Fatigue testing and properties of hardmetals in the gigacycle range

Author(s)
Agnieszka Betzwar Kotas, Herbert Danninger, Brigitte Weiss, Ken Mingard, Jose Sanchez, Luis Llanes
Abstract

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.

Organisation(s)
Physics of Nanostructured Materials
External organisation(s)
Technische Universität Wien, National Physical Laboratory (NPL), CEIT, Universitat Politècnica de Catalunya
Journal
International Journal of Refractory Metals and Hard Materials
Volume
62
Pages
183-191
No. of pages
9
ISSN
0263-4368
DOI
https://doi.org/10.1016/j.ijrmhm.2016.07.004
Publication date
01-2017
Peer reviewed
Yes
Austrian Fields of Science 2012
103018 Materials physics
Keywords
ASJC Scopus subject areas
Ceramics and Composites, Mechanics of Materials, Mechanical Engineering, Metals and Alloys, Materials Chemistry
Portal url
https://ucris.univie.ac.at/portal/en/publications/fatigue-testing-and-properties-of-hardmetals-in-the-gigacycle-range(ee37d50d-0c23-4e05-af68-7d1de9b4655b).html