Influence of Cold Rolling and Direct Aging on Coarsening Kinetics of γ′ Precipitates and Hardness in UDIMET 720Li

The present paper examines the influence of cold rolling strain and direct aging on coarsening kinetics of γ′ precipitates and hardness in UDIMET 720Li. The specimens were characterized using scanning electron microscopy, and Vicker’s hardness was measured. Cold rolling accelerates the coarsening kinetics of γ′ precipitates. Cold-rolling increases the dislocation density in the γ matrix. These dislocations act as a diffusion path for precipitate-forming elements like Al and Ti in the γ matrix via pipe diffusion, which leads to an increase in the coarsening kinetics of γ′ precipitates. The growth kinetics of secondary γ′ precipitates ( -r_t--r_o ) show a linear relationship with the cube root of time ( t^1/3 ) for shorter aging times and deviate significantly for longer aging times. Aging for a longer time leads to coalescence events of γ′ precipitates dominating the growth process. The precipitation hardening contribution decreases with the increase in deformation strain, which can be attributed to static recovery.