Research On Microstructure Regulation And Tensile Properties Of GH4151 Alloy

GH4151 alloy is a new kind of wrought superalloy for turbine disc.The alloy possesses admirably creep resistance,fatigue resistance and oxidation resistance.The service temperature can be up to 800℃.The alloy contains a large number of alloying elements,and the element segregation is serious in the solidification process,which precipitates a large number of harmful phases,and increases the difficulty of hot processing of the alloy.In addition,the alloy exhibits low plasticity in the medium temperature,which affects the service life of the alloy.Therefore,the effects of solidification segregation behavior and heat treatment process on the microstructure and mechanical properties of the alloy were studied in this paper.Meanwhile,the deformation mechanism of the alloy in the intermediate temperature was studied by adjusted the Co content,to improve the properties of alloy.The main results are as follows:The inter-dendritic precipitates of the as-cast GH4151 alloy mainly consist of(γ-γ’)eutectic,Laves phase,η phase and MC carbides.The main inter-dendritic segregation elements are Nb,Mo and Ti.According to the influence of carbon content on elements segregation,the optimal content of carbon was determined to be 0.04 wt%.Subsequently,the solution sequence of each phase was determined by single-step homogenization annealing experiment at different temperatures.Then,a two-step homogenization heat treatment system was developed according to the solution characteristics,which effectively ameliorated the dendrite segregation and improved the microstructure uniformity of the alloy.The solution temperature of γ’ precipitates of GH4151 alloy was determined to be about 1162℃ by DTA test.The effects of sub-solves heat treatment on the microstructure and tensile properties of the alloy at room temperature(RT)and 750℃were investigated.Meanwhile,the dissolution kinetics of γ’ precipitates at 1100℃,1120℃,1130℃ and 1140℃ were calculated.The results showed that the fine primary γ’ precipitates dissolve to the matrix firstly in the solution process,and the coarse primary γ’ precipitates dissolved gradually after 1130℃.Meanwhile,the grain size increased when the solution temperature above 1130℃.The size of secondary γ’ precipitates increased with the solution temperature rising.The alloy with solution at 1130℃ has the best mechanical properties at 750℃ tensile.The effect of Co content on the microstructures and tensile properties of GH4151 alloy at medium temperature was studied.The results showed that with the increasing of Co content the solution point and the area fraction of primary γ’precipitates decreased.The microtwins is mainly deformation mechanism of the alloy in the medium temperatures.Increasing Co content reduces the SFE(stacking fault energy)of the alloy reduced with the Co content increasing,and the low SFE alloy could promote the formation of microtwins at the medium temperature.And then improves the strength of the alloy.