Effects of Different Microstructural and Hardness Gradients Generated by Single and Combined Surface Treatments with a Nitriding Top Layer
This contribution utilizes the depth-dependent microstructure within the treated surfaces and the resulting hardness-depth profiles to discuss the relevant wear and corrosion mechanisms active in surfaces produced by single and combined treatment. The core interests comprise the morphology of the ledeburite (especially the orientation and size of the carbides) in the EB remelted layer, the composition and distribution of phases (γ’-, ε-nitrides), as well as the thickness of the compound and diffusion layers formed after nitriding. In this context, the often controversial role of the typically high silicon content of cast iron during nitriding – including the effect of the formation of silicon nitride on the hardness profile and, therefore, the wear behavior – was analyzed. Furthermore, the significant influence of the nitriding process used (plasma nitriding, gas oxinitriding) on both the layer structure and the load behavior was observed. For the gas oxinitriding process, the special role of the near-surface oxide layer was also examined.
Finally, the potentials and limitations of the single and combined surface treatments with respect to the improvement of the tribological and corrosion load behavior of cast iron were derived based on a cross-evaluation of the results of the treatments investigated.