EXPLORATION AND RESEARCH OF A NEW Re－FREE Ni－BASED SINGLE CRYSTAL SUPERALLOY

Ni-based single crystal superalloy has not only high temperature creep and fatigue resistance,but also excellent oxidation and corrosion resistance,which becomes a main selection of the advanced aero engine turbine blades.In order to enhance high temperature properties,Re is added into the superalloy,however,high density and high cost of the Re,especially promote the precipitation of harmful phases at high service temperature,which limit the use of Re.Therefore,how to reduce or even abolish the use of Re in the single crystal superalloy is the main trend to develop a new generation turbine engine material.A new Re-free Ni-based single crystal superalloy,7.5Cr-5Co-2Mo-6.1Al8W-6.5Ta-0.15Hf-0.05C-0.004B-0.015Y(mass fraction,%),Ni balance,has been designed by using the average electron vacancy number theory and the d-electrons concept.The microstructures of the as-cast,solution and aging treated specimens were observed by optical microscopy,scanning electron microscopy,energy dispersive X-ray spectroscopy.The mechanical behavior of the fully heat treated single crystal superalloy and the appearance of fracture at 760℃ were studied.The calculation results indicate that the microstructure of the designed alloy is stable and the main performance criteria,such as Bot(the bond order between alloying elements and Ni atoms),T_(γ'solvus)(γ' solvus temperature), P(the parameter which predicts the merit of the composition),etc.,are comparable to those of the second generation of the Ni-based single crystal superalloy.The experimental results indicate that W and Mo enriched in the dendrite cores,while Al and Ta enriched in the interdendritic region.The size and volume fraction of 7' phase in the dendrite cores is smaller than that in the interdendritic region. After solution heat treatment at 1300℃,3 h,air cooling,γ/γ' eutectics are dissolved and composition segregation is significantly improved.After fully heat treatment at 1100℃,4 h,air cooling and 870℃,24 h,air cooling,γ' phase with cube-shaped distributes in the γ matrix channels uniformly, whose ultimate tensile strength at 760℃ is 1009 MPa,comparable to the second generation of Recontaining Ni-based single crystal superalloy considerably.