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Fatigue testing and properties of hardmetals in the gigacycle range
Kotas, Agnieszka Betzwar; Danninger, Herbert; Weiss, Brigitte; Mingard, K.P.; Sánchez, José; Llanes Pitarch, Luis Miguel
Universitat Politècnica de Catalunya. Departament de Ciència dels Materials i Enginyeria Metal·lúrgica; Universitat Politècnica de Catalunya. CIEFMA - Centre d'Integritat Estructural i Fiabilitat dels Materials
Hardmetal products are frequently fatigue loaded in service, such as e.g. cutting tools for milling or percussion drills. In the present work, the fatigue behaviour of hardmetals was investigated into the gigacycle range using ultrasonic resonance fatigue testing at 20 kHz in push-pull mode at R = - 1. Liquid cooling was afforded using water with addition of a corrosion inhibitor. Hourglass shaped specimens were prepared, the surface being ground and polished with subsequent stress-relieving anneal to remove the high compressive residual stresses introduced during grinding. S-N curves with fairly low scatter were obtained, which indicates microstructure-controlled and not defect-controlled failure. Low binder content as well as fine WC grains were found to improve the fatigue endurance strength. In no case, however, a horizontal branch of the S-N curve was observed, i.e. there is no fatigue “limit” at least up to 1010 cycles. The initiation sites were in part difficult to identify; in such cases when the site was clearly visible, decohesion of the binder from large WC grains seems to have caused crack initiation. This further corroborates that microstructural features and not singular defects as e.g. inclusions are the initiation sites, which underlines the high purity of the hardmetal grades used. Based on fracture mechanical consideration a damage diagram was determined allowing to deduce critical defect sizes.
Peer Reviewed
Àrees temàtiques de la UPC::Enginyeria dels materials
Materials--Fatigue
Carbides
Gigacycle fatigue
WC-Co hardmetals
Ultrasonic fatigue testing
Fatigue endurance strength
Fracture mechanics
Crack initiation
Materials -- Fatiga
Materials durs
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info:eu-repo/semantics/submittedVersion
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