Jozef Roos

A Mathematical Model for the Electrolytic Codeposition of Particles with a Metallic Matrix

Over the last decade the general knowledge of the electrolytic codeposition of inert particles with metals has increased markedly, and a few models have been proposed. In this paper a new model that overcomes several of the shortcomings of the previously proposed models is developed starting from a statistical approach of the incorporation of particles. The validity of the new model is shown for two experimental codeposition systems, namely, from acidic sulfate baths and from additive‐free potassium cyanide baths.

Analysis of the Electrolytic Codeposition of Non‐Brownian Particles with Metals

A model for the electrolytic codeposition of spherical particles with metals on a rotating disk electrode is presented, based on a trajectory analysis of the particle deposition, including convective mass transport, geometrical interception, and migration under specific forces, coupled to a surface immobilization reaction. A number of relevant forces were included and their effects determined. Theoretical predictions of this model are compared with experimental results for the codeposition of spherical polystyrene particles with copper during electrolysis from an acid copper sulfate solution. The influence of fluid flow velocities, particle concentration, and current density on the rate of particle deposition is illustrated. Experiments done on a rotating disk electrode allow the adhesion forces to be determined from the distribution of particles on the surface. It is shown that codeposition is governed by colloidal interactions that can, in first order, be approximated by the Derjaguin‐Landau‐Verwey‐Overbeek interactions plus an additional short range repulsion that was associated with the hydration force.

Laboratory testing of displacement and load induced fretting

Abstract A conceptually new simulation system for the laboratory investigation of fretting wear is described. Fretting vibrations are generated either directly by oscillating a linear relative displacement device of constant stroke between the contacting bodies or indirectly by oscillating the applied contact load resulting in a cyclic radial expansion of the contact zone. The principles of both actuation mechanisms are outlined in detail, indicating the precision and performance range of the simulation system. A data acquisition and evaluation strategy has been developed for the on-line characterization of the mechanical contact response. It is based on the measurement of the contact displacement, tangential force and normal load. Typical experimental results obtained under different testing conditions are presented for hard coatings such as TiN and diamond deposited on flat samples and vibrating against corundum counterbody balls.

Kinetics of the Deposition of Alumina Particles from Copper Sulfate Plating Baths

In 1972 Guglielmi proposed a physical model describing the codeposition mechanism of inert particles from electrolytic baths. The proposed mechanism was based on two successive adsorption steps. The present authors demonstrated the validity of that mechanism for the codeposition of alumina and copper from acidified copper sulfate plating baths. From an experimentally derived relationship between electrolytic conditions and codeposition, the importance of the reduction of copper ions adsorbed onto is shown. The influence of monovalent cations like thallium is discussed based on the mechanism proposed by Guglielmi.

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.

Sol-gel preparation of high-Tc Bi-Ca-Sr-Cu-O and Y-Ba-Ca-O superconductors

High‐Tc superconducting oxides have been prepared by a liquid‐mix technique using etylene‐diamine‐tetra‐acetic acid (EDTA) as a complexing agent. Bi‐Sr‐Ca‐Cu oxides and Y‐Ba‐Cu oxides were made using this technique giving a better compositional homogeneity, a more precise control of the cation stoichiometry and a decreased firing temperature as compared to conventional material produced by a solid‐state reaction. This technique extends the amorphous citrate process to those systems where no citrate complex exists. EDTA binds with most metallic elements of the periodic table, making this technique a versatile tool in the production and study of these new ceramic materials. Therefore, the method is easily adapted to the preparation of new superconducting oxides.

Interrelationship between processing, coatingproperties and functional properties of steered arc physically vapour deposited (Ti,AI)N and (Ti,Nb)N coatings

Abstract In the framework of a European BRITE Project on “steered arc ion plating forthe development of new ternary and quaternary ceramic coatings for cutting and forming tools”, (Ti,Al)N and (Ti,Nb)N coatings were developed and optimized. The relation between bias voltage, N, pressure and composition of the coatings was established. Coating properties such as composition, crystal structure, lattice parameter, internal stress, Youngs modulus and hardness measured by nanoindentation were determined. The oxidation behaviour of (Ti,Al)N and (Ti,Nb)N was investigated with Auger electron spectroscopy. The performances of industrial TiN coatings and these new ternary coatings deposited on high speed steel substrates were compared in drill tests. (Ti,Al)N made by the steered arc appears to be more oxidation resistant than TiN and (Ti,Nb)N. Laboratory wear tests and field tests indicate that the interaction between workpiece and coated tool may give important clues as to the suitability of a coating type for a particular type of workpiece material.

The influence of humidity on the fretting behaviour of PVD TiN coatings

Abstract The influence of the relative humidity (RH) in ambient air on the friction and wear behaviour of PVD TiN coatings subjected to contact vibrations against corundum and bearing steel (100Cr6) counterbodies has been investigated. The fretting experiments were performed in the gross-slip regime on TiN coatings produced by three different PVD processes. The results indicate two basic friction characteristics. At low relative humidity (RH 80%). A transition from high to low friction was observed during the course of experiments performed in atmospheres of medium relative humidity. The duration of the high friction phase in such transitions was found to depend on fretting parameters such as the normal force and the vibration frequency. This humidity dependence of the friction force was found for both counterbody materials. The size of the damaged surface area as well as the volumetric wear on the TiN coatings were found to be largest at low relative humidity. Fretting damage occurs over a smaller area but extends more into the depth at high relative humidity. The size of the fretted surface area induced on TiN is larger for Cr-steel than for corundum counterbodies.

Dry sliding wear of TiN based ternary PVD coatings

In order to understand the tribological characteristics of TiN, (Ti, Al)N, (Ti, Nb)N and Ti(C, N) coatings, ball-on-disc experiments were performed under dry sliding ambient conditions. The coefficient of friction and the wear resistance against a corundum counterbody were determined as a function of coating composition and sliding speed. The wear of the (Ti, Nb)N coatings was found to be comparable to that of the TiN coatings and this was related to the formation of a similar type of oxide in the tribo-contact. In the case of the (Ti, Al)N coatings, the wear volume increased markedly as the aluminium) in the coating increased, and the tribo-oxide formed was found to be Al2TiO5. Ti(C, N) coatings exhibited an extremely low wear against corundum because of the low coefficient of friction. A mild-oxidational wear model was found to give a qualitative fit to the experiments. Measuring the coating wear as a function of sliding speed opens the possibility of calculating the activation energy for tribo-oxidation processes of thin coatings.

R.f. plasma-assisted chemical vapour deposition of diamond-like carbon: physical and mechanical properties

Abstract Hydrogenated amorphous diamond-like carbon coatings have been deposited on glass and silicon substrates using an r.f. plasma-assisted chemical vapour deposition process. The mechanical properties of these coatings such as stress (bending beam measurements), hardness and Youngs modulus (nanoindentation measurements) were studied as a function of the r.f. bias voltage in the range 50–500 V. IR absorption spectroscopy and elastic recoil detection analysis were used to correlate these mechanical properties with the total hydrogen content and the hydrogen bonding configuration. Compressive stress, hardness and Youngs modulus are shown to reach their maximum values simultaneously at a bias voltage of about 200 V. At the same time, the hydrogen-bonded sp 3 :sp 2 ratio reaches a local minimum.