Process Optimization of QPQ Complex Salt Bath Treatment of Ti6Al4V Titanium Alloy

The microstructure and phase composition of Ti6Al4V titanium alloy after QPQ (quenching-polishing-quenching) complex salt bath treatment were analyzed by scanning electron microscope and X-ray diffractometer. The effect of carbonitriding time, carbonitriding temperature, oxidation time and oxidation temperature on wear resistance of the titanium alloy was studied by using orthogonal test and compared with titanium alloy samples treated with salt bath nitrocarburizing. The results show that after QPQ complex salt bath treatment, a permeation layer formed on the surface of Ti6Al4V titanium alloy. There were oxidation layer, compound layer and diffusion layer from the surface to the interior of the permeation layer. When the titanium alloy was carbonitrided at 610℃ for 1.5 h and oxidated at 400℃ for 40 min, the average wear amount of titanium alloy was the minimum, which was 1.11 mg and reduced by 38.3% of the carbonitriding sample. When the titanium alloy was carbonitrided at 580℃ for 3.5 h and oxidated at 400℃ for 40 min, the average friction coefficient was the minimum, which was 0.246 7 and reduced by 21.8% of the carbonitriding sample. The wear resistance of titanium alloy treated by optimized QPQ complex salt bath treatment was improved obviously.