Mechanochemical assisted synthesis of NiTi intermetallic based nanocomposite reinforced by Al2O3

Synthesis of NiTi/α-Al2O3 nanocomposite by mechanical alloying (MA) of a powder mixture containing NiO, Al, Ti and Ni was investigated. The structural evaluation of milled and annealed powders was studied by X-ray diffraction, scanning electron microscopy and microhardness measurements. The mechanochemical reaction between NiO and Al took place shortly in a combustion mode leading to increase of vial temperature and formation of NiTi, Al2O3 and a small amount of Ti2Ni which transformed to NiTi at further MA times. NiTi/Al2O3 nanocomposite exhibited larger grain size of NiTi, higher microhardness and smaller particle size compared to NiTi.Annealing of the milled powder showed that the products are dependent on the cooling rate. The presence of Al2O3 dispersoids in the NiTi matrix leads to decrease of grain growth and ordering degree of NiTi and finally high thermal stability of nanocomposite during annealing.