Ion implantation, which has made great progress as a method of impurity doping in semiconductors, has lately attracted considerable attention as a surface modification process for metals, ceramics, polymers and other materials. This report reconsiders ion implantation processing from the standpoint of surface layer treatments (i. e. by comparing it with physical or chemical vapour deposition), and a related technique known as ion beam enhanced deposition is introduced. The ability of high fluence implantation to form new metastable surface alloys and compounds is described and as an example the reasons for improvement in the wear resistance of steels by nitrogen implantation are explained.

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The basic structure of modern ion implanters and related machines for surface-layer modification is reviewed. Four kinds of machines-ion implanters, direct ion implanters, ion-beam enhanced deposition apparatus, and high-energy ion implanters-are introduced and their components are described, in an effort to increase understanding and facilitate proper use.

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Ion implantation is a unique technique for creating non-equilibrium phase surfaces or films, since atomic injection and atomic mixing can be effected at low temperatures without the restrictions of thermal diffusion or equilibrium phase diagrams. In this report we describe how ion implantation, including ion irradiation, can modify the microstructures of metals and synthesize specific structures such as metastable precipitates, amorphous phases, and quasicrystal phases. The application of ion implantation to surface and film modification to control the physical and chemical properties of the materials is also reviewd.

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The current status of research on mechanical properties is reviewed with emphasis on ion-implanted metals. Ion implantation has been successfully used to produce significant improvements in the wear resistance, hardness and fatigue endurance of metals such as steel, titanium, aluminum and copper. Some attempts to study how ion implantation affects mechanical properties of metals are shown.

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Application of ion implantation to the modification of the electrochemical properties of metals are reviewed. It has been observed that ion beam radiation, alloying, and chemical compound formation associated with an ion implantation influence the electrochemical reaction properties of metals. The anodic dissolution reaction of metals is an important process in corrosion, and its suppression by ion implantation is expected to be a useful modification for corrosion inhibition. The anodic dissolution of ion-implanted surface layers has been investigated by means of multisweep cyclic voltammetry. The ion implantation of metal ions, such as Cr⁺, Ti⁺, and Ta⁺, to form a passive surface layer has been found to be effective in the corrosion inhibition of iron substrates. The effect on corrosion behavior due to the amorphization associated with ion implantation has also been investigated, and B⁺-implantation was found to be effective in the amorphization of pure iron and martensitic stainless steel, but not in that of austenitic stainless steel. Modification of metal substrates, such as Ti, Al, Mg, Cr, Ag, has been studied from various points of view, and the formation of TiN by N⁺-implantation has been extensively studied because of its high hardness, wear reduction, gold color, and high corrosion resistance. In future, extremely high-dose implantation will be investigated as a means of forming surfaces offering new properties and functions.

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The structure of ion-implanted ceramics and the relationship of implantation to hardness, strength, resistance to cracking, friction and wear are reviewed. Ion beam modification of the interface of ceramics coated with metallic films, and its influence on adhesion, friction and wear characteristics are also described.

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The effect of nitrogen implantation on the wear behavior of a series of hard electroplated chromium specimens which were plated under various current densities from Sargent bath was studied.
In the unimplanted condition, chromium layers deposited at higher current density showed poorer wear resistance, but large improvements in wear properties and increases of surface hardness were obtained by nitrogen implantation. Futher, the electrochemical properties of the implanted speciemens by multi-sweep cyclic voltammetry showed that the anodic dissolution of the chromium electrode is suppressed to a great extent by implantation of nitrogen.
Concentration depth profiles and binding energy were measured for chromium, nitrogen and oxygen by AES and XPS. In the outer layer both Cr (III) oxide and Cr₂N were found, and the following layer was Cr₂N.
These results suggest that improving the properties of hard electroplated chromium is closely related to modification of the composition of the chromium surface.

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A study has been made of the microstructure and mechanical properties of chromium subjected to high-dose nitrogen implantation. The substrate used was polycrystal chromium plates 1mm in thickness with a purity of 99.9%. The implantation of nitrogen (N⁺) ions was performed to doses of from 1×10¹⁷ to 1×10¹⁸ ions/cm² at an energy of 100keV. The substrate temperature during N⁺-implantation was kept at approximately 20°C. The depth profiles of atoms in the implanted layers were estimated by Auger electron spectroscopy combined with Ar⁺ sputter etching. The identification of nitrides produced by implantation was practiced by X-ray diffraction. Near-surface hardness was measured by a Knoop hardness tester. Friction coefficients were measured using a Bowden-Leben type friction testing machine. The nitrogen depth profile for the highest-dose sample showed a quasi-rectangular distribution, and maximum concentration did not exceed about 50at%. The X-ray diffraction patterns revealed that various nitrides were formed at each dose, and the increase in hardness corresponded to the dose increase. The friction coefficient for the highest-dose sample was less owing to the formation of chromium nitrides. It is concluded that the formation of nitrides by high-dose nitrogen implantation is useful for improving the mechanical properties of chromium plate.

