Study On Volatilization Behavior Of Ni-Cr-Co Ternary Alloy During Electron Beam Smelting

Nickel-based superalloys have excellent thermosetting properties,like thermal fatigue resistance,creep fatigue resistance,thermal stability and corrosion resistance,so it can be applied at extreme high temperatures and widely applicated in hot end parts of turbofan engines.Most superalloys are smelted by vacuum induction melting.Ni,Cr and Co are main elements for many kinds of superalloys.W is widely used as a strengthening element in superalloys.The price of Ni,Cr and Co is more expensive with the increase of purity.Ni-Cr-Co ternary alloy purified by electron beam purification can take the place of high-purity Ni,Cr,Co element for melting,and the cost of melting can be reduced.The electron beam has a strong ability to purify the alloy,but the volatility of the element during electron beam smelting and purification is less studied.and it is easy to imagine that the W element is segregated and the composition distribution is uneven.The metallurgical quality of the alloy ingot is poor and the melting cost is high.For the above problems,Ni-Cr-Co ternary alloy was prepared and purified by electron beam,studied the volatility of Ni,Cr and Co elements in the smelting process,including changes of alloy composition,evaporation rate of elements,average temperature of the melting surface and mass loss rate in the paper.The changes of element mass fraction during electron beam smelting FGH4096 master alloy was predicted exactly.Ni-W master alloy was prepared by electron beam.FGH4096 master alloy was prepared by electron beam smelting with Ni-W alloy that was used instead of W.The main component,microstructure and macroscopic element distribution of FGH4096 master alloy ingot were detected and analyzed.The results show that the mass fraction of Ni increased,the mass fraction of Cr decreased,and the mass fraction of Co did not change much during the electron beam smelting Ni-Cr-Co ternary alloy.Compared with Ni and Co,the mass loss rate of Cr was the largest,which was the element that needs to be controlled during the smelting process.Under the electron beam smelting power of 15 kW,the average temperature of the melting surface during smelting was 1980.4K.The mass loss rate of the three elements Ni,Cr and Co calculated at the temperature in the electron beam smelting process was in good agreement with the experimental results.During the process of electron beam smelting the FGH4096 master alloy,the mass fractions of Ni,Cr and Co were accurately predicted by the volatilization of the Ni-Cr-Co ternary alloy.The theoretical calculations were in good agreement with the experimental measurements.The problem that the raw material was severe burning loss in the smelting process due to the excessive melting point of W can be solved by using Ni-W alloy instead of W element.The cross-sectional metallographic structure of the FGH4096 master alloy prepared by electron beam smelting was mainly divided into three regions: the bottom fine crystal region,the middle column crystal region and the top large grain region.The elemental distribution except Ti in the transverse direction and longitudinal direction of the cross section were relatively uniform.The Ti content gradually decreases from the center to the edge of the ingot,and gradually increases from the bottom to the top of the ingot center.