Impact of fracture toughness on surface properties of PVD coated cold work tool steel

Limited load-carrying capacity and impact loading resistance greatly restrict the use of hard coatings in forming applications, making substrate hardness and resistance crack initiation and propagation very important. Therefore, the aim of this research work was to investigate the effect of substrate fracture toughness and hardness on the load carrying capacity and impact wear resistance of coated tool steel, coated by monolayer (TiAlN), multilayer (AlTiN/TiN) and nano-composite ((Ti,Si)N) PVD coatings. By using different combinations and parameters of vacuum heat treatment and deep cryogenic treatment effect of the substrate fracture toughness and hardness on the load-carrying properties was determined under progressively loading dry sliding conditions, while ball-on-plate impact fatigue test was employed to investigate impact wear resistance. Results clearly show, that substrate hardness is the most important property influencing load-carrying capacity and impact wear resistance of the coated surface. However, with increased hardness and brittleness of the coating increase in fracture toughness although on the expense of the reduced hardness becomes beneficial.