K. H. Kloos

Fundamental properties and wear resistance of r.f.-sputtered TiB2 and Ti(B,N) coatings

Thin films of TiB2 and Ti(B,N) were deposited by means of r.f. sputtering. Fundamental properties such as structure, adhesion, hardness and internal stresses were determined as a function of the deposition parameters. By systematically changing the substrate voltage and in the case of Ti(B,N) the nitrogen flow, the film properties could be influenced over a wide range. The coatings have been tested with regard to their tribological behaviour by means of a model wear-testing apparatus. It is shown that Ti(B,N) is a promising coating for wear protection.

Structure, internal stresses, adhesion and wear resistance of sputtered alumina coatings

Abstract Thin alumina coatings have been produced by means of reactive r.f. magnetron sputtering. The layers, deposited onto metallic substrates, show an amorphous crystallographic structure. Scanning electron microscopy analysis shows that the structure is variable within a wide range, from rough fibrous to smooth glass like, depending on the deposition parameters. Measurement of internal stresses was performed by using the bending beam method. The magnitude of the measured compressive stresses depends on the film thickness, deposition pressure and sputtering power. Some correlations between internal stress and adhesion of the coatings are evident. As well as scratch-test measurements the amount of layer detachment of bending specimens gave information about the adhesion behaviour of the coatings. Some of the alumina coatings have been tested with regard to their tribological behaviour by means of a model testing apparatus. The coatings showed excellent wear behaviour even under severe tribological conditions.

Tribological properties of r.f. sputtered Ti-B-N coatings under various pin-on-disc wear test conditions☆

Abstract TiN, Ti(B,N) and TiB 2 hard coatings have been deposited on steel substrates by means of r.f. sputtering. The fundamental coating properties, such as the structure, adhesion, hardness, internal stresses and chemical composition, have been determined. The coatings have been tested with regard to their tribological behaviour by means of unlubricated pin-on-disc model wear tests under an ambient atmosphere as well as under vacuum conditions. Balls made of ball bearing steel and high speed steel have been used as pin materials. It was found that the dominant type of chemical bonding within the film is an important coating property with regard to the wear behaviour under pin-on-disc test conditions. It is shown that TiB 2 films are of limited benefit in a sliding contact against steel. Ti(B,N) and the well-known TiN are much more promising coating materials.

Tribological behaviour and corrosion performance of Ti-B-N hard coatings under plastic manufacturing conditions☆

Abstract During plastics processing, an increasing content of abrasive fillers and corrosive components in combination with high working temperatures up to 450°C produce extreme wear conditions. As shown in previous work, TiN coatings are wear resistant against hot molten plastic material. In this paper we deal with thin hard single-phase and multiphase coatings within the extended coating system Ti-B-N. The films were deposited onto steel substrates using an r.f. sputter process with r.f. substrate bian. In order to cover a broad spectrum of Ti-B-N coatings, the substrate bias, nitrogen gas flow and total deposition gas pressure were all varied systematically. The coatings were tested with regard to their fundamental mechanical properties such as hardness and adhesion. Additionally, the coating structure was investigated by scanning electron microscopy. Corrosion tests were also done to see how the coatings performed under this important condition. Following these tests the wear behaviour of the coating systems under plastics processing conditions was investigated in a model wear test. Corresponding to the melting zone of screw barrel systems, the test pieces were subjected to abrasive-corrosive wear under elevated temperatures. It is shown that the combination of high hardness, dense structure, good adhesion and—most important—excellent corrosion resistance leads to superior wear resistance of r.f. bias sputtered Ti-B-N coatings. The wear behaviour can be further improved if a dense covalent Al2O3 surface layer is deposited on top of the Ti-B-N film.

Analysis of r.f.-sputtered TiB2 hard coatings by means of X-ray diffractometry and Auger electron spectroscopy

Abstract The bias voltage can be a very important parameter in r.f. sputtering. Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were used to investigate the influence of this parameter on TiB 2 hard coatings. As a result of the AES measurements the boron-to-titanium ratio depends on the bias voltage. With XRD, significant differences in the various coatings can be observed.

