Abstract
In this paper, quaternary Ti48.5-xNi49.5Nb2Zrx (x=0∼5at%) shape memory alloys were prepared by non-consumable vacuum arc melting. The microstructure and phase compositions of the shape memory alloys were investigated by scanning electron microscope and X-Ray Diffraction. The effects of Zr element and thermal mechanical heat treatments on the transformation temperature were studied by using differential scanning calorimetry. In addition, the mechanical properties of the alloys were tested. The results showed that the microstructure of ternary TiNiNb alloy was comprised of TiNi matrix and a Nb-enriched secondary phase. As for Zr element addition, when its content is lower than 3at.%, the Zr element was mainly dissolved in the TiNi matrix. When the content of Zr reaches 3at.%, a new secondary phase(Ti, Zr) 2Ni appeared and resulted in a degradation of workability. The martensite start temperature of the alloys decreased from 28.5°C to 16.1°C with the content of Zr element increasing from 0at.% to 5at.%. For Zr element increasing from 0at.% to 2at.%, the room temperature yielding strength of the alloys increased from 692MPa to 873MPa and the fracture strength increased from 472MPa to 578MPa.
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