Effect of different cooling rates on directional solidification microstructure and elemental segregation of GH4151 superalloy
In order to further reduce the degree of alloy solidification segregation and optimize the vacuum consumable smelting(VAR)process,directional solidification experiments were conducted on GH4151 superalloy using liquid metal cooling(LMC)method.The effect of cooling rate on directional solidification structure and element segregation of the GH4151 superalloy was studied means of optical microscope,scanning electron microscopy and electron probe microanalysis.The results show that as the cooling rate increases,the primary dendrite spacing λ 1 and secondary dendrite spacing λ2 both gradually decrease,and the relationship between them and the cooling rate is similar.Moreover,the γ'phase size between dendrite arm and interdendritic decreases gradually with the increase of cooling rate,and the uniformity of the microstructure improves.The electron probe microanalysis of the elemental composition distribution in the solidification structure shows that the main segregation elements of the GH4151 superalloy are W,Nb and Ti,with a deviation degree of more than 20％.The microsegregation degree of all three elements increases with the increase of cooling rate,because as the cooling rate increases,the time available for solute diffusion in the solidified front solid layer decreases,and the diffusion effect weakens.
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