Laser metal deposition of cermet material such as tungsten carbide-cobalt (WC-Co) is a promising means of improving the wear resistance of metal products. However, laser metal deposition of WC-Co has constraints on its practical use because a clad bead of WC-Co often includes numerous pore defects.


Our group has revealed that CO gas generation in a molten pool by reaction of carbon and oxygen was main reason of gas porosity in a WC-Co clad bead. Moreover, we have demonstrated that the addition of elements with strong affinity for oxygen such as aluminum was effective for porosity reduction in a clad bead. However, the addition of high reactive pure aluminum particles on WC-Co powder has difficulty for industrial use.


In this study, zirconium diboride (ZrB₂), a chemically stable compound, was used as an additive to WC-Co powder. WC-Co powder with adherent ZrB₂ particles was prepared by wet granulation process and laser metal deposition was conducted. Zirconium stemming from the dissolution of ZrB₂ in the molten pool was found to have effect of trapping oxygen elements as solid zirconium oxides. As a result, the gas generation in the molten pool by the reaction of carbon and oxygen was restrained and the clad bead having few pores and fine microstructure was obtained. From the observation of the molten pool behavior using a high speed camera, we revealed that ZrB₂ addition drastically improved the process stability as compared to the process using conventional WC-Co powder.