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.
COBISS.SI-ID: 28797479
Fatigue damage is a parameter which plays an important role in lifetime and reliability predictions of randomly loaded structures. In this paper, four different forms of the Miner linear accumulation damage rule are examined. They are used to compare observed experimental damage and the results of numerical simulations for both uniaxial and multiaxial fatigue. First, critical fatigue damage values for all forms of the Miner accumulation damage rule are calculated for uniaxial cases. Based on the results presented in this paper, it has been established that for high strength materials the critical damage value is around 0.3. These results are then applied to the multiaxial cases. The multiaxiality is taken into account using either the signed von Mises or critical plane method. Finally, the fatigue fracture surface has been calculated and compared to the experimental pattern of fatigue fracture. The results show that the fatigue fracture surface determined by the numerical simulation is comparable to the fatigue fracture observed experimentally.
COBISS.SI-ID: 14219547