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This paper reports the results of preliminary assessment of the relative adherence of diamondlike carbon coatings on typical metal, ceramic, and polymeric total joint prosthesis materials. Coatings were applied, using an ion assisted method, from a hydrocarbon precursor. The latter was generated in vacuum and allowed to condense on the workpiece surface while simultaneously being subjected to 20–50 keV nitrogen ion bombardment. Such ion energies lead to disruption of CH bonds, with most of the hydrogen escaping in gaseous form; this leaves behind a principally carbonaceous amorphous residue, i.e. DLC. A cobalt-chrome alloy, an alumina, stainless steel, and a high density polyethylene (HDPE) were coated with DLC under varying surface preparation, and ion deposition conditions. Adhesion was measured qualitatively by means of scratch hardness testing. The smoothness of the DLC coating on glass was examined by atomic force microscopy. Differences in adhesive strength and damage mechanisms are discussed in terms of coating conditions, and implications for performance under realistic total joint loads of 6 to 10 MPa are considered.

The use of thin metal interlayers to promote the adhesion of coatings is documented. For instance a thin titanium interlayer has been found to improve the adhesion of titanium nitride coatings deposited by a range of physical vapour deposition (PVD) processes. However, much less has been reported about coatings produced by ion beam assisted deposition (IBAD) techniques which have the advantage of low deposition temperatures (

Films of amorphous carbon have been produced by ion-beam decomposition of polyphenyl ether and pentaphenyl trisiloxane. The composition of the films has been elucidated using Rutherford backscattering and elastic recoil detection analysis. Secondary Ion Mass Spectroscopy has revealed the elemental depth profile of the coatings. Microstructural information is inferred from laser Raman spectroscopy. The stress has been measured by the curvature change in single crystal silicon and by radial crack measurements on glass substrates. A comparison of tribological properties, such as hardness, coefficient of friction and adhesion, is made for a variety of substrate materials. The dependence of these properties on coating process parameters is also discussed.

The range and distribution of ions in matter is of major importance in the modification of materials by implantation. In this investigation the metal vapor vacuum arc (MEVVA) ion source was used as a versatile means of generating beams of metallic ions to implant 26 different species into carbon targets to a dose of 10 16 ions cm -2 . Vitreous carbon was chosen as the target in order to provide an electrically conducting low Z value material in which no channeling can occur and redistribution of implanted atoms by diffusion is very unlikely. Range distributions were determined by Rutherford backscattering spectroscopy. The charge state distribution for each ion species was monitored and used in conjunction with PRAL and TRIM code calculations to arrive at the theoretically predicted ion ranges. Mean ion energies were between 78 and 192 keV. The results show significant anomalies in range which are not inconsistent with an oscillatory Z 1 dependence. For ion species in the region around Z 1 =75, the ratio of measured to calculated ranges can rise as high as 1.28 ± 0.08, while around Z 1 = 41 this ratio is significantly lower than 1.0. These findings are discussed in relation to other experimental observations and current theoretical ideas.

Ion beam mixing in cobalt silicide has been studied using silicon, argon and helium ions. Both Co-Si and Co-SiO2-Si systems have been studied, the latter in the form of coated silicon wafers which have not had their native oxide removed. Dose and temperature dependence and the effects of post-bombardment annealing have been studied. Oxide free samples show both temperature dependent and temperature independent mixing regimes. Mixing is retarded in samples with an oxide layer and this is reflected in the mixing activation energies which for Si+ ions are 0.90+or-0.28 eV and 2.17+or-0.79 eV for the two types of sample. There is evidence that implanted Si dilutes the interfacial barrier and enhances migration. The results indicate that the chemical species of the ion is important in determining the degree of mixing. Argon ion dose dependence experiments indicate a minimum dose of 1*1016 ions cm-2 for the onset of mixing (at 350 degrees C) in both types of sample. Temperature dependence studies have yielded mixing activation energies for Ar+ ions of 0.46+or-0.10 eV from the Co-Si samples and 0.64+or-0.18 eV for the samples with oxide present. These values are intermediate between those obtained for Si and Xe bombarded samples. He+ ion bombardment studies indicate that mixing is not associated with ionization spikes. Considerations of ion concentration, bombardment flux, silicide thickness and activation energies favour thermal spike mixing rather than models based on radiation enhanced diffusion.

