Nanocrystalline Ti–Ni–Cu shape memory alloys: Metallurgical, mechanical and thermal properties

• The mean crystallite size was found to be about 23 nm.
• The microhardness of the powders increased with milling time.
• Cu addition resulted in enhances the shape memory effect.
• Martensitic transformation occurred in single manner.

In this paper, the metallurgical properties, microhardness and thermal behavior of NiTiCu12 shape memory alloy were studied by means of X-ray diffractometry, scanning electron microscopy, microhardness measurements and differential scanning calorimetry. For this purpose, the nanocrystalline samples were prepared via mechanical alloying of high-purity elemental powders followed by heat treatment. Milling of powders was performed in a planetary high-energy ball mill in different milling condition. Annealing of milled samples was executed in a quartz tubes under high-vacuum. The experimental results indicated that during milling, the B2 phase with nanocrystalline uniform structure, grain size of 23 nm, and high microhardness of 861 HV can be obtained. Martensitic transformation during annealing occurred in a single-stage manner and thermal hysteresis was found to decrease. Annealing also resulted in larger crystallite size and decreased microhardness.