Plastic strain of cobalt-based hardfacings under friction loading

Abstract : Aeronautic forging dies are subjected to very high loads and temperatures for a long contact time between the pre-heated parts and dies. Cobalt-based hardfacings are commonly deposited on dies and their main wear mechanism is large plastic deformation of the die radii. This paper deals with the wear damage mechanisms of three different cobalt-based hardfacings: Stellite 21 deposited by a MIG process, Stellite 21 and Stellite 6 deposited by a LASER process. The tribological tests are carried out on a high load Ring on Disc tribometer at room temperature. The postmortem investigations are undertaken by SEM observations, micro-hardness measurements as well as by X-ray diffraction analyses. Results show that the increase of the hardness, in order to improve the wear behaviour, can be achieved by a higher carbon content and by a lesser iron dilution that depends on the deposition process. A very important work-hardening, up to 90%, is also observed under sliding conditions and a relationship is established between the increase of the micro-hardness and the plastic strain level. Two different plastic strain mechanisms are observed. For high (MIG) or low (LASER) iron dilution levels, the plastic strain causes respectively a reorientation of grains or a FCC to HCP phase transformation; the latter being associated with a lower friction coefficient.
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https://hal.archives-ouvertes.fr/hal-01611012
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Submitted on : Wednesday, September 19, 2018 - 11:08:07 AM
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Elodie Cabrol, Christine Boher, Vanessa Vidal, Farhad Rezai-Aria, Franck Touratier. Plastic strain of cobalt-based hardfacings under friction loading. Wear, Elsevier, 2015, 330 (SI), p. 354-363. ⟨10.1016/j.wear.2015.01.082⟩. ⟨hal-01611012⟩

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