Effect of Boron Addition on the Microstructure and Properties of Ti-22Nb-6Zr Shape Memory Alloys

Ti-22Nb-6Zr (at%) shape memory alloys with various amount of boron (B) addition (0.02 wt% similar to 1.5 wt%) were fabricated using a powder sintering method. Optical microscope, XRD and SEM were used to investigate the microstructure and phase constituents of the sintered alloys. It is shown that boron addition induces the precipitation of a phase and TiB phase in beta matrix, which facilitates distinct refinement of microstructure. The addition of boron exerts only little influence on the Young's modulus (around 30 GPa) and superelasticity (over 3%), but affects strongly the compression strength and yield strength of sintered Ti-22Nb-6Zr-B alloys. In order to acquire a relatively high yield strength and compression strength, the amount of boron addition into Ti-22Nb-6Zr shape memory alloys should be around 0.02 wt%similar to 0.1 wt% and 1 wt%. Polarization curves analysis shows that the corrosion resistance of these Ti-22Nb-6Zr-B alloys is very good when boron content is about 0.02 wt%similar to 1 wt%. Taking into account microstructure, mechanical properties and corrosion resistance, the appropriate amount of B addition for Ti-22Nb-6Zr shape memory alloys is 0.02 wt%similar to 0.1 wt% and 1 wt%. Key words: Ti-22Nb-6Zr alloy; boron; microstructure; mechanical properties; corrosion resistance