Investigation Of Segregation And Homogenization For GH4169G Alloy

GH4169 alloy is widely used to fabricate critical components in fields of aerospace, petroleum industry, and the production of it numbered in first place among wrought superalloys, due to its excellent properties. With micro-alloying with phosphorus and boron, GH4169G alloy could significantly improve the rupture life and creep properties, and has no obvious effects on other properties. The segregation tendency of phosphorus and boron are seriously in GH4169G alloy with high content of strong segregation element niobium. The process of vacuum arc remelting with helium gas cooling has advantage in enlarging the size of ingot, decreasing elements segregation or improving the production efficiency with the same segregation condition. It notices that many ingots are supplied without total homogenized in projection, and even with some residual Laves phase. So this paper did the following study, the microstructure and elemental segregation of GH4169G alloy in 120 mm diameter, the effects of vacuum arc remelting with helium gas cooling on the GH4169 ingots in 508 mm diameter, the homogenization system of GH4169G alloy in 120 mm diameter.It is found that the content of phosphorus in Laves phase increases from the edge to the centre of the 120mm diameter, while other elements nearly same. It is in the interdendritic that titanium enriched most and the content increase from the edge to the centre. And the contents of elements in interdendritic in different parts of the ingots are almost same while molybdenum reached most in the centre. The content of elements in the dendrite arm is fair equally. The phosphorus is enriched in Laves phase and boron is found enriched in two phases, one is niobium carbide and the other is new phase with melting point between 1130℃and 1140℃. Boron segregates most among all the phases that could be homogenized in the alloy. Keeping 45 minutes at 1150℃, new phase is melted and then phosphorus and boron are segregated together. The homogenization system consists of three steps,1120℃×5h+1160℃×5h+1190℃×50h,AC. Deformation energy savings and the size of the ingot are found to be the two factors that influence the precipitation time of 8 phase when kept at 910℃. With the improvement of segregation in the ingot, the precipitation condition ofδphase changed from needle-like clusters to rod-like clusters and finally the granular well-distributed.The surface quality of the ingots is very poor with lots of shrinkage porosities, foreign inclusions. Columnar crystals grow up inclined, and the zone of interdendritic distributed uniformly. The direction of dendrite disappears with interdendrite zone clustered segregated, and most amount of phase precipitated unevenly in the centre of the ingot. The helium gas pressure on the solidification behavior could improve the shape of molten pool. With high pressure, fine crystal zone is enlarged and equiaxed crystal zone is decreased while all grains are fined in every zone. Also the primary dendrite arm spacing decreases, especially the second dendrite arm spacing is refined significantly. Laves phase in interdendritic decreases seriously compared with low pressure. Shrinkage porosities and cracks are all found in both of the ingots with helium gas cooling, but ingot with low pressure is more serous, so the parameters of the process should be adjusted.