Precipitation behavior of grain boundary M₂₃C₆ and its effect on tensile properties of Ni-Cr-W based superalloy

Precipitation behavior of grain boundary (GB) M₂₃C₆ and its effect on tensile properties at elevated temperature were investigated systematically in a Ni-Cr-W based superalloy. The results show that the M₂₃C₆ precipitation behavior is influenced obviously by grain boundary character (GBC) and interfacial energy. The Σ≤9 GBs and low angle GBs have low interfacial energy, and no M₂₃C₆ carbide precipitates at these GBs. Plenty of M₂₃C₆ carbide particles precipitate at the large angle GBs with high interfacial energy. The coherent orientation relationship between M₂₃C₆ and the matrix plays an important role on the precipitation morphology of M₂₃C₆. M₂₃C₆ carbides with four typical morphologies distribute at the large angle GBs, including lamellar carbide which grows into the matrix near one side or both sides of the GBs, rod-like carbide and small lamellar carbide both of which grow along GBs. Moreover, the decrease of both tensile and yield strength of the aged alloy is mainly caused by the lamellar M₂₃C₆ carbide breaking. The tensile properties vary irregularly with increasing aging time.