Microstructual evolution of Co-7Al-7V novel cobalt-based superalloy during hot deformation
Thermal compression deformation experiments were conducted on a novel cobalt-based Co-Al-V superalloy.The deformation temperature was in the period of 800℃ and 1 050 ℃,and the strain rate varied from 0.001 to 1 s-1.The experimental results indicate that twins occurred after dynamic recrystallization of the alloy at low temperatures and low strain rates(800 ℃,0.001 s-1),at moderate temperatures and higher strain rates(950 ℃,0.1 s-1),as well as at higher temperatures and higher strain rates(1 050 ℃,1 s-1).The flow stress curves exhibited a trend of initially decreasing after reaching a peak,followed by an increase.At 800 ℃ and 950 ℃,twins were more easily formed under high strain rates.As the strain rate decreased,the degree of dynamic recrystallization gradually increased.At 1 050℃,twins were prone to formation at low strain rates,and the degree of dynamic recrystallization also de-creased as the strain rate decreased.With the increase of deformation temperature,the degree of dy-namic recrystallization increased,and the grain size of the recrystallized grains gradually became lar-ger.Analysis of the EBSD test results revealed that the grain size of the recrystallized grains under high-temperature and low strain rates(1 050 ℃,0.001 s-1)conditions was larger compared to that under high-temperature and high strain rates(1 050 ℃,1 s-1)conditions.The twin boundaries at high temperatures were majorly Σ3 boundaries,and the fraction of Σ3 bounda-ries increased with decreasing strain rate at high temperatures.These findings provide a theo-retical basis for optimizing the processing technology of the novel cobalt-based high-tempera-ture alloy.
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