The Influence of Deep Cryogenic Treatment (DCT) on the Microstructure Evolution and Mechanical Properties of TC4 Titanium Alloy.

Deep cryogenic treatment (-196 °C, DCT) is an emerging application that can make significant changes to many materials. In this study, DCT was applied to Ti6Al4V (TC4) titanium alloy, and we delved into an examination of the impact on its microstructural morphologies and mechanical properties. It was observed that DCT has a significant effect on the grain refinement of the TC4 titanium alloy base material. Obvious grain refinement behavior can be observed with 6 h of DCT, and the phenomenon of grain refinement becomes more pronounced with extension of the DCT time. In addition, DCT promotes the transformation of the β phase into the α' phase in the TC4 titanium alloy base material. XRD analysis further confirmed that DCT leads to the transformation of the β phase into the α' phase. The element vanadium was detected by scanning electron microscopy, and it was found that the β phase inside the base material had transformed into the α' phase. It was observed that DCT has a positive influence on the hardness of the TC4 titanium alloy base material. The hardness of the sample treated with 18 h of DCT increased from 331.2 HV to 362.5 HV, presenting a 9.5% increase compared to the sample without DCT. Furthermore, it was proven that DCT had little effect on the tensile strength but a significant impact on the plasticity and toughness of the base material. In particular, the elongation and impact toughness of the sample subject to 18 h of DCT represented enhancements of 27.33% and 8.09%, respectively, compared to the raw material without DCT.