Author : Ali Hussein, Rasha
Engineering and Technology Journal,
2013, Volume 31, Issue 16, Pages 3035-3051
Ni-Ti samples were prepared by powder metallurgy. The prepared samples
were master samples M1 (55% Ni- 45%Ti) and M2 (56% Ni- 44%Ti). The
additive percentage of Ta was 5%, 7% and 9% to master sample M1 and M2,
while Nb addition was 1%, 2% and 4% to M1 and M2. The pressure of
pressing was 800 Mpa. The samples were sintered at 950 °C for a time of 9 hr.
Samples were then examined by using SEM technique, XRD, DSC, Vickers
hardness. The porosity was measured according to Archimedes method.
Scanning electronic microscopy images showed that most prepared
samples have porosity, which in turn imparts decreasing microhardness values across the surface. Better increase of microhardness values is found in M2+5%Ta. Scanning electron microscopy indicated also the best martensitic structure in M1+4% Nb and M2+4%Nb. X-ray diffraction observations indicated that NiTi, Ni3Ti and NiTi2 phases exist in all samples. NiTi phase is playing a dramatic role in enhancing shape memory effect and superelasticity.
DSC results show that transformation temperatures range in (46-134°C). This indicates that all samples at room temperature have one phase which is martensite.