Electrochemical behavior of titanium implanted with nickel, tantalum or a combination of the two has been investigated in a sulfuric acid solution, as a fuction of fluences. The metallographically polished titanium surfaces were exposed to nickel or tantalum ion beam at fluences ranging between 1×1016 and 1×1017ions/cm2. The depth profiles of the implanted ion species in the near-surface regions were determined by Auger electron spectroscopy with sequential Ar bombardment. The structural change in the implanted layer was also examined by transmission electron microscopy. Polarization behavior for the implanted specimens was potentiodynamically measured in a boiling 10wt.% sulfuric acid solution. Electrochemical measurements revealed that nickel implantation significantly promoted the passivation of titanium with an increase of fluences, and that the corrosion potentials resided in the passive region of titanium at fluences above 1×1018ions/cm2. The transmission electron diffraction patterns suggested that the precipitation of Ti2Ni occurred in the nickel implanted layer. Tantalum implantation, which caused the formation of β-phase titanium, was effective in reducing the critical current densities for passivation and passive current densities with an increase of fluences. These effects were not observed at fluences above 7×1016ions/cm2. At such fluences, the concentration of the implanted tantalum was decreased by the self-sputtering effect. On the other hand, the polarization curves for combined implantation with tantalum and nickel ions exhibited stable passivation behavior with low passive current densities. It was concluded that excellent corrosion resistance of titanium in a sulfuric acid solution can be achieved by the complementary effects of the co-implantation with tantalum and nickel ions.
A study has been made of the electrochemical properties and of the microscopic characteristics such as surface composition and structure for oxygen-implanted iron surface layers. Oxygen implantation into pure iron was performed at fluences ranging from 1.4×10-2 to 2.2×10-1C·cm-2 and an accelelation voltage of 80kV, using non-massseparated ions. Electrochemical reaction was measured by multi-sweep cyclic voltammetry in an acetate buffer solution of pH=5.0. AES, RBS, XPS and XRD were used to analyze the depth dependence of atomic fractions and chemical bonding states, and the crystal structure of implanted layers. The atomic fraction of oxygen saturated at approximately 60% to form a trapezoidal distribution at high doses, and oxygen atoms combined with iron to form crystalline oxides. The peak anodic dissolution current density for iron subjected to high-dose oxygen implantation was approximately 1/20 that for pure iron, owing to the formation of surface layers with a trapezoidal oxygen distribution consisting of iron oxides.
The thermal oxidation properties of Al-ion-implanted Ni-based alloys used for thermocouples-such as Inconel 600, Alumel, Chromel and Constantan-were studied in humid O2 atmospheres at 970K for 180ks. Ion implantation was performed at doses ranging from 1×1016 to 1×1017ions/cm2 and an energy of 50keV. The depth profiles measured by AES showed that post-implantation concentrations of Al and O were higher near the surface. The implanted Alumel and Constantan showed no oxidation supperssing effect, but the implantation at 1×1017ions/cm2 caused significant slowing in the oxidation of Inconel 600 and Chromel, both alloys that contain Cr, oxidation behavior that was similar to that of Ni-Cr-Al alloys.
A typical heavy metal fluoride glass composed of 53ZrF4-20BaF2-4LaF3-3AlF3-20NaF in molar percentage was implanted with 15keV oxygen ions to the dose of 2×1017ions/cm2. The ion implantation did not affect the transmission spectra of the glass in the infrared or visible region in any detectable extent, although it did give rise to a slight drop at the ultraviolet edge. The surface layer fabricated by ion implantation exhibited excellent chemical durability which protected the glass from being corroded by water. Surface characterizations by RBS and XPS revealed that an oxyfluoride layer was formed on the glass surface and it is concluded that this compositional modification is responsible for the improvement in the water durability of the glass.
