Synthesis and characterization of novel NiTi-Ni3Ti/SiC nanocomposites prepared by mechanical alloying and microwave-assisted sintering process

Abstract

Equiatomic Ni-Ti alloy reinforced with 0, 2.5, 5, and 10 vol % SiC nanoparticles was synthesized through me-chanical alloying and microwave sintering process. In this method, a mixture of Ti and Ni powders and SiC nanoparticles (0-10 vol%) were mechanically milled for 30 h, compressed under 1 GPa pressure, and then sintered at 900-1100 degrees C by microwave heating. Microstructural analysis of the synthesized samples was per-formed using X-ray diffraction and scanning/transmission electron microscopy, and their hardness was deter-mined using a Vickers microhardness tester. Structural studies revealed the formation of a complex phase structure consisting of the austenite (B2-NiTi), the martensite (B19 & PRIME;-NiTi), and the nickel-rich (Ni3Ti) and titanium-rich (NiTi2) phases. HR-TEM investigations confirmed an increased Ni3Ti phase in the austenitic NiTi matrix nearby the martensitic NiTi phase. It was found that adding SiC nanoparticles to Ni-Ti increased the amount of hard Ni3Ti phase, promoted the stability of the martensite phase at room temperature, and retarded the matrix grain growth during the sintering process. Microhardness tests showed that when the content of SiC nanoparticles increased up to 5 vol %, the microhardness increased considerably to 9 GPa and then declined. The high microhardness of synthesized nanocomposites is due to the formation of Ni3Ti and NiTi martensitic phases and their nanocrystalline structure.