Rolling contact fatigue mechanism of a plasma-sprayed and laser-remelted Ni alloy coating

The rolling contact fatigue behaviour of the plasma-sprayed and laser-remelted Ni-Cr-B-Si alloy coatings under two different tribological conditions of contact pressure was investigated. Two sets of fatigue-life data of coatings were characterized by Weibull distributions. The failure mode of the coatings was identified on the basis of worn morphologies as observed at the surfaces of the failed coatings. The tribological mechanism leading to the formation of the fatigue spall was discussed on the basis of the subsurface morphologies observed in the failed coating. Experimental results showed that, the mean life and characteristic life of the coating decreased with increasing the contact pressure. The failure of the coatings can be termed as spalling-type failure. A refined 'ring-crack model' was proposed to explain the formation of the fatigue spall. In the refined model, it was postulated that the joining of the ring-type cracks and subsurface branched cracks was directly responsible for the spall formation.