Abstract
The influence of applied stress ratio on the fatigue strength of carbon steel coated with TiN was studied on the basis of the measurement of crack initiation by the DC potential method. Fatigue tests were performed under the stress ratios of R=0 and -1 in air by using the round notched specimens of 0.37% C steel normalized, JIS S35C, coated with TiN by PVD and CVD. From the experimental results, increase of fatigue strength was observed in TiN-coated specimens under the tests of R=-1, as compared with that of the uncoated specimen. However, the fatigue life of coated specimens by PVD was decreased under the tests of R=0, except for the region of low stress amplitude. Moreover, the fatigue life of specimens coated by CVD under R=0 was smaller than that of the uncoated one. The difference of fatigue life with applied stress ratio is explained by the fracture behavior of coating film on the specimen surface.
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