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Tests were carried out on nitrogen-ion-implanted cutting tools in respect of tool fracture during interrupted turning, cutting forces in continuous turing, and hardness in order to investigated the effect of nitrogen-ion implantation. The results were as follows.
(1) Nitrogen ion implantation reduced the initial rate of breakage, but had no effect on the chipping that occurs near the tip of the cutting edge, or on fractures in tools used for long periods.
(2) Cutting forces varied between nitrogen implanted cemented carbide tools and diamond tools, in the turning of pure aluminum and pure copper, but under several cutting conditions, the effect disappeared in a short time.
(3) The hardness of the nitrogen-implanted layer decreased in the case of cemented carbide and ceramics, but not in the case of pure metal.

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Nitrogen implantation into steel is expected to result in desirable surface characteristics such as resistance to wear and corrosion. The depth profile and chemical state of an implanted element have an important influence on the characteristics. Depth profiles of nitrogen implanted into steel as taken by various kinds of depth profiling methods were compared.
An as cold-rolled plain steel sheet (SPCC) was implanted with nitrogen at an energy of 20keV and doses of 1×10¹⁷-1×10¹⁸ions/cm². Nitrogen depth profiles were taken by glow discharge spectroscopy (GDS), as well as by AES, XPS, RBS and XRD. It was found that;
1) Results obtained by all methods were in good agreement.
2) The peak concentration of implanted nitrogen in steel saturated at about 25 at % and did not depend on ion dose.
3) A region of nitrogen implanted at a given energy level abnormally spread in accordance with increases in ion dose.
4) Implanted nitrogen ions combined with iron to form iron nitrides.

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Ion implantation in sintered SiC specimens was carried out with 150keV Cu⁺ ions at doses of 1× 10¹⁶-1×10¹⁸ions/cm². Characterizations of the specimens were examined by thin-layered X-ray diffractometry and Auger electron spectrometry. XRD patterns show no formation of new crystalline structures related to implanted copper. AES results show that implanted copper forms a Gaussian distribution up to a dose of 1×10¹⁷ions/cm², and at a dose of 3×10¹⁷ions/cm², the copper migrated toward the surface to reform in a certain shape with two peaks. Carbon in SiC was enriched in the implanted region and formed graphite at doses of 3×10¹⁷-1×10¹⁸ions/cm².

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Titanium nitride films were formed by the dynamic ion mixing process. In the process, titanium evaporation and nitrogen ion implantation were carried out simultaniously on to the suface of a substrate. The effect of process conditions on the composition of the films were studied by X-ray diffraction. On increasing the Ti evaporation rate, Ti₂N and Ti appeared but when the rate saturated, only TiN was formed. On the other hand, no film was formed by sputtering when an excess N ion-beam to evaporated Ti was charged. Ti-N films were formed on silicon substrate and cross-sections of the specimens were observed by transmission electron microscopy, and the TEM images showed intermediate layers between the substrate and the Ti-N film. These intermediate layers were thought to be the N ion implanted Si and intermixed layer of vaporized Ti, sputtered out substrate atoms and implanted N ions.
Field testing was done, in which Ti-N films were formed on tools made of WC-Co alloy by the dynamic mixing process. The Ti-N coated tools showed performance twice as good as that of uncoated tools.

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A magnetic sector type ion mixing machine has been developed for surface modification research purposes. High current refractory-metal ion beams (e.g. Cr⁺: 0.82mA) were obtained by modifying a conventional Freeman type ion source.
A gas assisted ion mixing method is proposed in which a Ti compound film can be formed from evaporated Ti molecules and a gas species ion beam in the same gas environment. This proposal has been verified by high rate TiN deposition using an N₂⁺ ion beam and N₂ gas flow, with the following results: (1) Crystallinity of the deposited TiN film changed from a preferential orientation of (111) to (200) with increasing N₂⁺ ion beam energy dose; (2) TiN films having a Vickers hardness of >2000 was formed by small current of N₂⁺ ion beam radiation; (3) the hardness and crystallinity of TiN films were closely related; and (4) this method may realize high-rate deposition of hard TiN films (≥20Å/sec).

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The metallugical structure and wear resistance of TiN film formed on high C-high Cr roll steel specimens by ion beam and vapor deposition (IVD) and chemical vapor deposition (CVD) techniques were studied. The main results obtained were as follows: 1) Two-cylinder wear resistance tests showed that the IVD and CVD films significantly improved the were resistance of high C-high Cr roll steel. Wear resistance of IVD specimens was better than that of CVD specimens. 2) The concentration of Ti varied continuously in the IVD and CVD specimens in the boundary zone between the base metal and the coated film. The width of the transition region in the IVD was comparable to that of CVD specimens. Good adhesion of the IVD specimens can be explained in terms of the existence of mixed layer in the boundary zone. 3) Both the films always consisted of TiN as a main compound and TiO₂ as an additional one. The ratio of TiO₂ to TiN in CVD film was larger than in IVD film. The ratio of TiO₂ to TiN contents differed corresponding to film formation techniques, and had a clear correlation to wear resistance.
It is suggested that the IVD technique is most suitable for application to an actual roll.

