Microstructural Evolution And Recrystallization Behavior Of Directionally Solidified DZ125 Superalloy

DZ125 is a kind of directional solidified nickel base superalloy,which is the main material of turbine blade of aero engine.In this dissertation,the microstructure and morphology of DZ125 directional solidified superalloy was observed and analyzed by metallographic microscope,scanning electron microscope(SEM),field emission scanning electron microscope(FESEM),energy spectrum analysis(EDS),differential scanning calorimetry(DSC)and other methods.The microstructure evolution of DZ125 alloy as-cast state,heat treatment and long term aging process includes ?? phase morphology,carbide morphology and eutectic microstructure were studied,and the influence of different loading methods,different heat treatment conditions on the recrystallization behavior of DZ125 alloy were investigated.The experimental results show that the as-cast microstructure of DZ125 directional solidified superalloy is a typical dendritic structure,and the interdendritic region contains more ?/?? eutectic microstructure and MC primary carbide,rich in Ta and Hf.During the solution treatment,?/??eutectic all dissolved,and the MC carbides are dispersed into granules.In the aging process the secondary MC type carbides are precipitated in grain and enrich in Cr,Mo and W of M6 C carbides were found in the grain boundaries.During the whole heat treatment,the content of Hf element in MC carbides increases obviously.In the process of long-term aging,the higher the aging temperature,aging time and the ?? phases coarsening rate is larger,and found dendrite ?? phases coarsening rate significantly higher than the interdendritic.In the process of the long-term aging,the number of TCP phase is less which shows that DZ125 alloys have good structure stability.With the increase of sand blowing pressure or sand blowing time,the surface deformation of DZ125 alloy increases.The thickness of recrystallization layer increases obviously after standard heat treatment,blowing sand time on the influence of recrystallization is especially serious.When the heat treatment temperature is less than or equal to 1150?,recrystallization are as cellular recrystallization;and when the heat treatment temperature is higher than 1150?,the cellular recrystallization gradually transformed into equiaxed recrystallization.Thickness of the recrystallization layer significantly increased with the rise of heat treatment temperature.The thickness of recrystallization increases with the heat treatment time,but increases rapidly in the first 30 minutes,then gradually slows down,and the thickness of the recrystallization layer does not change much after the heat treatment time exceeds 2 hours.For three initial state(as-cast,solid solution and aging state)of DZ125 alloy specimen,blowing sand and then found that after standard heat treatment as-cast specimens of recrystallized layer the thickest,followed by solid solution state,and then the aging state.Stress relief annealing at 870? hasn't changed the recrystallization temperature of DZ125 alloy,but both reduced the recrystallization layer thickness.With the increase of stress annealing time,thickness of recrystallized layer gradually reduce;when the stress annealing time reaches 500 h,the thickness of recrystallization layer is reduced by about 50% compared with the non-stress annealed state.