Al ion implantation was carried out to aim for suppressing an absorption of hydrogen from environment into Ti-Ni shape memory alloy. A layer of 100nm thick with high density Al was formed at the surface by ion implantation. Starting stress of martensite accommodation did not change by ion implantation and hydrogen absorption. On the contrary, the deformation stress corresponding to a strain of 4% in martensite phase and shape recovery stress changed by both the ion implantation and hydrogen

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... rption. The implanted specimen with a low dose revealed an effect of suppressing the hydrogen absorption. In this case, the surface ion implanted layer was supposed to prevent diffusion of hydrogen, which absorbed near the surface, toword the inside of the specimen. While, the implanted specimen with a high dose lost their shape memory properties due to the composition change indicated by the shift of transformation temperatures. In any cases, the ion implantation affected the shape memory properties with and without existence of hydrogen into massive of cross section, although the ion implanted layer was limited in the vicinity of the outmost surface.