Growth and properties analysis of metal-organic chemical vapor deposited MgxZn1-xO films on C-Al2O3 substrates

Mg_xZn_1−xO (0 〈 x ⩽ 0.12) thin films with the wurtzite structure have been successfully grown on c-Al₂O₃ substrates by metal-organic chemical vapor deposition (MOCVD). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), photoluminescence (PL) spectrometry, and transmission measurements are performed to study the characteristics of Mg _x Zn_1−x O thin films. Results show that with increasing Mg content, the diffraction peak of Mg _x Zn_1−x O thin films shifts towards a higher diffraction angle (the biggest shift is 0.22°), and the full width at half maximum (FWHM) of the diffraction peak is broadened. Meanwhile, a blue-shift occurs at the near-band-edge (NBE) emission peak and the largest blue-shift of the band gap of the Mg _x Zn_1−x O films is 113 meV with Mg content x50.12. Therefore, the energy band gap of the Mg _x Zn_1−x O films is determined by Mg content in the thin films and the energy band gap increases with an increase of Mg content.     

The Adhesion of Monomolecular Hydroxyl-terminated Perfluoropolyether Liquid Films on the Sputtered Silicon Nitride Surface as a Function of End Group Acidity and Mobility

The intermolecular interactions at the interface between monomolecular hydroxyl-terminated perfluoropolyether (PFPE) liquids (Zdol, Zdol-TX, Z-Tetraol, Zdiac) and a sputtered amorphous silicon nitride film (SiN_x) are investigated using contact angle goniometry, Fourier transform infrared spectroscopy, and ab initio computational chemistry. The results demonstrate that the adhesion between the PFPE liquids and the SiN_x surface occur via the polar interactions between the PFPE end groups (-OH, -COOH) and the polar sites on the SiN_x surface (e.g., SiOH). The attractive interactions lead to a lowering of the polar surface energy with increasing PFPE coverage up to a monolayer. The binding energy is computed to be approximately −4 to −9 kcal/mol, depending upon the polarity of the PFPE end group. Adsorbed water is shown to compete with PFPE for surface bonding sites on SiN_x (−4.4 kcal/mol) that can lead to a significantly reduced level of adhesion for some of the hydroxyl-terminated PFPEs. A higher level of adhesion between the PFPEs and SiN_x can be attained by increasing the strength of the hydrogen bond and/or increasing the configurational entropy of the PFPE end group to facilitate the hydrogen bonding reaction.     

Tribological properties of spark-plasma-sintered ZrO2(Y2O3)-CaF2-Ag composites at elevated temperatures

Spark-plasma sintering is employed to synthesize self-lubricating ZrO₂(Y₂O₃) matrix composites with different additives of CaF₂ and Ag as solid lubricants by tailoring the composition and by adjusting the sintering temperature. The friction and wear behavior of ZrO₂(Y₂O₃) matrix composites have been investigated in dry sliding against an alumina ball from room temperature to 800 °C. The effective self-lubrication at different temperatures depends mainly on the content of various solid lubricants in the composites. The addition of 35 wt.% Ag and 30 wt.% CaF₂ in the ZrO₂(Y₂O₃) matrix can promote the formation of a well-covered lubricating film, and effectively reduce the friction and wear over the entire temperature range studied. The friction coefficients at low temperatures were at a minimum value for the composite containing 35 wt.% of silver. At this silver concentration, low and intermediate temperature lubricating properties are greatly improved without affecting high-temperature lubrication by the calcium fluoride in ZrO₂(Y₂O₃) matrix composites. The worn surfaces and transfer films formed during wear process have been characterized to identify the synergistic lubrication behavior of CaF₂ and Ag lubricants at different temperatures.     

Tribological properties of ZrO2 (Y2O3)-Mo-BaF2/CaF2 composites at high temperatures

ZrO₂ (Y₂O₃) with different contents of BaF₂/CaF₂ and Mo were fabricated by hot pressed sintering, and the tribological behavior of the composites against SiC ceramic was investigated from room temperature to 1000 °C. It was found that the ZrO₂ (Y₂O₃)-5BaF₂/CaF₂-10Mo composite possessed excellent self-lubricating and anti-wear properties. The low friction and wear were attributed to enhanced matrix and BaMoO₄ formed on the worn surfaces.     

