The morphology and characteristics evolution of MC carbide during homogenization in hard-to-deform superalloy GH4975

Abstract

Microstructure control of hard-to-deform nickel-base superalloy with high content of γ′ phase is a hot topic, while the characteristic of MC carbide is often ignored. In present work, the morphology and characteristic evolution of MC carbide in a typical hard-to-deform superalloy GH4975 during high temperature homogenization is investigated by multiple characterization methods. The effect of MC carbide characteristic on deformation coordinate of the alloy is also studied by Gleeble isothermal hot compression. The precise chemical formula of MC carbide in as-cast GH4975 alloy is determined by precise micro-chemical analysis to be (Ti0.474Nb0.361Mo0.029W0.129)C. Typical morphology of MC carbide in as-cast alloy is large irregular particle with sharp corners and the elastic modulus of carbide is much higher than that of matrix. The morphology and elastic modulus of MC carbide result in apparent crack during hot deformation. The weight fraction of MC carbide decreases by 1/3 after 1180 ℃− 50 h homogenization. Chemical composition of MC carbide changes during homogenization with rejection of W and Mo to make the phase more stable. The morphology of MC carbide tends to be round to lower Gibbs free energy and elastic modulus decreases at the same time. No crack is detected during hot compression in homogenized sample. The morphology and elastic modulus evolution of MC carbide during homogenization increase the deformation coordination of the alloy. Hence, enough attention should be paid on MC carbide in wrought superalloy in the investigation of microstructure control.