Pulsed laser processed NiCrFeCSiB/WC coating versus coatings obtained upon applying the conventional re-melting techniques: Evaluation of the microstructure, hardness and wear properties

Abstract

In the present work, the influence of pulsed laser re-melting on the structure, hardness and wear resistance of Ni-WC metal matrix composite (MMC) coatings was investigated. The NiCrFeCSiB/40%WC powder was used for experiments. The microstructural analysis upon applying the scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometry was conducted along with microhardness measurements and wear resistance tests. The obtained properties of laser-processed layers were compared with the analogical coatings re-melted using three different conventional heating techniques. The evolution of the structure in Ni-WC layers during heating was studied and it was found that upon using conventional heating techniques, the optimal microstructure of the WC containing Ni-based coating that provided the highest hardness (~880 HK) and the best wear resistance was obtainable in a narrow range of heating duration. An incomplete re-melting process results in an absence of metallurgical bond between coating and substrate. When overheated, tungsten carbides dissolve in metal matrix. The laser processing provided stable ultrafine W-rich dendrites in Ni-rich matrix microstructure of deposited layer, which morphology did not change significantly with variation of the process parameters. The size of the finest tungsten-rich particles was about 200 nm and the hardness reached ~990 HK, providing 12–31% improvement as compared with the best results of induction, furnace, and flame heating. The wear rate of laser processed coating was 12% (by mass loss) and 42% (by thickness of removed layer) lower as compared with the highest results for conventionally heated coatings.