L.M. Stals

A quantitative model for the evolution from random orientation to a unique texture in PVD thin film growth

Abstract The continuous evolution from a random crystalline orientation (near the substrate) towards a definite texture (near the outer surface), established in the previous paper for PVD TiN coatings, was modelled quantitatively. The tendency for the smallest possible surface energy was considered as the driving force for the texture evolution. The experimental trends observed in the texture evolution could be reproduced, using realistic parameters. From an analytical treatment simple expressions for crucial characteristics of the texture evolution could be obtained, as for instance for the typical time (or thickness) at which the system will switch from a random to a peaked distribution, and for the time dependence of the spread of the orientational distribution of the crystallites in the growing film.

Oxidational wear of TiN coatings on tool steel and nitrided tool steel in unlubricated fretting

The fretting wear behaviour of PVD TiN coatings against corundum has been investigated in unlubricated contacts. Analysis of the debris indicated that titanium oxides of different composition are being generated. The volumetric wear on the TiN coatings is shown to be directly proportional to the dissipated friction energy measured on-line during the fretting tests. Furthermore, the effect of oxide debris present in the vibrating contact on the velocity accommodation and, consequently, on the coefficient of friction is discussed. The hardness of some of the ASP 23 tool steel substrates was increased with a plasma nitriding treatment prior to the coating deposition. It was found that the coefficient of friction and the fretting wear rate of the TiN coatings remain unaltered by the plasma nitriding treatment. After perforation of the TiN coating, however, wear proceeds faster on nitrided tool steel substrates.

Adhesion of diamond coatings on cemented carbides

WTCM,B-3590 DIEPENBEEK,BELGIUM.Nesladek, M, LIMBURGS UNIV CENTRUM,INST MAT RES,DIV MAT PHYS,CAMPUSLAAN 1,B-3590 DIEPENBEEK,BELGIUM.

State of the art for the industrial use of ceramic PVD coatings

Since the beginning of the 1980s ceramic PVD coatings have been used in industry for many applications. At present four types of PVD coatings are frequently used: TiN, Ti(C,N), (Ti,Al)N and CrN. Based on a materials triangle approach, it is shown which coating should be used for which application. Different industrial case studies will demonstrate the effectiveness of PVD coating. Some recent developments, of which various aspects are still mainly in the research phase, like diamond(like) coatings, duplex treatments, self lubricating coatings, Ti2N coatings and PVD coatings deposited at low temperatures (<250 °C), are also described.

Characterization of TiN coatings deposited on plasma nitrided tool steel surfaces

Abstract Wear-resistant TiN coatings deposited on tool steels are used frequently in industry. There is a trend towards further optimizing these coatings, e.g. by plasma nitriding the tool surface prior to TiN deposition. In this work the influence of the nitriding conditions on the surface properties of AISI 304 and ASP 23 tool steels was investigated. The plasma nitriding was carried out in a triode ion plating configuration normally used to deposit TiN coatings. At the surface of AISI 304 stainless steel, only a thin compound layer (Fe4N, Fe3N) was found, probably as a consequence of the rather slow nitrogen diffusion in the austenite matrix. For ASP 23 high speed steel, the different nitriding behaviour of the martensitic matrix causes the formation of a diffusion layer which results in an increasein hardness at the surface. On an analogous set of specimens the TiN deposition was started immediately after the plasma nitriding. To optimize this combined treatment, the influence of the nitrogen content of the nitriding medium and that of the thickness of an intermediate titanium layer were examined. By means of X-ray diffraction only an influence on the lattice parameter of TiN and the nitriding layers was found, as compared with the lattice parameter for the separate treatments. Bad adhesion of TiN coatings on plasma nitrided AISI 304 was observed and was explained in terms of the high internal stresses in the compound layer on the nitrided surface. For the ASP 23 substrate a better coating adhesion was observed, probably due to a different structure of the nitriding layer and to the enhanced substrate harness. At this stage of the research, none of the above-mentioned nitriding treatments results in a sufficient adhesion of the TiN layer, although some useful facts could be established for further research.

Effect of crystallographic orientation on fretting wear behaviour of MoSx coatings in dry and humid air

The tribological behaviour of MoS2 coatings in air of high humidity is critical for their application in air. An improved friction and wear resistance of sulfur-deficient MoSx coatings in humid air is reported based on fretting wear tests. For random-oriented MoSx coatings, the coefficient of friction and the wear volume are still significantly dependent on the relative humidity. On the contrary, basal-oriented MoSx coatings show an interesting low sensitivity to humidity. MoO3 and SO42− have been detected in the wear track and the debris. The amount of MoO3 and SO42− is related to the crystallographic orientation of the coatings and the relative humidity in the fretting wear tests. However, the structure and grain size of the MoO3 debris are not dependent on the relative humidity and the crystal orientation of the coatings. The effect of humidity on the friction and wear of these sulfur-deficient MoSx coatings with different crystallographic orientations is discussed.