This paper describes the effects of nitrogen ion implantion on the hydrogen absorption of transition metals of the IVa- and Va groups such as Ti, Zr, V, Nb, and (α+β) type Ti-6Al-4V alloy. Hydrogen charging was carried out by cathodic electrolysis, and the distribution of hydrogen concentration was obtained by glow discharge spectroscopy (GDS). Changes in structure produced by hydrogen absorption were investigated using X-ray diffraction (XRD). Results are as follows. (1) The hydrogen absorption behavior of Ti and Zr showed a gradual retardation effect as nitrogen ion dosage increased. Hydrogen absorption to V and Nb in the V-group transition metals having a large hydrogen solubility was markedly retarded even at low-dose implantation, and no hydride was formed. (2) This retardation of hydrogen absorption suggests that hydrogen diffusion paths were blocked by fine layers of precipitated nitrides formed by the nitrogen implantation. (3) Hydrogen absorption to Ti alloy was improved by implantation at dosages in excess of 3×1017ions cm-2. It is considered highly probable that V and Al bonded with the implanted nitrogen to form nitride, and that such nitrides contribute to the retardation of hydrogen absorption.
Monolayer TiN films often display poor corrosion resistance due to localized weak spots, and multilayer film composed of several TiN and thin Cr2N layers was therefore studied in an effort to improve pitting corrosion resistance. A thin Cr2N layer with a mixing layer formed with the underlying materials was produced by N++N2+ ion implantation into the Cr layer. The multilayer film showed a dense, homogeneous rupture face, unlike the columnar structure observed in the monolayer TiN film. In an anodic polarization test in 3.5wt.% NaCl solution, austenitic SUS 304 stainless steel coated with the multilayer film showed better pitting corrosion resistance than specimens coated with the monolayer TiN film. After this corrosion test, many shallow corrosion marks were observed in the surface of the multilayer film in contrast to the deep pits observed in the surface of the monolayer TiN film. It is thought that the improved pitting corrosion resistance of the multilayer film was due to its stronger inter-column characteristics obtained by the interposing of the multiple thin Cr2N layers.
Adhesion to the substrate is the most important property affecting the life of coating films. Means for improving adhesion in films formed by vacuum evaporation include heating or corona discharge treatment of the substrate, and heating is widely used because it effects dehydration and degassing as well as interfacial diffusion. Methods involving concurrent energetic particle irradiation during evaporation, on the other hand, can strongly modify the adhesive and chemical properties of the resulting thin film by the formation of a mixing layer. This paper reports the properties of Ti-evaporation films assisted by Ar+ ion beam irradiation during the initial evaporation and of ordinary evaporation films. Adhesion of Ti films to stainless steel, glass and polyimide substrates was measured by the scratch test, and their chemical properties on Fe substrates were measured by the AC impedance method. The adhesive force of assisted evaporation films was 1.4∼4.7 times as large as that of the ordinary evaporation films, and the interfacial impedance of the assisted evaporation films was about 10 times as large as that of the ordinary evaporation films. These results suggest that it may be possible to improve film properties by Ar+ ion beam irradiation.
Amorphous Ni-Ta-Pt alloys were deposited on Fe substrates by ion beam sputtering, and the electrode characteristics of ternary alloy films was investigated by an electrochemical test in 0.5M NaCl solution at 303K. Ion implantation to the substrate and ion irradiation were performed during deposition, and the effect of these processes on electrode characteristics was also investigated. It was found that: (1) The amorphous Ni-Ta-Pt films produced by ion beam sputtering were spontaneously passive and were immune to pitting corrosion. (2) When previously immersed in 46wt.% HF for surface activation the films showed very high activity for the production of chlorine by the electrolysis of 0.5M NaCl solution at 303K. (3) Film quality was improved by irradiation with nitrogen or oxygen ions during deposition. (4) Ion-implantation of corrosion resistant elements to the substrate had the effect of supperssing substrate corrosion due to NaCl solution that had reached through the pin holes.
Ion beam mixing was used to coat a Ti-Ni alloy substrate with Ti+ implant and co-evaporated Ti metal to prevent Ni dissolution. The corrosion resistivity of the Ti-coated substrate was evaluated using an anodic polarization technique. The experimental results suggested that this coating could effectively improve the corrosion resistance of the Ti-Ni alloy even under severe conditions simulating an actual medical operation. The cytotoxity of Ti-coated Ti-Ni disks were evaluated using L-929 cells cultured on a millipore filter medium. The disks were found to be inert to the cells.
