Influence of WC/Co Coating on Fatigue Performance of 300M Steel at Stress Level Close to Fatigue Limit

The effects of both WC/Co spray coating and chromium electroplating on the fatigue performance of 300M low alloy steel were investigated at the stress level close to fatigue limit.The fatigue strength of WC/Co coated specimen,chromium electroplated specimen and 300M substrate was 753,600 and 720 MPa respectively.The fatigue life of WC/Co coated specimen at stress level close to fatigue limit was 1.5-2 times of the substrate,and 8-10 times of chromium electroplating coated specimen.The main crack initiator,composed by alumina and silica,was found in the substrate,and that the crack in the chromium electroplating extended through the interface,finally into the substrate and formed new sub-crack initiators at the substrate surface,which hastened the formation of main crack initiator and the extension of main crack in substrate.However,the sub-crack in WC/Co coating deflected at the interface,propagated through its interface,which finally led to spalling from substrate.