Solidification of alloys is a complex phenomenon arising in many modern experimental techniques and industrial technologies related to casting and surfaces processing. The variation of different conditions of solidification (such as undercooling or cooling rate) gives a possibility to control the morphology and size of crystal structure, which substantially influence physical and chemical properties of alloys. In particular, deep undercooling of alloys below equilibrium liquidus, and eutectics results in rapid solidification and yields materials with improved mechanical, magnetic and electrical properties. The proposed 3 year project is a collaboration between Canada and France involving three teams of researchers. We will generate powder and spray formed samples using Impulse Atomization (IA) - a single fluid rapid solidification technique (Canada). Al-Cu(Sc) alloys will be generated. The latter is expected to be supersaturated in the alpha matrix due to undercooling. Pilot tests on strip casting will also be carried out at Novelis. The solidified samples will be characterized using SEM, X-Ray diffraction, differential scanning calorimetry and microhardness (Canada). In addition, state of the art characterization such as 3D-micro and nano-tomography and Neutron Diffraction will be carried out (Canada and France). The Collaborators all have experience in these areas as well as have been working together for over a decade. Finally, the internal dendritic structure and the shrinkage porosity of a rapidly solidified droplet and skin of the cast strip will be modeled using the level set method (France). The characterization data collected will be used to verify the models. We will provide a basis for understanding the solidification structure resulting from casting processes such as strip casting, rheo-casting and spray deposition where cooling rates and heat fluxes are similar to IA. The proposed alloy systems are important for automotive applications where Canada plays a major role in production and manufacturing. Two graduate students and one undergraduate will be trained in Canada.

"Nowadays, the forming process steps and the design phases of real parts are most of the time unrelated. The mechanical design of these components under service conditions does not account for the thermomechanical and microstructural history of the materials used. This leads sometimes to approximate estimations of their mechanical strengths and to too high safety coefficients. Recently, some numerical simulation forming process codes allow to estimate the mechanical properties of a component after the forming process. They also give information on the microstructure with regard to the thermomechanical conditions used during the process. The damage fatigue models (low cycle and high cycle fatigue regimes, uniaxial and multiaxial loading conditions) and the related design codes, do not yet use these informations as input data. It is now important to identify the principal mechanical and microstructural characteristics induced by the forming process and playing a role in the fatigue strength. This knowledge will make possible the increase of the fatigue model predictivity and will lead to consider the process phase as the previous step of the fatigue design approach. The DEFISURF project main objective is to carefully study the effects of the surface defects and microstructural heterogeneities on the fatigue damage mechanisms of forged components in order to give better predictions of their mechanical properties and conduct the best possible design. It is more exactly planed to analyze and model the influence of the surface state (microgeometry, gradient of microstructure, residual stresses intensity and distribution) on the fatigue behavior of forged parts generally highly loaded. This project is composed of several tasks dealing with: 1. The assessment of the principal defects (geometrical and metallurgical) occurring in forged parts together with their origins 2. The estimation by relevant techniques (that can be used in the industrial framework) of the defects distribution in a component 3. The use of advanced experimental devices (tomography, EBSD 3D, nanoindentation …) to characterize surface geometrical and metallurgical defects 4. The fatigue testing under different loading modes and path of three steels showing different defect contents and shot-peening conditions (residual stresses distribution, surface hardening …) 5. The numerical modeling, at the microscopic and the macroscopic scales, of the nucleation and growth of different defects along the forming process steps 6. The numerical modeling, at the microscopic and the macroscopic scales, of the fatigue response of different steels showing several defect and microstructural heterogeneities content. Different loading conditions will be applied like very high compressive loading for the rod."