Mechanical (Compressive) Form of Driving Force Triggered the Phase Transformation from Beta to Omega & Alpha Phases by Means of Dislocation Slips in Metastable Beta Phase Field Ti-5553 Alloy

Abstract

Most of structural alloys' applications are under static, dynamic and cyclic forms of loading, for which Ti-5553 alloy in beta phase field is being investigated to confirm the mechanism of deformation and phase transformation upon quasi-static and dynamic compression. To achieve the fully beta phase field, Ti-5553 alloy was heated at 900oC (almost 50oC above beta tarsus temp.) for one hour of soaking time followed by air quenching. Thereafter, Dynamic compression (DC) by Split Hopkinson Pressure Bar (SHPB) and Quasi-static compression (QSC) were performed at strain rate of 103/s and 10-3/s, respectively. Recovered specimens were thoroughly examined by using different tools such as OM, SEM, HRTEM, EBSD to get reliable data for justification of logical conclusions. It's found that the prominent mode of deformation was dislocation slips along with twining to some extent in both of QSC and DC but sliding and spalling of grain boundary was more noticeable in former. Transformation of phases occurred in saturated dislocation slips grains in which from beta (BCC) to omega transformation has been completed by mechanical form of driving force in a way when set of two adjacent (110)ᵦ planes covered ±1/6 of total separation distance between two next to each other (111)ᵦ planes, equal but opposite shears, in (111)ᵦ direction and it could be justified by the 3% shrinkage of two closely existed (110)ᵦ planes after transformation to omega. Furthermore, it is noticed that the omega phase and alpha transformation occurred in the grains which were saturated with dislocation slips.