Thermal Stability of Cathodic Arc Vapour Deposited TiAlN/AlCrN and AlCrN/TiAlN Coatings on Tungsten Carbide Tool

Abstract

TiAlN/AlCrN and AlCrN/TiAlN bilayer coatings were deposited on tungsten carbide cutting inserts using the plasma enhanced physical vapour deposition process. Their thermal stability was varied by annealing the specimens at different temperatures and time durations. The thermal stability was evaluated from hardness measurement, oxygen absorption and X-ray diffraction (XRD) patterns. TiAlN/AlCrN coating initially shows an increase in hardness, but it decreases when the annealing temperature is increased. A high hardness of 46 GPa is measured in the TiAlN/AlCrN coating annealed at 600 °C for 08 h. But, AlCrN/TiAlN coating displays a decrease in hardness after annealing at 600 °C, and the hardness increases to 47 GPa on increasing the annealing temperature further (1000 °C for 6 h). From weight measurements, it is clear that the TiAlN/AlCrN bilayer coating results in weight reduction initially, but it increases with a further increase in the annealing temperature. In contrast, in the AlCrN/TiAlN coating, the weight increases monotonically, but gradually, with increasing temperature of annealing. The XRD results are discussed with reference to the different oxide phases formed in the two bilayer coatings during annealing.