Georg Reiners

Hard coatings on magnesium alloys by sputter deposition using a pulsed d.c. bias voltage

Abstract An increasing use of magnesium-based light-metal alloys for various industrial applications was predicted in different technological studies. Companies in different branches have developed machine parts made of magnesium alloys (e.g. cars, car engines, sewing and knitting machines). Hence, this work was started to evaluate the ability of hard coatings obtained by physical vapour deposition (PVD) in combination with coatings obtained by electrochemical deposition to protect magnesium alloys against wear and corrosion. TiN hard coatings were deposited onto magnesium alloys by unbalanced magnetron sputter deposition. A bipolar pulsed d.c. bias voltage was used to limit substrate temperatures to 180 °C during deposition without considerable loss of microhardness and adhesion. Adhesion, hardness and load-carrying capacity of TiN coatings deposited directly onto magnesium alloys are compared with the corresponding values of TiN coatings deposited onto substrates which had been coated electroless with an Ni-P alloy interlayer prior to the PVD.

Evaluation of optical properties of decorative coatings by spectroscopic ellipsometry

Abstract Some of the hard coatings ( e.g. TiN, TiCN, TiCN, TiAlCN) occur in different colours. Using goniospectroscopy in the visible wavelength range colours are deduced by measuring the spectral reflectance factor R λ . This factor depends on both the samples and the white reference as well as on the geometry of illumination and measurement. It is very difficult or even impossible to distinguish colours according to their origin and to relate them to bulk material composition, thin film coatings and interference layers by means of goniospectroscopy as unpolarized light is used. By using polarized light in spectroscopic ellipsometry these difficulties could be overcome as there is no reference to white and the geometric influences of illumination and measurement are negligible, but on the contrary the visual impression is not correctly described. From the measurement of the relative amplitude ratio tan Ψ and the relative phase shift cos Δ it is possible to calculate either the parallel and normal components R p and R s of the reflectivity R or the complex refractive index N = n + i k as well as the dielectric function e = e 1 + i e 2 which are strongly related to the electronic structure of the material used. It is shown that in this way it is possible to describe optical properties more physically, to separate interference effects and to detect changes in stoichiometry.

Decorative hard coatings: new layer systems without allergy risk

Abstract Combinations of physically vapour deposited (PVD) coatings and electroplated layers are widely used for decorative applications. The electroplated layer beneath the PVD coating acts as a diffusion barrier. Conventionally electroplated barrier layers make use of nickel which has to be replaced in allergy-free systems by for example Ni/NiPd and CuSn(Zn). The PVD coating has to meet a variety of requirements: attractive colour, high wear resistance and good corrosion resistance. Within the scope of the search for new colours a number of nitrides of binary IVa metal-based alloys such as (Ti,V)N, (Zr,V)N, (Zr,Al)N, (Zr,Cr)N, (Zr,Y)N were deposited by reactive magnetron sputtering. To describe the colour the CIE L ∗ a ∗ b ∗ system was used. Spectroscopic ellipsometry (SE) was introduced to determine material related parameters. In general, both the stoichiometry and the structure can influence the colour of a coating. The correlation between colour, stoichiometry and structure was determined by surface analytical methods (glow discharge optical spectroscopy, Auger electron spectroscopy, X-ray diffraction). Proper selection of process parameters (target composition, N 2 flow rate, etc.) results in coatings with colours exceeding the conventional spectrum of decorative coatings. As an example of structural and stoichiometric influences on colour, ZrN and (Zr,Y)N coatings are discussed.

Decorative optical coatings

Abstract The paper gives a survey of current research on decorative coatings. In the first part the main deposition techniques as well as characterization techniques are discussed. The paper is restricted to decorative physically vapor deposited hard coatings with electrochemically deposited barrier coatings. The influence of stoichiometry, structure, and surface roughness on the colour of physically vapor deposited hard coatings is reviewed. In the last decades, a number of different coating deposition techniques have been developed. The demand for environmental compatibility of low cost large-scale production techniques has resulted in the development of combinations of physical vapor deposition and electroplating. Coating systems have been developed using NiPd and CuSn(Zn) instead of Ni electroplated coatings as interlayers, strongly reducing the allergy risk. New industrial applications demonstrate the increasing economic importance of decorative hard coatings.

Decorative hard coatings: advances in optical characterization techniques

Abstract Transition metal compounds are finding increasing use in decorative coatings, combining intense colour, high wear resistance and good corrosion resistance. From the decorative point of view, colour and gloss are the most important features. The physiological colour impression is well described by the CIE-L∗a∗b colour space. Integrating sphere measurement (ISM) and goniospectroscopy (GS) derive colours from a measurement of the spectral reflectance factor Rλ relative to a white reference. Spectroscopic ellipsometry (SE) is a reference-free technique for measuring amplitude ratios and phase changes of polarized light upon specular reflectance. ISMs of (Zr,Y)N coatings are presented, which show considerable yellow and red values at intermediate lightnesses. The effect of the surface roughness is discussed for TiN coatings. The angular dependence of L∗a∗b∗ and the behaviour of Rλ are shown by means of GS for these TiN coatings in off-specular directions. These results of ISM and GS are compared with the SE data. The high sensitivity of SE to changes in stoichiometry as well as the capability of separating additional interference effects are demonstrated for (Zr,Cr)N and (Zr,Zl)N coatings. However, it is shown especially in the case of rough surfaces that each technique is helpful in distinguishing features of physical and physiological interest.

