Investigation of bonding strength and failure mechanisms for sustainable free-form remanufacturing via laser directed energy deposition.

The repair and remanufacturing industry is a key contributor to the green technological revolution in manufacturing. Laser Directed Energy Deposition (LDED) is one of the most suited techniques for remanufacturing complex 3-D parts. The localized repair of a free-form component requires the nozzle to be inclined, which can affect the deposition process and the bonding strength. Once repaired, the functional performance of the restored part strongly depends upon the quality of the bond between deposition and substrate. Typically, the determination of bonding strength involves using epoxy for carrying out the tensile test or machining the deposition to carry out shear tests, which are not very effective in determining the bonding strength of ultra-high strength depositions like CPM 9V steels used in remanufacturing. Hence, a novel 'tapered key in a slot' specimen is specially designed to measure the bonding strength of high-strength depositions. The effect of various LDED parameters on the bonding strength of the deposits has been characterized via a designed experiment. Detailed fractography of the failed specimens exhibited three distinct failure patterns: melt interface (MI), deposit-substrate interface (CSI), and deposit cross-section (CC). MI failures occur at low deposition heights and low melt depths. CSI failures are observed at higher deposition heights, and low melt depths and CC failures occur above a critical combination of deposition height and melt depth. These specimens were analyzed for residual stresses, material composition, and porosity. The most prominent failure pattern MI (∼63%) could be attributed to a synergistic effect of peak tensile residual stresses, a sharp transition in the concentration of hard vanadium carbide particles, and intergranular porosity. Based on this study, a set of process recommendations has been developed for sustainable remanufacturing. [Display omitted] • Developed a novel 'tapered key in a slot' technique for determining bonding strength of ultra-hard deposits via DED. • Fractography studies of failed keys identified three primary bonding failure modes: MI, CC and CSI. • Intergranular porosity, residual stresses, and VC concentration were investigated in the dpeosition and substrate. • MI mode occurs most frequently due to a synergistic interaction of residual stresses, VC diffusion, and micro-cracks. [ABSTRACT FROM AUTHOR]