Recrystallization Behavior Of A Single Superalloy DD6

As a kind of important nickel-base single crystal superalloy material with independent intellectual property rights in our country,DD6 alloy has invested to the actual production and practice.The greater decreases of mechanical property under higher temperature due to recrystallization of single crystal superalloy,it is necessary to study the influence of recrystallization in DD6 superalloy in order to provide theoretical basis for alloy production and practice in the future and ensure the use safety.When indentated or shot peening on the surface of DD6 superalloy,plastic deformation occurred,recrystallization on the surface appeared after heat treating.Behavior of recrystallization in alloy by surface indentation or shot peening and influence of recrystallization depth on stress rupture property of DD6 superalloy by grit blasting have been discussed in the dissertation.The results show that indented on the surface of DD6,during pre-treatment at the lower temperature(<1200?),there was no recrystallization in DD6 alloy,after pre-treatment at the higher temperature,equiaxed recrystallization appeared.After solution treatment,there was recrystallization obviously.Recrystallization grain boundary was thin and and was made of fatter ?? phase.Compared with the microstructure after solution treatment,the depth of recrystallization became little change.During aging treatment,grain boundary changed into bigger cellular one,then granular M6 C carbide precipitated from grain boundary.With the increasing of loading(>250kg)in the test,the area of recrystallization was increased distinctly after solution.With shot peening,cellular recrystallization occurred on the surface after lower temperature(1000?-1250?),equiaxed recrystallization appeared above 1250?.Different loading mode,different behavior of recrystallization.There was no cellular recrystallization of alloy indentated after lower temperature(<1200?),small amount of cellular recrystallization appeared in the stressed zone,equiaxed recrystallization occurred gradually above 1200?.The depth and area of recrystallization of as-cast state was less than that of heat treatment state specimen.The dissolution of ?? phase is the necessary condition for recrystallization of DD6 alloy.The nucleation mechanism of recrystallization are the subgrain combination and grain boundary migration by strain.At the temperature up to ?? phase solvus,?? phase had little effect on recrystallization,recrystallization may nucleate at carbide(MC and M6C),porosity,and ?+?? eutectic.When the as-cast specimen was grit blasted and then standard heat treated,it can obtain the equiaxed recrystallization.When the solution specimen was grit blasted and then aging heat treated,it can obtain thinner cellular recrystallization.The thickness of the recrystallization layer of the two kinds of samples all increased with the increasing of the blasting time.The stress rupture lives decrease with the increase of the thickness of recrystallization layer.