Die Materials Modulated Pulsed Power Magnetron Sputtering for Die Surface Engineering

The utility of hard tribological coatings based on transition nitrides (e.g. CrN, TiAlN, CrAlN, etc.) as protective layers on various forming tools (e.g. die and its components used in high pressure die casting) has led to improvements in increased die life, reduced machine down time, and improved product quality. Moreover, recent advances in the coating design made it possible to obtain nanoscale multilayer and nanocomposite coatings that exhibit outstanding multifunctional properties to meet a wide range of demands including high hardness, good toughness, chemical inertness, and good thermal stability, in comparison to traditional monolithic/single phase coatings.1, 2 Besides the coating architecture design, the deposition technique has strong effects on the structure and properties of the coatings. So far, traditional physical vapor deposition techniques, including continuous dc magnetron sputtering (dcMS), pulsed dc magnetron sputtering (PMS), cathodic arc evaporation (CAE), and ion plating have been the major techniques used for the die casting surface engineering. As compared to the evaporation techniques, the ions generated in the magnetron sputtering plasma can be controlled to bombard the growing film surfaces with tailored energies, which increase the adatom mobility and favor the growth of metastable phases in a non-equilibrium condition. It can be foreseen that an even greater advantage can be achieved if the target material itself is ionized. Unfortunately, the ionization degree of the deposition materials in the dcMS and PMS plasmas is very low (<5%). The CAE technique has been a primary competitor to sputtering over the past twenty years. Originally developed in the Soviet Union, CAE quickly gained acceptance as an industrial process because of its low cost of implementation using low voltage and high current power suppliers in the 1980’s. CAE is an evaporation-like process in which a high current (hundreds of amperes) dc arc is struck on a metallic cathode surface, where the arc interacts with the cathode surface vaporizing the cathode materials with a high power density at the contact point3. Due to a high-power density on the arc electrodes, the CAE process is characterized by a combination of a high deposition rate and a high degree of ionization of evaporated species, which makes this process a versatile deposition technology for producing well adherent and dense metal and compound films such as TiN, CrN, Ti-Al-N and their variants for industrial applications. The main disadvantage of CAE deposition is the production of macroparticles due to the high power density on the cathode. These macroparticles become embedded in the films with a typical size from 0.2 to several micrometers (μm). These macroparticles are undesirable since they will degrade the uniformity of the film surface and impair the quality and properties of the deposited coatings. The macroparticle emission from the cathode spot can be greatly reduced or removed from the arc plasma by several approaches during plasma transport to the substrate, of which a magnetic filter with a positive bias has been the most successful that is known as filtered cathodic arc deposition (FCA). However, the FCA process is limited by its poor thickness uniformity resulting in difficulties to deposit multilayer films, and it will only work with limited coating materials.4