Role of intermediate phases on microstructures, wear and corrosion resistance in new-developed (α + β) titanium alloy

A new (α + β) Ti alloy has been designed and prepared in this work, and the results show that three intermediate phases will be transformed including α′′ martensite, O′ and ω. Upon continuous heating, the α′′ martensite decomposes gradually and disappears before α precipitation. The ω and O′ domains are generated continuously upon aging, and such two intermediate phases co-exist when α phase nucleation occurs. It has been proved that the ω and O′ domains play a direct role in promoting α phase formation. Through the ω and O′ domains assisting α nucleation mechanism, a uniform distribution of fine α precipitates can be obtained after aging. Under the treatment of pre-aging at 300 °C plus aging at 600 °C, the α phase having smallest size and largest number density is obtained, resulting in highest wear resistance and corrosion resistance. For this sample, its average friction coefficient and wear ratio are 0.174 and 3.75×10 ⁻⁴ mm ³/(N·m), respectively. During friction tests, the mixture of abrasive wear, adhesive wear and oxidation wear should be activated. Due to the formation of passivation films on the alloy surface, this alloy has exhibited better anti-corrosion properties than Ti-6Al-4 V alloy, and its corrosion current density in 3.5 wt% NaCl solution can be reduced to 1.79×10 ⁻⁸ A·cm ⁻². Compared with the samples under duplex aging treatments, the direct aged sample also presents outstanding anti-corrosion properties.