Damage evolution in WC–Co after repeated dynamic compressive loading detected by eddy current testing

Abstract

The failure behaviour of WC–Co hard metals with binder contents of 6 and 12wt.% was investigated under repeated dynamic loadings. The materials were consolidated by field-assisted sintering and exhibited WC grain sizes of about 200nm. Static and dynamic strength tests on a servo-hydraulic testing machine and a modified split Hopkinson pressure bar (MSHPB), respectively, resulted in compressive fracture strengths between 4370MPa and 6660MPa depending on the Co content and the applied strain rate. Moreover, the hard metal samples were repeatedly loaded in the MSHPB below their compressive strength at different stress levels, and subsequently investigated by eddy current testing after each loading step. The measured eddy current signal was dependent on the stress level and the number of impacts. Additionally, the damage of the samples was examined with the help of images from the scanning electron microscope (SEM).Static strength tests of the pre-damaged material revealed that the residual strength of WC–6Co decreases with an increasing number of impacts. In contrast, WC–12Co shows strain hardening caused by the multiple-impact loadings. The size of the fragments revealed intensified microcrack initiation.