Tailoring Microstructure and Properties of a Superelastic Ti–Ta Alloy by Incorporating Spark Plasma Sintering with Thermomechanical Processing

Abstract

A powder metallurgy Ti–35 at.% Ta alloy was produced using a spark plasma sintering process. The sintered alloy exhibited Ta-rich regions at a sintering temperature of 1100 °C. Complete diffusion of elemental powders was achieved via homogenization heat treatment at 1500 °C for 12 h, but the ductility declined drastically. The brittle behavior of the homogenized sample was due to the high-oxygen content, continuous grain boundary α-phase and high-angle grain boundaries. Excellent mechanical properties were achieved when hot forging was used along with preheating the homogenized specimen at 1100 °C. The mechanisms underlying this phenomenon were suppression of the solid grain boundary α-phase, high fraction of low-angle grain boundaries and dynamic recrystallization. Tensile strength improved to the maximum value of 868 MPa. The strain recovery ratio increased to 90% in the first cycle during a cyclic loading–unloading test. Incomplete strain recovery of the first cycle was due to the presence of the martensite phase (α″).