Understanding Microstructure Evolution and Control During Hot Deformation: Application to Solid State Joining of High Strength Alloys

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In recent years, the advent of new solid state joining technologies such as Friction Stir Welding (FSW) and Linear friction welding (LFW) have opened new avenues in process development, particularly, in the areas of net shape manufacturing which are of very high interest to industry. In both processes, frictional heat softens the surfaces to be joined and the application of a forge pressure plasticizes the interfacial region and consolidates the joint.3D printing of metallic materials has been proved to be one of the best ways to improve design, reduce manufacturing cost of high value added products and develop more efficient and higher performance components. However, one of the major short comings of 3D printed components is their cast structure. These structures are inherently characterized by heterogeneous microstructures and non-uniform distribution of chemical elements (micro and macro segregation). One of the innovative approaches, introduced recently, has been to use the 3D printed part as a preform and then deform it to reach the final shape. This approach has the great advantage to convert the inhomogeneous cast structure to a more isotropic and homogeneous one (wrought structure). Such data generation will significantly expand the application of 3D printing technology to a large number of components where cast structures can't be accepted because of service conditions.From a scientific point of view, it is therefore, very important to understand the fundamental mechanisms governing microstructure evolution of 3D printed materials as a function of hot deformation process parameters. The present research program has been defined in this context and has for objective to study the hot deformation behavior of 3D printed Ni base superalloys with the view of developing the knowledge base for the manufacturing of 3D printed blades to forged disks using the Linear Friction Welding technique which is a modern manufacturing technology in the aerospace industry.To this end, the evolution of the microstructure will be studied using optical, scanning (EBSD) and TEM. Based on these results and the developed expertise during the previous studies a microstructural model will be developed that would take into account the mutual interactions between the microstructures of the two materials. The model will also include the kinetics of phase transformation, recrystallization, microtexture changes, and second phase precipitation in each material and their mutual influences. The FEM software FORGE NXT will be used to assess the validity of the model. Finally, post weld heat treatment will be applied and its influence on mechanical properties of the joint including fatigue life will be examined. Two PhD and two MSc along with 5 undergraduate students will be trained during the next five years.