Effect of γ′ precipitation during hot isostatic pressing on the mechanical property of a nickel-based superalloy

Effect of high pressure on the solid–liquid phase change of a nickel base superalloy during hot isostatic pressing

“…4 obtained for 30H11 suggests this case: the diffraction from (2 0 0) plane was intensified, compared to that of AR. Such intensification was also noticed for the same alloy treated at 1230 • C and 120 MPa, and subsequently precipitation-strengthened at ambient pressure [6]. The morphological evolution of ␥-␥ eutectics in 30H11 also supports this argument.…”

“…XRD patterns for these coatings showed a distinctive decrease in the peak intensity for (1 1 1) plane, and an increase in the intensity for (2 0 0) plane after HIPing. It was found in our previous work that the intensity of diffraction from (2 0 0) plane depended on the temperature of precipitation of ␥ phase in the ␥ matrix [6]: The lower precipitation temperature under the pressure of 120 MPa resulted in the lower diffraction intensity from (2 0 0) plane. This suggests that the phase change ␥ → ␥ induces a disordered state, which is more effectively frozen at lower temperatures under the action of high pressure.…”

“…The possibility of dissolution of eutectics and reprecipitation of ␥ particles may also be excluded, because a eutectic transformation takes place at 1332 • C at ambient pressure, according to Trexler et al determined by DTA on cooling [11]. At the pressure of 120 MPa, the dissolution temperature could be even raised, due to lower diffusivity of constituent elements and the strain energy induced by phase change [5,6].…”

“…This DS alloy was also used for our previous work [5,6], and hence a detailed explanation is not given here. Briefly, this alloy was invest-cast as a cylindrical rod with the length of 200 mm, and the diameter of 15 mm.…”

“…Kimura and Yamaoka [4] also reported in a study on the influence of high pressure on the microstructure of a Cr steel that martensitic microstructure was obtained by normalizing heat treatment under high pressure of 4 GPa, instead of a ferrite with coarse particles found in the steel heat treated at atmospheric pressure. Our recent work [5,6] focused on the pressure effect on the phase transformation between the ␥-Ni matrix, ␥ -Ni 3 (Al, Ti) for a directionally solidified (DS) nickel base superalloy, GTD-111. It was noticed that the precipitation of ␥ phase under high pressure resulted in an improvement in the mechanical properties.…”