Carbon-Doped Titanium Oxide Films by DC Reactive Magnetron Sputtering Using CO2 and O2 as Reactive Gas

CO2and O2were employed as reactive gases to fabricate carbon-doped titanium oxide films using DC reactive magnetron sputtering.Microstructure,composition and optical band gap of the films were investigated by X-ray diffraction,X-ray photoelectron spectroscopy,and UV–visible spectrophotometer,respectively.The results showed that carbon-doped titanium monoxide films(C-TiO) with a carbon concentration of 5.8 at.% were obtained in an Ar/CO2mixed atmosphere.However,carbon-doped rutile and anatase(C-TiO2) with a carbon concentration of about 1.4 at.% were obtained in an Ar/CO2/O2mixed atmosphere.The optical band gaps of C-TiO and C-TiO2were about 2.6 and 2.9 eV,respectively.Both of them were narrower than that of pure TiO2films.Films with narrowed optical band gap energy are promising in promoting their photo-catalytic activity.     

Nano/Micro-Laminated (ZrO2–Y2O3)/(Al2O3–Y2O3) Composite Coatings and Their Oxidation Resistance

Nano/micro-laminated (ZrO₂–Y₂O₃)/(A1₂O₃–Y₂O₃) composite coatings were deposited onto an Fe–25Cr–7Ni–N alloy substrate by using alternate electrochemical and sintering processes. The thickness of each layer was in the range of 80–500 nm. Experimental results indicated that the multi-laminated coatings were more effective in providing oxidation resistance than monolithic ZrO₂–Y₂O₃ or A1₂O₃–Y₂O₃ coatings, with the oxidation resistance of the former increasing with increasing number of laminated layers. The microstructural studies suggest that the laminated coatings possess the advantages of these two types of coatings and avoid the weakness of single ZrO₂–Y₂O₃ or A1₂O₃–Y₂O₃ coatings. Reactive elements Y and Zr also played a role in this nano-layered setting in improving the oxidation resistance of the coatings.     

Corrosion Behaviour of TiN/a-C Superhard Nanocomposite Coatings Prepared by a Reactive DC Magnetron Sputtering Process

Nanocomposite coatings of TiN/a-C were prepared on tool steel substrates using a multitarget reactive DC magnetron sputtering process at various TiN layer thicknesses (0.6-2.8 nm). The a-C layer thickness was approximately 0.45 nm. Structural characterisation of the coatings was done by X-ray diffraction (XRD). Incorporation of an a-C phase in TiN matrix reduced crystallite size of the coatings, as revealed by XRD and atomic force microscopy. XRD data showed that the nanocomposite coatings exhibited {111} texture and the average crystallite size was ca. 7.5-9.0 nm. Nanoindentation data showed that 1.5 μm thick nanocomposite coatings exhibited a maximum hardness of 5100 kg mm^?2. The potentiody-namic polarisation of 1.5 μm thick coatings in 0.5 M HCl solution indicated that the nanocomposite coalings exhibited superior corrosion protection of the tool steel substrate as compared to the single layer TiN coatings of similar thicknesses. Enhancement in the corrosion behaviour of the nanocomposite coatings has been attributed to small crystallite size and dense microstructure. Potentiodynamic polarisation studies conducted on ca. 100 nm thick nanocomposite coatings revealed that for a given a-C layer thickness the corrosion current decreased with a decrease in TiN layer thickness. This was supported by scanning electron microscopy (SEM) studies on the corroded samples. The SEM micrographs showed that density and diameter of the corrosion pits were smaller for nanocomposite coatings as compared to single layer TiN coatings of similar thicknesses.     

Formation of Al2O3 Scales on Single-Phase RuAl Produced by Reactive Sintering

The oxidation behavior of single-phase RuAl produced by powder metallurgy combined with arc melting was investigated. Oxidation was conducted at 1000°C; oxide scale growth and phase formation were studied using scanning-electron microscopy (SEM) and x-ray diffraction (XRD). A dense protective scale with an Al–depleted sublayer was formed during oxidation. The oxide scale is the stable -Al₂O₃. The oxide-scale morphology shows the presence of whiskers, with a needle-like form, which suggests that the growth of the oxide scale is produced by outward diffusion of Al. At the beginning, oxidation follows a parabolic law, but, after 100 hr of oxidation; the growth rate is slower than expected from a parabolic law.     