Effect of post-implantation annealing on the current-voltage characteristics of IR photodiodes based on <Emphasis Type="Italic">p</Emphasis>-HgCdTe

Current-voltage characteristics of IR photodiodes and distributions of charge carriers in n ⁺-n ⁻-p-structures based on vacancy p-doped Hg_{1 − x} Cd _x Te films with x = 0.22 are examined. Three-dimensional numerical modeling of the distribution of charge carriers and current-voltage characteristics during photodiode annealing is performed. The calculations predict that large tunnel currents in diodes after implantation can result from an elevated (more than 10¹⁵ cm⁻³) concentration of donors in the n ⁻-layer, which enhances tunneling by decreasing the thickness of the space charged region of the n-p-junction, and also from a small (less than 3 μm) depth of the p-n-junction.     

Reciprocating Sliding Friction and Wear Property of Fe<Subscript>3</Subscript>Si Based Alloys Containing Cu in Water Lubrication

Fe₃Si, Fe₃Si alloys containing Cu were fabricated by arc melting followed by hot-pressing. The friction and wear behaviors of Fe₃Si based alloys with and without Cu addition against Si₃N₄ ball in water-lubrication were investigated. The friction coefficient and the wear rates of Fe₃Si based alloys decreased as the load increased. The wear rate of Fe₃Si was higher than that of AISI 304. The addition of Cu can significantly improve the friction and wear properties of Fe₃Si based alloys and substantially reduce the wear rates of Si₃N₄ ball. The wear rate of Fe₃Si–10%Cu was 2.56 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 20 N and decreased to 1.64 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 90 N. The wear rate of Si₃N₄ ball against Fe₃Si–10%Cu was 1.41 × 10⁻⁶ mm³ N⁻¹ m⁻¹, while the wear rate of Si₃N₄ ball against AISI 304 was 5.20 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 90 N. The wear mechanism was dominated by micro-ploughing. The combination of mechanical action (i.e., shear, smear and transference of Cu) and tribochemical reaction of Si₃N₄ with water was responsible for the improved tribological behavior of Fe₃Si alloys containing Cu under high loads.     

Tribological Properties of Spark-Plasma-Sintered ZrO2(Y2O3)–Al2O3–Ba x Sr1?x SO4 (x?=?0.25, 0.5, 0.75) Composites at Elevated Temperature

Self-lubricating ZrO₂(Y₂O₃)–Al₂O₃–Ba _x Sr_1−x SO₄ (x = 0.25, 0.5, 0.75) composites have been fabricated by spark plasma sintering (SPS) method. The tribological properties have been evaluated using a high-temperature friction and wear tester at room temperature and 760 °C in dry sliding against alumina ball. The composites exhibit distinct improvements in effectively reducing friction and wear, as compared to the unmodified ZrO₂(Y₂O₃)–Al₂O₃ ceramics. The ZrO₂(Y₂O₃)–Al₂O₃–Ba _x Sr_1−x SO₄ (x = 0.25, 0.5, 0.75) composites have great low and stable friction coefficients of less than 0.15 and wear rates in the order of 10^− 6mm³/Nm at 760 °C. Delamination is considered as the dominating wear mechanism of the composites at room temperature. At elevated temperature, the formation and effective spreading of Ba _x Sr_1−x SO₄ (x = 0.25, 0.5, 0.75) lubricating films during sliding play an important role in the reduction of the friction and wear.     

Quantification of the Ti oxidation state in BaTi1−xNbxO3 compounds

The Ti oxidation state of a series mixed-valence BaTi_1−xNb_xO₃ compound (where x=0.002, 0.004, 0.02, 0.10, 0.20 and 0.50) is investigated using high resolution electron energy loss spectroscopy (EELS). The energy loss near edge structure (ELNES) of the Ti-L_2,3 and O-K edges was recorded with high energy resolution. The fraction of Ti⁴⁺ and Ti³⁺ components is determined in each compound by linear profile fitting with Ti⁴⁺ and Ti³⁺ standard spectra obtained from reference compounds within the series. The fitting results indicate an increase in the fraction of the Ti³⁺ component as the Nb content increases. A deviation from the expected Ti³⁺ valence fraction based on the charge balance across the series was detected and discussed. By considering all detailed features on the spectra obtained with high energy resolution, this linear fitting method can be used to determine the oxidation state of transition metal oxides, especially for the early transition metals where conventional methods based on the L_2,3 edge ratio have shown to fail. The potential of this method to provide insight to mixed valence systems, vacancies and properties of oxides is discussed.     