Multilayer reference coatings for depth profile standards

Depth profiles of layer systems consisting of different film materials and having different thicknesses are of great practical importance. Multilayer reference coatings of conducting (Ti/Al) and non-conducting (SiO2/Si3N4) material are analyzed with Auger electron spectroscopy (AES) and glow discharge optical emission spectroscopy (GDOES) depth profiling. Deposition techniques, physical vapor deposition for Ti/Al layers and plasma-enhanced chemical vapor deposition for SiO2/Si3N4 layers, as well as measurement and testing procedures for the determination of layer thickness such as optical and mechanical stylus and spectroscopie ellipsometry are discussed. GDOES depth profiles in direct current (d.c.) and radio frequency (r.f.) mode are related to measurements of crater profiles and compared with line scans and depth profiles performed by AES. It is shown that such multilayer reference systems are appropriate for calibration of depth profiles, i.e. the definition and the evaluation of the depth resolution at the interface, the determination of sputter rates both for d.c.- and r.f.-GDOES and AES, the optimization of the conditions of analysis, and the quantification of analysis itself.

Structure and properties of decorative rare-earth hexaboride coatings

Abstract Hexaborides of the rare-earth elements are considered for applications as wear- and corrosion-resistant hard coatings for decoration of consumer products such as eye-glass frames and wristwatch casings. After a review of physical vapour deposition (PVD) methods used for the deposition of rare-earth hexaborides, a survey of studies is given that extends the range of suitable decorative coating materials. Within the scope of the search for new colours, the interdependence between deposition conditions, microstructure and mechanical and optical properties of boride coatings based on LaB6, CeB6, SmB6 and YB6 is presented and discussed. As a result of the strong directionally of covalent boron—boron bonds, hexaboride coatings show an increasing tendency to amorphous film growth with decreasing metallic radius of the rare-earth metal. Mechanical as well as optical properties are strongly influenced by the crystallographic structure of the hexaboride phase. The most pronounced visual colour impression is observed for LaB6-based coatings corresponding to a dark violet colour. Proper selection of process parameters for these coatings may widen the conventional spectrum of decorative coatings.

Decorative properties and chemical composition of hard coatings

Transition metal compounds (nitrides, carbides, etc.) find increasing use as decorative coatings combining intensive colours, high wear resistance and good corrosion resistance. While golden TiN and dark-grey TiC are limited in their colour variation, the addition of a second metal or a second metalloid widens the spectrum of decorative colours, e.g. to dark blue with (Ti, Al)N. In the search for new colours, a number of nitrides of binary IVa metal-based alloys were deposited by reactive magnetron sputtering. The correlation between colour and stoichiometry was determined by surface analytical methods. Proper selection of the process parameters (target composition, N2 flow rate, etc.) results in coatings with different colours exceeding the conventional spectrum of decorative coatings.

Dielectric reference coatings for the evaluation of thin film characterization techniques

Abstract Thin film technology has an increasing demand for industrial reliable characterization techniques. A precise absolute determination of layer thickness, interface width and the quantification of depth profiles in dependence on resolution limits of the measurement are required. Certified reference materials, certified reference coatings (CRCs) and non-destructive evaluation techniques can meet these requirements. Dielectric reference coatings (SiO2, Si3N4) were used for metallographic preparation (e.g. bevelled cross-sections), optical characterization techniques (e.g. spectroscopic ellipsometry (SE)), and films of SiO2, Si3N4 and Al2O3 were applied to reference measurements in depth profiling of layer stacks (e.g. radio frequency glow discharge optical emission spectroscopy). Thickness and refractive index of these dielectric single-and multilayer coatings on different substrate materials are accurately determined in advance by means of SE. These values are subsequently used for precise angle determination of bevelled cross-sections, for reference and re-calibration purposes in thin film characterization (system reproducibility) and in surface analysis (determination of sputter and erosion rates, depth profiles). Examples are discussed for different applications and the calculated data are compared with experimental results. It is shown that reproducible commercial coatings are also of importance for use as CRCs.

INO–A WWW information system for innovative coatings and surface technology

Abstract In the last years, a lot of research work has been performed in the field of surface coatings and thin films technology, often supported by governmental research programs, as i.e. in Germany, the ‘Thin Film Technology’ and ‘OSTec’ research programs. But up until now, there is still a lack in transfer of this large amount of knowledge created by research activities on to industrial application and commercialization. To overcome this problem, a new web based information system has been developed (http://www.schichttechnik.net), which in a first step will make the whole content of the German OSTec research program (approx. 180 research reports) of the last 10 years available. In further steps, data from products of coating suppliers and other research programs will be taken into account. The database contains the following sections: definition of the coating system, deposition equipment, deposition processes, application properties, test procedures and test equipment, information about standardization and base information about coating processes etc. It will be possible to search for coatings by material properties and functions of coatings, considering also restriction on the substrate. In addition, searching regarding combination of properties, e.g. for wear-resistant, conductive, decorative coatings etc. will also be possible.