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There are many methods of metal surface modification, including ion plating, ion cluster beam evaporation, ion dynamic mixing and ion static mixing.
Ion dynamic mixing is superior to other methods because the thin film produced has excellent properties, and adheres strongly to the base metal.
Producing a thin film by ion dynamic mixing, requires equipment having a large-bore ion-beam outlet. We conducted many tests on thin films produced using such equipment.
The equipment was used to make thin films of TiN and AlN by ion dynamic mixing, ion static mixing, and ion implantation, and the films were comparead. The results showed that thin films made by ion dynamic mixing were superior to those made by other methods, and that thin films of AlN were inferior to those of TiN.

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Atomic mixing between TiNi metallic thin films and glass substrates (silica and borosilicate glass) was induced by Ar ion bombardment and inverstigated by means of Auger electron spectroscopy. Ar ion bombardment at 150keV was carried out at room temperature to doses of 5×10¹⁶ and 1×10¹⁷ions/cm². The Auger analysis demonstrated that significant intermixing occurred at the TiNi-glass interface after Ar ion bombardment, and that the degree of atomic mixing varied depending on the constituent atom species. It was found that Ti atoms were always transported deeper into the glass substrate than Ni atoms, and Si atoms diffused into the TiNi overlayer more than O atoms. The lighter B atoms in borosilicate glass were found to diffuse least during Ar ion bombardment. It is suggested that some metal silicides and oxides are formed in the reacted interface regions. Indentation-fracture tests revealed that adhesion between the TiNi films and the glass substrates was improved substantially by Ar ion mixing. The atomic mixing of each of the constituent atoms was discussed qualitatively using a model of isotropic cascade mixing. The improved adhesion at the interface was thought to result from interface mixing and the resultant formation of metal silicides and titanium oxides of various valence states in the interface region.

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Glancing angle X-ray diffractometry and conversion electron Mössbauer spectroscopy (CEMS) were used to study the effects of ion implantation in 17/7 stainless steel. Kr⁺, Ar⁺ and Fe⁺ ions were used to bombard the sample surface at energy ranges of 90-150keV. It is shown that a martensitic transformation of γ→α phase is induced after irradiation to fluences larger than 10¹⁶ions/cm². The efficiency of martensite formation is mainly related to the stress relief associated with secondary radiation damage, because the highest degree of transformation was observed for the fluences of noble gas implantations where bubble formation occurs. The results are consistent with the efficiency difference in the γ→α phase transformation in 18/8 stainless steel (SUS 304) induced by 8keV He⁺ and H⁺ implantation.

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In a previous paper, we have shown that noble gas ion implantation to austenitic stainless steels has induced γ→α (martensitic) transformation, and we have discussed a mechanism for this phase transformation. In the present paper, phase transformations in austenitic stainless steels implanted with metal ion have been investigated by conversion electron Mössbauer spectroscopy (CEMS) and X-ray diffraction. Observation by CEMS and X-ray diffraction, showed clearly that different metal ion species make different contributions to ion-induced γ→α transformation. It was confirmed that γ→α transformation in 17/7 steels implanted with Fe ion and Ni ion occured by both the effect of compositional change (the alloying effect) and that of damage-induced stress (the stress effect). In case of Snion-implanted 17/7 steel, on the other hand, it seems that only the stress effect is a driving force for γ→α transformation.

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O₂⁺ implantation in Ti was carried out to doses of 2×10¹⁷-2×10¹⁸ ions/cm² at 150keV. The effect of target temperature on the formation of titanium oxide induced by ion implantation was investigated by means of X-ray diffractometry (XRD). In the case of room temperature implantation, XRD patterns show that TiO was formed at doses of 4-6×10¹⁷ ions/cm² and polycrystalline rutile TiO₂ was formed at doses over 1×10¹⁸ ions/cm². In the case of low temperature (-50°C) implantation, only TiO (220) formation was observed even at doses above 1×10¹⁸ ions/cm². The difference in the formation of titanium oxide on targets at room temperature and at -50°C, and the mechanism of the oxide formation were discussed.

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The influence of processing temperature on the modification of pure-aluminum by nitrogen ion implantation was studied experimentally.
Surface hardness and electrical resistance increased with decreases in processing temperature, but strface wearability was independent of processing temperature. It was concluded that control of processing temperature is necessary in surface modification by ion implantation.

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SiC whisker reinforced alminum alloys were implanted with N⁺ ions to investigate the effect of implantation on the tribological properties. N⁺ ion was implanted to 10¹⁸ ions/cm² at 90keV. Wear tests was made using a pin-on-plate type testing machine at various loads. Appreciable improvements in wear properties were observed.

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