Microstructure and tribological characteristics of ZrO2–Y2O3 ceramic coatings deposited by laser-assisted plasma hybrid spraying

ZrO₂–Y₂O₃ ceramic coatings were deposited on AISI 304 stainless steel by both a low-pressure plasma spraying (LPPS) and a laser-assisted plasma hybrid spraying (LPHS). Microstructure and tribological characteristics of ZrO₂–Y₂O₃ coatings were studied using an optical microscope, a scanning electron microscope, and an SRV high-temperature friction and wear tester. The LPHS coatings exhibit distinctly reduced porosity, uniform microstructure, high hardness and highly adhesive bonding, although more microcracks and even vertical macrocracks seem to be caused in the LPHS coatings. The ZrO₂ lamellae in the LPHS coatings before and after 800°C wear test consist mainly of the metastable tetragonal (t′) phase of ZrO₂ together with small amount of c phase. The t′ phase is very stable when it is exposed to the wear test at elevated temperatures up to 800°C for 1 h. The friction and wear of the LPHS coatings shows a strong dependence on temperature, changing from a low to a high wear regime with the increase of temperature. At low temperatures, friction and wear of the LPHS coatings is improved by laser irradiation because of the reduced connected pores and high hardness in contrary to the LPPS coating. However, at elevated temperatures, the friction and wear of the LPHS coatings is not reduced by laser irradiation. At room temperature, mild scratching and plastic deformation of the LPHS coatings are the main failure mechanism. However, surface fatigue, microcrack propagation, and localized spallation featured by intersplat fracture, crumbling and pulling-out of ZrO₂ splats become more dominated at elevated temperatures.     

High-temperature tribological properties of spark-plasma-sintered Al2O3 composites containing barite-type structure sulfates

Al₂O₃–50BaSO₄–20Ag, Al₂O₃–50BaSO₄–10SiO₂, Al₂O₃–50(mass%)SrSO₄, Al₂O₃–50PbSO₄–5SiO₂, Al₂O₃–50BaSO₄ and Al₂O₃–50BaCrO₄ composites (mass%) were prepared by spark plasma sintering and their microstructure and high-temperature tribological properties were evaluated. Al₂O₃–50BaSO₄–20Ag composites (mass%) showed the lowest friction coefficients at the temperature ranging from 473 to 1073 K. Thin Ag film was observed on the wear tracks of the composites above 473 K. In addition, the friction coefficients of Al₂O₃ composites containing SrSO₄ and PbSO₄ were as low as those of Al₂O₃–BaSO₄ and Al₂O₃–BaCrO₄ composites at the temperatures up to 1073 K. The thin films formed on the wear tracks of the Al₂O₃–SrSO₄ composites were composed of Al₂O₃ and SrSO₄ phases, while the films formed on the wear tracks of the Al₂O₃–PbSO₄–SiO₂ composites consisted of Al₂O₃, PbSO₄ and SiO₂ phases.     

Investigation on the impact behavior of Al2O3-SiC-MgO nanoceramic/metal laminated composite

Lightweight laminated composites containing a ceramic front layer and a metallic backing layer were used in order to protect people, moving equipment, and mobile vehicles from high velocity impact and the increased mobility of mobile vehicles. In this study, by adding10 vol% SiC and 500 ppm MgO nanoscale particles on the microstructure of Al ₂ O ₃ matrix and applying optimum sintering conditions, ceramic performance against high-speed projectile impact was improved. To perform this investigation, a number of target samples with two different types of front layers (alumina and Al ₂ O ₃-SiC-MgO nanocomposite ceramic) were produced. Impact tests were conducted on these samples using 7.62 mm projectiles with a velocity of 820 ± 15 m/s. The amount of bulge and bending of the backing layer caused by impact tests was measured. The results of the impact tests on the samples made of Al ₂ O ₃-SiC-MgO nanocomposite ceramics and alumina were also compared and analyzed. The results indicate that the substitution of Al ₂ O ₃-SiC-MgO ceramic layer — which is proffered in this paper — instead of pure alumina ceramic layer, decreases the areal-density of the samples by at least 30% and improves mechanical properties by about a 60% increase in flexural strength and 100% growth of the energy distribution factor, which impressively increases impact energy absorption.     

Tribological properties of Fe7Mo6-based alloy under two ionic liquid lubrications

The tribological properties of Fe₇Mo₆-based alloy, Mo, Fe and ASTM class no. 45 cast iron disk specimens were investigated against ASTM 52100 steel balls under the lubrication of two different kinds of hydrophobic ionic liquid: N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13-TFSI) and N-N-N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI). When lubricated with PP13-TFSI or TMPA-TFSI, the Fe₇Mo₆-based alloy disk specimens exhibited lower friction coefficients and lower wear rates than the Mo, Fe and ASTM class no. 45 cast iron disk specimens. The low friction coefficients and low wear rates of the Fe₇Mo₆-based alloy were considered to be caused by the formation of low friction materials such as MoO₃ and FeSO₄ on the worn surface.     

