The effect of zirconium content on mechanical and shape memory properties in high temperature TiVaL shape memory alloys

In this study, the effect of zirconium content on microstructure, shape memory and mechanical properties of Ti-12V-4Al-xZr (x: 0; 0,5; 1; 1,5 and 2) (wt%) master alloys was investigated. For this purpose, Ti-12V-4Al-xZr (x: 0; 0,5; 1; 1,5 and 2) (wt.%) alloys were produced as master alloy by Arc-Melting technique. Among these alloys, Ti-12V-4Al-0,5Zr (wt.%) alloy, which has the best martensite transformation temperature, was produced in ribbon form by Melt-Spinning technique which is one of the rapid solidification methods. Differential Scanning Calorimetry (DSC) analysis was performed to determine the phase transformation temperatures of the both master alloys and ribbon alloy. As a result of DSC analysis, phase transformation was observed in all alloys. It was found that the increase in Zr amount caused an increase in the austenite finish temperature of Ti-12V-4Al-0,5Zr (wt%) alloy and a decrease in other master alloys. DSC analysis of Ti-12V-4Al-0,5Zr (wt%) ribbon alloy showed that phase transformation was materialized twice. SEM observations together with XRD analysis showed that the structures of both master alloys and ribbon alloy had two different phases which were austenite and martensite at room temperature. According to TEM analysis of Ti-12V-4Al-xZr (x: 0; 0,5; 1; 1,5 and 2) (wt.%) master alloys, it was observed that martensite plate amount decreased and plate thickness reduced with increasing Zr amount. The mechanical properties (hardness, elastic modulus, superelasticity) of the master alloys in both austenite and martensite phases were characterized by using a high temperature microindentation device. Accordingly, superelasticity behavior of alloys decreased at room temperature (24oC) with the increase of Zr amount while this behavior increased at high temperatures (450oC). It was determined that the hardness and elastic modulus values of the alloys decreased with increasing Zr amount.