EFFECT OF COMPACTING PRESSURE ON MICROSTRUCTURE,PHYSICAL AND MECHANICAL PROPERTIES OF NiTi SMA
AbstractThis study investigates the effect of different compacting pressures on microstructure ,physical and mechanical properties of NiTi shape memory alloys. The sample were prepared by powder metallurgy technique. The powder mixture containing 55wt% Ni and 45wt% Ti were mixed for 5hours,compacted at different pressures (400,600,800 and 900)MPa to cylindrical samples, and sintered in two stages. First heating the compacted samples at temperature of 500°C for 2 hours and at a temperature of 950°C for 6 hours under vacuum conditions (10-4 torr ) . The XRD test shows that the sample compacted at 800 MPa are consisting of three phases (NiTi monoclinic phase ,NiTi cubic phase , Ni3Ti hexagonal phase ).From the results, it was found that compacting pressure has essential effect on; improvement of shape memory effect properties(1.30-5.60)%, increasing hardness(from80.4to137) and compressive strength(from127.43to431.04)MPa and decrease porosity percentage(from32to22)%.
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