Processing of titanium niobium shape memory alloys by hot pressing

For the production of Ti-Nb alloys, generally the casting methods (vacuum induction melting or vacuum arc remelting) have been used up to now. Since the melting temperatures of pure Ti and Nb are extremely high (1668 and 2477°C, respectively), it is not economical to produce Ti-Nb alloys by casting. In the case of powder metallurgy, it is possible to produce these alloys economically at much lower temperatures (less than melting temperature of Ti) completely in solid state. In the present study, Ti74Nb26 alloys were produced using pure Ti and pure Nb powders by combination of hot pressing and high temperature sintering for the first time. The influence of processing temperature and time on density, microstructure, and mechanical behavior were investigated. Density measurements showed that hot pressing at 800 °C provides full density. XRD and SEM investigations revealed that amount of β phase formed increases with increasing sintering time. In addition to main phase β, little amount of α phase and a very small amount of pure Nb was observed in the microstructure. Mechanical properties were measured by means of uniaxial compression and Micro Vickers indentation tests. The results indicated that 4hr of sintering at 1200 °C exhibited the highest value of hardness (336 HV), elastic modulus (44 GPa), yield strength (894 MPa), and compression strength (1178 MPa).