Fatiga de contacto por rodadura en acero SAE 1050 recubierto con TiN, posteriormente templado

AUTOR(ES)
FONTE

Matéria (Rio J.)

DATA DE PUBLICAÇÃO

19/07/2018

RESUMO

ABSTRACT The use of ceramic coatings of the nitride, carbide, or diamond type on steel substrates promotes the improvement of tribology properties. Nevertheless, high hardness gradients and adhesion problems may deteriorate the performance of these coatings when subjected to Rolling Contact Fatigue (RCF). Some studies on steels with ceramic coatings were carried out on steels that sustain hardness at elevated temperature. In the present study, a low cost steel, SAE 1050 was used with a combined surface treatment consisting of a TiN Physical Vapor Deposited (PVD) coating plus a subsequent induction hardening, in order to give the coating high substrate hardness, necessary to withstand the contact stresses. The proposed treatment sequence (different to that usually employed as quenching + PVD), was intended to sustain the high hardness of the quenched steel, even though the consequences on the previous PVD coating are unknown. The tests to evaluate RCF were carried out with a washer type fatigue tester in which a disc sample is rotated under load against a thrust bearing acting as a counterpart. All the system is lubricated by immersion in ISO VG 100 industrial oil. The RCF life values for the individual tests were statistically analyzed and the wear tracks were studied by optical and scanning electron microscopy. Also mappings by X-ray dispersive spectroscopy (EDS) were carried out. The proposed sequence for the surface treatment allowed to obtain some of the typical improvements for coatings as for example those related to low friction, adhesion and abrasion resistance, without impairing the RCF resistance. These benefits are possible even tough plain medium carbon steel was used. X ray diffraction analyses were also carried out in order to evaluate the coating degradation after quenching.

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