Properties of metal-dielectric codeposited films

Optical, electrical, mechanical and corrosion properties have been investigated in the following codeposited metal-dielectric systems: CrSiO₂, CuSiO₂ and (Cu, Zn)SiO₂. The studies were performed in a compositional range of 9–95% Cr, 17–87% Au, 87–99% Cu and 65–85% brass. The films were codeposited in an NRC triode sputtering unit where a variable target aperture was used to control the composition during a single pumpdown. The composite film thicknesses ranged from 200 to 1500 Å. The scratch and corrosion resistance and hardness of the composite films showed considerable improvement over the metal component alone. Marked changes were observed in the reflectance and transmittance spectra with relatively small compositional changes. The data on the optical properties including solar reflectance factors DW (nm) and P%, sheet resistance, scratch and corrosion resistance are presented as a function of composition and thickness of the codeposited films.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

Plasma and wet oxidation of (63Cu37Zn) brass

A twin study of the oxidation mechanism of (63Cu37Zn) brass foil in oxygen plasma and in alkaline aqueous solution is reported. Brass foil was exposed to low-pressure rf oxygen plasma in given working conditions and the resulting surface was studied by means of linear sweep voltammetry. The plasma oxidation mechanism involves oxygen radicals, and results from their strong oxidising character. The precursor oxide Cu_xO, Cu₂O and CuO were identified in the passive layer, in addition to ZnO. Most of these oxides also form as corrosion products when brass samples are oxidised in alkaline solution. The corrosive process involves oxygen depolarisation, which develops on a 63Cu37Zn brass rotating disc electrode. Complementary investigation performed for neutral 0.5 M NaCl solution results in voltammograms which evidence a four-electron reduction mechanism.     

Hard transparent dielectric coatings

Hard transparent corrosion-resistant dielectric coatings were investigated (a) for application to the direct protection of glass surfaces, (b) for application to the protection of thin film metallic window coatings used for reflection or transmission of solar radiation and (c) for use in codeposited metal-ceramic coatings. The dielectric coatings were Al₂O₃, SiO₂ and SiC in the thickness range 100–100 000 Å. The coatings were deposited under varying conditions of substrate temperature, gas composition, r.f. power and substrate preparation. The results of the following measurements on the dielectric coatings are presented: diamond pyramid hardness tests, optical reflectance and transmittance in the region 0.6–4.0 eV and corrosion resistance tests under cyclic conditions. The results showed a considerable improvement in the scratch resistance and hardness of glass by layering of hard dielectric coatings 2–5 μm thick.     

Silicon dioxide as a high temperature stabilizer for silver films

Silver films cannot at present be used as high temperature reflectors because of severe agglomeration in the presence of oxygen at temperatures in excess of 200 °C. Cr₂O₃, Al₂O₃, SiO₃ and CrO_x were tested for their effectiveness as thin barrier layers, and SiO₂ is the best of those tested. The use of SiO₂ allows the process of hole healing to compete with the normal hole growth process. Hole healing does not last indefinitely but is superseded by a slower rate hole growth process with an activation energy of 49 kcal mol^-1.Because of this last mechanism, stabilized silver is less than 1% transmitting after 50 h at 650 °C in air, whereas bare silver agglomerates to 66% transmittance after only 3 min under the same conditions. Therefore 500 Å SiO₂ films can be used as long term stabilizers for silver films in oxygen atmospheres with temperatures of up to 650 °C.     

SnO2 films prepared by activated reactive evaporation

Transparent conducting films of SnO₂ doped with antimony were prepared on glass substrates by activated reactive evaporation for the first time. The sheet resistance and optical transmittance in the wavelength range 0.4–1.6 μm were studied as functions of various deposition parameters such as the ambient pressure of an 85%Ar15%O₂ mixture, the substrate temperature and the antimony doping concentration in the SnSb alloys. The sheet resistance and optical transmittance showed a strong dependence on the above-mentioned deposition parameters. The best results were obtained for a 90at.%Sn10at.%Sb alloy evaporated in 85%Ar15%O₂ at a partial pressure of about 5 × 10^?4 Torr with a substrate temperature about 350°C. These films, with a sheet resistance of 10 μ/□ had an average transmittance of 95% over the wavelength range 0.4–1.8 μm. The film thickness was about 0.25 μm. Thicker films (about 0.5 μm) had a sheet resistance as low as 1.5 ω/□ with an average transmittance 85% in the wavelength range 0.4–1.6 μm.     

