Influence of initial microstructure on the γ′-coarsening behavior in a corrosion-resistant Ni-based superalloy

Abstract

To clarify the initial microstructure dependent γ′-coarsening behavior, a corrosion-resistant Ni-based superalloy with the varied γ′-size were prepared by changing the primary aging heat treatment temperature. The microstructural evolution was investigated during long term thermal exposure (up to 3000 h) at 900 °C and 1000 °C, respectively. It was found that Cr, Co, and Mo preferentially partition to γ-matrix, while Ta, Ti, Al, Ni, and W partition to the γ′-phase. The abnormal partition of W to the γ′-phase can be attributed to the low content of Ta in CM247 LC alloy. Furthermore, the γ′-coarsening behavior can be divided into two stages. During the early stage of coarsening (<1000 h), the coarsening rate obeys the classical LSW model with the cube rate law. As the increase of the initial γ′-size, the γ′-coarsening rate obviously increases, which can be mainly attributed to the increased solute diffusion capability in the γ-matrix and the higher γ'/γ interfacial energy. By contrast, there is an apparent γ′-coalescence during the later stage of coarsening (1000 h–3000 h). The temperature plays a more dominant role on the γ′-coarsening rate than the duration times during thermal exposure.