Mechanical (compressive) form of driving force triggers the phase transformation from β to ω & α’’ phases in metastable β phase-field Ti-5553 alloy

Abstract

Most of the structural alloys’ applications are under static, dynamic, and cyclic forms of loading. Ti-5553 alloy in the beta phase field is being investigated to confirm the mechanism of deformation and phase transformation upon quasi-static and dynamic compression. The Ti-5553 alloy was heat-treated at 900 °C (almost 50 °C above beta transus temperature) for one hour of soaking time followed by air quenching to achieve a fully β phase field. After that, Dynamic compression (DC) by Split Hopkinson Pressure Bar (SHPB) and Quasi-static compression (QSC) were performed at a strain rate of ̴103/s and 10−3/s, respectively. Recovered specimens were thoroughly examined by using different tools, such as an Optical microscope (OM), Scanning electron microscope (SEM), High-resolution transmission electron microscope (HRTEM), and Electron backscatter diffraction (EBSD) to get the reliable data for justification of logical conclusions. It is found that the dominating mode of deformation was dislocation slip along with twinning ({332} <113>) to some extent in both of QSC and DC, but sliding & spalling of the grain boundary is observed more in the former. Stress-induced phase transformation, i.e., β to α’’ and β to ω, took place in the grains saturated with dislocation slips, where the former transformation occurred simultaneously with {332} <113> twinning, while β to ω transformation was completed when a set of two adjacent (110)ᵦ planes covered ±1/6th of the total separation distance between two (next to each other) (111)ᵦ planes, by equal but opposite shear in (111)ᵦ direction, and it caused 3% shrinkage of two closed packed (110)ᵦ planes after transformation.