The high strength and creep resistance of modern titanium alloys makes them potentially attractive for aero engine compressor blades operating at temperatures above 500° C, to improve thermal efficiency and performance. However, all these alloys suffer from oxidation at such elevated temperatures and the in-diffusing oxygen stabilizes the more brittle alpha-phase of the alloy making it prone to crack under stress. There is thus a need for protective highly adherent coatings. In the present work, chromium was deposited with simultaneous ion bombardment using 60 keV nitrogen ions, to a thickness of 1 μm. Ion assisted deposition provides excellent adhesion and a very compact, pore-free coating with a small grain size. However, at high temperatures titanium diffuses into the chromium and impairs its protectiveness. To combat this, a diffusion barrier of silicon nitride was deposited first, by evaporating silicon and matching the rate of arrival of Si atoms with a 0.5 keV nitrogen ion beam from a Kaufman source to produce Si3N4 to thicknesses from 0.1 to 0.3 μm. As an added protection, in some experiments an overlay coating of about 0.3 μm of silicon nitride was deposited after the chromium layer. Oxidation was carried out in air at temperatures between 600 and 800° C and for periods up to 100 h. Subsequent analysis by SIMS showed excellent protection up to at least 700° C but diffusion across the barrier occurred at 800° C. Titanium nitride was less successful than silicon nitride for barrier purposes.

The effects on the oxidation resistance of nickel of nitrogen ion bombardment and boron coatings have been studied. Reductions in thermal oxidation of up to 80% have been observed. Ion bombardment causes intermixing of the boron and nickel which is maximized when the peak of the ion distribution coincides with the nickel-boron interface. Boron nitride formation increases oxidation resistance and also improves the mechanical strength of the surface film. This allows substrates with thicker boron layers to withstand interfacial stress associated with the out-diffusion of nitrogen. Thin boron layers tend to rupture after high dose bombardment leading to increased oxidation. Analysis by secondary ion mass spectrometry indicated out-diffusion of nickel during oxidation but diffusion of boron inwards over the full diffusion range of the oxygen. Studies using scanning electron microscopy showed random island growth of the oxide although grain orientation in some cases affected the oxidation rate. No localized enhancement of oxidation around grain boundaries was observed, suggesting that bulk diffusion dominates short-circuit diffusion paths during oxidation.

Ion beams can provide the most versatile and sophisticated family of methods for tailoring the surface properties of all classes of material (semiconductors, metals, ceramics, polymers, etc.). Their usefulness is due to the particle energies they carry which are much greater than conventional thermal energies or interatomic bond energies. Consequently, non-equilibrium modifications can be brought about, the results of which are rapidly quenched into place. This paper deals with the application of these methods for the improvement of tribological, optical, electrical, corrosion, and catalytic properties of material surfaces.

The strength of adhesion between a scale and substrate metal is considered in the light of a recent analysis of grain boundary weakening in terms of the embedded atom method. It is shown that this can explain the behaviour of impurities such as sulphur or rare earths in a variety of oxidized alloys.

Energetic ions beams may be used in various ways to modify and so improve the tribological properties of metals. These methods include: — ion implantation of selected additive species; — ion beam mixing of thin deposited coatings; — ion-beam-assisted deposition of thicker overlay coatings. The first of these techniques has been widely used to modify the electronic properties of semiconductors, but has since been extended for the treatment of all classes of material. Tool steels can be strengthened by the ion implantation of nitrogen or titanium, to produce fine dispersions of hard second-phase precipitates. Solid solution strengthening, by combinations of substitutional and interstitial species, such as yttrium and nitrogen, has also been successful. Both ion beam mixing (IBM) and ion-beam-assisted deposition (IBAD) use a combination of coating and ion bombardment. In the first case, the objective is to intermix the coating and substrate by the aid of radiation-enhanced diffusion. In the latter case, the coating is densified and modified during deposition and the process can be continued in order to build up overlay coatings several μm in thickness. The surface can then be tailored, for instance to provide a hard and adherent ceramic such as silicon nitride, boron nitride or titanium nitride. It is an advantage that all the above processes can be applied at relatively low temperatures, below about 200° C, thereby avoiding distortion of precision components. Ion implantation is also being successfully applied for the reduction of corrosion, especially at high temperatures or in the atmosphere and to explore the mechanisms of oxidation. Ion-assisted coatings, being compact and adherent, provide a more substantial protection against corrosion: silicon nitride and boron nitride are potentially useful in this respect. Examples will be given of the successful application of these methods for the surface modification of metals and alloys, and developments in the equipment now available for industrial application of ion beams will also be reviewed.

