Unveiling the transformation pathways of hierarchical γ

Deformation-induced martensitic transformation (γ-austenite → ε-martensite/α’-martensite) in austenitic steels has garnered significant interest owing to its transformation-induced plasticity effect. To elucidate the orientation-dependent intricate γ/ε/α’ phase microstructure at deformation-induced...
Ausführliche Beschreibung

Deformation-induced martensitic transformation (γ-austenite → ε-martensite/α’-martensite) in austenitic steels has garnered significant interest owing to its transformation-induced plasticity effect. To elucidate the orientation-dependent intricate γ/ε/α’ phase microstructure at deformation-induced ε-ε intersection, a single crystal of 316 austenitic stainless steel was compressed along the [001]γ axis at a cryogenic temperature (173 K). Electron backscattered diffraction analysis was employed to reveal the deformed microstructure on the (110)γ surface. A hierarchical triple phase structure was discovered at ε–ε intersection, where the γ rotated 90° from the matrix (γ90), { 10 1 ¯ 2 } ε-twin, and α’ phases coexist. Depending on the operative shear angle with a common intersection axis, either 90° (Type I) or 30° (Type II), three distinct atomic rearrangements of the intersection volume were observed: γ90 was present at Type I intersection, and α’-phase was developed at Type II intersection, respectively. { 10 1 ¯ 2 } ε-twin also occurred at Type I intersection, serving as an accommodation mechanism alongside the intersection γ90. EBSD results confirm the Shoji–Nishiyama (SN), Kurdjumov–Sachs (KS), and Burgers (B) orientation relationships within the complex γ – ε – α’ triple phase structures at ε–ε intersection. Transformation paths for three intersection products were visualized by the unified tetrahedron model, considering T/2 or T/3 γ-twinning shear as an intermediate state. Moreover, a novel scheme is proposed to index the α’-martensite crystallographic variants at ε-ε intersections by establishing a correlation between the Bain distortion and double shear process. Ausführliche Beschreibung