# Application of Directed Energy Deposition-Based Additive Manufacturing in Repair
## 1 Introduction  
It has been reported that to markedly mitigate climate change, the level of material and energy used in the current manufacturing methods should be reduced. Indeed, almost 30% of total greenhouse gas (GHG) emissions belong to the industry. The main part of this significant fraction of industrial GHG emission is coming from the material processing. In general, material processing involves the conversion of natural resources into materials stocks followed by the manufacturing process and ultimately into the final products. By developing the new generation of manufacturing techniques, it would be possible to reduce the level of GHG emissions [1; 2; 3]. Following the recent research in the development of production processes, additive manufacturing (AM) technologies have been introduced as new techniques that can support environmental sustainability in manufacturing field [1; 4; 5]. AM technologies, like advanced manufacturing technologies, are capable of producing high-value, complex, and individually customized components [6; 7; 8; 9; 10; 11]. After producing and placing the components in service, local impact, corrosion, fatigue, and thermal cycles are the main working conditions that can cause local defects or cracks. For instance, in turbine shafts and blades, cracks can be initiated due to high-cycle fatigue (HCF) or corrosion. It is reported that several high-performance and high-value components are discarded as scrap after failure, which is mainly initiated by fatigue and stress cracks. Several types of research have beencarried out to reduce the level of failure and increase the lifetime of the components. For example, ultrasonic and x-ray computed tomography techniques are established as non-destructive methods to detect subsurface defects in components at the initial stages to prevent failure during the working period [12; 13; 14; 15]. Thereafter, depending on the level and location of damages, the part is prepared for repair. Repair and remanufacturing are processes restoring damaged parts to a workable condition. For the first time, in 1988, [PERSON] and [PERSON] defined the remanufacturing process as an industrial process to restore the used components to 'as good as new' condition [16]. According to the Steinhilper procedure, the steps of the remanufacturing process can be defined as (1) disassembling of the product, (2) comprehensive cleaning of all parts, (3) inspection of components, (4) repairing or replacement of damaged components, (5) reassembling the product, (6) final testing. After that, in 2015, the Ellen MacArthur Foundation showed that in some cases, repaired components could behave better than manufactured ones. They defined the refurbishment as the process that could be used to recover the products by repairing or replenishment of major parts. After recovering the components, in addition to the small changes that could be occurred within the process, their performances, in the best condition, could be as same as a new component. This recovery of the component, which was defined as refurbishment, is also known as the reconditioning process. In 2006, [PERSON] et al. defined a procedure to correct some specific faults in a component and named it as'repairing'. They showed that the final performance of repaired products was less than of the reconditioned or remanufactured parts [17]. When a part is damaged, its damage must be assessed from the repairing point of view. After this assessment, it would be possible to decide that the damaged part could be repaired or should be discarded or send for recycling. To bring back the recoverable parts, an appropriate repair or remanufacturing methods should be employed and thereafter, some qualify controlling must be implemented on the repaired part to evaluate its reliability to work in the working condition. From the theoretical point of view, it is believed that the remanufacturing process can be implemented on the components that are feasible to be produced.