This paper begins with a review of recent studies of the progressive mechanisms of degradation in total hip and knee replacements. It is concluded that wear is a major problem due to resulting tissue reactions especially to fine polymeric debris. Methods of lessening or overcoming these problems by modern methods of surface modification are considered, among these being ion implantation and ion beam-assisted deposition. It is argued that the physical and chemical properties of diamond-like carbon (DLC) coatings make them especially promising for the reduction of friction and adhesive wear in all forms of total joint replacement. An ion beam-assisted method of depositing DLC efficiently at low temperatures is described, together with the physical properties of the resulting material.

Diamond-like carbon (DLC) is produced by the simultaneous condensation of a vapour of polyphenyl ether and the impact of a 40-80 keV nitrogen ion beam on a substrate. The cracking of the hydrocarbon produces a hard, amorphous carbon coating with a low hydrogen content (14 atomic %), as determined by Raman spectroscopy and nuclear reaction analysis. The Raman spectra show that the microstructure of 65-110 nm thick coatings made simultaneously on a wide range of substrates varies between amorphous DLC, on substrates such as silicon and stainless steel, and disordered graphite, on substrates such as silica. Measurements of the curvature of coated silicon wafers show that the coatings are compressively stressed, even though the thermal mismatch stresses are tensile. Dry friction measurements over several passes on the DLC material gave values between 0.11 and 0.18, dependent mostly upon substrate surface finish. This deposition process for DLC allows coatings to be made over large areas (up to 1 metre diameter) at low temperatures (

Harwell's Blue Tank ion implantation facility has been used to deposit diamond-like carbon (DLC) coatings between 0.065 and 17.5 microns thick over areas of up to 1 metre diameter, at temperatures below 140°C. A 40-80 keV beam of nitrogen ions, from a Harwell-designed bucket type ion source, is used to crack a vapour of polyphenyl ether diffusion pump oil onto a substrate of any material. The deposition process and equipment are described in detail, and the properties of the coatings produced are presented.

Carbon films having many of the properties of diamond have been deposited using a laser plasma technique which involves no hydrogen contamination. Laser ablation of graphite feedstock enables growth rates of typically 0.5 μm hr−1 over large areas (≤100 cm2) on a variety of substrate materials and geometries without pre-treatment. Mechanical measurements are described for such a coating ~1μm thick deposited onto a single crystal germanium substrate. Hardness measurements were made with both Knoop and Vickers indent systems and the latter data was analysed to remove the substrate effects and indentation size effect (ISE) contributions. The coating material hardness was found to be in the range 3500-4000 Vickers, well above that of the coating/substrate composite (1150) and Ge substrate (1000). The coating-substrate system failed by brittle fracture of the substrate during scratch testing measurements (~1 kg load) so that no measurement of the adhesion was possible. Friction measurements (μ~0.1 at 100 gms load) and laser Raman spectroscopy were performed to assess further the properties of the material.

The effect of implantation induced radiation damage on the oxidation of aluminium has been studied using implanted krypton. Annealing studies have revealed a complex recovery process tentatively ascribed to the repair of point defects, dislocation loops and subsequent grain growth. Higher dose (1O17 ions cm−2) xenon implants resulted in implant out-diffusion and surface exfoliation during annealing.