Electrochemical and stress corrosion cracking behavior of 67Cu–33Zn alloy in aqueous electrolytes containing chloride and nitrite ions: Effect of di-sodium hydrogen phosphate (DSHP)

A continuing challenge in materials design is the achievement of greater operational efficiency through improvements in performance criterion, particularly high strength and service life-time characteristics. In this study we report on the evaluation of di-sodium hydrogen phosphate (DSHP) as an inhibitor for the stress corrosion cracking (SCC) of 67Cu–33Zn alloy in 0.1 M NaNO₂ and 3.5% NaCl aqueous electrolytes under both open-circuit potential (OCP) and relatively high anodic potential (300 mV_NHE) using the slow strain rate (SSR) technique. DSHP has been found to inhibit SCC of the tested brass alloy which is in parallel with the results obtained from electrochemical measurements. The inhibitive effect of DSHP can be attributed to the formation of a three dimensional film of zinc phosphate on the alloy surface which in turn inhibits dezincification and subsequently the SCC of the 67/33 brass alloy. On the other hand, the addition of 0.1 M DSHP was found to change the failure mode from brittle transgranular cracking to ductile failure. The results of both electrochemical and SCC measurements were combined together to investigate the inhibitive mechanism of DSHP.     

Corrosion resistance property of micro–arc oxidation coatings on Mg–Li alloy obtained in different systems

通过三种优化工艺体系在Mg--5%Li合金表面上生长陶瓷膜层, 分析了膜层的厚度、显微结构、相组成和耐蚀性. 结果表明, 三种膜层都含有MgO相, 微弧氧化试样的耐蚀性能都明显提高. 使用Na₃PO₄体系制备的膜层含有MgF₂, 膜层最厚、表面有大量裂纹; 使用Na₂SiO₃体系制备的膜层含有橄榄石型Mg₂SiO₄, 耐点蚀性能最好; 使用Na₂SiO₃--Na₃PO₄体系制备的膜层含有MgSiO₃, 致密性最好, 膜层耐均匀腐蚀性能最好.     

Microstructural analysis of the brass seat of a valve from the 1907 steam tug “Hercules”

The steam tug Hercules was an ocean-going and bay tug for 55 years before being retired. It is now being restored by the National Park Service (as of 1993 printing of this article). A broken steam valve was obtained for microstructural examination. The body was gray cast iron, and the stem and seat were brass. The examination centered on corrosion of the brass components. The seat and shaft were α brass, with a hardness of 64 and 79 DPH, respectively. A nut held the shaft onto the seat and was α-β brass with a hardness of 197 DPH. Welded on the end of the shaft was a ring of hard (DPH 294) α-β brass, which seated against the nut. The brass seat and stem showed little corrosion. However, the α-β brass nut and welded tip show extensive dezincification. This process of removal of Zn and the retention of Cu began in the high Zn β phase, but eventually both phases were attacked. The depth of penetration was consistent with dezincification rates reported in the literature for such brasses in salt water if the valve had been in service about 55 years. Reprinted from Microstructural Science, vol. 20, Metallographic Characterization of Metals after Welding, Processing and Service, Proc. of the Twenty Fifth Annual Tech. Meeting of the International Metallographic Society, W.R. Kanne Jr., G.W.E. Johnson, J.D. Braun, and M.R. Louthan, Jr., ed., The International Metallographic Society, Columbus, Ohio, and ASM International, 1993, pp. 471–484.     

Sol–gel derived ZrO2–SiO2 highly reflective coatings

In this paper, colloid-based highly reflective coatings consisting of alternating layers of quarterwave thick high- and low-refractive index components were deposited on glass substrates by a sol–gel spin-coating method. SiO₂ was used as the low-refractive index component, and ZrO₂ as the high-refractive index material. The colloidal suspension of ZrO₂, prepared by hydrothermal hydrolysis of ZrOCl₂, contained monoclinic nanocrystalline ZrO₂, with an average particle size of 15 nm. A minimum transmittance of 1% near 1064 nm was obtained from a 20-layer SiO₂–ZrO₂/PVP multilayer film. The ZrO₂ particles were deposited in an ethanolic suspension containing polyvinylpyroldione (PVP) as a binder. The maximum transmittance in the visible range was about 85%. A 1-on-1 laser-induced damage threshold of 16 J/cm² for the 20-layer SiO₂–ZrO₂/PVP film was observed using a Q-switched Nd:YAG high power laser at a wavelength of 1.06 μm and with a pulse width of 2.5 ns.     

