ICMCTF2001 Session B4-1: Emerging Technologies & Critical Issues in Vapor Deposition

In Practical Applications on Precision Components, Carbon-based coatings can mainly be divided into coatings with addition of other elements like metals (Me-C:H), and pure, amorphous a-C:H coatings. More advanced, H-free films of very high hardness are also possible, but have no significance on precision components until yet but are used for special tools today.

Carbon-based coatings deliver advantages regarding friction behaviour, dry and lubricated running, abrasive wear resistance, resistance against scuffing and seizure, and corrosion. Carbon coatings can decrease cost in running, design and maintenance, increase lifetime, improve service behaviour and enable higher performance of tribological systems. Carbon-based coatings can provide the automotive and other industries with improved performance on precision components in tribological applications. This broad range of properties improve the surface characteristics of selected functional surfaces and parts. Additionally, the performance of systems is enhanced by increased fuel efficiency, increased technical system performance and lower running cost.

Coatings on the basis of Me-C:H have superior frictional properties. The friction coefficient dry against steel is found to be between 0.1 and 0.2. This means a much improved frictional behaviour compared to the uncoated tribological system. This type of coating is becoming widely distributed in industrial applications, where protection against adhesive wear, scuffing and seizure, increase of lifetime and improvement of sliding behaviour is required. An overview about todays market will be presented.

The metal-free a-C:H coatings (DLC) have a higher hardness than Me-C:H-coatings, due to high internal stresses and do not show a nanolayered structure, since the growth mechanism is significantly different from the Me-C:H-process. The high hardness gives the base for a much higher abrasion resistance in tribosystems with highly abrasive tribocomponents. Thus the friction coefficient can be similar to Me-C:H systems, depending on the partners in the tribosystem. Historically, the higher internal stresses led often to problems with the adhesion of the coating to the substrate. With a suitable process, this problem can be overcome and also the deposition of a coating thickness up to 10 microns is technically solved, without having to compromise the hardness of the coating. Advantages of the new Balzers Balinit DLC will be presented and market expectations will be discussed.

Me-C:H and a-C:H systems show significant differences regarding structure, properties and behaviour. The coating structure is a very important variable for the performance of the coating in a tribosystem. The relationship between structural features of the coating families and the tribological behaviour in selected tribological systems was investigated using modern FEG-SEM and supported by additional results from tribological benchtests. The results thereof will be discussed.

DLC coatings are the most suitable coatings for industrial applications , where high wear resistance and low friction are needed. Nevertheless, because of their weak adhesion to steel substrates , and the coatings have not been able to have wide applications.

Adhesion strength of DLC-Si(Silicon-containing DLC) coating on steel substrates has been remarkably improved by a special activation process for the substrate surface prior to the DC-PACVD DLC-Si coating operation. The coating has the critical load (Lc) as high as over 50N in a scratch test and did not spall off in the application tests whereas the conventional DLC coatings easily spalled off.

The activation process consists of pre-liminary nitriding and ion-etching and needs no intermediate layers of Si and SiC . The process is continuously followed by DLC-Si coating within the same DC-PACVD equipment.

The DLC-Si coating shows tribological properties different from those of conventional DLC coatings: high resistance to wear and siezure, and low friction in poor lubricate atomspheres (such as dry, water gasoline, light oil etc.).

The process features considerably higher deposition rate (5µm/h), larger throwing power, and lower equipment cost and treating cost comparing to conventional method like as RF-PACVD and sputtering etc. Therefore, it has a large potential for wide applications in various industries including automobile.

The process of adherent DLC-Si coating and the tribological performance of DLC-Si coated parts will be presented.

In recent years, a great attention is devoted to the development of magnetrons with (i) enhanced ionization to realize sputtering at low pressures (≤ 0.1 Pa) and (ii) high target power loading (W_t ≥ 100 W/cm²) to form films with high deposition rates (a_D ≥ 1 µm/min) and to realize self-sputtering when the sputtering discharge is sustained in the vapor of sputtered material and the films are formed from ions of sputtered material. Present sputtering systems, however, suffer from two fundamental drawbacks: (1) contamination of the discharge with material sputtered from the rf coil used to enhance ionization in the ionized magnetrons and (2) gas density reduction in front of a target of the magnetron operated at high values of W_t. The second phenomenon can result in decrease of the deposition rate or even in interruption of the magnetron discharge, i.e. cw operation can be converted into pulse mode of operation. Therefore, new magnetrons which avoid these drawbacks are strongly required.

The article reports on the magnetron with a gas injection through hollow cathodes machined into the sputtered target. The hollow cathodes in the form of cylindrical holes with an optimum diameter d are located along the magnetron racetrack on the radius of maximum erosion. The neutral gas, which is fed directly into holes, is ionized in the hollow cathode discharges. The reduction of gas density at high target loadings (W_t > 100 W/cm²) is automatically completed from the holes. The injection of the ionized gas into interior of the discharge considerably changes operational characteristics of the magnetron. The current-voltage (I-V) characteristics of a round planar magnetron with the target of diameter 100 mm equipped with holes of diameter d are given. A comparison with a conventional magnetron is carried out and advantages of a new magnetron are outlined. As example, the sputtering of nitride films using this new magnetron is also shown.