Pancake-like antiphase domains in perfect nitrogen-expanded austenite by TEM characterization

Abstract

Elongated superstructure diffraction spots were observed in perfect nitrogen-expanded austenite without stress or plastic strain, which was prepared by plasma-based low-energy nitrogen-ion implanting Fe-Cr-Ni austenitic alloy foils at low temperature of 380 °C. The Fe _4 N-like ordered nitrogen-expanded austenite ( γ ′ _N ) antiphase domains formed in the disordered nitrogen-expanded austenite ( γ _N ) matrix. Only the high Cr-content alloys presented elongated diffraction spots. The reconstruction of the diffraction spots strength distribution shows an elongated egg-shape in reciprocal space. This elongation corresponded to a pancake-like antiphase domains distribution in matrix, which was confirmed in dark field images as a lamellar structural feature. The Cr-N short-range ordering (SRO) and anisotropic elastic module rather than the constrained strain in the γ _N phase layer determine the formation of γ ′ _N antiphase domains.

Keywords

• expanded austenite
• austenitic stainless steel
• nitriding
• antiphase domain