Lüders-like martensitic transformation in a Cu/carbon-steel nanocomposite: An in situ synchrotron study

A Cu/carbon-steel nanocomposite is fabricated by pressing, rolling and wire drawing. The average layer thickness is about 69 nm for steel and 67 nm for Cu. Cu suppresses the growth of prior austenite at elevated temperature, and thus the steel layer thickness barely increases during austenization. Subsequent quenching results in a large amount of metastable retained austenite within the steel layers. The martensitic transformation behavior of the composite during plastic deformation is investigated by in situ tensile test using synchrotron X-ray diffraction at room temperature. It is found that the retained austenite, rather than Cu, dominates the plastic deformation of the nanocomposite. In situ results verify that the transformation of retained austenite initiates in a manner of Lüders-like band due to stress-induced martensitic transformation, followed by strain-induced martensitic transformation until fracture.