Fatigue properties of a Ck45 steel coated with a post-heat treated Ni–Cu–P electroless deposit

Fatigue tests under rotating bending conditions were carried out on samples of a quenched and tempered Ck45 steel (AISI 1045) in two different conditions: (a) uncoated, (b) coated with an electroless Ni–Cu–P deposit, followed by a post-heat treatment (PHT) at 400 °C for 1 h. Such a deposit had a thickness of approximately 7 μm, with Cu and P contents of 6 wt.% and 13.7 wt.% respectively. The results indicate that coating of the steel with this kind of deposit leads to a reduction in fatigue life of the material. This reduction in fatigue life has been quantified in terms of the Basquin parameters of the materials tested under different conditions. Microscopic observations of fracture surface of samples indicate that the reduction in fatigue life is associated with the nucleation of fatigue cracks on the coating–substrate interface and the deposit remains well adhered to substrate during fatigue testing since interfacial cracks have been very rarely observed. It is therefore concluded that, in the present case, the interface acts as a stress concentration site or surface notch, which decreases the fatigue life of the coated material by shortening the crack nucleation stage.