Temperature profile, microstructural evolution, and wear resistance of plasma-sprayed NiCrBSi coatings under different powers in a vertical remelting way

Abstract

The remelting of sprayed coatings was always conducted horizontally. However, the temperature profile, microstructural evolution, and the performance of the remelted coats in a vertical way are still unclear. In this work, plasma-sprayed NiCrBSi coatings were vertically remelted at 20 kW, 25 kW, and 30 kW (denoted as S20, S25, and S30), respectively, to investigate the relationship between coating temperature and remelting power by thermocouples. Optical microscopy, scanning electron microscopy, X-ray diffraction, and tribological tests were conducted to evaluate the microstructures and wear performance of the coatings. The differences in peak temperature (530 °C for as-sprayed coating, 760 °C for S20, 905 °C for S25, and 1100 °C for S30) are found in different parts of the coating during vertical remelting. The remelting process reduces the porosity, eliminates the lamellar boundary, and promotes the formation of metallurgical bonding in the coatings. However, a high remelting power may result in the loss and microstructural coarsening of the coating. Therefore, a suitable power plays a crucial role in preparing high-performance remelted NiCrBSi coating. The results showed that S25 has a 28.6% higher hardness (883 HV0.5) than the as-sprayed sample (686 HV0.5). The friction coefficient of S25 is the lowest, only about 0.6495. All coating samples show abrasive wear and adhesive wear, while severe adhesive wear is presented for S30.