In order to investigate the mechanical properties of ion-implanted aluminum alloy, disk samples of AC8A were irradiated with 130keV Ar+, 100keVB+, 100keVN2+, or 200keV N2+ at doses of up to 3×1017, 1×1017, 1.5×1018, or 1.5×1018ions/cm2 respectively. Knoop hardness (load: 98mN) increased with ion implantation, and in the case of N2+ ion implantation, hardness increased from 117 to 165. To measure the tribological property, pin-on-disk tests were performed using steel (SUJ2) balls of 5mm in diameter as pins. Sliding conditions were load: 460mN, speed: 25mm/s, oil lubrication (SAE 7.5W-30). The coefficient of friction for ion implanted AC8A disks was 0.1∼0.2, which was higher than the 0.07 obtained for unimplanted disks. Ion implantation improved the wear resistance of the disks, and in the case of N2+ ion-implanted disks, the wear volume was below the detection limit (<10-4mm3). X-ray diffraction analysis for N2+ ion-implanted samples revealed that AlN formed beneath the sample surface. It is suggested that the formation of AlN improved the wear resistance of N2+ ion-implanted AC8A disks by surface hardening.
Surfaces of AlN ceramics were modified by Ar and N ion beams generated from a bucket-type ion gun, and the sliding wear characteristics in a vacuum were investigated. According to SEM observation of machined AlN surface before and after wear tests, it was found that wear debris was formed by the breaking off of the plastic flow layer that was deformed around the depressions made by machining during machining and sliding. The plastic flow layer on the machined AlN surface was removed by Ar ion beam sputtering at an energy of 10keV and an incident angle θ of 70°. After which, N ions were implanted at an incident angle θ of 0°. In wear tests where the sliding distance was 10μm in a vacuum, the amount of wear debris from the AlN was markedly reduced by N ion implantation after sputtering with an Ar ion beam.
Cutting force and wear in continuous turning were measured for cutting tools made of high speed steel, high speed steel coated with TiN, SKS3 steel, S55C steel and pure titanium that had been subjected to nitrogen ion implantation. Auger electron spectroscopy was used to obtain depth profiles of the implanted nitrogen, and an ultra-micro hardness tester provided depth profiles of hardness. The results were as follows. (1) Under specific conditions all cutting tools except those made of S55C steel showed lower cutting force after implantation than before. (2) When cutting S45C steel, crater wear on the rake face of high speed steel were reduced by implantation. (3) Nitrogen ion implantation to high speed steel showed a Gaussian distribution having peak intensity at 0.11μm depth and disappearing at 0.68μm or more. (4) Ion implantation increased the hardness of SKS3 steel, but decreased that of high speed steel. (5) In all materials tested, the rate of elastic deformation of the surface layer underwent a change with implantation.
Ion-beam machining has been investigated for its effect in decreasing surface roughness, and it has already been reported that low surface roughness can be obtained by low-energy argon ion-beam machining. In this study, low-mass helium ions were used to decrease the roughness of a mirror finished SKD 1 (high chromium-high carbon steel) surface. The results obtained were as follows: (1) A greater decrease in surface roughness was obtained with helium ion-beam machining than with low-energy argon ion-beam machining. (2) There is an optimum machining condition for decreasing the surface roughness, and the lowest surface roughness (6nm Rmax) obtained at a beam energy of 2keV, a beam current density of 4A/m2 and a beam angle of 70°. (3) The decrease in surface roughness is obtained within the oxide layer (about 0.03μm). (4) The mechanism of the decrease in the surface roughness is discussed in terms of the knock-on cascade model.
