Microstructure And Mechanical Properties And Corrosion Behaviour Of TiNb Shape Memory Alloy

The microstructure, phase composition, mechanical properties, shape memory effect and corrosion behavior of TiNb alloys were investigated by means of optical microscope, TEM, XRD analysis, bending test, tensile test, SEM, EDS, electrochemical measurement and XPS.The as-cast TiNb alloys are mainly composed of two phases: α" phase and p phase. With the increasing of Nb content, the diffraction peaks of α" become less and weaker and in Ti-26.5Nb alloy the diffraction peaks of α" are absent. The Ti-16Nb alloy is mainly composed of α" phase and β phase, while Ti-25Nb alloy and Ti-26.5Nb alloy have a single β phase after hot-rolling. In the solution treated condition, the TiNb alloys are also mainly composed of α" phase and β phase, but there is only one weak diffraction peak of α" both in Ti-25Nb and Ti-26.5Nb alloys, while the TEM observation proved that there is a little amount of ω phase in Ti-16Nb alloy.At the same time, the martensite lath with a sub-structure of (111) type Ⅰ twin was found in Ti-16Nb alloy during TEM observation.The elastic modulus values of TiNb alloys are almost among 50GPa～70GPa at room temperature. The temperature of solid solution treating does not affect the elastic modulus values too much. The Ti-16Nb alloy, while solution treated at 750℃, has the best combination of mechanical properties with the highest strength and elongation rate. And for Ti-25Nb alloy and Ti-26.5Nb alloy, the strength increases but the elongation rate decreases with the increasing of solution treated temperature. When solution treated at the same temperature 750℃, the Ti-25Nb alloy has the largest elongation rate (22.1%) and the highest ultra tensile stress (751MPa) as well as yield stress (662MPa), compared with the other two TiNb alloys. After aging treatment, the mechanical...