¹Effect of sputtering parameters on Ta coatings for gun bore applications, DW Matson et. al., Surface Coatings and Technology (in press).

Time, money, and materials are unnecessarily wasted when galling prevents equipment from being disassembled or results in excessive friction that causes equipment to perform poorly. Thin, highly adherent engineered surfaces of soft metals (such as gold and silver) significantly reduce the risk of galling under harsh conditions where conventional lubricants are often not effective. These harsh conditions include elevated temperature, heavily loads, and long periods of time where the interface remains stagnant. The thin metallic films create a substantial "contrast" in the chemical composition and physical properties between the two contacting surfaces and were applied using the PlasmaBond process. This metallurgical contrast results in a gall-resistant interface. Typically the temperature of the substrate increases by only a few degrees during deposition so it is possible to deposit adherent metal surfaces on plastic or elastomeric substrates without changing their bulk physical or chemical characteristics.

Laboratory tests have been developed to assess the galling resistance of these soft-metal engineered surfaces under simulated service conditions. These tests include disassembly of heavily loaded bolts from steel blocks that had been heated for a month, measuring fastener performance (the conversion of applied torque to fastener preload) on successive assembly cycles, and measuring friction between a valve stem and packing over thousands of valve strokes. For threaded fasteners, the test objectives have focused on assembling leak-free gasketed joints and on trouble-free disassembly of gall-prone joints. Each of these test programs included both high-quality conventional lubricants and soft-metal engineered surfaces. TXU Electric began using components with soft-metal engineered surfaces in its generating stations in 1992. This field experience confirms that soft-metal engineered surfaces are more effective against galling than conventional lubricants in harsh conditions.

The oxidation resistance of steel substrates used for mechanical applications may be enhanced not only by plasma diffusion process, but also hard coating deposition. It is well-known that transition metal nitride coating such as TiN, CrN and TiAlN are widely used for mechanical applications. Especially TiN is often deposited on cutting tools such as mills and drills, whereas CrN is rather used for forming applications such as drawing dies and moulds. Cathodic arc deposition process is a powerful and commonly used technology. For such hard coating deposition it offers a wide range of advantages. However, nitride coating, which have good tribological properties, are rarely developed for hot temperature applications and, in most cases, it is difficult to both provide good oxidation resistance of a coating and keep its surface mechanical behavior.

In this study the Cr-Al-N and CrN/AlN films were deposited on the working tool steels (AISI H13steel) by cathodic arc plasma deposition (CAPD) process. The Cr-Al-N films were deposited under various Al concentrations of 20% to 60%. Relative chemical compositions of the deposited Cr-Al-N films were evaluated by EDX as well as AES. The microstructure and morphology were studied by XRD and SEM respectively. The microstructures of Cr-Al-N films were strongly depended upon target current ratio of the chromium and aluminum. Moreover, we found that the microhardness of the Cr-Al-N films were higher than that of the CrN film.

Nano-scaled super-lattice CrN/AlN films were deposited by jig rotation speed control. Lattice images of CrN/AlN films were observed by HRTEM. Micro-hardness of the super-lattice CrN/AlN coatings(Hk 4000) was greater than that of multi-components Cr-Al-N coatings(Hk2400-3500). Detail results including oxidation behavior will be presented.