W. Ensinger

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.

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.

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.

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.

Microstructural investigations on titanium nitride films formed by medium energy ion beam assisted deposition

Abstract Titanium nitride was deposited in the rare gas mode of ion beam assisted deposition by evaporation of titanium in an atmosphere of backfilled nitrogen under bombardment with argon ions with current densities up to 70 μA/cm 2 . The ion energy was 12 keV which is in the medium to high energy range of IBAD. High ion energy, mass and fluence strongly influence morphology and topography of the resulting TiN films. Upon increasing ion irradiation intensity, the grain size increased from typically 10 nm up to 80 nm in diameter. The crystallographic orientation of the grains changed from a preferred [111] orientation which is typical for evaporated fcc material to the [100] orientation. The latter is a favourable channeling orientation and is therefore less damaged by ion bombardment. In the topography of the films a strong dependence on irradiation intensity was found. Several zones of varying roughness could be identified. Development of smooth or rough surfaces is attributed to several effects directly connected with ion bombardment, among which are adatom mobility, sputtering and ion incorporation.

A comparison of IBAD films for wear and corrosion protection with other PVD coatings

Abstract Ion beam assisted deposition is presently introduced into fabrication processes in industry. Now the question arises which are the advantages and disadvantages of IBAD in comparison with other PVD-techniques and where its application potential is. In this paper results of comparative studies of IBAD and methods such as sputtering and ion plating are discussed. The subjects are medium energy ion beam assisted deposition and films for wear and corrosion protection. As a general result it turns out that IBAD films show superior performance when low process temperatures are required, as it is the case for special heat treated steels and aluminium alloys. In these cases, both elemental IBAD coatings such as Al and compound coatings such as TiN are able to offer a better protection against corrosion, partially also wear, than most of the other PVD techniques. The reasons for this observation are higher structural density and adhesion of the IBAD films. The required film growth conditions, mainly energy input, are provided by highly energetic ions while the bulk of the substrate can essentially be kept at low temperature.

Ion beam assisted deposition for metal finishing

Abstract Ion beam assisted deposition during the last half decade turned out to be one of the most interesting techniques for finishing of metals, ceramics and other materials. Providing energy to a growing film by energetic ions allows control and variation of film properties like adhesion, porosity, density, intrinsic stress and structure. Different techniques for the generation of ion beam assisted coatings are described. Applications of these coatings in different areas of science are discussed. Results are presented for Al, Si, a-C:H, CrNx, AlN and TiN films on iron and steel substrates. All films had excellent adhesion, and in some cases hardness and stress could be manipulated in a controlled way. Most coatings had very good protective power against aqueous corrosion.

A multipurpose implanter with various target chambers for basic studies on the influence of ion bombardment on material properties

Abstract A multipurpose apparatus with several exchangeable target chambers for implantation of gaseous and metal ions into various target materials is described. An ion beam from a Penning-type ion source with energies between 20 and 120 keV is mass-analyzed with a sector magnet and directed into a primary target chamber with target holders for flat and rotating cylindrical samples. In addition to this chamber several exchangeable chambers can be brought into the beam line. They serve for irradiation of large area targets, under various angles with a goniometer, in situ Mossbauer spectroscopy, ion beam assisted vapour deposition or powder irradiation.

Microporosity and adhesion of ion bombarded thin silicon surface films

Abstract Adhesion tests and electrochemical measurements were performed on thin silicon films evaporated onto steel to evaluate the influence of ion bombardment on mechanical properties, corrosion protection potential and microporosity. The results are compared to those obtained by a combined process, i.e. ion bombardment during evaporation.