레이저 클래딩 공정 조건이 코발트 합금-텅스텐 카바이드 혼합 코팅층의 균열 발생에 미치는 영향

Abstract

In this study, cracking susceptibility of laser cladding was investigated according to the processing parameters such as laser power, scan speed and feeding rate with blended powders of stellite#6 and technolase40s(WC+NiCr). The solidification microstructure of clad was composed of Co-based dendrite structures with γ+Cr7C3 eutectic phases at the dendritic boundaries. The crack propagation showed transgranular fracture along dendritic boundaries due to brittle chrome carbide at the eutectic phases. From results of fractography experiments, the fracture surface was typical cleavage brittle fracture in the clad and substrate. The number of clad cracks, caused by a tensile stress after the solidification, increased with increase of laser power, scan speed and feeding rate. Increase of the laser power caused large pores by facilitating WC decarburizing reaction. And the pores affected increase of crack susceptibility. High scan speed caused increment of clad cracks due to thermal stress and WC particle fractures. Also, increase of the feeding rate accompanied an amount of WC particles causing crack initiation and decarburizing reaction.