Microstructure and creep behavior of FGH95 nickel-base superalloy

Abstract

By means of the measurement of creep curves and the microstructure observations, the influence of the solution temperatures on the creep behavior of FGH95 nickel-base superalloy is investigated. Results show that, after solution treated at 1150 °C, some coarser γ′ precipitates are distributed in wider boundary regions where no fine γ′ phase is precipitated. As the solution temperature is raised to 1165 °C, the grain size of the alloy increases obviously, and the carbide is continuously precipitated to form the film along the boundaries. When the alloy is solution treated at 1160 °C, the coarser γ′ phase in the alloy is fully dissolved, the fine γ′ phase with higher volume fraction is dispersedly distributed within the grains, and some particles of (Nb, Ti)C are precipitated along the grain boundaries, which can effectively hinder the grain boundary slipping and dislocation moving. Thereby, the alloy displays a better creep resistance under the applied stress of 1034 MPa at 650 °C. The deformation mechanism of the alloy during creep is twinning, dislocation shearing or bypassing the γ′ phase, and the 〈1 1 0〉 super-dislocation which shears into the γ′ phase may be decomposed to form the configuration of (1/3)〈1 1 2〉 super-Shockleys partial and stacking fault. In the later stage of creep, the deformation features of the alloy are the single and double orientations slipping of dislocations activated in the alloy. As the creep goes on, some dislocations piled up in the regions near the boundaries may bring the stress concentration to promote the initiation and propagation of micro-cracks, which is thought to be the fracture mechanism of the alloy during creep.