Elastic and transformation behavior of equiatomic NiTi shape memory alloys fabricated at different sintering temperatures

Abstract

The growing demand for bulk Nitinol in ball and roller bearing applications is focused on in this article. The uniaxial compaction and sintering process is considered for the fabrication of the alloys where the sintering temperatures vary from 950 degrees C to 1150 degrees C. Better homogenization and diffusion are achievable except for the 950 degrees C sintered sample. The results of XRD of 950 degrees C and 1050 degrees C sintered samples show the presence of the Ni3Ti phase but in all the Samples sintered above 950 degrees C, NiTi is the major phase, unlike Ni3Ti in 950 degrees C. The TEM analysis shows a trace amount of TiO2 which comes from the impurity of the purged Ar gas. The O2 in the samples can be accommodated inside a few Ti2Ni phases to form Ni2Ti4O phases. Ni4Ti3 precipitates formed at higher temperatures help in precipitation strengthening. At room temperature, both austenitic B2 and martensitic B19 ' coexist. The DSC analysis shows that an increase in the sintering temperature increases the response time by consuming more energy. The elastic modulus and hardness have been increased up to 1100 degrees C and then decreased. Above Af temperature successful transformation of B2 to B19 ' takes place.