An evaluation of surface properties and frictional forces generated from Al–Mo–Ni coating on piston ring

Surface properties of the Al–Mo–Ni coating plasma sprayed on the piston ring material and the frictional forces obtained by testing carried out under different loads, temperatures and frictional conditions were evaluated.

Al–Mo–Ni composite material was deposited on the AISI 440C test steel using plasma spraying method. The coated and uncoated samples were tested by being exposed to frictional testing under dry and lubricated conditions. Test temperatures of 25, 100, 200, and 300 °C and loads of 83, 100, 200, and 300 N were applied during the tests in order to obtain the frictional response of the coating under conditions similar to real piston ring/cylinder friction conditions. Gray cast iron was used as a counterface material. All the tests were carried out with a constant sliding speed of 1 m/s.

The properties of the coating were determined by using EDX and SEM analyses. Hardness distribution on the cross-section of the coating was also determined. In addition, the variations of the surface roughness after testing with test temperatures and loads under dry and lubricated conditions were recorded versus sliding distance.

It was determined that the surface roughness increased with increasing loads. It increased with temperature up to 200 °C and then decreased at 300 °C under dry test conditions.

Under lubricated conditions, the roughness decreased under the loads of 100 N and then increased. The roughness decreased at 200 °C but below and above this point it increased with the test temperature.

Frictional forces observed under dry and lubricated test conditions increased with load at running-in period of the sliding. The steady-state period was then established with the sliding distance as a normal situation. However, the frictional forces were generally lower at a higher test temperature than those at a lower test temperature. Surprisingly, the test temperature of 200 °C was a critical point for frictional forces and surface roughness.     

High-temperature oxidation studies of cold-sprayed Ni-20Cr and Ni-50Cr coatings on SAE 213-T22 boiler steel

The high-temperature oxidation behavior of cold-sprayed Ni-20Cr and Ni-50Cr coatings on SAE 213-T22 boiler steel has been investigated at 900 °C in air under cyclic heating and cooling conditions for 50 cycles. The kinetics of oxidation of coated and bare boiler steel has been established with the help of weight change measurements. It was observed that all the coated and bare steels obeyed parabolic rate law of oxidation. X-ray diffraction, FE-SEM/EDAX and X-ray mapping techniques were used to analyse the oxidation products of the coated and uncoated boiler steel. The uncoated steel suffered corrosion in the form of intense spalling and peeling of its oxide scale, which was perhaps due to the formation of unprotective Fe₂O₃ oxide scale. Both the coatings showed better resistance to the air oxidation as compared to the uncoated steel. The Ni-50Cr coating was found to be more protective than the Ni-20Cr-coated steel. The formation of oxides and spinels of nickel and chromium may be contributing to the development of air oxidation resistance in the coatings.     

Mechanically formed loss-tunable long-period fiber gratings realized on the periodic arrayed metal wires

A new method to tune the peak loss of mechanically formed long-period fiber gratings (MLPFGs) is proposed. Periodic arrayed metal wires are used to obtain the gratings along a single mode fiber (SMF). Self-maintaining gratings are achieved by the bonding force of an UV-adhesive between two glass plates. The initial index modulation formed at room temperature creates a maximum attenuation of −9 dB and −12 dB for coated and uncoated SMF, respectively. By changing the temperature, the peak loss is tuned due to the large thermal expansion of the UV-adhesive. Thermally tunable characteristics caused by the coating layer of the SMF are also described and compared with the results of the device with an uncoated SMF.     

The Tensile Properties of Uncoated and TiO2 Coated Bombyx Mori Silk Yarns Exposed to Thermal Treatment

Bombyx mori silk yarns were coated with a TiO₂ network by sol-gel processing. The tensile properties of TiO₂ coated silk yarns heated at various temperatures were examined and compared with those of uncoated silk yarns. The thermal properties of uncoated silk yarns and TiO₂ coated silk yarns were also discussed. Prominent changes were seen in the rigidity and Young's modulus. The Young's modulus of TiO₂ coated silk yarn increased by 13% at room condition and remained higher than that of uncoated silk yarns with increasing temperature. The shape of the stress–strain curve of TiO₂ coated silk yarns became the same as uncoated silk yarns and showed a similar tendency of change to uncoated silk yarns with increasing temperature. The rupture values of uncoated silk yarns and TiO₂ coated silk yarns decreased significantly, e.g., the breaking extension decreased from 17.28 to 2.44% and from 15.25 to 1.96% for uncoated silk yarns and TiO₂ coated silk yarns, respectively, when the temperature was increased from 25 to 225°C. Structural changes and degradation processes due to thermal effects for both uncoated and TiO₂ coated silk yarns are discussed.     

