Microstructure, hardness and corrosion behavior of Ni-Ti alloy with the addition of rare earth metal oxide (Gd2O3)

Microalloying of the rare earth metals are very effective to change the microstructure, phase transformation and mechanical properties of the newly developed alloys. In this research varying wt% of Gadolinium oxide (Gd2O3) is added in Ni-Ti to prepare the alloy using powder metallurgy method. Prepared alloys are sintered at 850 °C for one hour and annealed at 900 °C for 4 h in argon atmosphere. The microstructure and composition of the sintered and annealed samples are analyzed using SEM/Mapping with EDX analysis. SEM analysis showed white phase with dendrite structure of Gd2O3 in sintered alloy and this structure is more prominent at higher magnification in annealed alloy. XRD analysis of the sintered alloy shows Ti2Ni and NiTi phases whereas Ni3Ti, GdTi2 and TiO2 are found in annealed alloy. Hardness is decreased in sintered alloy due to incoherency and coarse grains in matrix of the alloy. However an improvement in hardness of annealed alloy was found due to formation of GdTi2 phase. The corrosion behavior of sintered alloy sample (a) to sample (e) showed decrease in Ni elution with increasing amount of Gd2O3 in Ni-Ti alloy. The current density was found decreasing from sample (a) to sample (e) with increasing amount of wt% of Gd2O3 indicating more corrosion resistance of sintered alloy. More positive value of break down potential (Ebd) was found in annealed samples showed biocompatibility of the alloy due to formation more stable oxide layer on Ni-Ti alloy.