Study On Microstructure And Properties Of Ni60A Laser Cladding Layer Strengthened By Ceramic Particles

In the field of petroleum, chemical, long-distance pipeline, shipbuilding, nuclear industry, cryogenic engineering, aerospace and marine oil and so on, economic losses caused by wear and corrosion of key components were very large.Therefore, it has remarkable economic benefit to make laser cladding layers on surface of these workpieces in order to increase their wear resistance and corrosion resistance. In this paper, Ni60A+WC composite cladding layers were made on surface of Q345steel by the use of laser cladding technology. Moreover, microstructure and properties of the cladding layers were systematically investigated by means of Optical microscopy (OM), X-ray diffractometer(XRD), scanning electron microscopy (SEM), micro-hardness tester, dry sliding wear tester and electrochemical test system.The influence of process parameters on surface formation and quality of cladding layers was studied. The test results showed that,the layers were provided with excellent properties and fabricability with large areas when the pcocessing parameters were at laser power of2500W, scanning speed of300mm/min, shield Ar gas flux of15L/min, preset layer thickness of about1mm, overlapping ratio of30%.The influence of the contents of components in alloy powder were studied on cladding layers. Affected by rapid heating of laser source and rapid cooling of workpiece, organizations of the cladding layers directionally grew along the opposite direction of temperature gradient beginning from interface to face of cladding layer. The growth forms of organizations were plane crystal, dendritic columnar crystal, cellular crystal, small dendrite cystal and exquiaxed crystal in turn. When content of WC was low, appearance of Cr, B compound zone aggravated the the heterogeneity of organizations in cladding layer; when WC content was30wt%, organizations of cladding layer were composited of fine and uniform y-(Ni,Fe) dendrites, interdendritic eutectic, rich tungsten blocky precipitates.The influence of different contents of WC on wear-resistant of cladding layer were research. With the increase of WC content, the wear resistance of cladding layers increased while the wear mechanism transformed from micro-cutting to abrasive wear. Because of high hardness and rich hard phases, the cladding layer with30wt%WC content was hard to be micro-cut so it showed excellent wear-resistance. Under the wear condition, the weight loss of composite cladding layer was only1/15of Q345substrate.The influence of different contents of WC on corrosion resistance of cladding layer were research. When WC content was low, the corrosion resistance of Ni60A+WC composite cladding layers was lower than Ni60A cladding layer because there was serious heterogeneity among organizations in composite cladding layers. When the WC content was25wt%, corrosion resistance of cladding layer improved because of fined microstructure, uniform components and the reduction of potential difference among organizations which had enhancement of the solubility of W,C; proceeding to add WC, corrosion resistance of cladding layers slightly decreased because the increase of WC content and precipited ceramic phases increased the number of original battery. When WC content was25wt%, the corrosion mass loss rate of cladding layer was only1/54of Q345substrate.