Preparation and properties of composite ceramic coating containing Al2O3–ZrO2–Y2O3 on AZ91D magnesium alloy by plasma electrolytic oxidation

A composite ceramic coating containing Al₂O₃–ZrO₂–Y₂O₃ was successfully prepared on AZ91D magnesium alloy by plasma electrolytic oxidation (PEO) technique in an alkaline aluminate electrolyte. The morphology, elemental and phase composition, corrosion behavior and thermal stability of the uncoated and coated samples were studied by environmental scanning electron microscopy (ESEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD), electrochemical corrosion test, high temperature oxidation test and thermal shock test. The results showed that the composite ceramic coating was composed of Al₂O₃, c-ZrO₂, t-ZrO₂, Y₂O₃ and some magnesium compounds, such as MgO, MgF₂ and MgAl₂O₄. After PEO treatment, the corrosion potential of AZ91D alloy was increased and the corrosion current density was significantly reduced. Besides, the coated magnesium alloys also showed excellent high temperature oxidation resistance and thermal shock resistance at 500 °C environment.     

Influence of oxide scale thickness on electrical conductivity of coated AISI 430 steel for use as interconnect in solid oxide fuel cells

The use of conductive coating on interconnect ferritic stainless steel can reduce electrical resistivity. In this study, an AISI 430 ferritic stainless steel interconnect was coated with a manganese base pack mixture by pack cementation. The effect of oxide scale thickness on electrical conductivity was evaluated by applying isothermal oxidation at 750?°C. This effect was also investigated at different temperatures (400?C900?°C). The formation of manganese spinels during annealing improved the oxidation resistance and electrical conductivity. Results showed that the increase in isothermal oxidation time and temperature increased the oxide thickness, and this resulted in the relatively low values of electrical conductivity. Manganese spinels enhanced the electrical conductivity and oxidation resistance of coated substrates as compared to uncoated substrates.     

Preparation of anti-oxidative carbon fiber at high temperature

In this paper, carbon fibers with improved thermal stability and oxidation resistive properties were prepared and evaluated their physical performances under oxidation condition. Carbon fibers were coated with SiC particles dispersed in a polyacrylonitrile solution and then followed by pyrolyzed at 1400 °C to obtain the SiC nanoparticle deposition on the surface of the carbon fiber. The SiC coated carbon fiber showed extended oxidation resistive property as remaining 80-88% of the original weight even at high temperature 1000 °C under air, as compared with the control of zero weight at 600 °C. The effects of the coating conditions on the oxidation resistive properties of the coated fibers were studied in detail.     

Deposition and characterization of TiAlSiN nanocomposite coatings prepared by reactive pulsed direct current unbalanced magnetron sputtering

This work reports the performance of high speed steel drill bits coated with TiAlSiN nanocomposite coating at different Si contents (5.5-8.1 at.%) prepared using a four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. The surface morphology of the as-deposited coatings was characterized using field emission scanning electron microscopy. The crystallographic structure, chemical composition and bonding structure were evaluated using X-ray diffraction, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, respectively. The corrosion behavior, mechanical properties and thermal stability of TiAlSiN nanocomposite coatings were also studied using potentiodynamic polarization, nanoindentation and Raman spectroscopy, respectively. The TiAlSiN coating thickness was approximately 2.5-2.9 μm. These coatings exhibited a maximum hardness of 38 GPa at a silicon content of approximately 6.9 at.% and were stable in air up to 850 °C. For the performance evaluation, the TiAlSiN coated drills were tested under accelerated machining conditions by drilling a 12 mm thick 304 stainless steel plate. Under dry conditions the uncoated drill bits failed after drilling 50 holes, whereas, TiAlSiN coated drill bits (Si = 5.5 at.%) drilled 714 holes before failure. Results indicated that for TiAlSiN coated drill bits the tool life increased by a factor of more than 14.     

Investigation of oxidation inhibition properties of vaporized self-assembled multilayers on copper nanopowders

Stability against oxidation was investigated for vaporized self-assembled multilayers on nano-sized Cu powders. 100 nm-sized copper powders were coated with 1-octanethiol to make a passivation layer against oxidation.As a result, the surface resistivity of the coated and uncoated nano-sized copper powders differed by two orders of magnitude. XPS analysis was used to monitor changes in the amount of sulfur and oxygen on the surface of octanethiol-coated Cu nano powders over a period of time. While sulfur was detected for up to 75 days, the amount of oxygen increased dramatically after 35 days, indicating sign of partial oxidation. Furthermore, HR-TEM images showed that the octanethiol film was consistently 10 nm thick, for up to 35 days. After 35 days exposure to the air, the octanethiol film was partially damaged and its diffraction pattern detected the presence of Cu₂O. Based on these findings, vaporized octanethiol coating protected the copper nano powders from oxidation for up to 35 days. Therefore this oxidation inhibition property of VSAMs coating method on Cu powders achieves a great milestone toward inkjet printing technology.     

