Solidification Segregation Behavior and Homogenization Heat Treatment of GH4151 Alloy
GH4151 alloy is a new type of casting and deformation superalloy of turbine disk with the temperature bearing capacity up to 800 ℃.The alloy has severe elemental segregation during solidification,and main segregation elements include Nb,Ti and Mo.Meanwhile,the alloy contains a large amount of element C.In the late stages of solidification,due to the enrichment of elements in the residual liquid phase,a large number of harmful phases,including(γ-γ')eutectic,Laves phase,η phase and MC carbides,precipitate between the dendrites.The influence of C content in the GH4151 alloy on the segregation elements was investigated.Result show that increasing C content can reduce the segregation of Nb elements between dendrites.In addition,with the increase in C content,the dendrites become more developed and the interdendrite area decreases.The effects of homogenization heat treatment were studied at different temperatures from 1160 ℃ to 1210 ℃.The melting points of(y-y)eutectic and Laves phases are about 1180 ℃,that of η phase is about 1200 ℃ and that of MC carbide is higher than 1300 ℃.At the same time,it is found that the 1170 ℃/16 h+1200 ℃/8 h double step homogenization heat treatment can not only eliminate the segregation in the ingot,but also avoid the holes caused by the overburning of the low melting point phases,which makes the billet more conducive to the subsequent billet deformation.
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