Effects of hydrogen on the hot deformation behaviour of Ti-6Al-4V alloy: experimental and constitutive model studies
Hot deformation behaviour of Ti-6Al-4V alloy with different hydrogen contents (0, 035 and 0.6 wt percent) was investigated over the temperature range from 1050 to 1100 degrees celcius and strain rate range from 0.005 to 5s-1. The effects of hydrogen on the microstructural evolution, flow stress, working hardening, strain energy density and strain rate sensitivity were systematically analysed. Constitute models for Ti-6Al-4V with diferent hydrogen contents were established by using a stepwise multiple-linear regression method. The results show that s hydride with an FCC crystal structure exists in the deformed matrix of hydrogenated speciments. Teh size of s hydride is refined when the deformation temperature is raised from 1050 to 1100 degrees celcius. The work hardening rate increases with hydrogen when the strain is lower than 0.01. when the strain is higher tha n 0.01, however hydrogen does not show significant effect on the work hardening rate. Both the flow stress and the strain rate sensitivity show an increasing trend with hydrogen, and the strain rate sensitivity increases gradually with strain and temperature.The selected optimum variables for the constitutitve equations after stepwise multiple-linear regression are different for the Ti-6Al-4V alloy with different hydrogen contents. The calculated flow stress is in good agreement with the tested value.