Experimental study of the growth evolution from random towards a (111) preferential orientation of PVD TiN coatings

Abstract The evolution of the preferential orientation of TiN coatings deposited on martensitic steel with the evaporation ion plating method is studied with the Field-Merchant X-ray diffraction technique for different coating thicknesses and as a function of the energy dissipation per unit volume, S E , in the growing layer. It was shown that TiN starts to grow on the martensitic substrates with randomly oriented grains, and that the texture evolves towards a fibre texture with the (111) lattice planes of most crystallites preferentially parallel with the substrate surface. The quantification of the evolution of the preferential orientation is based on the mosaic spread of the preferential orientation factor p 111 (Ψ)-curve around Ψ = 0 °. The mosaic spread of the (111) fibre texture decreases from 34±1 ° to 10±1 ° for an approximately 1.5 μm thick coating as S E increases from 1.0 ± 0.4 MJcm −3 to 2.8 ± 1.1 MJ cm −3 . The mosaic spread of the (111) fibre texture decreases from 15 ± 1 ° to 8 ± 1 ° as the coating thickness changes from 0.9 μm to 2.9 μm for S E = 2.5 ± 1.0 MJ cm −3 . It is thus clearly demonstrated that the texture evolves from random towards a pure (111) texture, progressively with increasing layer thickness, and that evolution is more pronounced for a higher energy dissipation per unit volume in the growing layer.

Humidity resistant MoSx films prepared by pulsed magnetron sputtering

It is well known that MoS 2 is a good lubricant, but the lubricity of MoS x thin films is greatly affected by the deposition parameters, especially when used under environmental conditions of high relative humidity. In this work, MoS x films were prepared by magnetron sputtering using a bipolar pulsed power supply. Several deposition parameters such as argon pressure, substrate temperature, substrate bias voltage, cathode power and deposition time were varied. Composition, morphology and structure were investigated by a number of techniques including energy dispersive spectroscopy (EDS), Rutherford back scattering (RBS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Tribological properties were measured with a ball-on-disk fretting tester. The results show that MoS x films prepared at low argon pressure (below 0.4 Pa) and low substrate temperature (room temperature) have a low friction coefficient and long wear life. These films have a remarkable low sulfur content (x = 1 and even smaller, in contrast to frequently reported values of x = 1.2 ∼ 1.8), a featureless morphology and only a strong basal plane (002) diffraction peak. The relative humidity, up to values of 90%, has only a small effect on the friction coefficient and wear life. The structure of the films and the friction and wear mechanism are discussed in view of the low sulfur content.

Correlation between the OES plasma composition and the diamond film properties during microwave PA-CVD with nitrogen addition

Abstract The mechanisms of nitrogen incorporation in diamond are still an unsolved riddle. This is mainly due to the complexity of the processes involved as they not only depend on empirical parameters (e.g. vessel pressure, substrate temperature, the gas phase composition, type and concentration of the nitrogen containing compound used), but also on the plasma chemistry and the surface chemical reactions. In this study, small quantities (ppm range) of diatomic nitrogen are added to a conventional hydrogen-methane feed gas mixture in order to investigate the effect of nitrogen incorporation in diamond films prepared by microwave plasma assisted chemical vapour deposition (CVD). Optical emission spectroscopy (OES) is used to survey the plasma composition during deposition. The intensities of the CN, CH and C2 emitting radicals and the Balmer atomic hydrogen emission lines are correlated to the Raman film quality and to the nitrogen content in the film measured by secondary ion mass spectrometry (SIMS).

Introduction in industry of a duplex treatment consisting of plasma nitriding and PVD deposition of TiN

Abstract Recent results point out that it is possible to optimize the adhesion of a TiN coating on some pre-nitrided tool steel surfaces. This combination of plasma nitriding and physical vapour deposition (PVD) TiN coating has been investigated in various research groups as part of a broader objective to obtain an enhanced wear resistance of tools. The implementation of these results in industry, however, usually faces upscaling problems which hinder an efficient evaluation of the industrial performance. Two industrial applications were chosen to demonstrate the possibilities of tools treated by the duplex process. A steel milling tool consisting of 14 high speed steel teeth and knives made out of M2 tool steel for tube cutting were plasma nitrided and subsequently PVD coated. By application of various intermediate steps between nitriding and coating, a good coating adhesion could be obtained. The adhesion behaviour of both coating systems was evaluated by scratch tests. This laboratory performance of the duplex treatment was compared with a tool wear and lifetime evaluation in industry after producing a certain number of workpieces. First results point out that the duplex treatment gives a much better wear resistance for both applications. Extrapolation of laboratory performance to industrial conditions seems to be possible only when based on a close collaboration between industry and research groups.