Comment on “Pulsed Laser Deposition and Properties of Mn+1AXx Phase Formulated Ti3SiC2 Thin Films”

A recent paper by Hu et al. claimed synthesis of the MAX-phase Ti₃SiC₂at 100–300 °C using pulsed laser deposition. In this comment, we find that the evidence presented by Hu et al. is insufficient to show Ti₃SiC₂ formation. In fact, there is a simpler interpretation of their results from X-ray diffraction and transmission electron microscopy, namely that the material produced is a cubic TiC-based compound.     

毫米级微型机器人操作手的研制和操作特性

采用单晶片型压电悬臂梁制作了一种双悬臂梁结构的微型夹持器,用作毫米级微型机器人的微操作手.该微夹持器整体尺寸为15mm×2mm×2mm,重量为100mg.在分析该悬臂梁操作原理的基础上,选用PbNi_1/3Nb_2/3-PbZrO₃-PbTiO₃三元系压电陶瓷准同型相界的配方作为悬臂梁压电驱动材料,这种压电陶瓷具有高压电常数 (d₃₁) 和机电耦合系数 (K_p).进一步研究了压电微夹持器的操作特性.结果表明:50V电场下,其最大张口距离可以达到40μm,最大夹持力为25.7×10^-3N.     

The effect of Al2O3 on the friction performance of automotive brake friction materials

This study consists of two stages. In the first stage, bronze-based break linings were produced and friction-wear properties of them were investigated. In the second stage, 0.5%, 1%, 2% and 4% alumina (Al₂O₃) powders were added to the bronze-based powders and Al₂O₃ reinforced bronze-based break linings were produced. Friction–wear properties of the Al₂O₃ reinforced samples were aslo investigated and compared to those of plain bronze-based ones. For this purpose, friction coefficient and wear behaviour of the samples were tested on the grey cast iron disc. The hardness and density of the samples were also determined. Microstructures of the samples before and after the sintering and the worn surfaces of the wear specimens were examined using a scanning electron microscope (SEM). The sample compacted at 350 MPa and sintered at 820 °C exhibited the optimum friction–wear behaviour. With increase in friction surface temperature, a reduction in the friction coefficient of the samples was observed. The lowest reduction in the friction coefficient with increasing temperature was for the 2% and 4% Al₂O₃ reinforced samples. The SEM images of the sample indicated that increase in Al₂O₃ content resulted in adhesive wear. With increase in Al₂O₃ content, a reduction in mass loss of the samples was also observed. Overall, the samples reinforced with 2% and 4% Al₂O₃ exhibited the best results.     

Friction and wear behaviour of plasma-sprayed Cr2O3 coatings against steel in a wide range of sliding velocities and normal loads

This study investigates the influence of sliding speed and normal load on the friction and wear of plasma-sprayed Cr₂O₃ coatings, in dry and lubricated sliding against AISI D2 steel. Friction and wear tests were performed in a wide speed range of 0.125–8 m/s under different normal loads using a block-on-ring tribometer. SEM, EDS and XPS were employed to identify the mechanical and chemical changes on the worn surfaces. A tangential impact wear model was proposed to explain the steep rising of wear from the minimum wear to the maximum wear. The results show that the wear of Cr₂O₃ coatings increases with increasing load. Secondly, there exist a minimum-wear sliding speed (0.5 m/s) and a maximum-wear sliding speed (3 m/s) for a Cr₂O₃ coating in dry sliding. With the increase of speed, the wear of a Cr₂O₃ coating decreases in the range 0.125–0.5 m/s, then rises steeply from 0.5 m/s to 3 m/s, followed by a decrease thereafter. The large variation of wear with respect to speed can be explained by stick-slip at low speeds, the tangential impact effect at median speeds and the softening effect of flash temperature at high speeds. Thirdly, the chemical compositions of the transfer film are a-Fe₂O₃ in the speed range 0.25–2 m/s, and FeO at 7 m/s. In addition, the wear mechanisms of a Cr₂O₃ coating in dry sliding versus AISI D2 steel are adhesion at low speeds, brittle fracture at median speeds and a mixture of abrasion and brittle fracture at high speeds. Finally the lubricated wear of Cr₂O₃ coating increases sharply from 1 to 2.8 m/s.     

