Controlling WC/Co two-phase microstructure of cemented carbides additive-manufactured by laser powder bed fusion: Effect of powder composition and post heat-treatment

In this study, an attempt is made to control the WC-Co two-phase microstructures by laser powder-bed fusion (LPBF) process using cemented carbide powders with different compositions of WC-25Co (mass%) and WC-17Co (mass%) and post heat-treatment at 1380 degrees C. The as-built cemented carbide samples had different microstructures from those of the cemented carbides fabricated by conventional manufacturing methods. The microstructures of the as-fabricated WC-25Co and WC-17Co cemented carbides were char-acterized by two types of regions. Region 1 consisted of W2C and W3Co3C phases, including numerous pores and defects. Region 2 consisted of WC and Co phases. Post heat-treatment of the LPBF-built WC-25Co sample at 1380 degrees C led to the formation of a defect-free WC-Co two-phase microstructure. In con trast, the W3Co3C phase remained in the LPBF-built WC-17Co sample even after heat treatment. The addi-tion of carbon to the WC-17Co powder prevented the formation of the W3Co3C phase in the cemented carbide processed by LPBF and subsequent heat treatments. The addition of carbon to the WC-17Co pow-der had a slight effect on the hardness of as-fabricated samples, but reduced the hardness of heat-treated samples. The reduced hardness was attributed to the increased volume fractions of the WC and W3Co3C phases. (C) 2021 The Author(s). Published by Elsevier Ltd.

Automated summary

The study successfully controlled the WC-Co two-phase microstructures through LPBF process, with post heat-treatment eliminating defects. Addition of carbon prevented the formation of W3Co3C phase, but reduced the hardness of the samples after heat treatment.