WEAR BEHAVIOUR OF R.F.-SPUTTERED TiN, TiB2 AND Ti(B,N) COATINGS ON METAL FORMING TOOLS IN A MODEL WEAR TEST

Abstract Within the last few years grey cast iron tools have been widely used for sheet metal forming owing to their low friction coefficient and excellent emergency running properties. Low hardness values and therefore reduced abrasive wear resistance are the main restrictions for this material. As shown in previous work, TiN coatings reduce the abrasive wear of cast iron test pieces under several tribological conditions. In this paper we deal with thin hard coatings of the system Ti-B-N deposited onto cast iron by means of an r.f. sputter process with r.f.-biased substrates. The coatings were tested with regard to their fundamental properties such as hardness, adhesion and structure. The most promising TiN, TiB 2 and Ti(B,N) coatings were tested under metal forming conditions. It is shown how the graphite lamellae of grey cast iron substrates disturb the coating structure. The main wear mechanism results from cracking of the coatings in the areas of graphite lamellae. The cracking leads to highly abrasive wear debris containing hard coating and substrate particles. Therefore a 1 μm thick pure titanium layer is deposited prior to the hard coating to reduce the influence of the graphite on the growth of the hard coating. As a main result the wear behaviour of the coated tools is remarkably improved without a significant change in coating hardness or adhesion.

Fatigue performance and tribological properties of r.f. sputtered TiN coatings

Abstract TiN coatings were deposited onto steel substrates and grey cast iron by means of an r.f. sputtering unit by varying systematically the deposition parameters bias voltage and deposition time. The fundamental properties such as adhesion, hardness and structure were determined and correlated with results of investigations of the wear and fatigue properties of the coated samples. It was shown that the coatings with high hardness combined with good adhesion to the substrate have the best wear properties. The fatigue resistance increased by about 10% as a result of the coating process and was only negligibly influenced by variations in the deposition parameters.

Comparison of fundamental properties of r.f.-sputtered TiNx and HfNx coatings on steel substrates

Abstract Titanium and hafnium based coatings in this work were sputtered on steel substrates in a r.f. sputtering unit with a diode arrangement. By feeding nitrogen in addition to the inert processing gas argon, TiN x and HfN x coatings were deposited under reactive sputtering conditions. Deposition pressure, nitrogen flow in the chamber and bias voltage on the substrates were systematically varied to get optimized coating systems. The coatings were investigated on their fundamental properties in order to compare titanium and hafnium based films, sputtered under identical process conditions. The results for hardness, deposition rate, internal stress, adhesion, structure, phase analysis and wear show that the properties of HfN x coatings are less influenced by the deposition process than the coatings of TiN x in the field of selected deposition parameters. The behavior of HfN x is comparable to TiN x , owing to a very similar crystal structure of the materials, but the conclusion of this present paper the well known TiN x has to be preferred for tribological applications in mechanical components.

X-ray diffractometry analysis of r.f.-sputtered hard coatings based on nitrides of Ti, Cr, Hf

Abstract Hard coatings for wear protection based on Ti, Cr and Hf and their nitrides were deposited by means of a commercial magnetron sputterung unit with r.f. bias and compared in their physical and mechanical properties. All films were reactively sputtered with nitrogen atmosphere from a target of the pure metal. In the present paper the most important results of the X-ray diffraction (XRD) for studying the influence of the deposition parameters nitrogen flow, bias voltage and deposition pressure are shown for optimizing the coating properties and the deposition process. The investigations also show that with XRD as an important analytical tool differences can be observed in the microstructure of thin films, which help to understand their technological properties such as adhesion and wear behaviour.

Fundamental and tribological properties of R.F.-sputtered TiN coatings in plastic manufacturing model wear tests

Abstract In plastic manufacturing an increasing content of abrasive particles and corrosive components in combination with working temperatures up to 450 °C have led to a new dimension of wear. As shown in previous work, TiN coatings have been wear resistant under corrosive conditions and elevated temperatures. In this paper we deal with thin hard TiN coatings deposited onto steel substrates by means of an r.f. sputter process with r.f. substrate bias. The coatings were tested with regard to their fundamental properties such as hardness, adhesion and structure. An increased substrate bias voltage up to —100 V leads to higher hardness values and a more dense coating structure. Adhesion and cohesion of the coatings are best in the range from —30 V to —50 V. The wear behaviour of the coatings under plastic manufacturing conditions was investigated by two model wear tests. Corresponding to the conveying and the melting zones of screw barrel systems the test pieces were subject to abrasive and abrasive-corrosive wear under elevated temperatures. It is shown that the combination of high hardness, dense structure and good adhesion leads to superior wear behaviour of r.f. bias sputtered TiN coatings. For the melting zone model wear test a remarkable improvement in wear resistance by a factor of more than 10 was achieved.