Influence of different laser re-melting paths on the microstructure of a spray coating: Defect prevention and tribological properties

Abstract

The laser re-melting process parameters exerted a significant effect on the improvement of microstructure defects and tribological properties of the coatings. In this paper, four different laser re-melting trajectories coating, including dot, rectangle, parallel, and circular, were provided on the Fe based Ni/WC ceramet composite coating by flame spraying. The effects of different laser remelting trajectories on the microstructure defects and tribological properties of the coatings were discussed. The results showed that the formation and development of pores and cracks could be effectively inhibited by the circular remelting trajectory. Due to the original holes and cracks existed in the flame-sprayed coating, the inhibitory effect on microstructural defects of dot re-melting coating was not satisfactory. Under the circular re-melting trajectory, the microstructure of the remelted layer was fine equiaxed crystal, and no preferred orientation or fragile interface existed in the coatings. Besides, the strengthening mechanism of the coating after laser remelting changed from the original deformation strengthening to second phase strengthening, fine grain strengthening and solid solution strengthening. The W2C and other hard phases distributed in the re-melted coatings and played a role of dispersion strengthening. The wear loss of the coating under circular remelting trajectory was 30.2% of that under spot remelting trajectory. The higher hardness, lower friction coefficient, and more precipitation of the hard phases were found in the remelting coatings under circular remelting trajectory and parallel remelting trajectory than that under other two trajectories (Figs. 6, 7, 8), which meant these two trajectories were the ideal remelting coating track.