Optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high temperature tensile testing machine were used to systematically study the microstructure and high temperature tensile properties of FGH98 alloy with different Ta content. The results show that the addition of tantalum can obviously eliminate the Prior Particle Boundary (PPB), promote the morphological instability of secondary γ 'phase and increase the number of tertiary γ' phase. The addition of tantalum improves the tensile strength and yield strength of the alloy at high temperature to a certain extent. The ductility of the alloy with 2.4% Ta content (mass fraction, the same below) is the best. The tensile fracture of Ta - free and 1.2%Ta alloy is crystalline. There are many equiaxed dimples on the fracture of 2.4%Ta alloy, which is ductile fracture. The 3.6% Ta and 4.8%Ta alloys are characterized by transgranular and intergranular cleavage fractures, which are typical crystalline fractures. In the Ta - free alloy, a large number of twins and dislocation bypass γ 'phase and deform. The addition of Ta reduces the stacking fault energy of the alloy, and with the increase of Ta content, a large number of stacking faults occur in the dislocation shear γ' phase.
Throughout the composition design of the third generation of powder superalloys at home and abroad, the addition of alloying element Ta is a significant feature. Ta is a strong carbide-forming element, which can improve the stability, crack propagation resistance and thermal corrosion resistance of carbides when added to nickel-based superalloys [4,5,6,7]. Ta has a large atomic radius and its Vigard coefficient is second only to Hf and Zr, so it can significantly increase the lattice constant of γ 'phase and improve the solid solution strengthening effect of γ' phase. Ta added to the alloy mainly enters γ 'phase, which improves the thermal stability of γ' phase, delays the aggregation and growth of γ 'phase, and improves the high temperature strength of the alloy. At the same time, Ta can also improve the oxidation resistance and corrosion resistance of the alloy, which is conducive to improving the high-temperature fatigue crack growth and creep resistance of the alloy [10,11,12,13]. The high temperature tensile strength and room temperature microhardness can be improved by adding Ta to Cast IN617 alloy. However, when Ta content reaches 2.0%, TA-rich MC carbides in supersaturated matrix lead to reduced plasticity and fracture toughness. Ta alloys exhibit dislocation Orowan bypass and partial dislocation climbing mechanisms at high temperatures. J.j. Yu et Al. 's study showed that Ta affects the tensile deformation mechanism of co-Al-W-based single crystal superalloys at high temperature. The deformation mechanism of 0Ta and 1.8Ta alloys is that dislocation bypass γ' phase, while that of 2.8Ta alloys is that dislocation cuts through γ 'phase. In this paper, the microstructure, tensile properties and deformation behavior of ni-base powder superalloys with different Ta contents were studied by precipitation strengthening ni-base powder superalloys with multi-mode distribution of γ 'phase size.
