Cyclic Oxidation of Titanium Grade 2

Impact of thermal oxidation parameters on micro-hardness and hot corrosion of Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr alloy

Protective oxide layers on Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr (TC21) alloy with equiaxed microstructure considerably influence micro-hardness and hot corrosion resistance. The present work's thermal oxidation of TC21 alloy was performed at 600, 700, and 800 °C for 5, 20, and 50 h durations. Hot corrosion methods in NaCl and NaCl + Na₂SO₄ salt media were applied to raw (unoxidized) and oxidized samples at 600 and 800 °C for 50 h. Hot corrosion was conducted at 600 °C for 5 cycles with 10-h steps. The best oxide layer thickness was observed at 800 °C, which increased with increased oxidation time and temperature. The surface hardness of the oxide layer at 800 °C was 900 ± 60 HV_0.05 owing to the formation of TiO₂ and Al₂O₃ phases. Raw material hardness was 342 ± 20 HV_0.05, increasing threefold due to thermal oxidation. In the case of NaCl, weight loss dominated all samples except at 800 °C for 5 h. In the case of NaCl + Na₂SO₄, weight gain occurred at 600 and 800 °C for 5 h. Weight loss occurred for the raw samples and those processed at 800 °C for 20 and 50 h, where the oxide layer flaked off. Surface hardness increased upon hot corrosion testing because of the formation of brittle phases, such as TiO₂ and Na₄Ti₅O₁₂. Samples that oxidized at 800 °C for 5 h had the highest hardness and corrosion resistance.

Mechanical Properties and Frictional Wear Characteristic of Pure Titanium Treated by Atmospheric Oxidation

Pure titanium was treated by atmospheric oxidation, and the effect of the treatment temperature on its performance was studied. X-ray diffraction, scanning electron microscopy, wear testing, and scratch testing were used to evaluate the performance of the treated specimens. In order to evaluate the difficulty of compound formation during the different processing temperatures, Gibbs free energy was calculated. The experimental results show that the surface hardness of the sample can be improved at a certain oxidation treatment temperature. When the processing temperature is 850 °C, the surface hardness reaches the maximum value. The results of the scratch testing show that the hardened layer produced at this processing temperature has excellent peeling resistance. In addition, the wear depth and wear width are also at their minimum values at this processing temperature. Since the specimen treated at a processing temperature of 850 °C provides sufficiently high surface hardness and wear resistance in this research report, it is considered to be the optimal condition during practical application.