performance breakthroughs are attributed to the occurrence of ultra-fine alpha grain and the FCC phase, which breaks the trade-off between strength and ductility. (C) 2022 Published by Elsevier B.V.