Comparison with results for thermally oxidised titanium and anodised aluminium show agreement for Bi+ and Pb+ implants, which cause enhanced oxidation, but differing behaviour for implants such as Ce+ and In+. Pt+ causes a marked inhibition in the oxidation rate, and the distributions of this impurity and oxygen after anodic oxidation show anomalous features which seem to be connected with this inhibition. Self-implant and annealing studies indicated that radiation damage was of little importance in the present work.

A study has been made of the influence of the surface ion implantation of platinum, silicon, aluminium with and without yttrium and cerium upon the oxidation behaviour of a 20% Cr-25% Ni-Nb stabilized stainless steel. The oxidation tests were in carbon dioxide (1 atm pressure), at 825°C, for periods up to 5900 h. Platinum, silicon and aluminium implantation had no significant influence upon either the extent of kinetics of oxidation or of spallation. An additional implantation of yttrium into a surface layer containing implanted aluminium improved the oxidation resistance slightly but had no effect on oxide adherence. Cerium implantation exerted the greatest influence on the oxidation behaviour of the steel. It reduced by at least a factor of two the attack of the steel throughout the exposure period and also improved oxide adherence. It was combined, probably with chromium, as a mixed oxide. The improvement in oxidation resistance with the incorporation of cerium in the protective barrier film derived from a more effective restriction to cation movement than with the film formed on the steel alone. The mechanical properties of the outer layer were also improved by the incorporation of cerium to account for the improved oxide adherence.

Ion implantation can lead to great modifications of titanium oxidation at 600°C in oxygen atmosphere. Oxygen short circuit diffusion is enhanced by the ion bombardment of the metal but can be reduced if the amount of the implant exceeds its solubility limit in α-Ti. Kinetic measurements have been performed with Rb, Cs or Ba implanted samples. The results suggest that heavy alkaline implants inhibit the Ti (+III) Ti (+IV) oxidation whereas barium decreases the oxygen diffusion coefficient in TiO2.

The wear-reducing effect of ion implantation can be investigated with a high accuracy in a single experiment if implanted and unimplanted regions of a symmetrical wear part are subjected to the same tribological conditions. By labelling these different surface sections with individual radioactive tags it is possible to compare the wear behaviours of differently processed surfaces at the same time using modern radionuclide wear measurement techniques. This procedure is illustrated for a gear. In order to obtain some initial ideas of the wear-reducing effect of ion implantation on gears a conventional gear with 16 teeth was tested on the Forschungsstelle Zahnrad und Getriebe rig. For direct demonstration of the effect of implantation the eight teeth of one half of the gear were implanted with nitrogen ions over the tooth flanks, while the other eight teeth remained untreated. For the wear measurement by the two-component concentration method, one half of the gear was irradiated with deuterons to convert iron into 57Co, and the other half was irradiated with protons of a different energy to convert iron into 56Co. Both radionuclides are clearly distinguishable in the γ spectrum. During the 614 h test a high quality oil was used over all the load range of the standardized test rig; this mainly caused slight wear. The wear rates of the implanted half were up to 58% lower than those of the other half. The higher load showed a clearer distinction between the two halves. It is possible to measure continuously and simultaneously the wear on two different iron surface sections by the two-component concentration method in one test run. Depending on the load the wear of the gear can be reduced below 50% by ion implantation. A final judgement of the influence of ion implantation on pitting or fatigue wear on a gear is not possible before further investigations have been completed.

The thermal oxidation of polycrystalline zirconium implanted with 21 different ion species has been studied by using the nuclear reaction 16 O( d , p 1 ) 17 O. A very good agreement has been found between the oxidation kinetics of unimplanted zirconium as determined by the nuclear reaction and those previously measured gravimetrically. Oxidation kinetics show a time dependence which is cubic or parabolic depending upon the surface treatment before oxidation. Ion implantation produces significant changes in oxidation rate but the time dependence remains the same. A strong correlation has been found between the behaviour of ion implanted systems and that reported for binary alloys, confirming the hypothesis that the ionic size of the additive is the major parameter governing the influence upon the oxidation of zirconium. The implanted species which inhibit oxidation possess ionic radii lying between 80% and 100% of that of Zr 4+ . An explanation of their beneficial effect based on an increase of the plasticity of the growing oxide is presented.

