Porosity reduction in WC-12Co laser cladding by aluminum addition

Abstract

Laser cladding of WC-Co cermet materials has been limited by defects such as pores and cracks. Especially, numerous pores with a large size in clad beads are typical defects in laser cladding of WC-Co, in comparison with other cladding materials. Previous studies show that pores in WC-Co laser clad beads are generated from CO gas reaction between oxygen and carbon dissociated from WC. CO gas formation also leads to decarburization of WC-Co, resulting in a brittle phase such as W2C or M6C. In this study, we attempted to add an element with a strong affinity for oxygen to reduce porosity by preventing CO gas formation. We prepared an aluminum-added stainless steel substrate by laser alloying, followed by laser cladding of WC-Co on the laser-alloyed substrate. The addition of aluminum drastically reduced pores in the clad bead. The clad bead on the laser-alloyed substrate contained Al-oxide particles with a sub-micron size. Oxygen elements can be trapped as solid state Al-oxide before CO gas formation, contributing to lower porosity. Preventing CO gas formation also resulted in the microstructure without any W2C.