Internal nitridation behavior during long-term creep in a nickel-base superalloy

A complex internal-nitridation zone was formed at the near-surface and at the front of crack tips after long-term creep in Udimet 500 superalloys. In this internal nitridation zone, both of large blocky AlN and needle TiN phases precipitation at the expense of the dissolution of γ phase accompanied by the outward diffusion of these elements. Applied stress promotes the internal nitridation development, while the contents of Al, Ti and the stress level have little effect on the internal-nitridation depth in this experiment range. High temperature and long creep time result in a greater thickness of the internal nitridation zone, even up to 654 μm at 900°C/53 MPa.