Oxidation Resistance of a Cr0.50Al0.50N Coating Prepared by Magnetron Sputtering on Alloy K38G

A Cr_0.50Al_0.50N coating has been prepared by a reactive-magnetron-sputtering method on alloy K38G. The coating possesses mainly the B1 type with a small amount of B4-type crystal structure phase. Isothermal oxidation tests were performed at 900–1,100 °C for 20 h by thermogravimetric analysis (TGA) in air. The results reveal that the coated samples have much lower mass gain than that of the bare alloy. The parabolic rate constants of the coated samples decrease by 2 orders of magnitude compared with the bare alloy at 1,000 and 1,100 °C. During the oxidation of the coated samples below 1,000 °C, the main oxide is Cr₂O₃, but above 1,000 °C, the scale changes to α-Al₂O₃. The observed oxidation behaviors demonstrate that the Cr_0.50Al_0.50N coating can provide good protection against corrosion over a wide temperature range.     

Microstructure and properties of WC reinforced Ni-based composite coatings with Y2O3 addition on titanium alloy by laser cladding

ABSTRACT

In this study, WC reinforced Ni-based composite coatings with Y₂O₃ addition were deposited on Ti-6Al-4V titanium substrate by laser cladding. The phases, microstructure, microhardness and wear resistance of the composite coatings were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, microhardness tester and wear tester. The results showed that good metallurgical bonding was achieved between the composite coatings and substrate. The phases mainly were γ-Ni, TiC, TiB₂, Ni₃B, M₂₃C₆ and WC. Most of the WC was dissolved in small pieces of WC during the laser cladding process. The microhardness of the composite coatings was about 3 times that of the titanium substrate and the wear resistance of the composite coatings had a significant increase.     

Roles of humidity and heat treatment temperatures on YBa2Cu3O7-x coated conductors by trifluoroacetic acid-metal organic deposition process

YBa₂Cu₃O_7−x(YBCO) films were fabricated on an LAO substrate using the trifluoroacetic acid-metal organic deposition (TFA-MOD) method and the effects of the humidity and heat treatment temperatures on the microstructure, degree of texture and critical properties of the films were evaluated. In order to understand the combined effects of the humidity and the calcining and firing temperatures on critical properties, heat-treatment was performed at various temperatures with the other processing variables fixed. The films were calcined at 400–430 and fired at 750–800 °C in a 0–12.1% humidified Ar-O₂ atmosphere. The texture was determined by pole-figure analysis. The amount of the BaF₂ phase was effectively reduced and a sharp and strong biaxial texture was formed under a humidified atmosphere, which led to increased critical properties. In addition, the microstructure varied significantly with firing temperature but changed little with calcining temperature. The highest I_C of 40 A/cm-width, which corresponds to J_C value of 1.8 MA/cm², was obtained for the films fired at 775 (in 12.1% humidity) after calcining at 400–430 °C. It is likely that °C the highest I_C value is due to the formation of a more pure YBCO phase, c-axis grains, and a denser microstructure.     

Deposition and characterization of CrN/Si3N4 and CrAlN/Si3N4 nanocomposite coatings prepared using reactive DC unbalanced magnetron sputtering

Nanocomposite coatings of CrN/Si₃N₄ and CrAlN/Si₃N₄ with varying silicon contents were synthesized using a reactive direct current (DC) unbalanced magnetron sputtering system. The Cr and CrAl targets were sputtered using a DC power supply and the Si target was sputtered using an asymmetric bipolar-pulsed DC power supply, in Ar + N₂ plasma. The coatings were approximately 1.5 μm thick and were characterized using X-ray diffraction (XRD), nanoindentation, X-ray photoelectron spectroscopy and atomic force microscopy. Both the CrN/Si₃N₄ and CrAlN/Si₃N₄ nanocomposite coatings exhibited cubic B1 NaCl structure in the XRD data, at low silicon contents (< 9 at.%). A maximum hardness and elastic modulus of 29 and 305 GPa, respectively were obtained from the nanoindentation data for CrN/Si₃N₄ nanocomposite coatings, at a silicon content of 7.5 at.%. (cf., 24 and 285 GPa, respectively for CrN). The hardness and elastic modulus decreased significantly with further increase in silicon content. CrAlN/Si₃N₄ nanocomposite coatings exhibited a hardness and elastic modulus of 32 and 305 GPa, respectively at a silicon content of 7.5 at.% (cf., 31 and 298 GPa, respectively for CrAlN). The thermal stability of the coatings was studied by heating the coatings in air for 30 min in the temperature range of 400-900 °C. The microstructural changes as a result of heating were studied using micro-Raman spectroscopy. The Raman data of the heat-treated coatings in air indicated that CrN/Si₃N₄ and CrAlN/Si₃N₄ nanocomposite coatings, with a silicon content of approximately 7.5 at.% were thermally stable up to 700 and 900 °C, respectively.     

