Mechanische Bruchuntersuchungen zur Ermittlung der Haftfestigkeiten von WC-Co-Schichten auf Metallsubstraten

摘要

Metals often require coatings with wear resistant metals like ceramics or WC-Co for applications in mechanical engineering. Due to the different classes of materials of substrate and coating in these systems, the mechanisms of adhesion available are mainly mechanical interlocking bonding. In this paper a process is described, which makes use of these bonding mechanisms to apply mainly WC-Co coatings by a thermal sprayed process (HVOF). In order to assess the adhesive strength of the coatings a fracture mechanical test was developed. Furthermore it is shown that some reliable and numerical effective local energy method (crack closure integral method), which offer special advantages for mixed-mode fracture analysis of inhomogeneous materials, like WC-Co coated metals, work well successful. This is done by the finite element analysis of a modified compact tension specimen, the MOCH-specimen. In addition to that, the adhesive strength of the WC-Co layers is optimized by a variation the parameter of the thermal spread process. The results show different criteria of failure, as there is premature crack propagation depending on spread parameters and the damaging of the composite material accompanied by low energy release rates and low adhesive strength.