Some aspects of the hard bubble suppression mechanism have been investigated in LPE grown magnetic bubble garnets, (Y1.65Sm0.18Lu0.21Ca0.96) (Fe0.96Ge4.04) O12. Following implantation of neon ions at a standard suppression dose of 5*1014 cm-2 collapse field measurements indicate effective hard bubble suppression. For this dose however, 57Fe Mossbauer spectra indicate the pressure of a non-magnetic surface layer while X-ray diffraction traces and alpha particle backscattering measurements indicate that the layer is structurally disordered. These observations are inconsistent with the capping layer model of hard bubble suppression. Implantation of nitrogen ions resulted in similar hard bubble suppression but produced a totally different form of radiation damage. Axial channelling of 800 keV nitrogen ions along the (111) direction is observed.

The Rutherford backscattering of nitrogen ions at 3.5 MeV has been applied to the analysis of metallic deposits collected on carbon probes inserted into the plasma region of the DITE Tokamak. Static probes enabled the radial impurity distribution to be measured, while rotating probes were used to obtain a time-resolved analysis. The sensitivity of the method is very high, so that data can be obtained from a small number of discharges. The results are consistent with other evidence that arcing to the wall and limiter is a major source of impurities. Other applications in atmospheric contamination studies and clean-room monitoring are discussed briefly.

The ion implantation of chosen species into a variety of technologically important metals and carbides has been shown to bring about striking changes and improvements in tribological and corrosion behaviour. There is considerable scope for research into these important phenomena, using ion implantation as a versatile tool. The industrial applications for surface treatment of components and tools of many kinds also appear to be widespread, and equipment for carrying out the process on a production scale has been developed to the point of commercial manufacture.

Mo, Au, and Cu ions of 150−350−keV energy have been implanted, off axis, in

The origin of the tail on the distribution of phosphorus atoms implanted into misaligned silicon crystals has been established by measuring the number of phosphorus atoms transmitted through thin silicon crystals during implantation. Experiments on 〈110〉 and 〈100〉 crystals show that the tail is due entirely to atoms which are scattered into channels. The preparation of crystals 0.4–0.8 μm thick from epitaxial layers by selective electrochemical etching and ion beam thinning is described and the measurement of their thickness by backscattering techniques is discussed. It is suggested that the tails on the profiles of other dopants in silicon are also due to atoms which have entered channels in the crystals.

Ion implantation as a method for the treatment of metals to improve, for instance, their resistance to wear and corrosion, is reviewed from the standpoint of general principles. A closely related technique, in which ion bombardment is used to enhance the properties of deposited coatings, is briefly set in perspective as a means of extending the scope for the application of industrial equipment. A few industrial examples are given to show how ion implantation can have important economic benefits, especially when carried out on a large scale.

As a result of novel techniques and the greater availability of sources of intense, large-area ion beams, the process of ion-assisted coating (IAC) is receiving attention worldwide. Reactive deposition in selected backfill atmospheres, use of ion energies ranging from 100 eV to 100 KeV, in concurrent or sequential deposition and ion bombardment are some of the modern techniques being actively exploited. It has been shown possible to prepare coatings at low temperatures on polymeric substrates. Applications include hard, low-friction coatings for tools and bearings, coatings of controlled optical properties, for example, as IR antireflection coatings, transparent coatings on polymers, decorative coatings etc. Nitride, oxide and oxynitride films have been investigated, produced by ion bombardment with nitrogen or oxygen ions, sometimes in reactive atmospheres containing CO or O 2 . Surface chemistry has been shown to play a major part in determining the final composition, and non-equilibrium diffusion of absorbed species can be important even at the lowest temperatures. A review will be given of work in progress in the U.S.A., Europe, Japan and Australia in this field, and notable achievements such as the production of cubic BN and diamond-like coatings will be assessed.

