Papers by Author: Francis Delannay

Abstract: Mg-Al-Zn alloys have been reinforced with carbon fibres using either the liquid state process of squeeze casting (SC), or friction stir processing (FSP), a solid state process developed more recently and that appears as a promising alternative for the large-scale production of C-Mg composites. Both processes have shown their ability to produce sound composites with enhanced strength compared to the non-reinforced alloys. In SC composites, the unsized woven C fabric remains intact while in the FSP composites the sized C fabric is fragmented in short fibres, with an aspect ratio typically equal to 4, homogenously distributed in the Mg alloy matrix.

Abstract: Twinning-Induced Plasticity steels (TWIP steels) are extensively studied due to their ultra-high strain-hardening rate, that brings about a remarkable combination of ductility and strength. Twinning can be observed in high manganese-carbon steels. This paper considers hardening by combination of mechanical twinning with carbide precipitation. The kinetics of precipitation and the morphological evolution of carbides with annealing time were studied for two different TWIP steels with high manganese and carbon contents. The steels are first cold-rolled and then annealed at 800°C for recrystallization and carbide precipitation. Depending on the steel composition, the kinetics of precipitation and the morphology of the carbides are quite different. The influence of the annealing cycle on the mechanical properties has also been assessed. The results are used to discuss the influence of composition, stacking fault energy (SFE) and carbide precipitation on twinning. We show that the usual criteria based on the SFE only are not sufficient to characterize the twinning ability of a steel.