G.K. Wolf

Ion-beam-assisted coatings for corrosion protection studies☆

Abstract For corrosion protection, modified surfaces or coatings prepared by ion implantation or ion beam mixing often are not sufficient for technical long-term applications. The main problem, i.e. the shallowness of the films, can be overcome by ion-beam-assisted deposition which offers the positive effects of ion beam treatment, e.g. high adhesion, low porosity, and a low process temperature without thickness limitation. The corrosion protection behaviour of a number of coatings, e.g. boron, chromium and their nitrides, chromium oxide, silicon, hard carbon and aluminium, are discussed. The results demonstrate ion-beam-assisted deposition to be appropriate for producing adherent coatings which are well suited to long-term protection against corrosion, and partly also against tribological deterioration, even for technical rough surfaces.

Surface properties of silver doped titanium oxide films

Silver doped titanium oxide coatings for biomedical application were prepared by ion beam assisted deposition in an oxygen atmosphere. X-Ray photoelectron spectroscopy (XPS) was used to examine the chemical states and composition. Critical surface tension, dispersive and polar components of the surface energy were investigated by contact angle analysis. The influence of experimental conditions on the chemical states, composition and surface energy were investigated. The chemical state of silver was not affected by the process parameters and silver existed always in metallic state. XPS analysis confirmed the presence of TiO, Ti2O3 and TiO2, and the concentrations of the different oxidation states were influenced by the deposition rate of Ti and Ag. The oxygen flow rate had only a minor influence. On the other hand, dispersive and polar components of the surface energy were significantly affected by the oxygen atmosphere. The results also showed that samples with a higher concentration of silver exhibited a somewhat larger critical surface tension.

Hardness and corrosion resistance of single-phase nitride and carbide on iron

Abstract With ion beam synthesis, closed homogeneous nitride and carbide layers have been produced. The hardness and the corrosion resistance potential of γ′-Fe 4 N, ϵ-Fe 2.6 N and Fe 3 C cementite single-phase layers have been determined. The results are compared with samples implanted in a conventional way with the same N concentration, resulting in precipitates, and with untreated iron. The hardness is found to be increased by a factor of 2.5 in comparison with pure iron; no significant difference between the different samples is found. In cyclovoltammetric tests, the dissolution of iron is found to be suppressed considerably by three orders of magnitude for γ′-Fe 4 N, 1.5 for cementite and 1 for ϵ-Fe 2.6 N, while implantation of precipitates even promotes the corrosion.

A comparison of the corrosion behaviour and hardness of steel samples (100Cr6) coated with titanium nitride and chromium nitride by different institutions using different deposition techniques

Abstract Deposition of hard coatings may influence the mechanical properties of the bulk material and its corrosion resistance. In this work we study the hardness of the coated and the back side of 100Cr6 steel plates. Electrochemical corrosion tests were performed in O2-saturated acetate buffer of pH 5.6 at 25 °C. Chromium nitride and titanium nitride coatings prepared by different physical vapour deposition processes, such as arc, thermionic arc evaporation, magnetron sputtering and ion-beam-assisted deposition (IBAD) were compared. The results show that, for sufficient corrosion protection, chromium nitride layers have to be thicker than 500 nm. An increased nitrogen partial pressure in the evaporation chamber of the IBAD process improves the corrosion resistance significantly. The hardness of the substrates was reduced in the case of thermoionic arc evaporation only, indicating a deposition temperature of more than 250 °C. For this process, however, we obtained the best corrosion results.

Corrosion and mechanical studies of chromium nitride films prepared by ion-beam-assisted deposition

Abstract Chromium nitride films are known as good protective layers for both corrosion and wear attack. In the case of corrosion protection in particular they are expected to be superior to comparable titanium nitride layers. Therefore they are very interesting as a partial or complete substitute for the “classical” electrolytically deposited hard chromium coatings that have been in use for decades, an issue more and more critical from an ecological point of view. As it is not possible to synthesise chromium nitride, as in the case of titanium nitride, by simply evaporating chromium in a nitrogen atmosphere, the layers had to be prepared by evaporation and simultaneous irradiation with nitrogen ions. Hereby the main parameter determining the composition and properties of the films is the arrival ratio of impinging nitrogen ions to condensing chromium atoms ( I/A ). The formation of chromium nitride was proved by means of Auger electron spectroscopy and additionally by corresponding X-ray diffraction (XRD) measurements. Compared with pure chromium deposited under argon irradiation, these coatings show a compressive instead of a tensile stress as measured in situ with the bending cantilever method and subsequently will be investigated with XRD. Corrosion tests and hardness measurements with the films on metal substrates were also performed. Taking into account the optimisation possibilities of the ion-assisted-beam deposition technique, these results, indicate very promising potential for future applications.