陕西土壤模拟液中3种典型接地金属材料的腐蚀行为

为了弄清3种典型接地金属材料(H62黄铜、Q235钢、镀锌钢)在陕西土壤中的腐蚀情况,采用失重法(外加电流浸泡)、电化学测试、扫描电镜(SEM)和X射线衍射(XRD)研究了其在陕西中部土壤模拟液中的腐蚀行为和电化学规律。结果表明:在有外加电流的模拟液中浸泡,随浸泡时间延长,Q235钢腐蚀速率逐渐变慢,镀锌钢表面镀锌层腐蚀较快,H62黄铜的腐蚀速率变化不大;Q235钢、镀锌钢、H62黄铜的腐蚀产物分别主要为α-FeOOH、β-FeOOH、Fe3O4,ZnO、Zn(OH)2、FeOOH、Zn5(CO3)2(OH)6和Cu2O、CuO、CuCl2;在含相同NaCl浓度的模拟液中,H62黄铜的耐腐蚀性能最好,镀锌钢的次之,Q235钢的最差。     

Retarding intermetallic compounds growth of Zn high-temperature solder and Cu substrate by trace element addition

Since the thickness of layers of intermetallic compounds (IMCs) at the joining interface has an apparent effect on the joint reliability, understanding the growth mechanisms of IMCs is important for die-attachment applications. In the present study, the interfacial reaction between elements (Ca, Mn, Cr, and Ti) added to Zn alloys and Cu substrate were investigated in detail, focusing on IMCs grown by isothermal aging at 150 °C. The reaction layers included two types of Cu–Zn IMCs i.e., γ-Cu₅Zn₈ and ε-CuZn₅ phases. The joining interface with trace elements containing Zn solder reduced the growth rate of the IMCs. In particular, the addition of 0.1 wt% Cr to pure Zn solder decreased the growth rate of the IMCs by approximately 50 %. The mechanism we propose assumes that a phase containing the small Cr atoms exists between the solder and ε-CuZn₅, which suppresses the diffusion of metal atoms. To summarize, the Cr additive showed beneficial effects in terms of suppressing the growth of IMCs during the solid-state isothermal aging.     

Ion beam synthesis of the diamond like carbon films for nanoimprint lithography applications

Ion beam deposited hydrogenated undoped as well as SiO_x (SiO_x + N₂, SiO_x + Ar) doped DLC thin films were deposited and evaluated as possible anti-adhesive layers for nanoimprint lithography. Film surface contact angle with water was investigated as a measure of the surface free energy and anti-sticking properties. Contact angle of the DLC films was independent of SiO_x doping and ion beam energy. Air-annealing resistance in terms of the contact angle with water of the synthesized diamond like carbon films was investigated. Optical transmittance spectra of the DLC films in UV-VIS range were measured to investigate it as possible anti-sticking layers for UV imprint lithography applications. DLC films with the most promising combination of the UV absorption and anti-sticking properties were revealed. Preliminary imprint tests with uncoated and thin DLC film coated hot imprint stamps were performed.     

Enhancement of the corrosion resistance of substrates by thin SiO2 coatings prepared from alkoxide solutions without catalysts

The corrosion resistance of aluminium coated with SiO₂ films, prepared by the sol-gel method using alkoxide solutions without catalysts, was extremely enhanced. The corrosion resistance depended on the coating conditions. Only 0.02–0.05% of the surface of aluminium with the SiO₂ film, of which the thickness was submicrometre, was corroded after the corrosion test. Small etch pits were observed in surfaces of aluminium with the SiO₂ films, which showed good corrosion resistance, after the corrosion test.     

Mechanical behavior of segmented oxide protective coatings

Mechanically and thermally induced fractures were examined in sputtered coatings consisting of an NiCrAlY underlayer, either a thin or a thick transition layer grading from NiCrAlY to ZrO₂, and an outer ZrO₂ layer. A pronounced columnar (fibrous) microstructure was obtained, although the columnar boundaries in the ZrO₂ layers and in the thick transition layers were much more open than in the NiCrAlY, effectively producing a more segmented structure. Some coatings also included a continuous fine-grained outer NiCrAlY sealing or close-out layer.For this complex metal and ceramic coating, a stress applied parallel to the layer plane always resulted in fracture perpendicular to the layer plane along open columnar boundaries. If the transition layer was thick, no fractures other than those at columnar boundaries were observed. If the transition layer was thin, fracture parallel to the layer plane occured in the ZrO₂-rich portion of this layer. When stress was perpendicular to the layer plane, fracture parallel to the layer plane occurred first at the outer ZrO₂(NiCrAlY) interface if an outer NiCrAlY sealing layer was present. Otherwise the ZrO₂-rich portion of the transition layer failed first, followed by fracture in the ZrO₂ layer.     

