Excess deposition for suppressing interfacial defects induced on parts repaired using direct energy deposition

While repairing parts using direct energy deposition (DED), defects, such as pores and cracks, can occur at the interface between the substrate and the area to be repaired. Such interfacial defects are due to the thermal stress induced by the temperature gradient resulting from repeated melting and solidification cycles during the powder deposition by laser. These cracks deteriorate the mechanical properties of the repaired parts. This study reports on the suppression of cracks formed at the interface of parts repaired using DED. To this end, excess deposition was introduced such that the deposition volume is greater than the volume to be repaired, to cool down slowly. The excess deposition was performed by varying the width and height of the repairing volume. The experimental results showed the formation of macro-scale cracks in the absence of excess deposition, whereas only micro-scale cracks (10 μm or less) were observed in the repaired sample with a low repair depth in the presence of excess deposition. The cooling rate decreased with the increase in the excess deposition height for the same volume; this is believed to have helped suppress the cracks formed at the interface. With the increase in the height and width of excess deposition, no hardness variations were observed in the deposited layer; however, the hardness values of the substrate tended to decrease. The tensile strength and elongation of the specimen repaired with excess deposition increased by 112 and 175%, respectively, compared with those of the specimen repaired without excess deposition.