Z箍缩驱动混合堆第一壁热-力学瞬态响应分析

利用ANSYS程序对Z箍缩驱动聚变-裂变混合堆(Z-FFR)第一壁在瞬态热流加载下的热-力学响应进行了模拟计算,分析了第一壁温度、应力随时间和深度的分布。结果表明,周期性脉冲加载不会导致第一壁产生温度累积效应,第一壁温度峰值409 ℃,出现在钨层表面,钨层最大应力140 MPa,锆合金基底最大应力33 MPa。     

Electrodeposited cobalt coating on Crofer22APU steels for interconnect applications in solid oxide fuel cells

A gas-tight cobalt-based protective coating was successfully applied by electroplating and subsequent oxidation. The coating covered all the surfaces of the machined gas channels of the metallic interconnect and adhered well to this substrate. Such a gas-tight coating offers effective blocking of Cr diffusion or evaporation from the interconnect and hence a reliable protection against Cr poisoning of the SOFC cathode. Chemical interactions were observed between the cobalt coating and the LSM contact layer, resulting in layer spallation during oxidation under pressureless conditions. Applying a pressure to the layers, spallation was effectively prevented. Although the area specific resistance (ASR) of the coated interconnect was higher than the uncoated one, it decreased steadily with time within the measurement period. The ASR was 28 mΩ cm² after an exposure of 1170 h. It seems thus that electroplating followed by oxidation is a promising method for the fabrication of spinel protective coatings for SOFC interconnects or other balance-of-plant components with complicated gas flow paths.     

不锈钢管道低温溅射镀TiN薄膜技术

设计了一套适用于加速器细长管道真空室的低温溅射镀TiN薄膜装置。利用该装置,对86 mm×2 000 mm的不锈钢管道真空室进行溅射镀TiN膜实验,并对镀膜实验结果进行分析,得到了适用于加速器管道真空室内壁溅射镀TiN膜的表面处理参数。样品测试结果表明：在压强为80～90 Pa、基体温度为160~180 ℃的镀膜参数下,不锈钢管道内壁获得的TiN薄膜最佳,薄膜沉积速率为0.145 nm/s。镀膜后真空室的二次电子产额明显降低。     

不锈钢管道低温溅射镀TiN薄膜技术

 设计了一套适用于加速器细长管道真空室的低温溅射镀TiN薄膜装置。利用该装置，对86 mm×2 000 mm的不锈钢管道真空室进行溅射镀TiN膜实验，并对镀膜实验结果进行分析，得到了适用于加速器管道真空室内壁溅射镀TiN膜的表面处理参数。样品测试结果表明：在压强为80～90 Pa、基体温度为160~180 ℃的镀膜参数下，不锈钢管道内壁获得的TiN薄膜最佳，薄膜沉积速率为0.145 nm/s。镀膜后真空室的二次电子产额明显降低。     

The effect of cerium oxide argon-annealed coatings on the high temperature oxidation of a FeCrAl alloy

Ceria coatings were applied in order to improve the adherence of alumina scales developed on a model Fe–20Cr–5Al alloy during oxidation at high temperature. These coatings were performed by argon annealing of a ceria sol–gel coating at temperatures ranging between 600 and 1000 °C. The influence of these coatings on the alloy oxidation behaviour was studied at 1100 °C. In situ X-ray diffraction (XRD) was performed to characterize the coating crystallographic nature after annealing and during the oxidation process. The alumina scale morphologies were studied by means of scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The present work shows that the alumina scale morphology observed on cerium sol–gel coated alloy was very convoluted. On the cerium sol–gel coated alloy, argon annealing results in an increase of the oxidation rate in air, at 1100 °C. The 600 °C argon annealing temperature results in a good alumina scale adherence under thermal cycling conditions at 1100 °C.     

The evaluation of the performance of two pyroelectric detectors with vertically aligned multi-walled carbon nanotube coatings

Two LiTaO₃ pyroelectric detectors coated with vertically aligned multi walled carbon nanotube (MWCNT) black coatings were assembled and evaluated using NPL’s detector characterisation facilities. The vertically-aligned nanotube array (VANTA) black coatings were grown on a silicon substrate and subsequently lifted off the silicon and bonded on the pyroelectric crystal substrates. Despite some drawbacks, this method was shown to provide a reliable way of coating delicate substrates such as pyroelectric crystals with VANTA coatings. The performance of the coated and uncoated detectors was evaluated and compared by coating only half of the active area of the test detectors, leaving the other half uncoated. The relative spectral responsivity of the VANTA-coated pyroelectric detectors was shown to be spectrally flat in the 0.8–14 μm wavelength range within the uncertainty of the measurements. The spatial uniformity of response of both detectors exhibited fine structure which was assigned either to the thickness of the VANTA coatings or to their bonding to the pyroelectric crystal. Both coated and uncoated detectors exhibited a super-linear response. This observation was expected in the case of the uncoated detectors, but was surprising in the case of the coated detectors and indicates that the thermal conductivity of vertically aligned multi-walled carbon nanotubes is high along their long axis. The spatial variations of the phase delay experienced by the signal propagating through the VANTA coatings indicate that the thermal diffusivity of the coatings is not spatially uniform.     

