Compared with the conventional In 718 alloy, the addition of Al at the level of 1.24% and 1.50% greatly increases the precipitation of γ′ phase and the compact form of γ″/γ′/γ″ structure, which has been demonstrated in previous studies. The δ phase precipitation at the grain boundaries is noticeably suppressed. Large amount of Laves phase (( Fe , Ni , Cr )2( Nb , Mo )), small amount of M 7 C 3 carbide and σ phase (( Fe , Ni )( Cr , Mo , Nb )) are precipitated at the grain boundaries. After aging at 680°C, the grain boundary precipitates are increased significantly. Large amount needle-like σ phase is precipitated at the grain boundary in the alloy with 1.50% Al . After aging at 680°C for 1000h, the grain boundary precipitates are worsened further, but the coarsening of the compact form γ″/γ′/γ″ is lighter than the γ″ phase in the normal In 718 alloy. The tensile strength at room temperature and 680°C are increased due to Al increasing. While the tensile ductility and impact toughness of the alloy decrease significantly, and a sharp decrease has been found during the long term aging at 680°C. The mechanism by which Al influencing the microstructure and mechanical properties of In 718 alloy is to be discussed.
Effect of Mo on δ phase precipitation and tensile properties in cast alloy IN625