Variations in the Microstructure and Hardness with Solution Treating and Aging Conditions in New α+ β Titanium Alloy Ti-4.5%Al-6%Nb-2%Fe-2%Mo

摘要

Variations in the microstructure and hardness with solution treating and aging conditions in new α+ β titanium alloy Ti-4.5%Al-6%Nb-2%Fe-2%Mo were investigated. Solution treating (ST) temperatures were varied from 1 048 to 1 173K with both cooling conditions of water quenching and air cooling. Cooling rate after solution treating was varied from 1 to 60 K/s using a hot working simulator. Age-hardening was investigated at temperatures ranged from 573 to 823 K and aging time periods were varied in the range from 0.36 to 32.4 ks. An extremely fine two-phase microstructure with α grain size of around 1 μm was obtained at ST temperature of 1 048 K. The large amount of retained β phase was obtained by solution treating at temperatures below 1 098 K, and the amounts of α″ martensite and athermal ω phase increased with an elevation of ST temperature above 1 098 K. For solution treating with water quenching, no hardness variation with solution treating temperature was observed. Age-hardening at the temperatures above 723 K took place at an extremely short aging time. Peak-age was observed in such a short aging time period as 0.36 ks, and hardness value at peak-age increased markedly and continuously with an elevation of solution treating temperature. Age-hardening was confirmed to be caused by very fine a precipitates, and age-hardening behavior noted above was explained by athermal ω phase playing a role of a nucleus for a precipitate.