Abstract: Effect of cryogenic treatment on barrel polishing and finishing and surface properties of the TC4 titanium alloy was studied. The TC4 titanium alloy specimen was subjected to cryogenic treatment, and the specimens under different cryogenic time were barrel polished and finished. After determining the appropriate cryogenic time according to the surface roughness, the changes of microstructure, microhardness and residual stress of the alloy specimens before and after cryogenic treatment were compared and analyzed. The change of surface morphology of the alloy after cryogenic treatment and barrel polishing and finishing was investigated by means of scanning electron microscope. The results show that the surface roughness of the specimen is the smallest after cryogenic treatment for 12 h, and the structure is affected by the internal stress of cold shrinkage, so that the proportion of α phase rises from 56.45%(untreated) to 85.42%, and the structure becomes uniform and dense. The microhardness of the alloy is the highest when cryogenic treated for 12 h, which is increased by 3.47% compared with untreated specimen. The surface residual compressive stress of the specimen increases by 26.26% after cryogenic treatment for 12 h and barrel polishing and finishing, compared with untreated specimen. Roughness measurement and scanning electron microscope results show that cryogenic treatment enhances the machinability of the titanium alloy specimen. The surface roughness of the specimen cryogenic treated for 12 h can reduce from about 0.500 μm(untreated specimen) to about 0.250 μm after barrel polishing and finishing, and the surface quality is significantly improved.

Key words: TC4 titanium alloy, cryogenic treatment, microstructure, microhardness, residual stress, surface roughness