Adhesion properties of TiB2 coatings on nitrided AISI H13 steel

This study investigated the effect of nitriding on the hardness and adhesion properties of TiB2 coatings. Inductively coupled plasma (ICP) was used for both nitriding and deposition. By applying ICP, H13 steel was nitrided at a high rate of 50 μm/h. After nitriding, a Fe4N compound layer or a diffusion layer was formed according to the hydrogen/nitrogen ratio. Both layers could improve the load-bearing capacity of the substrate by increasing the substrate hardness. The adhesion of the TiB2 coatings increased to ∼30N after nitriding, but the hardness of the coating was lowered to 20–30 GPa. However, the adhesion of the TiB2 coatings with a high hardness (>60 GPa) could not be improved substantially by nitriding due to the large difference in hardness between the coating and the substrate. The grain size of the TiB2 coating was larger on the nitrided substrates, resulting in a decrease in the hardness of the coating.