Abstract
In the present study, pulsed laser post-processing was applied to improve the properties of the thermally sprayed NiCrCoFeCBSi/40 wt.% WC coatings. The powder mix was deposited onto a mild steel substrate by flame spray method and then the as-sprayed coatings were processed by Nd:YAG laser. The peak power density applied was between 4.00 × 106 and 5.71 × 106 W/cm2, and the laser operating speed ranged between 100 and 400 mm/min, providing processing in a melting mode. Scanning electron microscopy, energy dispersive spectroscopy, Knop hardness measurements, and “ball-on-disc” dry friction tests were applied to study the effect of the processing parameters on the geometry of laser pass and microstructure, hardness, and tribology of the processed layers. The results obtained revealed that pulsed laser processing provides a monolithic remelted coating layer with the microstructure of ultrafine, W-rich dendrites in Ni-based matrix, where size and distribution of W-rich dendrites periodically vary across remelted layer depth. The composition of W-rich dendrites can be attributed to a carbide of type (W, Cr, Ni, Fe)C. The cracks sensitivity of coatings was visibly reduced with the reduction of power density applied. The hardness of coatings was between ~1070 and ~1140 HK0.2 and correlated with microstructure size, being dependent on the processing parameters. The friction coefficient and wear rate of coatings during dry sliding were reduced by up to ~30% and up to ~2.4 times, respectively, after laser processing.
Highlights
Ni alloy–WC metal matrix composite (MMC) coatings are widely used in various fields of industry and technology to protect the working surfaces of parts from corrosion and wear, which is primarily due to the unique properties of nickel itself and the excellent properties of tungsten carbide as a hardening phase, as well as their good compatibility—WC is well wetted by nickel alloy melts [1]
Summarizing the results presented in the abovementioned works, it can be argued that some progress has been achieved in the development of laser cladding technologies, and some solutions can already be applied in the industry
The flame-sprayed NiCrCoFeCSiB/WC coatings were postprocessed with pulsed Nd:YAG laser, and the effect of the processing parameters on the coatings’ cracking, pass geometry, microstructure, hardness, and tribology were analyzed
Summary
Ni alloy–WC metal matrix composite (MMC) coatings are widely used in various fields of industry and technology to protect the working surfaces of parts from corrosion and wear, which is primarily due to the unique properties of nickel itself and the excellent properties of tungsten carbide as a hardening phase, as well as their good compatibility—WC is well wetted by nickel alloy melts [1]. WC possesses a high melting point (2600–2850 ◦C), high fracture toughness (28 MPa·m1/2), and high hardness (16–22 GPa) [3]. It is widely recognized, as well, that cemented tungsten carbide, which is usually used in coatings, has some degree of plasticity, especially when compressive loads are applied [4]. It is shown that at the later deformation stage dislocations’ density of WC in cermet dominates, indicating a more important WC role in the plasticity than a role of a metal binder [5]. This gives an advantage to WC over brittle hard materials
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