Sliding wear characteristics of plasma-sprayed Al2O3 and Cr2O3 coatings against copper alloy under severe conditions

Al₂O₃ and Cr₂O₃ coatings were deposited by atmospheric plasma spraying and their tribological properties dry sliding against copper alloy were evaluated using a block-on-ring configuration at room temperature. It was found that the wear resistance of Al₂O₃ coating was superior to that of the Cr₂O₃ coating under the conditions used in the present study. This mainly attributed to its better thermal conductivity of Al₂O₃ coating, which was considered to effectively facilitate the dissipation of tribological heat and alleviate the reduction of hardness due to the accumulated tribological heat. As for the Al₂O₃ coating, the wear mechanism was plastic deformation along with some micro-abrasion and fatigue-induced brittle fracture, while the failure of Cr₂O₃ coating was predominantly the crack propagation-induced detachment of transferred films and splats spallation.     

Influence of Al2O3 reinforcement on the abrasive wear characteristic of Al2O3/PA1010 composite coatings

In the present study, the abrasive wear characteristics of Al₂O₃/PA1010 composite coatings were tested on the turnplate abrasive wear testing machine. Steel 45 (quenched and low-temperature tempered) was used as a reference material. The experimental results showed that when the Al₂O₃ particles have been treated with a silane coupling agent (γ-aminopropyl-triethoxysilane), the abrasive wear resistance of Al₂O₃/PA1010 composite coatings has a good linear relationship with the volume fraction of Al₂O₃ particles in Al₂O₃/PA1010 composite coatings and the linear correlation coefficient is 0.979. Under the experimental conditions, the size of Al₂O₃ particles (40.5-161.0 μm) has little influence on the abrasive wear resistance of Al₂O₃/PA1010 composite coatings. By treating the surface of Al₂O₃ particles with the silane coupling agent, the distribution of Al₂O₃ particles in PA1010 matrix is more homogeneous and the bonding state between Al₂O₃ particles and PA1010 matrix is better. Therefore, the Al₂O₃ particles make the Al₂O₃/PA1010 composite coatings have better abrasive wear resistance than PA1010 coating. The wear resistance of Al₂O₃/PA1010 composite coatings is about 45% compared with that of steel 45.     

Lubrication of Si3N4 and Al2O3 in water with and without addition of silane coupling agents in the range of 0.05–0.10 mol/l

To improve water lubrication of ceramics at a lower sliding velocity, the effect of the addition of silane coupling agents was investigated. Si₃N₄ and Al₂O₃ were slid against themselves in water with and without the addition of silane coupling agents in amounts ranging from 0.05 to 0.10 mol/l. Silane coupling agents containing one or more amino groups were effective in reducing the friction of Si₃N₄ and Al₂O₃ in water. Si₃N₄ also showed significant wear reduction but not Al₂O₃. However, the addition of a silane coupling agent containing an epoxy group increased both friction and wear of Si₃N₄. Improved lubricative characteristics of Si₃N₄ in water and in silane coupling agent solutions were obtained when Si₃N₄ contained smaller amounts of sintering additives. The adsorption behaviour of a silane coupling agent on ceramics was examined using both Fourier transform infrared spectroscopy and thin layer chromatography to clarify the interaction between the silane coupling agent and the ceramics. The role of polysiloxane film formation on ceramics is discussed to demonstrate the lubrication properties of ceramics.     

Tribological Properties of Nanocomposite CrC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/a-C:H Thin Films

Recently we showed that coatings, prepared by unbalanced magnetron sputtering from a metallic Cr target in an Ar/CH₄ discharge are composed of nanocrystalline CrC _x embedded in an a-C:H matrix. This work investigates the structural correlation of such nanocomposite CrC _x /a-C:H coatings to their tribological properties. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the phase composition and the chemical bonding in the films deposited at different experimental conditions. The coating microstructure was investigated on selected samples by high-resolution transmission electron microscopy. For CrC _x -dominated coatings deposited at CH₄ partial to total pressure ratios (p_CH4/p_t) < 0.42, only minor changes regarding the friction coefficients and the abrasive wear rates were observed although microstructural changes towards a higher degree of crystallinity were proven by transmission electron microscopy and substantiated with XPS results. For a-C:H dominated coatings deposited at p_CH4/p_t > 0.42, the friction coefficients and abrasive wear rates were shown to decrease with increasing a-C:H phase content and its more sp²-like bonding configuration. It can be concluded that the microstructural changes in terms of CrC _x crystallite coarsening and bonding configuration of the a-C:H matrix phase are responsible for the observed changes of the friction coefficients and wear rates.