Modification of materials surface by ion beam technology is reviewed shortly with emphasis on the effect of ion bombardment on the microstructure of the surface. Ion-solid interactions are described in correlation with several ion beam processes and importance of ion beam dynamic mixing (IBDM) as well as metal ion implantation is demonstrated for the future trend of surface modification of materials by ion beam irradiation. Experimental results on the modification of metals and/or ceramic materials by various ion beam processes are given for the ion energy ranging from eV to MeV.

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This paper reviews a new method for surface modification to cover particle surface with fine particles mechanically in a dry phase by making use of comminution techniques.
First, the relation of comminution process with surface modification technology is discussed, and the advanced machines developed in Japan to treat core particles surface with fine particles based on grinding principles are introduced. Then, the details of the composite process of core/fine particles with these machines are explained.
In the second section, the effects of the controlling factors on the composite process such as mechanical actions, treating temperature and atmosphere are discussed.
The third section deals with the conditions of combinations of core/fine particles acceptable to this method, and it is demonstrated that this method has a great feasibility to fabricate composite particles by the combination of various kinds of core/fine particles. The scale-up of these machnines is explained in the fourth section, and a typical example is introduced.
The last section summarizes the applications of the composite particles fabricated by this method to create various kinds of new materials, which include the application for surface modification technology. The applications of this method are shown to expand for other types of processing such as rounding particles and mixing different kinds of powder materials precisely. Furthermore, it is also explained that this method can fabricate composite particles inside which different kinds of components are dispersed.

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Numerous publications demonstrate the great potential of lasers for surface treatment (hardening, cladding, alloying). Nevertheless, substitution of classical techniques has turned out to be difficult mainly due to high costs. The paper discusses ways to reduce laser-related costs by increasing the energy coupling efficiency. Following theoretical considerations, experimental results are presented.
A calculation of energy coupling requires reliable values of optical constants at process temperature. For materials of technical interest like steels those data are very rare if not lacking completely. An attempt was made, therefore, to calculate optical constants by an extrapolation based on well-known room temperature values of iron and on the electrical resistivity of the alloy. The results fit the existing experimental data satisfactorily in the wavelength range 0.5 to 15 μm.
A method is presented allowing to measure the coupling efficiency under process conditions. Results show additional contributions to the coupling rate from oxidation and additive materials. As expected from the theoretical results, a strong influence of the laser parameters wavelength and polarization is observed. e.g., reducing the wavelength from 10 to 1 μm increases the coupling rate by a factor two to three.

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Laser surface melting for the inner layers of cast bi-metallic pipes has been investigated. Three kinds of centrifugally cast bi-metallic pipes of which inner layers are made of the stainless steel 904L, the nickel-base alloys 825 and 625, respectively were used. Laser surface melting was performed using a 2.5 kW CO₂ laser unit with the beam traveling velocity being varied in order to achieve different cooling rates. Corrosion resistance was evaluated by the critical current density for passivation, the pitting potential and the density of pits after the FeCl₃ solution immersion test. Corrosion test results indicate that laser surface remelting has a remarkable effect to improve pitting corrosion resistance in the alloy clad layers. EPMA analysis has revealed that element distributions across the solidification cell in the laser-treated alloys become more homogeneous than those in the as-cast alloys. Consequently, the concentrations of molybdenum and chromium at the dendrite cores which decrease in the as-cast alloys, enhance with laser surface melting, which results in the improvement of corrosion resistance in the laser treated alloy layers of the bi-metallic pipes. The theoretical calculation using the Kurz-Giovanola-Trivedi model has demonstrated that the change in element distributions in the laser treated alloys can be attributed to the increased solidification rate by laser surface melting.

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A numerical program has been developed in order to calculate the time-dependent thermal gradient and isotherm velocity within a solidifying pool obtained by stationary laser treatment. The heat diffusion equation is solved for an axisymmetric geometry with an enthalpy formulation using a standard FDM implicit scheme. The program has been used to investigate to which extent the cellular dendritic growth orientation is affected by the direction and amplitude of the thermal gradient.
Experiments were carried out on Al-1 mass%Si dendritic single crystals oriented by Laue back reflection technique and cut along precise crystallographic orientations prior to laser irradiation and on Al-3 mass%Cu eutectic polycrystalline alloys. Deviation of cellular dendritic growth direction from crystallographic and heat flux directions are reported. In addition, the comparison of the microstructural spacings with theoretical predictions outlines the influence of crystallography on the microstructural development during stationary laser treatment.