The corrosion and wear resistances of magnesium alloy (LZ91) electroplated with copper and followed by 1 μm-thick chromium deposits

The Mg-Li-Zn alloy, LZ91, is a potential material for industrial application owing to its high specific strength. However, the LZ91 has so high chemical reactivity that it is easily corroded in air and an aqueous environment. In this study, an eco-friendly electrodeposition method was proposed to obtain a protective Cr/Cu coating on the LZ91 substrate. That is, the LZ91 surface electroplated a Cu undercoat in an alkaline Cu-plating bath and followed by decorative 1 μm-thick Cr electroplating in a plating bath with trivalent chromium ions. After electroplating, some of the Cr/Cu-deposited specimens were heated with a reduction flame for 0.5 s to increase the hardness of Cr-deposit. The wear resistance of as-plated and flame-hardened Cr/Cu-coated LZ91 specimens was estimated with ball-on-plate wear tester by using a steel-ball counterpart. Whereas, their corrosion resistance was evaluated in a 0.1 M H₂SO₄ solution before and after wear test. Experimental results show that a Cu deposit could be uniformly electroplated on the LZ91 surface by using our proposed electroplating method. The corrosion resistance of LZ91 was markedly improved after decorative 1 μm-thick Cr electroplating. After wear test, the steel counterpart was ground obviously with either as-plated or flame-hardened Cr/Cu-coated LZ91 specimen. According to the results of electrochemical corrosion test, some parts of the Cr deposit were peeled off from worn flame-hardened Cr/Cu LZ91 surface. This reduces its corrosion resistance significantly. On the other hand, the corrosion resistance of as-plated Cr/Cu LZ91 was not changed after wear test. That is, an as-plated Cr/Cu-coated LZ91 specimen could have good corrosion and wear resistance.     

The mechanical properties and microstructures of copper and brass joints soldered with eutectic tin-bismuth solder

The mechanical properties and microstructures ofcopper and brass soldered with eutectic tin-bismuth solder have been determined and the joints examined using metallographic techniques. Joints made with copper were stronger than those made with brass. At the copper/solder interface a uniform layer 2m thick of Cu_5.2Sn₅ was formed and at the brass/solder interface a uniform layer 2 m thick of (Cu, Zn)_2.9Sn and an irregular layer 2 to 5m thick of (Cu, Zn)_5.7Sn₅ were formed. Copper joints fractured etthocopper/solder interface and brass joints fractured in the internmetalic layer. Copper joints soldered with eutectic Sn-Bi were stronger than copper joints soldered with eutectic Sn-Pb and the reverse was true for brass joints. Results are also given for the effect of thermal shock on copper and brass joints soldered with Sn-Bi and Sn-Pb solders, and also for We fatigue and creep behaviour of joints soldered with eutectic Sn-Bi solder.     

Microstructure and interfacial reaction of Sn–Zn–x(Al,Ag) near-eutectic solders on Al and Cu substrates

Sn–Zn–x(Al,Ag) near-eutectic solders, namely Sn–8.3Zn–0.73Ag, Sn–8.4Zn–0.44Al and Sn–7.4Zn–0.26Al–0.68Ag (in wt%) with melting points of 200.74, 198.00 and 197.32 °C, respectively, as well as the Sn–9Zn eutectic solder, were used to join Al and Cu substrates. The addition of Ag led to the formation of dendritic AgZn₃ phases, while the addition of Al obviously refined the microstructure of Sn–Zn eutectic, as well as the AgZn₃ phases. The Sn–Zn–Al solder possessed the best wettability on both Cu and Al substrates among the four solders. Al_4.2Cu_3.2Zn_0.7 intermetallic compound (IMC) layers formed at the Sn–Zn–x(Al,Ag)/Cu interfaces while Al-rich (Zn) solid solutions at the Sn–Zn–x(Al,Ag)/Al interfaces of all the as-soldered joints. The shear strength of the Al/Sn–Zn–Al/Cu solder joints was the highest among the four solder joints. The declining degree of the shear strength of the Sn–Zn–x(Al,Ag) solder joints in 3.5 % NaCl solution was in agreement with the corrosion-resistance order of the bulk solders. The Al/Sn–Zn–Ag/Cu joint thus owned the best corrosion resistance.     

Effect of silicon on corrosion resistance of Ti-Si alloys

The corrosion resistance of Ti-Si alloys has been studied in acid solutions and the alloys exhibit a high resistance to corrosion. SEM examinations combined with EDAX allowed to conclude that the passive films on Ti-Si alloys are mainly composed of TiO₂/SiO₂ oxides. XPS analysis indicated the formation of Si-O and Si-O-Ti bonds in the passive film, respectively corresponding to SiO₂ and Si-doping TiO₂. The effect of silicon on the corrosion was correlated to the formation of a stable SiO₂ film, Si-doping on TiO₂ and the extended lattice imperfections formed along TiO₂/SiO₂ grain boundaries and phase-boundaries. The calculated donor densities based on the point defect model were shown to depend exponentially on pH and linearly on potential.