Material extrusion printing of WC-8%Co cemented carbide based on partly water-soluble binder and post-processing

Abstract

In this paper, WC-8%Co cemented carbide parts were fabricated by material extrusion additive manufacturing. Water debinding, thermal debinding and sintering were carried out to obtain densified parts. An optimized binder system consists of 50 vol% polyethylene glycol, 15 vol% polyvinyl butyral, 25 vol% high density polyethylene, 5 vol% stearic acid and 5 vol% polyethylene-wax was developed to prepare printable feedstock. The results show that polyvinyl butyral in binder is contributed to tight bonding of powders, but excessive high polyvinyl butyral content caused separation of binder and powder, inefficiency of debinding and formation of macroscopic defects. Extraction of polyethylene glycol is found to be controlled by both dissolution and diffusion. The insoluble binder can be further removed by heating, the products from pyrolysis of insoluble binder included volatile alcohols and aldehydes, carbon dioxide, hydrocarbon and water. Residual carbon and decarburization during thermal debinding can be minimized by using N2/H2 atmosphere in furnace. The complete debinding body was almost absolutely densified by sintering beyond 1340 °C. The sintered body shows a relative density of 99.0%, HV30 hardness of 1360 ± 16 and transverse rupture strength of 1678 ± 125 MPa with optimal post-processing, which are slightly inferior to those obtained by the conventional pressing method. Extrusion printing method is an alternative method for additive manufacturing of WC-Co cemented carbide with good printability and shape retention in process.