On the potential of magnetron sputtering for manufacturing of thin high Mn TWIP steel foils

Some high manganese austenitic steels are mechanically metastable. The addition of some alloying elements in the steel may result in a decrease of the materials staking fault energy, inducing a modification of the plastic deformation mechanism from classical dislocation glide to twinning or martensitic transformation. Theses steels are designated as TWIP (Twinning Induced Plasticity) and TRIP (Transformation Induced Plasticity) steels and show at different extents a very high strength and an excellent ductility. These materials are thus particularly appropriate for the forming industry. However, thin foils of these steels are not available due to the difficulty of rolling down TWIP and TRIP steel sheets to the desired thickness (15–30μm), which implies to regularly recover the original austenitic structure through several heat treatments. Moreover, most of the technical literature on the topic deals about samples with thicknesses around 1mm. Hence, very little is known about the behavior of TWIP and TRIP steel foils at the micrometer scale. In this study, magnetron sputtering was used to manufacture 30μm 25Mn-3Si-3Al steel foils and the influence of the process characteristics, in particular the target power, the roughness of the substrate and several annealing treatments on the tensile properties and the microstructure of theses foils was investigated. Scanning electron microscopy was employed to reveal the changes of morphology while the evolution of the microstructure and dislocation density were followed by x-ray diffraction. •25Mn-3Al-3Si TWIP steel films were deposited on 100 μm copper foil substrate using DC magnetron sputtering.•After annealing at 773 K the copper foil was removed by etching and 30 μm freestanding TWIP steel foils were thus produced.•The influence of the substrate, annealing and sputtering power on the foil tensile properties was investigated.•The TWIP steel foils show better ductility when they are deposited on a polished substrate.•After annealing at 1073 K, the best ductility was reached, whereas lower or higher temperatures resulted in early fracture.