The Research Of The Microstructure And Mechanical Properties Of TiN/TaN Multilayers

Property anomaly of nanoscale nitride/nitride multilayers makes it possess important values in theoretical investigation and practical application in engineering, which arouse much attraction. Therefore, isostructural TiN/TaN mutilayers has been deposited by magnetron sputter deposition technique. Their microstructures, mechanical properties including hardness, modulus, and tribological properties are investigated.The results reveal that the single-layer films of TaN_cub are more easily deposited under lower N₂ atmosphere or higher deposition power. Phase composition of TaN_hex is appeared with enhanced N₂ atmosphere or reduced deposition power, and excessively high deposition power will result in appearance of Ta₂N. Both the TiN layer and TaN layer within the mutilayer of little modulation period show cubic structure, superlattice is formed. Modulation structure affects the growth behavior and mechanical properties of TiN/TaN multilayers. Interface stress of TiN and TaN layers is an important factor the influence the growth behavior. Modulation structure not only changes growth rate, but also affects preferred growth direction. It is found that the multilayer has two kinds of independent modulation structures with [111] and [100] normal to the films, with slightly different modulation periods. Modulation period in 6nm, the hardness and module of the multilayers are increased by about 50% and 30%, respectively. The maximum values appear at the modulation ratio of 3:1, hardness, 34.2 GPa and modulus, 344.9 GPa. The hardness and module maximum value of TiN/TaN multilayers is 39.54GPa and 450.50GPa when modulation period is 9.07nm and the hardness of multilayers is increased by 100%. We discuss the hardening mechanism of TiN/TaN multilayers based on the analysis of structure and mechanical properties. The results indicate that the coherence strain effects are the main factor, and grain refinement and preferred oritantion of the multilayers also play an important role in the hardness. Despite the coefficient of TiN/TaN mutilayered films is lower than that single layer TiN coating, the wear rate of TiN/TaN is considerably lower than TiN during dry sliding. The wear mechanism mainly consists of ploughing, adhesion and local spalling.