Study On The Preparation Technology And Properties Of Porous Ta Prepared By Selective Laser Melting

There are about 2 million of patients in our country need to make joint replacement surgery every year, the demand for bone repair materials is too large; the sales of the bone repair materials are more than $ 200 billion in the world every year. Clinical trials showed that porous tantalum is an ideal material for bone repair. However, due to the high melting point of tantalum, about 2996℃, and Ta has a higher affinity for oxygen, which presents greater challenges for the preparation of porous tantalum.The preparing process of biomedical porous tantalum by Selective laser melting are studied in this paper. The pore characteristics, microstructure and fracture morphology of porous tantalum are observed and analyzed with scanning electron microscopy and optical microscopy, the micro-hardness is tested by micro-hardness tester, porosity and open ratio are measured using hydrostatic principle; compressive strength and elasticity modulus are tested using electronic universal testing machine, the formation mechanisms of main holes and micropores of porous tantalum and the effect of preparation processes of porous tantalum on their properties also studied in this paper, the porous tantalum prepared at optimum process parameters is compared with human bone. The defect formation reason of porous tantalum and its control method are also analyzed.The results show that porous tantalum has two types of holes such as main holes and micro-holes, the main holes formed due to some powder is not irradiated in selective laser melting process, some gas has not enough time to overflow from weld pool and form micro-holes in the co-opration of rapid melting/solidification mechanism and “Piston Effect”, Other process parameters under certain values, the hole diameter, porosity and open ratio of porous tantalum increase with the scanning space increased, but compressive strength and elastic modulus decrease, the hole diameter, porosity and open ratio decrease,with the current increases from 110 A to 125 A, compressive strength, elastic modulus and micro-hardness increase at the same time. The hole characteristics and mechanical properties have a relationship, compressive strength and elastic modulus decreased with the increase of porosity from 480 MPa to 56 MPa and 7.7GPa to 2.8GPa respectively when the porosity of porous tantalum increased from 35.48% to 50.00%. When the pulse width2.0ms, defocus distance 7mm, laser beam diameter 0.80 mm, current 115 A, scanning space0.80 mm, the average hole diameter, porosity, open rate, compressive strength, elastic modulus, micro-hardness are 300μm, 48.05%, 82.41%,253 MPa, 5.1GPa, 403 HV respectively, which matches with the hole characteristics, compressive strength, elastic modulus and hardness of bone graft material. There are two main fracture modes,intergranular and cleavage fracture, both are brittle fracture. Two types of defects such as balling phenomenon and a crack exist in the preparation process of porous tantalum primarily increasing the flow of the protective gas and adjusting the current appropriately can inhibit the formation of defects to some extent.