The effect of copper on phase transformation, microstructure and mechanical characterization of Ni50-xTi50Cux shape-memory alloy

Abstract

This research is related to the investigation of the influence of copper additions on phase transformation, microstructure and mechanical characterization of equiatomic NiTi shape-memory alloys. A typical vacuum arc melting furnace was used in the preparation of Ni50-xTi50Cux (x = 2, 5, 10, and 15 at.%) shape-memory alloys. The crystalline phase formation and phase transformation temperature were studied using X-ray diffraction and a differential scanning calorimeter. The morphology and chemical composition of the annealed samples were investigated using a field emission scanning electron microscope and energy-dispersive X-ray spectrometer analysis. The Vickers microhardness test was utilized in the analysis of the homogeneity of the alloy. The experimental results obtained from X-ray diffraction confirmed the coexistence of austenite and martensite phases along with the presence of a Ti2Ni and minor rutile phases. The crystalline sizes of the alloys were in the range of 42 to 78nm. An energy-dispersive spectrometer validated the distinct phases and precipitates in the alloys. The size and dispersion of the secondary phase in the alloy showed a significant influence on the increased hardness from 407HV to 470HV. The following NiTiCu alloy compositions were employed for low-temperature applications since their transition temperatures were below 100°C.