Effects of pulsed laser duty cycle on the macrostructure, microstructure and mechanical properties of TiN/Co-based cladding layers under the constant laser energy density

In this study, the macrostructure, microstructure and mechanical properties of TiN/Co-based cladding layers were investigated for different pulse laser duty cycles (95 %-50 %) under a constant laser energy density (i.e., heat input). The results indicated that under a constant laser energy density, the aggregation and uplift of TiN in the cladding layer disappeared with a decrease in the pulse laser duty cycle. The thicknesses of the cladding layer and heat-affected zone increased with a reduction in the pulsed laser duty cycle, which is related to the depression zone of the molten pool during laser irradiation. At 65 % of the pulsed laser duty cycle, TiN particles in the cladding layer were most finely and uniformly distributed, with an average grain size of 0.27 μm, forming a uniform white dendritic and WC-TiN core–shell structure. The mechanical properties of the cladding layer improved and then deteriorated as the pulsed laser duty cycle decreased. When the pulsed laser duty cycle was 65 %, the mechanical properties were optimal, with an average hardness, wear volume, and friction coefficient of 779.0 HV_0.2, 0.84 × 10⁷ μm³, and 0.34, respectively. Compared with a pulsed laser duty cycle of 95 %, the average hardness increased by 33.6 %, and the wear volume and friction coefficient were reduced by 40.0 % and 22.7 %, respectively.