The effect of the diode laser beam power on the behaviour of the ZrC powder pre-coat and the 145Cr6 steel substrate during laser processing

The paper presents both the production method and its impact on selected properties of composite coatings reinforced with hard ZrC particles. The Fe/ZrC coatings were produced using diode laser by remelting the pre-coat in the form of paste consisting of ZrC powder and binder. Different values of laser beam power (500 W, 700 W, and 900 W) and different pre-coat thicknesses (100 µm, 150 µm, and 200 µm) were used to produce the composite coatings. During all processes, the scanning speed of laser beam was 3 m/min. Laser beam spot diameter was 1 mm. Microstructure study, microhardness tests, as well as EDS and XRD analysis were carried out. The obtained Fe/ZrC coatings were also tested for the effect of the corrosive medium in a 3.5% NaCl water solution. The effect of applied parameters on wear resistance of Fe/ZrC coatings was also studied. The tribological properties were assessed both by mass loss measurement and by scanning electron microscopy. Fe/ZrC coatings produced using the highest thickness of the pre-coat were characterised by cracks arising during production process. The very high concentration of carbides and hence high hardness of the coating produced in this way contributed to it. However, a positive effect of laser beam power increase on reduction of these cracks was observed. The coatings were characterised by very high hardness, reaching in some cases even more than 2000 HV. It was found that the most favourable properties regarding both tribology and corrosion resistance were obtained for Fe/ZrC coatings produced using 150 µm of pre-coat thickness.