Influencing Factors And Mechanisms Of Near-net Shape FGH4096M Powder Metallurgy Superalloy With Hot Isostatic Pressing

Near-net shape of hot isostatic pressing(NNS-HIP)is an integrated technology of material forming and preparation based on the integration of traditional powder metallurgy(P/M)technology and advanced mold manufacturing technology.It has important application prospects in the preparation of difficult-to-machine superalloy complex components used in aerospace.In this thesis,the control of shape and machanical properties based on the distribution of powder particle size for nickel-based superalloy turbine disk components by NNS-HIP are systematically studied.The basic data and theory for the preparation of complex-shaped nickel-based superalloy components by NNS-HIP are provided.The main research contents and conclusions in this study are as follows:In this thesis,the FGH4096M superalloy powder were prepared by electrode induction melting argon atomization(EIGA)process,Which is a kind of ultra-clean powder preparation technology.The nearly spherical powder mainly has a normal distribution,the powder’s Dv10=16.6μm,Dv50=54.6 μm,Dv90=121.5 μm.With the increase of powder size,the microstructure on the powder surface changed from microcrystal,cellular crystal to dendrite,and the surface smoothness of the powder also decreased.The loose structure and pores began to appear inside the powder,and the number of hollow powder gradually increased.The composition of the powders is uniform,and there was no obvious element segregation phenomenon.The slight element segregation phenomenon between dendrite arms and crystallites was found on the microstructure.The oxygen content of powders was controlled below～143 ppm.The powder flowability index and the sprayability index are 91.8 and 81.3,respectively.The effects of four ranges of particle size(A<75 μm,B 50-100 μm,C 100-300μm,D a kind of particle size grading)on the shrinkage and densification of powder compacts during HIP were investigated.The shrinkage of powder compacts from small to large are as follows:A-HIP<D-HIP<B-HIP<C-HIP.The axial shrinkage is 10.9%,11.8%,13.3%and 14.0%,and the radial shrinkage is 10.2%,11.3%,11.7%and 14.8%,respectively.This result is consistent with the tap densities of powders for four ranges of particle size.Secondly,it was found that the radial shrinkage at the top is 0.8%-1.6%higher than that of the bottom for the four powder compacts.The phenomenon mainly caused by the particle size segregation of the powder in the tapping process.The effects of powder particle size ranges on the microstructure and properties were studied.Compared to the C-HIP sample,the A-HIP sample prepared by fine powders have more fine prior powder boundaries(PPB)and much better mechanical properties.As the crack propagation path in A-HIP sample is more tortuous,the deflections number in the A-HIP sample was greater than that of the C-HIP sample during crack propagation.The large amount of crack deflection increases the toughness,which makes the plasticity of the A-HIP increase by 78.6%-88.7%compared with the C-HIP.Compared to the C-HIP sample,the ultimate tensile strength of the A-HIP was increase by 11.3%-14.1%,because a large number of dislocation accumulations on the PPB in the A-HIP sample led to more serious work hardening,which is benefit to improve the ultimate tensile strength.The mechanical properties of the B-HIP sample exceeded that of the D-HIP sample except for the yield strength.It was believed that the mechanical properties of the B-HIP sample surpassed the D-HIP sample comprehensively was because the smaller difference in size between adjacent powder particles.The smaller difference in size between adjacent powder particles was benefit to increase the stress at the sintered neck,which is more conducive to the densification of the powder and the diffusion of atomic.The lower of the grain boundary energy was because the more matching positions on the grain interface formed between two particles,and the grain boundary is more stable.On the contrary,the crack propagation path between large and small particles is more easy.The traditional Shima constitutive model yield criterion is modified by HIP interruption test.The Shima constitutive model of the FGH4096M powder compact during hot isostatic pressing were obtained.The values of the yield criterion coefficients b1,b2,b3,b4,q1,q2,q3 and q4 were 0,1,1.09,5.15,75.94,-75.94,1,and-0.36,respectively.According to the modified Shima model criterion,the effect of the capsule characteristics on the densification of the powder compact was studied using the finite element software of MSC.Marc.Results show that the relative density of the powder compacts in the central area of the capsule was increased with the decrease of the capsule thickness.A conformal capsule was designed for the turbine disk component,and the deformation and shrinkage of the powder compact during HIP was studied.The maximum shrinkage in the X-axis direction is 4.92 mm(4.93%),and the shrinkage of the powder compacts in the Y-axis direction are 1.96 mm(9.07%),2.24 mm(17.36%)and 1.96 mm(16.33%),respectively.It provided the basis for the determination of the capsule size for the turbine disk.Based on the above results,the turbine disk components for aeroengine were fabricated by NNS-HIP.The microstructure,mechanical properties and the steel-FGH4096M interface were studied.The results show that the final size of the turbine disk was only～0.3 mm away from the target size at the third step of the turbine disk,and the dimensional control accuracy is comparable to that of precision casting.The ultimate tensile strength,yield strength and elongation at room temperature were 1424±12.7 MPa,986±9.9 MPa,18±0.7%,respectively.