Electromagnetic Control During The Solidification Process Of The K417 Superalloy Vacuum Casting

The superalloy casting is usually manufactured by two-ply vacuum casting,i.e.the raw materials are melted and casting into a master alloy ingot in a vacuum induction furnace,then the master alloy ingot is re-melted and casting into foundry goods in a vacuum induction furnace,so the quality of the superalloy cast are greatly affected by the quality of the superalloy master alloy ingots.At the present time,the master alloy ingot made by vacuum casting usually have quality problems of coarse grain,more shrinkage porosity,and more serious segregation,which reduces the percent of pass of superalloy casting.The main disadvantages of the conventional superalloys investment cast are coarseness and non-uniform of grain structures,which reduce the low cycle resistance and high tensile strength of the cast under the medium temperature.It has been demonstrated that the integral grain refinement is the effective method to improve the low cycle resistance and high tensile strength of the cast within the medium temperature ranges.The Electromagnetic Processing of Materials has become the important research field of the materials science.Therein,the electromagnetic stirring has advantages of refining the internal structures of the ingot,reducing the segregation and shrinkage cavity,and minimizing the inclusion.In order to improve the quality of superalloy master alloy ingots,the new technology of superalloy vacuum-electromagnetic casting,i.e.imposing rotating electromagnetic stirring to the solidification process of superalloy vacuum casting was developed,and the effect of rotating electromagnetic stirring on the quality of superalloy ingots was studied.The main conclusions can be listed as follow:Through imposing rational rotating electromagnetic stirring to the solidification process of superalloy vacuum casting,the equi-axed crystals in the superalloy ingots can be effectively refined and increased,and the central shrinkage porosity,the inclusion and the dendritic segregation of superalloy ingots are greatly reduced. The quality of superalloy ingots is obviously improved.In order to improve the quality of some superalloy master alloy ingots,which is easy to generate the negative segregated band under the action of the unidirection rotating electromagnetic stirring,the new technology of superalloy vacuum-electromagnetic casting, i.e.imposing linear electromagnetic stirring to the solidification process of superalloy vacuum casting was developed,and the effect of linear electromagnetic stirring on the quality of superalloy ingots was studied.The results indicate that the quality of superalloy ingots can be obviously improved through imposing rational linear electromagnetic stirring to the solidification process of superalloy vacuum casting.Furthermore,in order to obtain the good superalloy fine-grain casting,a new fine-grain casting technique of superalloy castings by applying reversible rotary magnetic fields and inoculants simultaneously was proposed,and effects of reversible rotary magnetic fields and inoculants on the crystal structure and performances of K417 superalloy cast were investigated.The main conclusions can be listed as follow:1.The coarse columnar grain surface can not be removed by increasing the current intensity or shortening the stewing time.By initiating the 50Hz and 150A reversible rotary electromagnetic stirring as soon as the molten metal was poured into the mould,which was coated with the inoculant CoAl₂O₄,the average equiaxed grain size of K417 superalloy cast can be refined to 95μm and the fraction of equiaxed grains can be increased to 100%.2.On condition that the average equiaxed grain size of K417 superalloy cast were refined to 95μm,the micro-segregation,the dendritic,the MC carbide,the(γ+γ') eutectic and theγ' phase in samples can be greatly improved,which is favorable to the increment of the K417 superalloy performances.3.Under 650℃,the strength,the plasticity and the low cycle fatigue lifes of K417 superalloy can be obviously increased by the grain refinement.When the test temperature is increased from 20℃to 650℃,the strength of K417 superalloy can kept invariable.However, the plasticity of K417 superalloy can be reduced.When the test temperature is increased from 20℃to 650℃,the low cycle fatigue lifes of K417 superalloy can be largely reduced.The reasons can be attributed to the increment of oxidized damage and fatigue damage.Therein, the increment of fatigue damage is the main factor.