Superalloy K418 And GH4169 Revert Purifying And Composition Controlling

Ni based superalloy revert contain kinds of rare matal elements,which are valuable for recycling and reuse.In this dissertation,the cold crucible remelting suction processing has been used to keep the design composition of K418 and GH4169 superalloys.Therefore,the inclusions,brought by chemical reaction between crucible and alloy melt during remeting process,have been removed,and the contents of oxygen and nitrogen in revert alloy reduced,and the microstructure and mechanical properties of these alloys improved.Two compound salts are found to remove inclusions in GH4169 and K418 revert alloys effectively,and the oxygen and nitrogen contents of GH4169 revert are controlled to lower than virgin alloys.These researches make new progresses in revert purifing and composition controlling for Ni based superalloy,and provide new thoughts and method for Ni based superalloy revert purification,which also have great theoretical meaning and realistic meaning.The following aspects have been investigated:After cold crucible remelting suction processing,for virgin and revert K418 superalloy,the contents of oxygen,nitrogen,sulfur and carbon reduce,while the mass fraction of oxide and nitride also reduce.The main alloying elements contents just fluctuate in the standard composition ranges of K418 virgin alloy.The precipitated phases in remelted K418 virgin and revert alloy are matrix phase y,strengthening phase ?',carbide MC,eutectic phase ?+?',?phase and small amount of oxide and nitride.The secondary dendrite arm spacing of remelted K418 virgin and revert alloy decrease,while the size and numbers of eutectic phase ?+?' and ? phase decrease,and carbides turn to be smaller.Therefore,the mechanical properties of remelted virgin K418 enhance fast under room temperature and 850?.After cold crucible remelting suction processing,for GH4169 virgin and revert alloy,the contents of nitrogen,sulfur and carbon reduce,while the mass fraction of nitride also reduces.The main alloying elements contents just fluctuate in the standard composition ranges of GH4169 virgin alloy.The precipitated phases in remelted GH4169 virgin and revert alloy are matrix phase ?',strength phase ?' and ?",Laves phase,eutectic phase y+Laves and small amount of oxide and nitride.The Laves phases are tiny and distribute more evenly in remelted alloy,but the size of ?" are bigger than before.The mechanical properties of remelted virgin GH4169 enhance at room temperature and 1150?.Purified by two compound salts,80%B2O3+20%Na2B4O2 and 50%CaF2+45%AlF3+5%CaO+trace amounts of(Al2O3+MgO),the oxygen and nitrogen contents of GH4169 revert alloy largely reduced to the standard levels of virgin alloy GH4169.The big size inclusions,Al2O3 and TiN,are absorbed and removed by molten compound salts.The main alloying elements contents just fluctuate in the standard composition ranges of GH4169 virgin alloy.As the superheat temperature increases,the contents of oxygen and nitrogen reduces in K418 revert alloy.When temperature reaches t0 1500?,the contents of oxygen and nitrogen reduce to 17ppm and 15ppm,which are lower than revert alloy with 5.6%and 75.4%.The main alloying elements contents just fluctuate in the standard composition ranges of K418 virgin alloy.As the revert proportion of K418 superalloy increases,the content of oxygen reduce,and the contents of nitrogen,sulfur and carbon increase.The main alloying elements just fluctuate in the standard composition ranges of K418 virgin alloy.In interdendritic region,the quantity and size of chinese character shape carbide MC reduce,and the quantity of eutectic phase ?+?'increase.The secondary dendrite arm spacing reduce,while yield strength ?0.2 and ultimate strength ?b increase,and total strain ?t and plastic strain ?p keep relatively stable.As the revert proportion increases,the contents of oxygen and nitrogen in GH4169 superalloy increase,and the main alloying elements just fluctuate in the standard composition ranges of GH4169 virgin alloy.The sizes of Laves phase and eutectic phase y+Laves increase before reduce.The 60%revert proportion GH4169 superalloy shows the maximum sizes of ?+Laves phase and the maximum width of interdendritic region.As revert proportion increase,the yield strength ?0.2 and ultimate strength ab of GH4169 superalloy increase.Under both room temperature and 1150?,the yield strength of 60%revert proportion GH4169 superalloy show the maximum value.Under 1150?,the compression strength of 80%revert proportion GH4169 superalloy show the maximum value.For K418 revert alloy,the raised nitrogen promote more carbonitride forming in interdendritic region,and the increased quantity of carbides would reduce flowability of residual liquid.The raised carbides increase the solute concentration of residual liquid,and move the alloy liquid components to the eutectic point.This provides the condition for more eutectic phase ?+?'forming.In addition,the reduced flowability of residual liquid causes the local cooling rate reduced,which provides advantage to form larger eutectic phase ?+?'.Thus,more carbonitride and larger eutectic phase ?+?' form in interdendritic regions.For GH4169 revert alloy,the raised contents of oxygen and nitrogen cause higher quantity of Al2O3 and TiN inclusions.As more Al2O3 and TiN inclusions concentrate in interdendritic regions,the viscosity of residual liquid increased,which reduces the flowability and heat convection of residual liquid.Thus,the local cooling rate of residual liquid in interdendritic regions declines,providing advantage to form more and larger eutectic ?+Laves phases.The hot deformation process of 80%revert proportion GH4169 superalloy shows three stages,which are work hardening,dynamic recrystallization and steady flow.When the strain ? is fixed,the temperature T and strain rate ? are two important factors affecting flow stress.When the deformation temperature are between 900? and 1150?,and strain rate ? are between 0.001s-1 and 1s-1,the hyperbolic sine flow stress constitutive equations could describe the hot deformation process,and the relative errors between calculated results and thermal simulation test results are under 12.8%.