Effect of nano Al2O3 addition on mechanical properties and wear behavior of NiTi intermetallic

• Nano Al2O3–NiTi composite was fabricated via vacuum sintering method.
• Addition of nano Al2O3 particles increased the stability of martensite phase.
• Hardness and elastic modulus for the composite samples considerably increased.
• Pseudoelasticity was not significantly reduced for nanocomposite samples.
• Wear resistance of the Al2O3–NiTi samples was much better than that in the pure NiTi.

It has been found that the high wear resistance of NiTi alloy is mainly attributed to its pseudoelasticity which is only effective within a small temperature range. It is believed that pseudoelasticity becomes ineffective by applying high-load wear condition which yields plastic deformation and temperature increment during wear test. Therefore, the enhanced wear resistance can be obtained from the improvement of mechanical property of the alloy without much reduction of pseudoelasticity. In this study, a low weight percentage of hard Al2O3 nanoparticles were added to NiTi atomized powders. The resultant powder mixture was homogenized by ball milling and sintered in a vacuum furnace in order to improve the wear property of the composite in comparison with the NiTi alloy. The results demonstrated that the addition of nanoparticles increased the stability of martensite phase. Nanoindentation test results showed that both hardness and elastic modulus were considerably increased in the composite samples in comparison with pure NiTi, while the pseudoelasticity was not significantly reduced. The worn surfaces were investigated using a scanning electron microscope equipped with energy dispersive X-ray. The wear test results confirmed the improved wear performance of NiTi matrix after the addition of nanoparticles under both low and high loads can be mainly attributed to superior mechanical properties combined with pseudoelasticity effect of the composite samples.