Crystallography of nanometre-sized α′-martensite formed at intersections of mechanical γ-twins in an austenitic stainless steel

Nanometre-sized !′-martensites (bcc, denoted by α), a few nanometres in cross-sectional diameter, formed at intersections of deformation twins, have been found in a heavily deformed 316-type austenitic stainless steel (fcc, denoted by γ) and examined by high-resolution transmission electron microscopy (HRTEM). An orientation relationship was found to be close to the Kurdjumov-Sachs relationship, that is (111)_γ//(101)_α, [10amp;1macr;]_γ//[11amp;1macr;]_α. HRTEM observations were conducted with a beam direction parallel to [10amp;1macr;]_γ//[11amp;1macr;]_α. The observed nanometre-sized !'-martensites exhibited a (2amp;5macr;2)_γ habit plane and the (10amp;1macr;)_γ//(11amp;1macr;)_α cross-section of the nanometre-sized !'-martensites were elongated along [545]_γ. It has been revealed that the nanometre-sized !'-martensites of a few nanometres diameter formed at the intersections of deformation twins have a typical habit plane of (2amp;5macr;2)_γ, which is identical with that reported for a fully grown plate such as !'-martensite. The origin of the observed habit plane is discussed on the basis of the ⟨112⟩{111}_γ shear displacements assisting the γ → α′ transformation.