Eddy-Current Testing of Fatigue Degradation in Additionally Heat-Treated Gas Powder Laser Clad NiCrBSi Coating under Contact Fatigue Loading

摘要

The paper studies the applicability of eddy-current technique to testing fatigue degradation in Ni-18.2Cr-3.3B-4.2Si coating, produced by gas powder laser cladding and subjected to additional high-temperature annealing at 1025 °C, under contact loading. It is demonstrated that eddy-current testing of fatigue degradation inNi-18.2Cr-3.3B-4.2Si coating under contact loading after high-temperature annealing has certain limitations caused by the high brittleness of this coating. In this case, it is possible to test only a sharp increase in the sizes of contact damages, which occurs at 8×10~5 cycles under these loading conditions and results from the formation of a great number of peripheral ring cracks in the fracture zone; the eddy-current readings a decrease due to the increasing electrical resistivity of the coating. Testing can be performed by eddy-current measurements at high excitation frequencies of an eddy-current transducer (f=72-120 kHz), when the effect of the ferromagnetic steel base on the eddy-current readings a is minimum.