EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Fatigue properties of hard metals are a concern in many of its applications. However, due to its low ductility and limitations in physical design fatigue testing may be difficult to carry out. Long life endurance, as in the Very High Cycle Fatigue (VHCF) range, is also of relevance in many hard metal applications as for metal cutting tools used in milling or intermittent cutting processes. Thus, it is crucial to acquire a deep understanding of their mechanical fatigue characteristics. The VHCF phenomenon covers lifetimes exceeding 107 cycles. At these life lengths time and cost constraints rule out the use of conventional fatigue tests, and high frequency cyclic loading using ultrasound oscillators becomes a viable testing method.

In the present effort, the VHCF properties in bending fatigue of Co/WC hard metals are assessed. Three sets of hardmetals were studied where WC fraction and grain size were varied. A 3-point bending fatigue test rig and bar specimens of rectangular cross-section were designed to operate in resonance at 20 kHz load frequency at R=0.1 loading. Fatigue strength at 108 load cycles was evaluated using the staircase test method, and with subsequent SEM-fractography to determine fracture mechanisms. Characterization of the different Co/WC microstructures was performed by SEM/EBSD analysis. Finally, the effect of microstructural features as inclusions and defects on VHCF behavior of the hard metal sets was discussed in detail.