Nano-hardness, wear resistance and pseudoelasticity of hafnium implanted NiTi shape memory alloy

NiTi shape memory alloy was modified by Hf ion implantation to improve its wear resistance and surface integrity against deformation. The Auger electron spectroscopy and x-ray photoelectron spectroscopy results indicated that the oxide thickness of NiTi alloy was increased by the formation of TiO2/HfO2 nanofilm on the surface. The nano-hardness measured by nano-indentation was decreased even at the depth larger than the maximum reach of the implanted Hf ion. The lower coefficient of friction with much longer fretting time indicated the remarkable improvement of wear resistance of Hf implanted NiTi, especially for the sample with a moderate incident dose. The formation of TiO2/HfO2 nanofilm with larger thickness and decrease of the nano-hardness played important roles in the improvement of wear resistance. Moreover, Hf implanted NiTi exhibited larger pseudoelastic recovery strain and retained better surface integrity even after being strained to 10% as demonstrated by in situ scanning electron microscope observation.

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► Hf implantation is able to form HfO2/TiO2 nano-film on NiTi alloy.
► Hf implantation decreases the nano-hardness of NiTi.
► Wear resistance of Hf-NiTi is improved by HfO2/TiO2 film and decreased hardness.
► Hf-NiTi exhibits improved pseudoelasticity and surface integrity under deformation.