Microstructure Evolution of Ti-6al-4v Under Cold Rolling + Low Temperature Nitriding Process

Abstract

To improve the poor wear resistance and low hardness of the titanium alloy surface, this paper proposes a new nitriding process in which the surface and the matrix are modified at the same time. The treatment methods are solid solution treatment, cold rolling, and low temperature nitriding. The results of the solution treatment experiment indicate that the structure of the Ti-6Al-4V(TC4) titanium alloy sample changes from the original α+β phase to the residual α phase、 metastable β phase and martensite α' phase after solution treatment. The results of cold rolling experiments indicate that with the increase of rolling amount, many defects are generated, the grains are first elongated and then partially broken. In the process of low-temperature nitriding, recrystallization occurs, which effectively avoids the problem of coarse matrix structure. After low-temperature nitriding, a thin strip-like α-phase dispersed distribution of aging structure is formed. The XRD test results indicate that steady state nitrides Ti2N is formed on the surface of the sample, but the content of Ti2N is relatively low. Combining the surface and cross-section topography, element content, special type of nitriding layer is formed after low-temperature nitriding. Mechanical performance test results indicate the wear resistance and hardness of the alloy increase.

Keywords: TC4 alloy, Microstructure, composite process, recrystallization, nitriding, mechanical properties