D.G. Teer

Deposition of Ti-N compounds by thermionically assisted triode reactive ion plating

Details are given of the influence of the ion current density on the properties of Ti-N compounds deposited at low temperatures (<600°C) by a thermionically assisted triode reactive ion-plating technique. As the chamber pressure increases, greater specimen currents are necessary, both to prevent the deposition of powdery TiN and also to ensure reaction for the formation of Ti2N and TiN at lower partial pressures of nitrogen. The ionization efficiency, being related to both pressure and current density, is suggested as a suitable parameter for defining optimum conditions. An ionization efficiency of about 0.3% is identified as the minimum required for the deposition of cohesive TiN, whilst values above this improve the densification and the hardness.

Characteristics of a thermionically assisted triode ion-plating system☆

Abstract There is increasing evidence to show that the properties of ion-plated coatings can be improved by increasing the specimen ion current density and by operating at low deposition pressures. This paper examines a technique of discharge support which facilitates such improvements. The characteristics of the discharge are presented and explanations are given for the effects observed. The recommended arrangement for maximized specimen ion currents utilizes a positive electrode and a thermionic source which is electrically floating so that the filament takes up a negative potential with respect to the earthed chamber. Direct biasing of the filament can also be used, obviating the need for the positive electrode.

Grain structure of ion-plated coatings☆

Abstract The structures of ion-plated copper coatings were studied and were related to plating parameters. It is shown that the structures vary from tapered or nodular growth structures with weak porous boundaries to dense fine-grained (1 μm) structures. If the discharge is intensified using a triode-supported system, dense structures with very fine grains (0.1 μm) are obtained.

The formation of low friction wear-resistant surfaces on titanium by ion plating

Abstract Titanium substrates were ion plated with aluminium, producing under certain conditions a graded interface 5 μm deep. The graded interface consists of a solid solution of aluminium in titanium together with TiAl 3 . The solid solution has a near perfect hexagonal close-packed structure and the hardness of the interface is about 850 VHN. The combination of increased hardness and modified structure results in low friction coefficients and wear rates, and the ion-plated aluminium film provides excellent corrosion resistance. Thus the method has immense practical application in preventing seizure and corrosion in aircraft fasteners.

Evaluation of coating wear resistance for bulk metal forming

A technique is described for the evaluation of wear-resistant coatings intended for metal-forming tools. This is based on the plane strain compression test and is intended to be suitable for laboratory operation. An approximate analysis of the frictional conditions is discussed. This facilitates the prediction of the onset of “sticking” between workpiece and tool, which should be avoided. Scanning electron micrographs are included showing typical wear effects on coated and uncoated dies. The effectiveness of the technique as a test for coating adhesion is also illustrated.

A comparison of vacuum-evaporated and ion-plated thin films using Auger electron spectroscopy☆

Abstract Auger electron spectroscopy was used to study the interfaces for copper on nickel and for silver on nickel formed by vacuum evaporation and by ion plating. It was found that for copper on nickel, i.e. a soluble pair of materials, vacuum evaporation and ion plating produce interfaces of similar depths but for silver on nickel, an insoluble pair of materials, ion plating produces an interface significantly deeper than that produced by vacuum deposition. The interface produced by ion plating is thought to be due to implantation of the high energy depositing particles.

Al-Zn coatings for the corrosion protection of steel

Abstract Aluminum coatings have been reported to be the most suitable for replacing toxic cadmium for the protection of steel and titanium alloys against corrosion. The relatively poor galvanic corrosion protection of aluminium coatings, however, has led to a search for a more effective coating. To this end, pure aluminium and controlled-composition Al-Zn alloy coatings were ion plated onto steel substrates. Over a range of coating conditions the aluminium and the Al-Zn alloy coatings have very similar columnar structures. They were equally successful in protecting the underlying steel. However, a simulation of the coating damage by masking the steel substrate during plating showed the galvanic corrosion protection of Al-2.5%Zn alloy coatings to be superior to that of aluminium. It is probable that this very effective sacrificial corrosion protection means that the structure of the coating is relatively unimportant and that excellent galvanic corrosion protection can be provided by low density columnar structure coatings of Al-Zn alloys.

Ion-plated aluminium bronze coatings for sheet metal forming dies☆

Abstract Aluminium bronze coatings on steel were deposited by the ion plating process using a slug-fed resistively heated evaporator. The coating material was Cu14Al4.5Fe1Ni alloy which is known to have good non-galling properties in sheet metal forming. The structures of the coatings deposited at various evaporation rates were studied by scanning electron microscopy, chemical microanalysis and X-ray diffraction. The composition of the coatings varied in a regular manner through the thickness and the grain size was small.

Influence of the deposition parameters on the structure of ion-plated chromium☆

Abstract A triode-assisted ion plating system was used to study the influence of deposition parameters such as bias voltage and gas pressure on the structure of chromium coatings. Three structure zones similar to those proposed by Movchan and Demchishin were observed. In particular it was possible by means of glow discharge intensification using the triode system to produce dense chromium coatings at low bulk substrate temperatures.

The ion plating of carbon

Abstract Ion-plated coatings of carbon have been deposited on several metal substrates The coatings are very adherent and in contrast with vacuum-evaporated films have a highly graphitic crystal structure. They are wear resistant and have a low friction coefficient. The method of deposition and the crystallographic and tribological studies will be described.