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Ti(C, N) films have been deposited by reactive ion plating and their tribological behavior against steel in air and in argon atmosphere was characterized. It was very effective to decrease wear rate of steel to coat Ti(C, N). The influence of atmosphere on wear of the Ti(C, N) coatings was studied in the dry sliding of steel pin using a pin-on-disk configuration. The wear rate in air was lower than that in argon atmosphere. The decrease of the sliding wear of the steel disk by applying the Ti(C, N) coating was due to formation and growth of iron-oxide particles on the surface of the coating and high shear strength of the coating. A lot of fine and thin iron-oxides were observed at the sliding surface of the Ti(C, N) coating in air and they were identified as magnetite (Fe₃O₄). It is suggested that small iron debris is derived from pin and oxidized by the reaction with oxygen in air and a protective oxide particle can be formed by growth of oxide debris. These oxides are considered to insulate steel substrate from steel pin, resulting in decreasing adhesive force between pin and disk. Wear behavior of the Ti(C, N) coatings by changing atmosphere is discussed in comparison with a case of steel pair.

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To study the ultra-low loss of TiN-coated silicon steel sheets, the influence of the coating conditions on magnetic properties was investigated, relating to the thickness, bias voltage and temperature used for TiN ceramic coating by the hollow cathode discharge (HCD) method on polished silicon steels sheets. The magnetic properties of the TiN-coated silicon steel sheets after ceramic coating were evaluated. Measurements by thin-film X-ray diffraction and color monitoring, and observations of the magnetic domain were also carried out.
The experimental results obtained are summarized as follows.
(1) The magnetic flux density and iron loss of the TiN-coated silicon steel sheets were progressively improved with increasing coating thickness up to 0.7 μm, and became saturated at 1.0-1.5 μm in thickness. This improvement in magnetic properties was most marked in silicon steel sheets with the highest magnetic flux density. For example, silicon steel sheet with B₈=1.93T had the magnetic flux density improved by 0.007T and the iron loss dramatically improved by 0.15 W/kg.
(2) With bias voltages in the range of –50 to –100 V, the iron loss in the TiN-coated silicon steel sheets was most improved. Thin-film X-ray diffraction inspection indicated a strong peak of (111) of TiN.
(3) With coating temperatures in the range of 573 to 673 K, the iron loss in the TiN-coated silicon steel sheets was most improved.

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Transition metal carbide is expected to have a new application in the future as a corrosion resistant material against nonoxidizing acids. The purpose of this investigation is to evaluate the corrosion resistance of titanium carbide in sulfuric acid. For this purpose, titanium carbide films of various compositions were produced by reactive ion plating. The deposition rate and carbon content of the product films tended to increase with an increase in the flow rate of acetylene as a reactive gas at a constant electron beam current for evaporating titanium. The increase in the acetylene flow rate also led to great improvement in the corrosion resistance of the product films. The potential/current density curves showed that the maximum of the active dissolution current decreased exponentially with the rate increase in the range of 0-2.80×10^–7 m³·s^–1. The most corrosion resistant titanium carbide film, produced at 6.20×10^–7 m³·s^–1, has an extremely low current density, e.g., 3.6×10^–4 A·m^–2 at 0.5 V vs. Ag/AgCl, which is less that 1/5 000 of the titanium film current density. The corrosion of the titanium carbide film was apparently inhibited even in 1 kmol·m^–3 H₂SO₄ at 373 K.

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A new coating technology by sputtering has been developed enabling decorative ceramics coating such as TiN, TiAIN and TiAICN on stainless steel sheets. The coated products have an attractive color appearance which maintains the original metallic surface finish and exhibits excellent adhesion and wear resistance. Details of the newly constructed sputtering plants for large stainless sheets are explained.

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Cavitation erosion and drain erosion are major causes of failure of mechanical devices in fluid handling systems. The authors investigated the application of plasma spraying technique to the formation of coatings with high resistance against the cavitation and drain erosion damage. By using low pressure plasma spraying, some coatings of cermet and metallic alloy materials were prepared and tested for the cavitation erosion behavior. Cobalt base alloy coating shows much more excellent resistance to the erosion than that of Stellite-6, which has been widely used as the wrought product to shield a steam turbine blade from the damage. In spite of the similar chemical composition of the Co alloy to that of stellite-6, the erosion-performance is different. Microscopic characterization of the deposite reveals that the superiority of the coating is caused by the extended solid solubility of carbon resulted from the rapid solidification of the sprayed droplets.