Ion beam mixing of Yb coated nickel films has been studied using Kr+ and O2 + bombardment. The use of a nickel overlayer was found to be effective in protecting the films from oxidation. By assuming the validity of a simple solution of the diffusion equation, effective diffusion coefficients at different Kr+ bombardment temperatures were obtained for Yb/Ni mixing. The diffusion was linear with an apparent activation energy of (0.18±0.03) eV. This result is discussed in the light of radiation enhdnced diffusion and cascade mixing theory. No mixing was observed with O2+ bombardment. This indicates that the chemical nature of the ions used is of importance and it is suggested that trapping of oxygen atoms in the impurity film is responsible for this effect.

Specific nuclear resonance reactions, 4He ion backscattering and ESCA have been used to investigate the depth distribution of oxygen, carbon, fluorine and magnesium in complex corrosion films formed on Magnox AL 80 after exposure to nuclear reactor coolant gas and to multi-component aqueous solutions. Results of experiments with water enriched in H218O have shown that magnesium hydroxide which is highly permeable to solution is formed at the metal/film interface. The oxide formed in hot CO2 contains carbon, carbonate and traces of carbide-like material. This oxide hydrates uniformly in solutions of pH ⩾ 11.5 but complete equilibration with solution is rather slow. In solutions containing fluoride ions which inhibit the corrosion reaction the product is a hydroxy-fluoride Mg(OH)2−x and fluoride also exchanges to an appreciable extent with pre-formed magnesium hydroxide.

Ion bombardment induced mixing of Ta-Si films has been studied using 400 keV argon ions. Doses varied from 7×1014 to 1×1017 Ar+ cm−2 with post-bombardment anneals of 180–900 s at temperatures in the range 600–860 °C using radiant heating. Silicide uniformity and stoichiometry were determined using alpha backscattering spectrometry. Optimum fabrication parameters were determined with regard to subsequent material sheet resistivity, temperature coefficient of resistance and application as a temperature sensing material. Similar measurements were made on CoSi2 layers prepared by annealing ion bombarded samples and comparison with silicide films arising from purely thermal annealing was made.

The effect of ten species of ion-implanted impurities on the thermal oxidation of copper has been studied. The majority of these increased the oxidation resistance of the copper, the greatest effect (85% decrease in oxidation) being caused by Ti. Only Xe and Cs caused significantly increased oxidation in dry oxygen, but in the presence of water vapour the effect of Ti+ implants was reversed and increases in oxidation rate up to 100% were observed. Electrical measurements on devices formed by applying a gold probe to the oxide surface showed a correlation between switching voltage and the effect of the implant on the oxidation rate. A simple model is proposed whereby the observed behaviour is ascribed to the creation of an n type region in the predominantly p type oxide such that inward hole diffusion is inhibited during oxide growth.

Cobalt silicide formation by ion beam mixing has been studied, under bombardment with inert (neon) ions. Mixing is found to be impeded by the presence of an interfacial oxide layer. Stoichiometric silicide formation is dependent upon the use of optimum ion dose and energy. In contrast to argon and xenon bombardment high doses of neon lead to exfoliation of the surface due to migration and localisation of the gas in the sub-surface layer. The mixing behaviour is discussed in terms of both radiation enhanced diffusion and thermal spike models.

An entirely new method of metal finishing, by the process of ion implantation, is described. Introduced at first for semiconductor device applications, this method has now been demonstrated to prod...

The effect on thermal oxidation of implantation of the alkali species Li, Na, K, Rb and Cs has been studied. A correlation is found with the atomic and ionic radii and atomic masses of the implanted species, the larger ions leading to greater oxidation. We propose that the implanted species may affect the oxide plasticity and that this may be the controlling factor which determines the degree of oxidation.

