Nanostructured Ni–Ti alloys obtained by mechanical synthesis and heat treatment

Abstract

The present work reports a synthesis by mechanical alloying and investigation of Ni–Ti alloys in a wide composition range during milling and after subsequent heat treatment. Ti67.7Ni33.3, Ni50Ti50 and Ni75Ti25 (at.%) mixtures were subject to ball milling for up to about 100 h. The microstructure of the milled and annealed powders was examined by X-ray diffraction method and scanning electron microscopy. It has been observed that a prolonged milling of Ti66.7Ni33.3 and Ni50Ti50 mixtures leads to formation of two fcc nanocrystalline disordered solid solutions: Ni(Ti) and Ti(Ni). The heating of these milled powders has resulted in a structural relaxation and ordering of previously formed solid solutions. In the intermediate stage of the milling the amorphous phase is created, which after heat treatment, turns into the mixture of Ti2Ni and Ni3Ti intermetallic phases. Mechanical alloying of Ni75Ti25 system produces nanocrystalline disordered fcc Ni(Ti) solid solution. After annealing, the presence of Ni3Ti phase and ordered Ni(Ti) solid solution is observed.