Effects of ECAP on the Formation and Tribological Properties of Thermal Oxidation Layers on a Pure Titanium Surface

Abstract

In this paper, thermal oxidation was used to prepare an oxide layer on a pure titanium surface using the equal-channel angular pressing (ECAP) treatment. Transmission electron microscopy, field emission scanning electron microscopy, X-ray diffraction and Raman spectrometry were used for morphology and structure characterization and investigation of the oxidation kinetics during the oxidation process. The results showed that the major phase of the oxide layer was rutile-type TiO2. The presence of voids in the oxide layer decreased with increasing temperature. The grain size of the TiO2 obtained on the ECAP-treated Ti surface was smaller than that on the as-received titanium. The ECAP treatment promoted the formation of the oxide layer; the activation energy (Q) for the oxidation reaction with ECAP treatment was 81.03 kJ mol−1 in the range of 650 °C to 850 °C, which was 26.3% lower than that of the as-received titanium. The hardness values of the oxide layers on the as-received titanium and ECAP-treated Ti were 705.8 HV and 805.1 HV, respectively. The friction coefficient of the oxide layer on the ECAP-treated Ti was lower than that on the as-received titanium. The wear rates of the oxide layers on the ECAP-treated Ti and as-received titanium were 4.66 × 10−8 mm3 N−1 m−1 and 6.28 × 10−8 mm3 N−1 m−1, respectively.