The implantation of 300 keV Ti + ions into 18W4Cr1V bearing steel to doses of between 10 13 and 10 17 ions cm −2 was found to alter significantly its mechanical behaviour under dry sliding conditions. Both friction and wear were measured continuously on a pin-on-disc machine during a 3 h test period. Friction was found not to be directly dependent on dose but the increase in hardness and the increase in wear resistance were observed to be linearly dependent on dose, for doses above 10 15 Ti + ions cm −2 . Only the medium doses (10 15 and 10 16 Ti + ions cm −2 ) reduced friction. Post-implantation heat treatment of the specimens produced further changes in the properties investigated. Generally, a reduction in the wear rate of the implanted disc resulted in a reduction in the wear rate of the unimplanted pin. These results are explained in terms of changes in the surface oxidation and the nature of the deformation of the implanted specimen. Topography and microscopy measurements on the wear tracks suggest that Ti + ion implantation alters the nature of the deformation of the treated material.

Four surface alloys in nickel produced by high dose implantation of Ta+, Sn+, Er+ and La+ ions were investigated. Rutherford backscattering and channelling of 2.9 MeV helium ion beam was employed to determine the substitutional solid solubilities and the bombardment-induced disorder. Ta, Sn and Er form substitutional solid solutions beyond solubility limits whereas La is found to be insoluble. It was shown that these and the other implanted alloys reported in nickel obey the recent “modified Hume-Rothery rules” proposed for metastable alloys formed by ion implantation. The radiation induced disorder extends well beyond the ranges of Sn+ and Er+ ions.

A 1200 A thick silicon layer has been diffused into pure iron under heavy ion irradiation over the temperature range 350–580°C. The enhanced diffusion coefficient was shown to exhibit no temperature dependence, consistent with annihilation of defects at fixed sinks. Specimens with the highest silicon concentration exhibited the best oxidation resistance at 600°C in pure oxygen.

Conventional microhardness and indentation (scratch) testing have been conducted on cemented tungsten carbide samples implanted with nitrogen ions at 90 keV as a function of ion dose and sample temperature during implantation. The main results obtained are (a) nitrogen implantation can increase the surface hardness up to 40%, (b) the optimum dose lies between 1 and 3 × 10 17 atoms cm −2 for the different grades evaluated, and an excess dose can cause softening and (c) there is little variation with implantation temperature of the hardening effect between 140 and 400°C. No hardening is observed at 550°C, with a reduced hardness increase obtained at 70°C. A programme of industrial trials considering several different applications of WC-Co tools has been commenced. In particular, field tests of drills and routers were conducted by a company specializing in computer-controlled drilling and cutting out of glass fibre/epoxy resin printed circuit boards. Preliminary results will be reported, together with microanalysis of the treated surfaces.

In addition to its use in the semiconductor device field, ion implantation is a valuable technique for modifying the surface properties of materials. Treating the surface of metals in this way can significantly reduce wear and high temperature oxidation

The implantation of electrically accelerated ions of chosen elements into the surface of material provides a method for improving surface properties such as wear resistance. High concentrations of nitrogen implanted into metals create obstacles to dislocation movement, and certain combinations of metallic and non-metallic species will also strengthen the surface. The process is best applied to situations involving mild abrasive wear and operating temperatures that are not too high. Some dramatic increases in life have been reported under such favourable conditions. A more recent development has been the combination of a thin coating with reactive ion bombardment designed to enhance adhesion by ion mixing at the interface and so provide hardness by the formation of finely dispersed nitrides, including cubic boron nitride. These coatings often possess vivid and decorative colours as an added benefit. Developments in the equipment for industrial ion implantation now offer more attractive costs per u...

An increase in the concentration of aluminium in a 0.25 μm thick surface layer of a 15%Cr-4%Al yttrium free Fecralloy steel by the implantation of up to 10 17 ions cm −2 had no significant influence upon the oxidation behaviour of the steel, in air, at 1100°C. An alloy addition of 0.86% yttrium reduced the attack and oxide spallation for at least 3271 h, while the surface implantation of 3 × 10 15 yttrium ions cm −2 , together with 10 17 aluminium ions cm −2 improved the oxidation behaviour of the steel for only a limited period (784 h). It is concluded that yttrium alloy additions in the Fecralloy steels exert their beneficial influence on the oxidation behaviour within the oxide film rather than the subscale.