Polycrystalline chromium metal plates (purity>99.99%) were implanted with nitrogen ions (N2+) at energies of 500keV, 1MeV, 1.5MeV and 2MeV and the doses of from 3×1017 to 1×1018N atoms/cm2. Multiple implantation at beam energies of 2MeV-1.5MeV-1MeV was undertaken in an attempt to form a thick nitride layer. Substrate temperature was varied from ca, 40°C to 400°C to investigate the temperature dependence of the crystallinity of the modified layer. The depth profile of nitrogen concentration was investigated by Rutherford backscattering spectrometry (RBS) and the crystallinity of the nitride layer was studied by XRD. An amorphous nitride layer was formed when substrate temperature was kept down to 40°C-80°C. When substrate temperature was higher than 170°C, the nitride layer formed had relatively good crystallinity. At 400°C, a homogeneous layer of Cr2N was formed.
Polycrystalline chromium metal plates (purity>99.99%) were implanted with nitrogen ions (N2+) at energies of 500keV, 1MeV, 1.5MeV and 2MeV and the doses of from 3×1017 to 1×1018N atoms/cm2. The implanted chromium plates were annealed repeatedly at varying temperatures from 250°C to 800°C. The depth profiles of nitrogen concentration was investigated by Rutherford Backscattering Spectrometry (RBS) and the crystallinity of the nitride layer was studied by XRD. At temperatures up to 400-500°C, CrN converted to Cr2N and phase transition were observed. However, the amorphous nature of the nitride layer formed was kept after annealing. The maximum Cr2N layer thickness of obtained by multiple implantation (2MeV-1.5MeV-1MeV, total=2.1·1018) and subsequent annealing was 650nm (from 200nm to 850nm in depth scale).
Cubic BN films were deposited on Si substrates by ion beam enhanced deposition (IBED) method, in which boron films were deposited at 2000Å/h by ion beam sputtering of a boron target, and an ion beam of argon and nitrogen was bombarded concurrently onto the growing film at an ion energy of 500eV and a current density of 100μA/cm2. The effects of argon ion bombardment on the formation of c-BN were investigated by depositing BN films under several flow rate ratios of Ar to N2 gases fed into the bombarding ion source. Infrared absorption spectra of the films changed with increasing Ar vol% from those of only sp2 (region I: Ar 0-50vol%) to those of sp2 and sp3 (region II: Ar 50-75vol%), and finally to those of only sp2 again (region III: Ar 75-100vol%). Almost single phase film of c-BN was obtained at an Ar vol% of 75. XPS analyses showed that the nitrogen content in the BN film satisfied the stoichiometry of BN in regions I and II, but decreased in region III. Compressive stress in BN films was estimated by bending beam method. With increasing Ar vol%, compressive stress increased remarkably in region I and saturated at a high value of about -400kgf/mm2 in regions II and III. These results show that both nitrogen and argon ion bombardments are necessary for the formation of c-BN, but their roles are different. Nitrogen should be supplied as active ions to form stoichiometric BN, while argon should be supplied with sufficient kinetic energy to make high temperature and high pressure state in atomic-scale by a thermal spike effect.
To study the formation process and thermal stability of ZrN layers under nitrogen ion implantation, zirconium films have been implanted with 15N2 ions of 100keV at doses of from 1×1017 to 10×1017N/cm2, at room temperature and 500°C. Effects of post-implantation annealing were also investigated. The depth distribution of the implanted nitrogen was measured in detail by nuclear reaction analysis using the 15N (p, α γ)12C reaction at Ep=429keV. The structure of the implanted layers was measured by thin film XRD, and hardness was measured by a Knoop microhardness indenter. It was found that nitrogen concentration exceeded 50% in the layers that were just shallower and deeper than the mean projected range of nitrogen for a dose of 7×1017N/cm2. The overstoichiometric layers were eliminated by the subsequent ion implantation and a trapezoidal distribution was obtained at a dose of 10×1017N/cm2. The distribution of nitrogen implanted at 500°C can be explained by thermal diffusion, precipitation of nitrogen in the surface layer, and sputtering by ion bombardment. The structure of the ZrN layer produced by nitrogen implantation at room temperature was improved by 500°C annealing, but thermal diffusion of the implanted nitrogen became obvious at 700°C annealing.
Experiments were conducted on controlling the wettability the surface of a solid by nitrogen ion implantation, and it was demonstrated that wettability could be controlled. Ion implantation increased the contact angle of glass relative to water while the contact angle of teflon decreased.