Fatigue Properties of a Ck45 Steel Coated with a Post-Heat Treated Ni-Cu-P Electroless Deposit

Abstract

The Fatigue tests under rotating bending conditions have been conducted on samples of a quenched and tempered Ck45 steel in two different conditions: (a) uncoated, (b) coated with an electroless Ni-Cu-P deposit, followed by a post-heat treatment (PHT) at 673 K for 1 h. Such a deposit had a thickness of approximately 10µm, with Cu and P contents of 6wt.% and 13.7wt.% respectively. The results indicate that plating the base steel with this kind of deposit leads to a reduction of the fatigue life of the material. The reduction in fatigue life has been quantified in terms of the Basquin parameters of the materials tested under different conditions. The microscopic observation of the fracture surfaces of the samples indicates 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 surface crack source or surface notch, which decreases the fatigue life of the coated material by reducing the crack nucleation stage.