氧化铝涂层的超音速等离子喷涂参数影响及硬度分析

目的初步明确超音速等离子喷涂参数对涂层的影响规律,优化工艺参数。方法采用超音速等离子喷涂技术制备Al2O3陶瓷涂层,对涂层进行表征,分析喷涂电流I、等离子发生气体压力Pair、喷距d对涂层显微结构的影响。基于涂层显微硬度HV设计工艺优化试验,建立喷涂参数与显微硬度之间的回归方程。结果 I=260 A或Pair=0.55 MPa时,涂层是α-Al2O3和γ-Al2O3双相复合结构;I=340 A或Pair=0.35 MPa时,涂层几乎全由γ-Al2O3相组成,基本不含有未熔颗粒;喷距变化对涂层相组成的影响不显著。I或d增大,或者Pair降低,显微硬度都呈增大趋势。结论在实验范围内,超音速等离子喷涂Al2O3涂层的显微硬度最优工艺是:Pair=0.35 MPa,I=340 A,d=230 mm。     

Microstructure and mechanical property evaluation of pulsed DC magnetron sputtered Cr–B and Cr–B–N films

CrB₂ and four Cr–B–N films with high Cr/B ratio and various nitrogen contents were deposited by a co-sputtering process using a bipolar asymmetric pulsed DC reactive magnetron sputtering system. The structures and BN bonding nature of the thin films were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. The surface and cross sectional morphologies of the thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface roughness of the thin films was explored by atomic force microscopy (AFM). Nanoindentation, microscratch and ball-on-disk wear techniques were used to evaluate the hardness, and tribological properties of the thin films, respectively.The microstructure of the Cr–B–N thin films changed from a coarse columnar structure to a glassy and featureless morphology as the nitrogen content increased from 15.2 at.% to 54.5 at.%, whereas the corresponding structure developed from an amorphous state to a nanocomposite structure consisting of CrN nanograins and amorphous BN phases. It was found that high hardness, good tribological and brittle properties were obtained for the CrB₂ coating. The hardness and elastic modulus of the Cr–B–N thin films decreased with increasing nitrogen content until the nanocomposite structure of nanocrystalline CrN grains and an amorphous BN matrix was formed. However, the hardening effect induced by the nanocomposite structure was limited due to the fact that the small CrN nanograins were surrounded by a thick intergranular soft amorphous BN layer. On the other hand, the fracture toughness and resistance against elastic strain to failure of the Cr–B–N coatings were effectively enhanced by the addition of nitrogen.     

Synthesis of Al2O3/SiC composites by the SHS microwave heating process

Alumina/silicon carbide composites were synthesized by the microwave induced SHS (Self-propagating High-temperature Synthesis) process. SiO₂/Al/C powders were used as starting materials and samples were ignited by using a 2.45 GHz multimode home microwave oven (700W). Effects of the mixing ratio of SiO₂/Al/C powders, reaction environments, and weight percent of KNO₃ as a reaction promoter on the formation of the final product were studied.     

Improvement of the hydrogen-storage kinetics of Mg by reactive mechanical grinding with 10 wt.% Fe2O3 and 5 wt.% Ni

The addition of Fe₂O₃ to Mg is believed to be able to increase the hydriding rate of Mg, and the addition of Ni is thought to be able to increase the hydriding and dehydriding rates of Mg. A sample Mg-(10wt.%Fe₂O₃, 5 wt.%Ni) was prepared by mechanical grinding under H₂ (reactive mechanical grinding). The as-milled sample absorbed 4.61 wt.% of hydrogen at 593 K under 12 bar H₂ for 60 min. Its activation was accomplished after two hydriding-dehydriding cycles. The activated sample absorbed 4.59 wt.% of hydrogen at 593 K under 12 bar H₂ for 60 min, and desorbed 3.83 wt.% hydrogen at 593 K under 1.0 bar H₂ for 60 min. The activated Mg-(10wt.%Fe₂O₃, 5 wt.%Ni) had a slightly higher hydriding rate at the beginning of the hydriding reaction but a much higher dehydriding rate compared with the activated Mg-10 wt.%Fe₂O₃. prepared via spray conversion. After hydriding-dehydriding cycling, Fe₂O₃ was reduced, Mg₂Ni was formed by the reaction of Mg with Ni, and a small fraction of Mg was oxidized.