Microstructural changes and mechanical properties of AerMet100 steel surface-treated by plasma nitriding

In this work, quenched AerMet100 steel is plasma nitrided at 460 °C for 8 h in a gas mixture of 50% N₂ + 50% H₂. The microstructures and mechanical properties are investigated. Results show that the current nitriding conditions can effectively inhibit the formation of brittle white compound layer in the surface of AerMet100 steel. Further investigations on orientations of martensite laths and prior austenite confirm that all 24 variants of martensite laths produced by one prior austenite grain follow the K[sbnd]S orientation relationship and this relationship holds during nitriding. Besides, a memory phenomenon that the orientation of precipitated γ′-Fe₄N is exactly the same as that of prior austenite is observed, due to the strong variant selection. Compared with the un-nitrided specimen, the microhardness of AerMet100 steel after nitriding treatment is remarkably improved, and volume wear rate is reduced by an order of magnitude. Such a large improvement is primarily attributed to a desirable combination of high surface hardness, considerable nano-grains and secondary hardening of the substrate.