Microstructure and sliding wear behaviour of Tribaloy T-800 coatings deposited by laser cladding

This work has focused on the obtainment of Tribaloy T-800 coatings by laser cladding on plane 18/8 stainless steel specimens (AISI 304). The appropriate selection of cladding parameters allowed defect-free coatings to be obtained with minimal dilution. In order to evaluate their microstructure, cross-sections of the coatings were examined by optical microscopy and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The elemental composition of the coatings was determined using an optical emission spectrometer with an excitation source (GDOES) and phase analysis was performed by X-ray diffraction (XRD). Several zones can be distinguished in the microstructure of the clad layer: a planar crystallization region at the interface with the substrate, followed by cellular and dendrite crystallization from the interface to the surface of the laser track and an overlap zone between tracks which is characterised by the coarsening of the structure and the formation of a lamellar eutectic phase. The mechanical properties were evaluated by hardness measurements and sliding wear tests (ball-on-disk and block-on-ring configurations) at room temperature and without lubrication. It was observed the great hardness (close to 850 HV0.3) achieved for the Tribaloy 800 laser coatings, which presented a wear coefficient (k) between one and two orders of magnitude lower than the substrate. The analysis of the clad worn surfaces showed that there was a transition from an adhesive-oxidational mechanism to a more severe plastic deformation and crack formation wear process with increasing the applied load.