A comparative study on surface modification of porous NiTi alloys by chemical oxidation and thermal oxidation

Two surface oxidation methods,i.e.,low temperature chemical oxidation in H2O2+HCl solution and thermal oxidation at 500℃ were used to treat porous NiTi alloy for surface modification.The morphology,Ni/Ti atomic ratio and growth kinetics of the oxide films formed on porous NiTi alloy through two oxidation techniques were compared and analyzed.The characteristics of the oxidations on the surface and inside the pores of porous NiTi alloy were discussed.The results show that the two oxidation techniques bring about the formation of the oxide films depleted in Ni.The Ni content on the pore wall is lower than that on the surface of porous NiTi alloy,which indicates that the conditions inside the pores inhibit the oxidation of Ni due to the low oxygen affinity.The growth rate of the oxide film inside the pore is lower than that of the oxide film on the outmost surface of porous NiTi alloy.