Effect of calcium ion implantation and of immersion in Hank's solution on shape memory properties of Ti-Ni alloy

Abstract

Ca ion implantation into equi-atomic Ti-Ni alloy and immersion test of the implanted alloy in Hank's solution were carried out to clarify the effect of surface properties on the shape memory phenomena. By the surface analysis using AES, Ca ion concentrated layer was observed at the outermost surface of the implanted materials, lowever, the thickness of that layer was very thin with the implantation dose of this study ( 3x10 20 ions/m 2 ). At the alloy surface, the oxide layer which includes Ti and/or Ni was also observed superposing with the Ca concentration layer. Shape memory properties after Ca ion implantation did not indicate apparent change in comparison with that of the non-implanted materials. However, the properties after the immersion of several months in the Hank's solution changed in some degree. The penetration of hydrogen into the alloy during the immersion test is considered to cause this change in the shape memory properties. Ca ion implantation seemed to suppress the penetration of hydrogen. From the viewpoint to maintain the shape memory properties in high performance level, a low ion implantation dose is favorable. However, when the suppressing of hydrogen penetration and/or Ni dissolution from the alloy are expected, higher dose of Ca ion implantation than in the present study will be preferred.