Hybrid Additive Manufacturing and Friction Stir Processing for Crack Repair Applications

Cracks are surface or subsurface discontinuities (fissure) that develop in the material due to mechanical, thermal, chemical loadings individual or combined. Crack repairs is a common maintenance practice in the industry. Different techniques are applied depending on the nature of the crack and the load conditions on the equipment; i.e. pressure, temperature etc. Techniques that are commonly used include but not limited to, stop-hole method, weld over lay, or patching. These methods has some limitations especially for techniques utilizing fusion-welding methods. Solid-state welding and joining technologies were developed to overcome conventional welding problems raised by melting-solidification and intensive heat input. Friction Stir Welding (FSW); an environmentally friendly process, was developed by The welding Institute (TWI) in 1991. The main objective was to join difficult to weld materials like Al and Mg alloys. With the development in FSW tool materials, the process expanded to include high strength and temperature materials such as titanium alloy, stainless steel and carbon steel. From FSW other processes were derived like Friction Stir Processing (FSP), which provide a solution for cast defects repair and altering surface/bulk microstructure as well as a process for synthase of metal matrix composites. Considering the advantages of FSW/FSP over fusion welding, the proponent are proposing to develop a hybrid method for crack repair by reinforcing crack zone with ceramic/metallic particles and process the crack zone using FSP. Although FSW/FSP has many advantages over fusion welding technologies, but it has some inherent issues. Some of these issues will be considered in this research project to ensure effectiveness of the proposed process for the application of crack repair on an industrial scale. Two inherent issues the proponent will be focusing on: first, thinning which usually occur due to FSP tool over-plunging, second is the keyhole; also called exit hole, ISO standard) left after tool retraction. Initially the process will be developed for light alloys such as AL or Mg alloys for two main reasons, firstly the ease of processing at low temperature/force; low cost tools, secondly, the research outcomes can directly serve the aviation, automotive, and Aluminium alloys rolling industries. In the proposed work, a special FSP tools will be designed considering both inherent issues described above utilizing the stat of art FSW technologies. Selection of reinforcement particles will be based on two main criteria, fabricated composite brittleness/fracture toughness and corrosion resistance. The artificial cracks will be repaired using proposed method, then after tested under different mechanical, metallurgical and corrosion tests. Mechanical testing will include both monotonic and impact tests. Based on tests findings, the process conditions i.e. tool traveling and rotational speeds, number of passes, and others will be optimized; Taguchi L9 method is proposed to minimize the number of needed experiments. The proponent believe that the proposed method can provide an environmentally friendly technology to the field of maintenance for crack repairs in different industrial sectors including oil and gas, automotive, and aviation