Preparation And Properties Of Gradient Porous TiNi Shape Memory Alloys

In this paper, the influence of NH4HCO3 on the pore characteristics and mechanical properties of porous TiNi alloy were studied. The gradient porous TiNi alloy was prepared according to the results, and then, the alloy's properties were tested.The results indicated that the connection of the pores, the porosity and open-porosity increased with the increasing of NH4HCO3, but the roundness of the pores decreased slightly at same time. The samples with a porosity of 60% were fabricated by adding NH4HCO3 about 35g in 100g mixed powder which proved NH4HCO3 is good in forming pores. In terms of the mechanical properties, the bending, Young's modulus, compressive strength and hardness were tested. The results indicated that these mechanical properties decreased with increasing NH4HCO3 content (which is equal to the increase of the porosity).Moreover, there was pseudo yield phenomenon according to the test curve of three points bending of the gradient porous TiNi alloy with three layers structure. The reason of this phenomenon was the obvious structure difference between the surface and interior layer.The bending strength of the gradient porous TiNi alloy was influenced by its structure. The strength improved greatly with the increasing of the interior layer proportion. Furthermore, the real strength was higher than the theoretical strength which proved the good compound effect of this gradient structure.Basing on the above experiments, the gradient porous TiNi alloy with pore characteristics of interconnected three-dimensionally meshy open structure have been fabricated by using domestic Ti and Ni powder through element powder metallurgy. The porosity range and mean big pore size range of the surface layer were 60% and 100-200μm. The porosity range and mean big pore size range of the interior layer were 30% and 10-60μm.The adhesion of the double gradient structure is firm, and its the adhesive strength is about 48MPa.