综合运用电子空位理论和d－电子理论, 设计了一种新型无Re镍基单晶高温合金7.5Cr－5Co－2Mo－6.1Al－8W－6.5Ta－0.15Hf－0.05C－0.004B－0.015Y(质量分数, %),Ni余量. 采用光学显微镜、扫描电镜、X射线能谱观察了其铸态、固溶处理和时效处理后的组织特征,研究了完全热处理后合金的760℃拉伸力学行为及断口形貌. 结果表明,合金的组织稳定, 合金元素间共价键平均结合强度Bot, γ′相固溶温度T_γ′solvus, 成分性能预测参数P,抗拉强度σ_b等与第2代含Re镍基单晶高温合金相当.

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－6.1Al－8W－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 γ′ 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 theγmatrix channels uniformly, whose ultimate tensile strength at 760℃ is 1009 MPa, comparable to the second generation of Re－containing Ni－based single crystal superalloy considerably.