Effect Of Heat Treatment On Microstructure And Creep Behavior Of FGH95 Powder Nickel-Base Superalloy

In the paper, by means of the treatment of the hot isostatic pressing at the different temperatures, heat treatment at different conditions, creep properties measurement and microstructure observation, an investigation has been made into the influence of heat treatment regimes on the microstructure and creep properties, and discussing the deformation and fracture mechanisms of FGH95 powder nickel-base superalloy during creep.Results show that the quantity and size of the primary thickerγ′phase in the previous particle boundary regions of FGH95 superalloy decrease as the HIP temperature is raised. When the different temperature HIP alloys are treated at 1155℃solution, lower temperature cooling and aging, there are only a few thickerγ′phase exist in the alloy, and many more blocky (Nb,Ti)C carbide particles are dispersedly precipitated in the alloy, which results in the better stress rupture properties of the alloy. When the 1150℃HIP alloy is solution treated at 1140℃, the poor areas of the fineγ′phase and significant amount of the thickerγ′phase still exist in the regions of the grain boundaries, and the amount of the thickerγ′phase and the poor areas of the fineγ′areas decreases with the enhancement of the solution temperature. After the solution temperature is enhanced to 1160℃, the thickerγ′phase in the alloy is fully dissolved, and the poor region of the fineγ′phase disappears, and theγ′phase with high volume fraction is dispersively distributed within the grains, thereinto, the particles of (Nb,Ti)C carbide phase are discontinuously precipitated along the boundaries to improve the boundaries bonding strength, which is thought to be a main reason of resulting in the alloy possessing a better creep resistance due to the pinning effect of them to restrain the boundaries slipping. After solution temperature raise to 1165℃, the sizes of the grain are obviously grown up, and the films of the carbide are continuously precipitated along the boundary. In the ranges of the applied temperatures and stresses, the activation energies and stress exponents of the "1150℃H IP/1160℃solution"and"1180℃H IP/1155℃solution"heat treated alloys during creep are calculated to be Q1 = 580.3kJ/mol and Q2 = 618.0kJ/mol, respectively. The deformation mechanism of the alloy during creep is that the dislocation bypassing and shearing theγ′phase, thereinto, the super-dislocation which shears into theγ′phases may be decomposed to form the configuration of partial dislocation and stacking fault, which can hinder the cross-slipping of dislocations to improve the creep resistance of the alloy. In the later creep stage, the deformed features of the alloy are the single and double orientations slipping of dislocations activated in the alloy, which brings out the stress concentration to promote the initiation and propagation of the micro-cracks along the boundaries, this is thought to be the fracture mechanism of the alloy during creep. And the fracture features of the alloy during creep are the occurrence of the intergranular and transgranular fracture, thereinto, the nonsmooth surface appeared in the fracture region is attributed to the finer carbides precipitated along the boundary.