Preparation And Properties Of Cr-Si-N Superhard Nanocomposite Coatings

As the surface protection for the cutting tools, coatings are playing important roles in significantly improving the properties and enhancing the life-span of the tools. Some traditional coatings, like the TiN and CrN, were widely used in various industrial applications. However, their applications are limited to the severer condition of the cutting environments and the higher demands of machining accuracy, which ultimately leads to the development of coatings with multi-elements and various enhanced properties. The nanocomposite coatings are the most promising, because their composite structure of thin amorphous matrix and crystalline effectively hinders the crack formation and propagation in the coatings, contributing to the significant enhancement of properties. Among all of the the nanocomposites, the nc-MeN/a-Si3N4 which consists of nanocomposite structure of nanocrystalline(nc) transition metal nitride(MeN) embedded in a thin amorphous(a) matrix Si3N4, is widely investigated and applied. In our work, two kinds of methods were adopted to obtain Cr–Si–N coatings and some of the key parameters were explored to optimize the coatings. Besides, by adopting the multi-arc ion plating, aluminum and oxygen were added to the Cr–Si–N coatings separately to obtain the Cr-Si-Al-N and Cr-Si-O-N coatings. The goal was to achieve the multifunctional coatings, and some of the properties of the coatings were also investigated and confirmed.The Cr–Si–N coatings were synthesized by the multi-arc ion plating and the main objective was to study the influence of bias voltages and arc currents on the coatings. The results showed that the Cr–Si–N coatings were consisted by composite structure mentioned above. The coatings deposited under bias voltage of-100 V and arc current of 70 A were well optimized. The coatings remained stable after annealing under 800℃ for 2 hours in the air but the structure were destroyed after the 1200℃ annealing.Also, the Cr-Si-Al-N coatings were obtained by the multi-arc ion plating, the results showed that the oxidation resistance of high-temperature of the obtained Cr-Si-Al-N coatings were significantly improved, which remained stable even after the 1200℃annealing. However, the properties of the deposited Cr-Si-O-N coatings were plummeted after the addition of the oxygen.At last, the Cr–Si–N coatings deposited by a hybrid coating system, the contents of Si on the obtained coatings increased with the increase of Si current. The deposited coating is composed of CrN nanocrystals with amorphous Si3N4. The Si content plays a critical role on the microhardness of the as-deposited coatings. The friction coefficients of Cr–Si–N coatings were reduced with the increase of Si content. The coatings remained intact after annealing under 800℃ for 2 hours but the external oxygenated coatings tended to be peeled off after annealing under 1200℃.