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In order to develop protective coatings for sink rolls used in a continuous hot-dip galvanizing, two kinds of the WC/Co sprayed coating were formed on mild steels by High Velocity Flame Spraying system using commercially produced WC-12 mass%Co powders and their durability in molten pure zinc (703-783 K) was studied on the basis of the constitutional changes.
It was found that the durability of WC/Co sprayed coating in molten pure zinc depends on the binding phase, which varies according to its powder-preparation process. Namely, the binding phase in the WC/Co sprayed coating (SD-coating) made of the powder prepared by the Spray-dried process mainly consists of Co phase, but another WC/Co sprayed coating (SC-coating) made of the powder prepared by the Sintered and Crushed process mainly consists of η-phase (Co₃W₃C and Co₆W₆C). In case of SD-coating, the binding phase (Co phase) dissolved into molten pure zinc so that the thickness decreased in a short time. In case of SC-coating, its thickness and microstructure did not change for a long time, though a Zn-rich and Co-poor layer was formed just below the surface where the hardness dropped to Hv 500-1000.
The apparent activation energy for the growth of the Zn-diffusion layer in SC-coating was 170 kJ/mol, which was nearly equal to that for dissolution of Co phase. It is considered that Zn diffusion path in SC-coating is Co phase and its excellent durability is caused due to much longer diffusion path than that in SD-coating.

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The penetration phenomena of liquid Mn to porous Al₂O₃ coating plasma-sprayed on SS400 steel substrate was studied by heating at 1 573 K in vacuum atmosphere. Moreover, the possibility of improving the Al₂O₃ coating properties was examined. The formation of MnAl₂O₄ was clearly recognized in the connected porosity of Al₂O₃ coating penetrated with liquid Mn. It was revealed that the hardness and the fracture stress of the composite coating consisted of Al₂O₃ and MnAl₂O₄ without porosities after heat-treatment with Mn increased greatly compared with as-sprayed Al₂O₃ coating.

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A commercial SUS 304 stainless steel was machined by EDM with a sialon electrode. The machined surface changed from the machining to the surface modification layer on the some proper machining conditions. The effect of the following factors to form the surface layer was investigated: Electrode polarity, work atmosphere and the working condition of the peak current, pulse duration and duty factor. Under the suitable machining conditions, the EDMed surface was covered with the alloyed layer, which consisted of the electrode and work piece components. The surface modified layer improved the corrosion and wear resistance.

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A numerical analysis for phase growth behavior in Fe-Zn multi-phase diffusion couple during non-isothermal diffusion has been proposed by taking formation process of a new phase into account. For the purpose, an equation which gives the beginning time of formation of new phase during the non-isothermal heating has been derived from an empirical equation which gives the beginning time during isothermal diffusion.
By use of some special techniques so as to save an amount of computation time, concentration-distance curve in a binary alloy model have been calculated under the experimental condition that finite/semi-infinite diffusion couples are heated isochronally with different constant heating rates.

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Electrodeposition of Zn-iron-group metal binary alloys, which has been applied in the production of highly corrosion-resistant alloy plated steel sheet, was conducted from sulfate and chloride baths and the alloy deposition behavior was compared between two types of baths. The current density-dependence of alloy composition showed a typical feature of an anomalous codeposition in the sulfate baths. In the chloride baths, the deposition behavior was shifted gradually from an anomalous to a regular type with increasing chloride ion concentration. On the basis of the factors determining the characteristic current density at which Zn deposition began, the alloy deposition behavior was discussed with the particular reference to the effect of catalytic chloride ions for iron-group metal deposition.

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Titanium deposits were prepared on nickel substrate by potential pulse method in molten LiCl-NaCl-KCl eutectic salts with 2 mol% K₂TiF₆. The influence of the electrolysis conditions on crystal orientation and morphology of the deposits was investigated by X-ray diffraction and scanning electron microscopy, respectively. The preferred crystal orientation of (110) of titanium deposits increased as temperature increases, and the crystal orientation of the deposits varied also with potential and pulse shape during electrolysis. The morphology of titanium deposits showed well-crystallized grains, which became larger with increase of temperature. The change in crystal orientation of the deposits was tried to be explained by the absorption inhibition model.

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The characterization of chromium silicide films and the formation process by disproportionation reaction in molten salts are investigated. The films were performed on steel by two step treatment process of molten salt with KCl, BaCl₂, NaF, metal halide and metal powder. Chromium carbide films were formed on a substrate at first step and chromium silicide films were formed at second step. The films performed at less than 800°C mainly consists of CrSi₂ and a slight SiC and is good hardness about more than 2 200 Hv and high corrosion resistance. The hardness of films performed at 900°C was, however, lower. This two step treatment of molten salt method makes it possible to form the intermetallic compound films, even if any component elements of those films do not exist in substrate.

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Although molten salt electroplating presents an innovative method for developing new pre-coated steels, there has been little commercial exploitation because of powdery and/or dendritic deposits. In this study, the electroplating of Al-based metals, especially Al-Mn alloy on steel sheets from AlCl₃-NaCl-KCl molten salt electrolyte is focused. High speed fluid flow of molten salts and co-deposition of Mn with Al were found to be most effective to generate smooth-faced Al-based deposits at high current density. It is of great interest that Al-Mn alloy deposits with amorphous structure exhibited ultra-smooth lustrous appearance.

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