Microstructure and Mechanical Property of Biomedical Ultrafine-grained β-type Ti28Nb2Zr8Sn Bulk Alloys Fabricated by Power Metallurgy

Abstract:

In order to further comparatively investigate microstructure and mechanical property of biomedical β-type titanium alloys with different compositions, ultrafine-grained β-type Ti28Nb2Zr8Sn bulk alloys with high strength and low elastic modulus were fabricated by mechanical alloying and spark plasma sintering in this work. XRD and SEM examinations indicate that the fabricated ultrafine-grained bulk alloys are fully bcc β-Ti structure by spark plasma sintering of 60h-milled alloy powders. Further TEM analysis proves that the grains of bcc β-Ti are equiaxed and their sizes are approximately 500-1000nm in the fabricated ultrafine-grained bulk alloys, which is far smaller than several micron-sized grains of similar titanium alloys prepared by casting method. In addition, mechanical property tests show that compressive strength increases and elastic modulus decreases gradually for the fabricated ultrafine-grained bulk alloys with the increased heating rate and decreased holding time. Under sintering temperature of 900℃, the heating rate of 150℃/min and no holding, the fabricated ultrafine-grained bulk alloy has the smallest grain size of bcc β-Ti,and thus the largest ultimate strength of 2675MPa, and the highest fracture strain of 0.54 along with lowest elastic modulus of 31.6GPa. Meanwhile, its work-hardening exponent 0.073 is far higher than that of Ti6Al4V alloy, indicating its excellent work-hardening ability and plastic deformation ability. This suggests that the fabricated ultrafine-grained bulk alloy can withstand high load and large deformation, and consequently can be an excellent candidate metallic material used as biomedical applications.

Key words:Power metallurgy; β-type titanium alloy; Elastic modulus; Microstructure; Mechanical property