Effects of Nb addition on microstructure and mechanical properties of TiNiNb alloys fabricated by elemental powder sintering

Porous TiNi binary and TiNiNb ternary alloys of four compositions (Ti50Ni47.5Nb2.5, Ti50Ni45Nb5, Ti50Ni42.5Nb7.5, and Ti50Ni40Nb10) were fabricated by the elemental powder sintering process. The effects of Nb addition on microstructure and mechanical properties of TiNi(Nb) alloys were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and tensile tests, respectively. With the increase of Nb contents, the TiNi matrix as the main phase is always retained, while the intensity of its diffraction peak gradually became weak with the appearance of β-Nb and TiNb phases. Most Nb particles are well-distributed in the TiNi matrix and (Ti,Nb)2Ni phase is found in the binding domain between Nb phase and TiNi phase. The tensile strength and elastic modulus of TiNiNb alloys increase with the increase of Nb contents, due to the solid solution strengthening effect of Nb-rich particles, the enlarged sintering neck and the strengthened bond between particles. Consequently, Nb plays a crucial role in adjusting composition and improving microstructure and mechanical properties of TiNiNb alloys.