Study On The Process And Properties Of Porous Metal Prepared By Laser Additive Manufacturing(3D Printing)

Laser additive manufacturing(3D printing) is a new and rapid laser prototyping technology. Since the porous metal has similar characteristics with the human bone in the pore structures and mechanical properties, laser additive manufacturing(3D printing) is widely applied to fabricate biomedical implants. Because the laser additive manufacturing(3D printing) is a rather new technology, there are not many reports on the preparation of porous metals on the microstructure evolution mechanism or on the biocompatibility of the porous metals. Therefore, there is a great need to perform the research on mechanical properties of the porous metal implant materials, microstructure and biocompatibility by laser additive manufacturing(3D printing) technology.Laser additive manufacturing(3D printing) technology is used to fabricate the biomedical porous metal materials. The influence of processing parameters(scanning interval d) on the pore structures, the mechanical properties, microstructure and biocompatibility of three different porous metal materials(porous tantalum, porous Ti6Al4 V alloy and porous 316 L stainless steel) is systematically studies. The results illustrate that with the increase of scanning interval, the overlapping rate of two adjacent laser melted zones decrease, then the compressive strength and elastic modulus of porous tantalum decrease too. Owing to the existence of laser heat-affected zone, the semi-melting powder of tantalum will attach to the internal walls of preset holes. Eventually, the actual pore size is smaller than the preset pore size. The porosity of the porous tantalum is 26.41%~43.28%, and average pore size is between 45μm~310μm, compressive strength is 312MPa~649MPa, elastic modulus is 5GPa~9GPa. The porosity of the porous Ti6Al4 V alloy prepared by laser additive manufacturing(3D printing) technology is 11.58%~36.11%, and average pore size is between 35μm~295μm, compressive strength is 487 MPa ~1800MPa, elastic modulus is 6.0 GPa ~10.8GPa. The porosity of the porous 316 L stainless steel prepared by laser additive manufacturing(3D printing) technology is 10.32%~31.26%, and average pore size is between 20μm~260μm, compressive strength is 2410MPa~3370MPa, elastic modulus is 9.8GPa~16.5GPa. The elastic modulus of porous metal materials is matched well to that of human bones.Microstructure studies show that the microstructure of porous tantalum is coarse dendrite which grow through the building directions of cladding layer, the original grain mainly hexagonal crystal structure and includes many plurality small grains. The microstructure of porous Ti6Al4 V alloy grow through the building directions of cladding layer and change into coarse columnar crystal epitaxial growth, and the growth direction of the columnar grains along the layer building directions. Due to the influence of temperature gradient, grain size far away from the substrate area is larger than the grain size near the substrate region, and microstructure of the original columnar crystal is composed of the fine acicular alpha phase coated at marten sites. The microstructure of porous 316 L stainless steel consists of equiaxed and columnar dendrites composition, and the average size of equiaxed grain is 1.2μm~1.4μm. The dendrite grain width is about 0.8μm~1.0μm, dendrite grain grows in the same direction with the layer building. When the temperature gradient reaches a certain degree, the dendrite grain changes to the equiaxed grain; compression fracture morphology indicates that the fracture consists of fine and uniform circular dimple, which confirms that the failure mode is ductile fracture.Biocompatibility study shows that the porous metal materials of rough surface and internal porous structure are beneficial to enrichment around nutrition liquid, allowing the cells to have adequate nutrient supply for growth in the growth process. The porous metal materials are suitable for cell growth environment and conducive the subsequent growth of cells. By using the method of WST-1 experiment study on cells proliferation of the three kinds of porous metal materials, it can be found that as the cells culture time prolonged, porous tantalum gradually shows strong ability to promote cells proliferation. When the incubation time is 7 days, the porous tantalum light intensity strength of surface is higher than porous Ti6Al4 V alloy and porous 316 L stainless steel, which is a further sign of the proliferation ability of porous tantalum stronger than the porous Ti6Al4 V alloy and porous 316 L stainless steel.