ICMCTF2000 Session G1: Innovations in Thin-film Manufacturing Processes

In the past few years, a sharp increase in interest for dry lubrication systems can be observed. Primary forces are exercised by ecological concerns. Also important are economics, namely the increasing cost of toxic waste treatment and having means on site to protect the workforce from the unhealthy influences of these used lubricants. paragrapph MoS₂ is one of the potential candidates to fulfil these requirements. Considerable improvements have already been obtained to make MoS₂ coatings, well- known for space applications, applicable to terrestrial systems. Multilayering and alloying with different metals are upcoming and partially already industrially-used techniques.

The basis for these improved coatings is still MoS₂ , so whatever variation will be chosen, the final macroscopic parameters of the film are determined by the MoS₂ lattice. Hardness can be considerably increase, but seems to be limited to values about 1000 HV.

This paper reports on a new way including the lubricating properties of MoS₂ into a by itself already very hard coating. CrN and TiAlN as well-known hard coatings are foreseen as basic matrix. MoS₂ is taken as solid lubricant, incorporated as nanometer-sized clusters in this hard, wear resistant coating.

These coatings were deposited on different steel substrates and were characterized for mechanical and tribological properties such as adhesion, hardness, Young ^,s modulus and friction and wear by using a variety of techniques including scratch tester, depthsensing indentation, pin-on-disk tribometer and micro-abrasion tester, respectively. The structure and composition of the films have been studied by optical microscopy, TEM, SEM, AFM, RBS, XRD, SIMS and EDX

Reactive deposition of nitrides and oxides of aluminum and other metals were done using a twin-cathode inverted cylindrical magnetron run with mid-frequency power. This geometry is particularly suited for coating three-dimensional objects of complex shape. However, high rate reactive sputtering in such an enclosed cathode has not been reported and presents unknown processing conditions. Dielectric coatings onto glass and polymer substrates have been successfully completed. Relatively high pumping speeds allow the investigation of process stability using gas flow control alone. The hysteresis behavior for the various systems studied will be presented.

Films were deposited under conditions of different pressure, power and reactive gas flow. In order to characterize the films, the reflectance, transmittance and absorbance of coatings deposited on glass slides were measured. Optical properties and deposition rates will be presented for the various conditions studied. In measuring these properties, particular attention was paid to the transition between metallic and poisoned modes of deposition. Adhesion and durability were also assessed.

Using conventional thin film technologies it is either difficult or expensive to increase the coating thickness above 5µm. On the other hand it is hardly possible to receive coatings with a thickness below 50µm using thermal spray technologies especially if bigger areas have to be coated. Due to this, application which require coatings of a thickness between 5 and 50µm are suffering from the compromises typically taken. Thermally sprayed coatings using the LPPS Thin Film technology can close the gap between thermal spraying and thin film technologies. The process is based on a low pressure plasma spray process which is modified to achieve a large plasma plume. This plasma realizes a spray spot of about 400mm diameter (15 inches) covering a rather large surface area to be coated. Using this thermally sprayed thin film technology it is possible to coat several square meters of a surface within some few minutes with a thermally sprayable material like ceramic, metal or composite.

This paper will present some aspects of the actual development work pointing out coating characteristics and analysis results of ceramic and metallic coatings. It further will provide an outlook on possible application, especially as it will be an additional coating technology rather than a competitive coating technology for conventional thin film and thermal spray techniques.

CrN/NbN superlattice coatings have been deposited by cathodic steered arc evaporation in an industrially sized PVD coater. Prior to coating the substrates were subjected to a high negative voltage of 1.2 kV steered arc chromium metal ion etching. A 0.3μm thick CrN base layer was then deposited by arc evaporation from two Cr targets to further enhance the adhesion of the coating. The CrN/NbN superlattice coating was deposited by operating two Cr and one Nb targets in steered arc mode in common nitrogen atmosphere.

Arc deposited CrN/NbN coatings exhibited single phase f.c.c. structure and strong {220} preferred orientation. A well-defined superlattice structure with pronounced healing of the growth defects originating from the arc-generated droplets was observed by the X-TEM technique. Coatings with superlattice period in the range between 3nm and 6.7nm were produced by controlling the rotation speed of the samples during the deposition process. Maximum hardness values of HK₂₅=36 GPa were obtained for coatings with superlattice period of 3.7nm. Coatings produced in two and three fold rotation of the samples showed low friction coefficient in the range of 0.3, however the wear coefficient was relatively high of 8.19.10 ^13 m² N^1. The corrosion resistance of the arc deposited CrN/NbN superlattice coating was superior to that of monolithically arc grown CrN and NbN and comparable to that of 25μm electroplated hard chrome.