Investigating the Effect of Phosphorous Content and Heat Treatment on Structure, Hardness and Wear Behavior of Co-P Coatings

Amorphous, nanocrystalline and mixed amorphous-nanocrystalline Co-P coatings were successfully coated on St37 via DC electroplating method using various phosphorous (P) content in coating compositions. In addition to phosphorous content, heat treatment caused structural changes of the alloy coatings. The effect of changes in the P content and hence phase structures were studied prior and post heat treatment on the hardness and wear resistance of the coating. A scanning electron microscope (SEM) with high resolution (HR-SEM) equipped with an energy dispersive spectroscope (EDS) and an X-ray diffraction (XRD) system were used to study the surface morphology and phase structure as well as the chemical composition of the coatings, respectively. Micro-hardness and wear resistance of the coatings were measured via Vickers hardness system and pin on the disc test, respectively. The results showed that by increasing P content, the coating micro hardness was in turn increased due to a remarkable enhancement of the hardness of the solid solution and that was applicable for the coatings after heat treatment because the interstitial phases productions. In the beginning and prior to the heat treatment by increasing the P content up to 5.6%, the wear behavior of the coatings was improved substantially, while at further P content, the wear result started to decline. However, after heat treatment, there was a direct relationship between the wear resistance and P content. Also the maximum hardness and wear resistance belonged to the amorphous coatings after heat treatment.