Investigation on creep properties and microstructure evolution of GH4169 alloy at different temperatures and stresses

Abstract

Creep is an inevitable problem in the design and maintenance of modern high-temperature machinery. Accurate understanding of the mechanism and law of material creep failure is the basis of structural creep performance evaluation. The microstructure of GH4169 alloy after creep at 873.15 K and 923.15 K was analyzed by OM, SEM, EBSD and EDS. In addition, the effect of different grain sizes on the creep behavior of the material and the ability of the phenomenological model to describe the creep curve are also discussed. The results show that there are inclusions formed by Nb and Ti inside the alloy, and local stress concentration is caused during the creep deformation and crack propagation, which leads to the initiation of microcracks or voids. The microstructure of the material before the third stage of creep or far away from the creep fracture is not much different from the original material. The initiation and propagation of cracks and crystal slip mainly occur near the fracture surface. During the creep process, oxygen will combine with aluminum element on the surface of the material to form an alumina layer, and cracks are mainly initiated at the interface between the oxide layer and the matrix. When the crack penetrates the oxide layer, oxide particles will be formed on the grain boundary. The grain size studied in this paper have little effect on the creep strain and rate curves. The results of grain refinement are mainly reflected in the slight increase of creep fracture strain and life. The constitutive model used according to the creep failure process of the material can describe the whole creep curve.