Evolution of microstructure and mechanical properties of Ti6Al4V alloy by multiple passes of constrained groove pressing at elevated temperature

Abstract

Constrained groove pressing (CGP) is one of the best available sheet material processing technique for grain refinement and improving material properties without changing the original dimensions of the specimen. In this work, CGP is successfully performed on 10 mm thick mill-annealed Ti6Al4V plates at a temperature of 550 °C up to three passes. Microstructure studies reveal that grain size decreased from 18.81 μm in as received (AR) sample to 9.24 μm after third pass. XRD studies confirm the lattice strain and grain refinement phenomenon by peak shifting and broadening. Work hardening and grain refinement lead to increase in microhardness from 346 HV in AR to 392.1 HV, 365.9 HV and 371.4 HV in one pass, two pass and three pass CGP processed (CGPed) Ti6Al4V respectively. CGP leads to improvement of YS from 964.75 MPa in AR to 1085.01 MPa, 1068.11 MPa and 1078.63 MPa in one, two and three pass CGPed Ti6Al4V respectively. Similarly, UTS is observed to improve from 1014.12 MPa in AR to 1118.26 MPa, 1015.21 MPa, 1098.05 MPa in one, two and three pass CGPed Ti6Al4V respectively. SEM fractography reveals change in the mode of fracture of Ti6Al4V from ductile to ductile-brittle mode before and after the CGP process. Work hardening behavior of CGPed Ti6Al4V changes from stage III and IV to purely stage III along with initial instantaneous hardening rate increases after the first pass and decreases for the subsequent passes. CGP on Ti6Al4V alloy at 550 °C is found to have a significant effect on the stabilization of its microstructure and mechanical properties which can be useful for extending CGP for HCP alloys and their applications in aerospace and defense sector.