It has been known for some years that ion bombardment of a material will bring about a redistribution of its constituents. This can take place by a direct recoil process or as a result of collisional relocation within the collision cascade, known as cascade mixing. Alternatively, there are several mechanisms of radiation enhanced diffusion which may occur if the temperature is sufficiently high. The time scales for these processes are very different. Recent developments have led to the exploration and use of these effects in order to introduce atoms from a coating layer into the substrate below by ion bombardment as an alternative to their direct implantation. This review attempts to clarify the physical processes that occur, and to describe some recent applications to contacts on silicon devices, wear resistant surfaces in titanium alloys, and to achieve corrosion resistance in iron and nickel.

A systematic study has been made of the effects of Group III and rare earth impurities on the thermal oxidation of chromium. The elements were introduced by ion implantation. The oxidation properties and impurity behaviour were studied using alpha particle Rutherford backscattering, nuclear reaction analysis, CAMECA ion microprobe analysis, X-ray diffraction and scanning electron microscopy. Cr+ ion implantation was used to study radiation damage and annealing behaviour. For unannealed chromium the oxidation rate was found to be reduced by 60-90% by all the implanted species. Some evidence was found for a correlation with the mobility of the implanted species, X-ray measurements indicate the possible formation of a binary oxide.

The level of activity both in research and in the commercial development of ion implantation as a means of improving wear resistance in metals has increased significantly over the past 2 years. The mechanisms of hardening, both by dislocation pinning and by the formation of hard precipitates, have become better understood. Structural factors and the role of the stacking fault energy are less well understood, but in general it appears to be more difficult to harden f.c.c. materials by implantation, perhaps because of the multiplicity of slip systems available. The first commercial machines developed specifically for industrial applications are now in routine operation; the chief areas of use are for the treatment of tools employed in the moulding of plastics, industrial knives, punches and dies. The simple process of nitrogen implantation has proved effective not only in steels but also in cemented carbide, titanium, chromium and aluminium. Mould tools typically last ten times longer after treatment. The low temperature of the process, the lack of surface degradation and the absence of any interface account for its success, but costs are still relatively high (approximately equal to that of coatings obtained by chemical vapour deposition). More powerful sources of ions are being developed, however, and it seems feasible to gain a further order of magnitude in throughput, which would improve the economics considerably. In addition, the more novel concept of ion beam mixing of a thin deposited coating (e.g. of tin, silicon etc.) by energetic ion bombardment extends greatly the versatility of equipment developed solely for gaseous ion beams. Dual implantations of metallic and gaseous ion species can now be done by sputtering ion sources. Applications relating to improved oxidation resistance thus become practicable. Ion beam mixing will also be discussed as a pretreatment before coating (e.g. by ion plating, electrodeposition or spray coating). The scope for tailoring the surface composition and structure is very wide.

The effects of ten ion-implanted impurities on the oxidation of cobalt have been studied. Initial studies of unimplanted cobalt showed that oxidation is critically dependent on the surface pretreatment of the cobalt metal. Comparison of implanted samples which had and had not been given a post-implantation anneal indicated that the presence of radiation-induced defects can mask the effect of particular atomic parameters such as valency and atomic size. For annealed specimens, some correlation was found between these parameters and oxidation behaviour. X-ray measurements failed to provide evidence for the existence of protective binary oxide barrier layers, but these may have been in too small a concentration or too dispersed to be detected. Secondary ion mass spectrometry studies showed the mobility of the implant species to be of importance, particular species either being incorporated in the growing oxide or segregating at the metal-oxide interface.

The effects of implanted in species Pt+, Lu+, Yb+ and Xe+ on the anodic oxidation of Ti in glycol borate electrolyte have investigated. Rutherford backscattering and nuclear reaction measurements have shown that post-implantation thermal treatment at 700°C produces a marked improvement in the resistance to surface oxidation of Ti with implanted Pt+ ions, which may form cluster to act catalytically. However, this treatment causes enhancement of oxidation for Ti with Lu+ and Yb+ implants. Radiation damage influence on oxidation has been examined using implanted Xe+ ions, with results which show that surface oxidation of Ti is enhanced, but there are indications that this enhancement may due, in part, to the lattice strain produced when the Ti accomodates the Xe+ ions.