Plasma and ion-beam-assisted deposition of multilayers for tribological and corrosion protection

Abstract Multilayers of Ti/TiN and Al/AlN were deposited on steel and silicon by magnetron sputtering and ion-beam-assisted deposition. Compositions and film thicknesses were determined by Rutherford backscattering. Hardness was measured with a dynamic ultramicrohardness tester. The corrosion protection potential in an aqueous environment was evaluated by electrochemical techniques. The results are discussed in terms of the structure and composition of the multilayer arrangement. It turns out that the multilayer coatings generally show a better corrosion protection performance than both the pure metal and the pure nitride films, with an optimum ratio of nitride film thickness to metal film thickness for a maximum corrosion protection effect. The hardness values are in between that of nitride single film and those of metal single films. Deposition of multilayers with the possibility of selecting the thickness ratio of metal to nitride film for particular mechanical and chemical requirements allows a controlled adaption of the film features to a given application problem.

Ion bombardment during thin film deposition and its influence on mechanical and chemical surface properties

Abstract Directed energy in the form of energetic ion beams is an excellent tool for the modification of thin film and interface properties. The easy control of ion beam parameters causes the high flexibility of the technique. The influence of ion bombardment during deposition of thin films and coatings (IBAD) on their mechanical and chemical behaviour is reviewed in this article. Firstly the controlled production of IBAD films or multilayers with well defined composition is described. Secondly the influence of ion bombardment on selected properties is considered. Adhesion, stress and structure or texture and their dependence on process parameters are discussed. Thirdly the role of adhesion, stress and porosity of films for their use for corrosion and oxidation protection is treated. Finally in the conclusion an attempt is made to define the present status of IBAD techniques compared with other PVD processes.

Plasma and ion beam assisted metallization of polymers and their application

Abstract Various high-temperature polymeric materials were preconditioned and metallized by using ion-assisted processes for adhesion improvement. The surface of the polymers was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and stylus profilometry. The adhesion of the coatings was controlled by pull-off and peel tests. The measurement of the specific electrical conductivity, the helium gas tightness and soldering experiments give valuable information concerning possible applications. In comparison to the pure copper evaporation onto polyphenylensulfid (PPS) the ion beam assisted deposition (IBAD) of copper films results in a distinct increase of the pull-off force. At ion energies around 2.5 keV and at low ion-to-deposited-atom ratio of 0.01 the film adhesion was enhanced from a pull-off strength of 10 N mm−2 up to 25 N mm−2. Plasma processes at a low pressure provide a high polymer etching rate by a plasmachemical attack and ion sputtering effects in a synergistic manner. The plasma etching process attack the polymer material preferentially. Therefore, mineral particles must still adhere strongly to the polymer to provide mechanical adhesion sites for the metal layers. An peel strength of about 1 N mm−1 was obtained on different substrate materials.

Equipment for ion beam assisted deposition

Abstract Ion beam assisted deposition (IBAD) is a powerful new technique for producing adherent surface coatings with special properties. A facility for this technique is described. It consists of a cylindrical vacuum chamber, a rotating cooled target holder, an electron gun with evaporation source, a duoplasmatron ion source for gaseous ions, and the necessary power supplies and controls. Evaporation and bombardment are possible in sequence or simultaneously. The ion source delivers ions up to 30 keV energy. The maximum beam current is ∼ 7 mA for argon. The results of recent preliminary experiments to produce aluminum coatings on steel are reported and discussed.

Are coatings produced by ion-beam-assisted deposition superior ? A comparison of chemical and mechanical properties of steel coated using different deposition techniques

Abstract The aim of this study was a comparison of chemical and mechanical properties of titanium nitride films prepared with arc evaporation (ARC), magnetron sputtering (MAG), activated reactive ion plating (ARIP) and ion-beam-assisted deposition (IBAD) in order to evaluate the advantages and disadvantages of the IBAD process on an objective basis. Hardened ball bearing steel was coated to thicknesses between 3 and 10 μm at low process temperatures. Ball-on-disc wear measurements showed that the friction coefficients vs. steel were around 0.48 for all techniques, with IBAD values slightly lower. Electrochemical measurements showed large differences in corrosion behaviour. ARC TiN turned out to be less effective because of microporosity connected with droplet formation. MAG TiN yielded an average corrosion protection. ARIP and IBAD showed best reduction of corrosion. IBAD values were the lowest in the initial phase of corrosion, but ARIP showed better long-term stability. Taking into account the present state of development, IBAD can compete with other deposition techniques. It is not superior in many cases, but there is still a high optimization potential for low temperature preparation of films with special features.