Mechanical and Tribological Performance of a Ni-Based Alloy Coating Deposited by Laser Directed Energy Deposition on Gray Cast Iron Substrate

Gray Cast Iron (GCI) is industrially used due to its balance between cost and properties. Large diesel engine blocks manufactured from GCI have high added value and can be repaired by the Laser Cladding (LC) with Ni-based alloys. However, LC complex thermal cycles, combined with the GCI brittle nature and the presence of graphite and impurities in its microstructure, make this task particularly demanding. This study aimed to parameterize the LC to deposit Ni-1031 alloy coatings on GCI substrates extracted from large, used diesel engine blocks. Besides parameterization, hardness and tribological performance of the coatings were investigated. LC parameters were defined through a design of experiments divided into single beads, single layers, and multilayers, in which geometric properties were analyzed as a function of laser power, travel speed, hatch spacing, and layer height. Parameters were adjusted to mitigate lack of metallurgical bonding and cracks originating at the interface with the C-rich GCI substrate. Coating microstructure exhibited refined dendritic grains. Coating hardness was higher regarding GCI, attributed to solid-solution strengthening, B and Cr-rich precipitates. Tribological performance under reciprocating ball-on-flat tests was superior for GCI, owing to a smoother contact and the lubrication provided by graphites, which reduced friction coefficient, wear rate and wear mechanisms action severity.