Effect of Oxidation Process on Mechanical and Tribological Behaviour of Titanium Grade 5 Alloy

Abstract

In this study, microstructural characterization, mechanical (tensile and compressive) properties, and tribological (wear) properties of Titanium Grade 5 alloy after the oxidation process were examined. While it is observed that the grey contrast coloured α grains are coaxial in the microstructures, it is seen that there are black contrast coloured β grains at the grain boundaries. However, in oxidised Titanium Grade 5, it is possible to observe that the α structure becomes larger, and the number and density of the structure increases. Small-sized structures can be seen inside the growing α particles and on the β particles. These structures are predicted to be Al-Ti/Al-V secondary phases. The nonoxidised alloy matrix and the OL layer exhibited a macrolevel hardness of 335 ± 3.21 HB and 353 ± 1.62 HB, respectively. The heat treatment increased Vickers microhardness by 13% in polished and etched nonoxidised and oxidised alloys, from 309 ± 2.08 HV1 to 352 ± 1.43 HV1. The Vickers microhardness value of the oxidised sample was 528 ± 1.74 HV1, as a 50% increase was noted. According to their tensile properties, oxidised alloys showed a better result compared to nonoxidised alloys. While the peak stress in the oxidised alloy was 1028.40 MPa, in the nonoxidised alloy, this value was 1027.20 MPa. It is seen that the peak stresses of both materials are close to each other, and the result of the oxidised alloy is slightly better. When we look at the breaking strain to characterise the deformation behaviour in the materials, it is 0.084 mm/mm in the oxidised alloy; In the nonoxidised alloy, it is 0.066 mm/mm. When we look at the stress at offset yield of the two alloys, it is 694.56 MPa in the oxidised alloy; it was found to be 674.092 MPa in the nonoxidised alloy. According to their compressive test properties, the maximum compressive strength is 2164.32 MPa in the oxidised alloy; in the nonoxidised alloy, it is 1531.52 MPa. While the yield strength is 972.50 MPa in oxidised Titanium Grade 5, it was found to be 934.16 MPa in nonoxidised Titanium Grade 5. When the compressive deformation oxidised alloy is 100.01%, in the nonoxidised alloy, it is 68.50%. According to their tribological properties, the oxidised alloy provided the least weight loss after 10,000 m and had the best wear resistance. This material’s weight loss and wear coefficient at the end of 10,000 m are 0.127 ± 0.0002 g and (63.45 ± 0.15) × 10−8 g/Nm, respectively. The highest weight loss and worst wear resistance have been observed in the nonoxidised alloy. The weight loss and wear coefficients at the end of 10,000 m are 0.140 ± 0.0003 g and (69.75 ± 0.09) × 10−8 g/Nm, respectively. The oxidation process has been shown to improve the tribological properties of Titanium Grade 5 alloy.