Abstract
The main objective of the present work is to determine the effects of laser processing on properties of WC-Co electro-spark deposited (ESD) coatings on steel substrates. Tungsten carbide coatings have been applied to steel substrates using a manual electrode feeder, model EIL-8A. The laser beam processing (LBP) of electro-spark coatings was performed using an Nd:YAG fiber laser. The microstructure and properties of laser treated/melted coatings were evaluated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), surface geometric structure (SGS) and roughness measurements and adhesion, microhardness, residual stresses, corrosion resistance and application tests. The obtained experimental data were subjected to statistical analysis and multidimensional numerical and visual exploratory techniques. It has been shown conclusively that the laser-treated ESD WC-Co coatings are characterized by lower microhardness, higher resistance to corrosion, increased roughness and better adhesion to the substrate. LBP homogenizes the chemical composition, refines the microstructure and heals microcracks and pores of ESD coatings. The laser treated ESD WC-Co coatings can be used in frictional sliding nodes (e.g., on the front seal rings used in pumps) and as protective layers.
Highlights
Surface layers with a specific structure and properties are usually produced on machine elements in various processes before they are used in practice
It is assumed that the use of tungsten carbide electrodes will broaden the application areas of WC-Co coatings after laser processing, e.g., in drilling tools used in the mining industry or press elements in the fabrication of structural ceramics, sealing technologies, tools for plastic treatment and etc
The measurements of residual stresses in electro-spark deposited (ESD) WC-Co coatings were carried out before and after laser treatment using the Waisman–Phillips method based on the Sachs– Davidenkov theory
Summary
Surface layers with a specific structure and properties are usually produced on machine elements in various processes before they are used in practice. In this article the laser beam processing was carried out in order to improve the application properties of ESD WC-Co coatings. The main objective of application of a laser beam was to reduce structural defects in coatings, to develop favorable compression stresses within the subsurface layer and to improve adhesion to the substrate material and anticorrosion properties. It is assumed that the use of tungsten carbide electrodes (manufactured with the pulse plasma sintering method) will broaden the application areas of WC-Co coatings after laser processing, e.g., in drilling tools used in the mining industry or press elements in the fabrication of structural ceramics, sealing technologies, tools for plastic treatment and etc. The measurements of residual stresses in ESD WC-Co coatings were carried out before and after laser treatment using the Waisman–Phillips method based on the Sachs– Davidenkov theory. The cathodic and anodic polarization curves were acquired by polarizing the tested specimens at 0.2 mV/s (within the area of ±200 mV from the corrosion potential) and 0.4 mV/s (within the area of higher potentials)
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