Deformation Mechanisms and Plasticity

On the different alloys studied, thermomechanical treatments were carried out in order to obtain various crystallographic textures. The influences of texture change on mechanical properties were thus highlighted. In addition, the deformation microstructures were observed by EBSD and MET (Conventional and In-situ Transmission Electron Microscopy) in order to precisely characterize the plastic deformation mechanisms. In beta-type titanium alloys, very high ductility was thus achieved. In the field of health, devices often have complex shapes and having a very high plasticity allows easier manufacturing. The deformation mechanisms of these alloys were therefore studied in order to highlight the different modes of accommodation of the deformation (slippage, maclage). 

Work was carried out at the experimental and numerical level on the cold extrusion test. A die has been designed and built to study this metal forming process. Emphasis was placed on identifying the rheological and tribological properties of a light alloy (AA5083 series aluminum). The study was conducted on this type of material, rather than on a material with a compact hexagonal structure (titanium or zirconium), to allow a better confrontation with  the many studies mentioned in the literature. X-ray diffraction and backscattered electron diffraction (EBSD) were used to characterize the global and local textures of deformed specimens as a function of extrusion rate. From the experimental curve giving the extrusion force as a function of the imposed displacement, the tribological parameters were determined by inverse analysis. The parameters obtained were also validated through measurements  with a tribometer.  

Some compositions of titanium-based alloys have revealed in a very original way TRIP-TWIP effects (transformation-induced plasticity and twinning-induced plasticity) due to the multitude of deformation mechanisms that operate simultaneously. These studies were conducted on a new family of titanium-based alloys that has emerged in recent years: Gum Metals. These alloys which have exceptional mechanical properties, , have been referred to as Ideal Engineering Alloys by the scientific community. Indeed, some compositions (Ti-Nb-O) have a very low modulus of elasticity, a very high yield strength combined with a ductility much higher than that of other titanium-based alloys available on the market. These alloys are thus promised to many industrial applications and in particular in the aeronautical and medical sectors.