Study On Formation And Influence Of Tungsten-rich Phase In High Tungsten Superalloy

As a typical high tungsten alloy,the W content(mass fraction)of K416B alloy was up to16.5%,which was the highest among superalloys in China at present.K416B alloy contained a large number of solid solution strengthening elements(W,Cr,etc.)and precipitation strengthening elements(Al,Ti,etc.).At the same time,the addition of Hf,Nb,C and other elements also made the carbide in the alloy very developed.These factors made the alloy have good thermal strength and temperature-bearing capacity,so it was an important material for the preparation of aero-engine guide vane.At the same time,the high W content made the alloy easy to precipitate rich tungsten phase during solidification,resulting in uneven composition and microstructure of the alloy and unstable properties of the alloy.In order to clarify the precipitation mechanism of tungsten-rich phase(?-W,M₆C)in K416B alloy and improve the stability of microstructure and properties of K416B alloy.In this paper,the tungsten-rich phase in K416B alloy was studied,its precipitation mechanism was clarified,the method of regulating its precipitation was found,and the microstructure and properties of the alloy with different composition and preparation process were studied.find out the effect of composition adjustment and preparation process on the formation of tungsten-rich phase,and further study the effect on the microstructure and properties of the alloy.The results showed that the tungsten-rich phase in as-cast K416B alloy is petal/spherical?-W phase and block/lamellar M₆C carbide,and their W content is more than 90%and 70%,respectively.The macrosegregation of K416B master alloy ingot was caused by the precipitation of rich tungsten phase,and the macrosegregation of the alloy could be weakened by adjusting W,Ti,Nb and rare earth elements,so that the microstructure and composition of the upper and lower parts of the alloy ingot were more uniform.As the content of Al,Ti and Hf in the alloy increases,the content of eutectic in the alloy increased significantly.When Al increased to 7.0wt.%/Ti to 1.5 wt.%,the eutectic in the alloy changed from a honeycomb shape to bulk,the tungsten-rich phase began to precipitate in the alloy,and the durability performance became worse.As the Nb content increased,the number of MC carbides in the alloy increased significantly.Reducing the W content in the K416B alloy could inhibit the precipitation of the tungsten-rich phase in the alloy.With the decrease of the casting temperature,the uniform temperature of the system also decreased,the grain size of the alloy was obviously reduced,the eutectic content in the alloy was increasing,and the morphology of the carbide changed from long strips and frameworks to granular and short rod shape,the size of the tungsten-rich phase became smaller and the number increased.There was little difference in the size and morphology of the?'phase of the dendrites of the alloys with different casting temperatures.Too low casting temperature caused the alloy to produce columnar crystal structures.The size of the tungsten-rich phase in the alloy prepared by buried sand is significantly reduced.The morphology of MC carbide in the alloy prepared by single shell was mostly skeleton-like and the content of eutectics was higher than that of samples prepared by other methods,while MC carbide in the sample prepared by buried sand was blocky.The morphology of eutectics in the alloys prepared by single shell and buried sand were honeycomb,and the size of?'phase was small,the morphology of MC carbide is intact,meanwhile the tensile strength at room temperature and creep life on the condition of 975?/235MPa are higher.The morphology of eutectic in the alloys prepared by buried sand was mostly bulk,some MC carbides decomposed into M₆C carbide,and?'phase coarsened obviously.Moreover the tensile strength at room temperature and creep life decreased significantly.