Study of some heat treatment effects on thermodynamic and structural properties of Ti-Ta biomedical shape memory alloys

Abstract

The shape memory effect (SME) in binary β-Ti alloys is associated with a reversible martensitic transformation from α”- orthorhombic martensitic phase to β-bcc austenitic phase. The present paper reports the experimental results obtained on TiTa alloys, containing 25, 30, 35 and 50 mass % Ta. The specimens were processed from as-cast levitation induction melt ingots, cut by wire electric discharge, hot/cold rolled (enabling to obtain 500-mm long thin ribbons), solution treated (900°C/30 min/water quenched, W.Q.) and aged (300°C/1 h/W.Q.). From each heat treated state, samples were cut for tests meant to emphasize the presence of thermal and mechanical memory behaviour. Thermal memory was highlighted by SME-work generating training cycles, investigated by cinematographic analysis. The respective results were corroborated with those recorded by dynamic mechanical analysis (DMA). Mechanical memory was revealed by winding-unwinding and tensile tests. The winding and tensile tests offered information about the capacity of cold rolled ribbons to memorize their room temperature (RT) profile. Tensile tests were applied up to complete failure or by RT loading-unloading cycles.