Thermal Stability of Plasma-Nitrided Layer on Surface of GH2132 Fe-Based Superalloy

Low temperature plasma nitriding was conducted on the surface of GH2132 Fe-based superalloy at 723 K, and then the nitrided tested alloy was treated at different temperatures (673,873,973 K) for 5 h. The sectional morphology, phase composition, hardness and corrosion resistance of the nitrided layer before and after treatment were analyzed. The results show that the nitrided layer on the surface of GH2132 Fe-based superalloy was mainly composed of supersaturated solid solution of nitrogen in austenite, namely expanded austenite γ_N phase. The thickness of nitrided layer increased with increasing heating temperature. The γ_N phase was undecomposed during heating at 673 K. During heating at 873, 973 K, the γ_N phase was decomposed to γ_N phase with lower lattice expansion and CrN phase. The lattice expansion rate of γ_N phase decreased with the increase of heating temperature. The hardness of nitrided layer was firstly increased then decreased with increasing heating temperature, and reached to the largest of 926 HV during heating at 873 K. The corrosion resistance of nitrided layer after heating at different temperatures for 5 h all decreased.