Spray Forming Characteristics And Changes In The Law Of High-temperature Alloy

Microstructure characteristics and evolution of various states in spray formed superalloy GH742y have been investigated by using optical microscopy, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry, phase analysis.The analysis of the microstructure characteristic of as spray formed GH742y indicates that the preform exhibits high density, fine and uniform microstructure. The mean grain size of most preform is in the range of 30～50μm. The smaller grain size in edge can be explained in term of the cooling effect of preform. A few pores, which distribute mainly in the edge and 30~50mm below the upper surface of preform, were affected by metal solidification, atomization gas and so forth. The second-phase of as spray formed GH742y consists ofγ′phase and M(C,N) richied Nb and Ti.The study of microstructure evolution in the flowchart of spary forming process, indicates that hot isostatic pressing can eliminate the pores of sprayed formed GH742y effectively. The relative density on the vertical section of preform can as high as 99.9% after HIP. The size and amount ofγ′phase, the combination properties can be changed after heat treatment. Very little coarsening and good stability of grains in both as sprayed formed and forged preform were observed after high temperature solution treatment. Theγ′solvus temperature of spray formed GH742y is about 1126℃.The main factors of grain growth inhibition were investigated, by conparing the influence of heat treatment on grain growth of as HIPed materials N2 atomized with that of Argon atomized alloy. The study reveals that the grain coarsening do not take place after 1250℃solution treatment for 4h and the limitingultimate grain size is abou 40μm in N2-atomized HIPed preform. However, for Ar-atomized preform, the grain size varies with the solution temperature and the limitingultimate grain size is 200μm.γ′phase inhibits grain growth by pinning grain boundary when solution treatment belowγ′solvus temperature. The dispersed MC phase restrain grain coarsening during solution treatment aboveγ′solvus temperature. The difference in volume fraction, size and distribution of carbonitride brings about the difference in limitingultimate grain size of as HIPed materials between N2 atomized and Ar atomized. Gladman equation can estimate limitingultimate grain size in HIPed preform N2 atomized. Zener equation can predict the limitingultimate grain growth in HIPed preform Ar atomized.