Hot tearing mechanism and control of superalloy for turbine disk served above 800℃

To meet the requirements of high-performance aero-engine, the alloying degree and mass fraction of γ′ phase keep increasing in newly wrought superalloys, which has led to an increase in the crack sensitivity of the alloys. The hot cracking behavior of the large size Φ350 mm GH4151 superalloy with Al+Ti+Nb content exceeding 10 wt.% and γ' phase content exceeding 50% was investigated via experiment and simulation. The solidification and strain aging cracking indexes of different deformed superalloys are also evaluated. The results showed that the crack type of GH4151 alloy is hot tearing. Cracks were consistently found to propagate intergranular and have a clear correlation with high-angle grain boundaries (HAGBs). The hot tearing is caused by the severe segregation of Mo, Nb, and Ti between dendrites in a wide freezing range, and the formation of MC phases, η phases, (γ+γ') eutectic phases, Laves phases, and M2B phases successively in the last stage during solidification, hindering the liquid phase replenishment and forming pore defects. These pores produce cracks under the induction of thermal stress and phase transformation stress. B and Zr elements have a great influence on reducing the freezing range of the alloy. The critical criterion of the freezing range for hot cracking and strain aging cracking in superalloys without B and Zr elements are 230K and 0.0008, respectively. By mold preheating and annealing process, the residual stress and microstructure of the alloy could be significantly improved, and finally produces a crack-free ingot.