Subsurface phase precipitation induced by oxidation of TNM alloy under high-temperature tensile

The diffusion of oxygen (O) and nitrogen (N) elements in the environmental atmospheric from surface defects into the subsurface results in the evolution of lamellar structure, forming an oxygen affected layer (referred to as AL) at the subsurface. A comprehensive investigation was conducted to understand the phase precipitation in the AL of TNM alloy after oxidation at 900 °C under high-temperature tensile. In the AL, the dispersed distribution of oxygen (O) and nitrogen (N) elements leads to the redistribution of elements in the lamellae, impeding the precipitation of β₀ phase and inducing the precipitation of Ti₂AlN both in the α₂ and γ lamellae. Due to the difficulty in elements diffusing from the γ lamellae to the α₂ lamellae, aluminum elements accumulate in the [011]γ lamellae, the (111) plane atom shear through 1/6[11 2‾], leading to the precipitation of [110]γ variants. The interface between [011]γ and [110]γ variants is pseudo-twin, which almost arrests crack propagation. The Ti₂AlN precipitation region, adjacent to the phase boundaries and dislocation entanglement, can also impede dislocation motion inside [110]γ variants. The synergistic effect of Ti₂AlN precipitates and the superior deformation ability of [110]γ variants slow down the movement of dislocations and improve the deformation ability of the oxidized lamellar structure in the AL.