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 Fe4N-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.