Preparation And Microstructure Of A New Medical Gradient Porous Ti-Mo-Ta-Nb-Zr Alloy

Medical ?-Ti alloy is one of the most widely used hard tissue implant materials currently. The porous ?-Ti alloys which have a higher strength and a matching human skeleton elastic modulus become a focus of the research and development. Elastic modulus reduce effectively with the introduction of porosity, but mechanical properties also will be greatly reduced at the same time, in particular the compressive strength.The new medical gradient porous Ti-14Mo-2.1Ta-0.9Nb-7Zr alloys with low modulus and high strength were fabricated by elemental powder metallurgy and porogen method. The effects of different process parameters, porogen amount and size, different gradient design on the porosity, phase, elastic modulus and compressive strength of the porous Ti alloys were investigated through Archimedes method, X-ray diffraction(XRD) and mechanical properties test. The alloy's surface morphology and compression fractographs were observed by scanning electron microscope(SEM). The results show that:The Ti-14Mo-2.1Ta-0.9Nb-7Zr alloys fabricated by elemental powder metallurgy are near ?-Ti alloy; the porosity and phase structure can be adjusted by regulating the forming pressures, sintering temperature and time, thus compressive strength and elastic modulus of the alloys can be controlled; The elastic modulus(20.91GPa) and compressive strength(1420MPa) of Ti-14Mo-2.1Ta-0.9Nb-7Zr alloy fabricated by200 MPa,1200?,3h have a fracture mode called quasi-cleavage fracture, and it can meet the requirements of biomedical implant materials.The porous Ti-14Mo-2.1Ta-0.9Nb-7Zr alloys fabricated by porogen method are near ?-Ti alloy. The average pore size of porous Ti alloys have no change with the increase of porogen amount, but porosity is linear growth. The compressive strength and elastic modulus take on the trend of decreasing with the increase of porogen amount, but elastic modulus has a linear change. The effect of porosity is not obvious,but the average pore size increases with the rising of porogen size. The compressivestrength and elastic modulus decrease with the rising of porogen size. With adding20wt% NH4HCO3(125~200?m), the porosity(38.9%), through hole structure, elastic modulus(9.19GPa), compressive strength(405MPa) of the new medical porous Ti-14Mo-2.1Ta-0.9Nb-7Zr alloys sintered at 1300 ? for 4h are suitable for the applications of implant materials.The gradient porous Ti-14Mo-2.1Ta-0.9Nb-7Zr alloys fabricated by adding different amount of pore-forming agent NH4HCO3 in the outer and inner layers are near ?-Ti alloy. When all the inner layers add 20wt% NH4HCO3, compressive strength and elastic modulus take on the trend of decreasing with the increase of outer layer porogen amount, porosity is linear growth. The gradient structure of TD1020 porous Ti-14Mo-2.1Ta-0.9Nb-7Zr alloy has a "within dense outer sparse" structure in imitation of human skeleton and the high strength, low modulus mechanical properties. It is suitable for using as human bone substitute material for medical implants.