Bowl piston geometry as an alternative to enlarged crevice pistons for rapid compression machines

Thermal inhomogeneity and physical processes like fluid dynamics reduce the utility of rapid compression machine (RCM) facilities to accurately study fuel combustion phenomenon relevant to internal combustion engines. Most current RCMs incorporate a large crevice volume in the piston to capture roll-up vortices that encroach into the combustion zone during compression. In this work, a bowl piston design similar to those used in diesel engines is proposed as an alternative to enlarged creviced pistons for creating a sufficiently thermally homogenous gas mixture prior to ignition without undesirable fluid motion found in flat piston configurations. The bowl piston also eliminates the possibility of cold unreacted gases entering the combustion chamber when the piston is retracted in rapid compression and expansion machines (RCEMs) like in creviced piston designs. In the work, a bowl piston was compared to creviced piston and flat piston configurations numerically and experimentally. Through non-reacting computational fluid dynamics simulations, the bowl piston reduced the roll-up vortex found for the flat piston and led to a higher temperature and more thermally uniform core of gas at peak compression compared to the enlarged crevice piston. Experimentally, three pistons were studied in a RCM facility with ethanol and n-butane as fuels. Results showed that the bowl piston yielded benefits over conventional piston geometries including: reduced heat loss due to lower surface area, higher turbulent Reynolds Number, stronger ignition, and higher heat release rate and combustion efficiency as estimated using heat release analysis. Based on the findings presented here, we conclude that bowl piston geometries are a promising alternative to creviced pistons for conducting fuel ignition studies in RCM and RCEM facilities.     

Alternating-current losses in two-layer superconducting cables consisting of second-generation superconductors coated by U-shaped ferromagnetic materials

Alternating-current losses in a two-layer superconducting cable, each layer being composed of 15 closely-spaced rectangular wires made up of second-generation superconductors when the ends of wires are coated by either a non-magnetic or strong ferromagnetic material having a U profile is numerically investigated. Computations are carried out through the finite-element method. The alternating-current losses do not increase significantly if the relative permeability of the coating is increased three orders of magnitude, provided that the current amplitude is less than half of the critical current in a superconducting wire. However, the losses are much higher for ferromagnetic coating if the amplitude of the applied current oscillating at 50 Hz is close to the critical current. The ferromagnetic coating is seen to accumulate the magnetic field lines normally on its surfaces, while the field lines are parallel to the long axes of the wires, leading to more significant flux penetration in the coated regions. This facilitates a uniform low-loss current flow in the uncoated regions of the wires. In contrast, coating with a non-magnetic material gives rise to a considerably smaller current flow in the uncoated regions, whereas the low-loss flow is maintained in the coated regions. Moreover, the current flows in opposite directions in the coated and uncoated regions, where the direction in each region is converse for the two materials.     

Development of copper coatings on ceramic powder by electroless technique

Electroless (EL) coating technique is one of the elegant ways of coating by controlling the temperature and pH of the coating bath in which there is no usage of electric current. EL nano-copper coating on ceramic particles of micron size is not reported. In this investigation, ceramic powders of ∼100 μm size have been coated with copper by EL technique in the pH and temperature ranges of 12-13.5 and 60-85 °C, respectively. The optimization of EL copper bath has been evaluated through the combination of process parameters like pH and temperature. The optimized value of pH is found to be 12.5 and temperature as 75 °C. The coated and uncoated powders have been subjected to microstructural studies by scanning electron microscope (SEM) and the phases present have been analyzed by X-ray diffraction. An attempt has been made to understand the bonding mechanism of coating. The adherence with the substrate is attributed to the chemical and mechanical bonding at the interface. A model has been suggested for the mechanical bonding effect at the interface.     

红外探测系统的激光辐照热效应仿真分析

为研究红外探测系统受激光辐照后的热效应与二次热辐射对探测器成像的影响,使用Ansys软件对红外探测器进行热辐射仿真和有限元结构仿真;采用黑体辐射定律和DO辐射计算模型模拟计算探测器内光学系统在不同激光辐照度下的温度随时间变化情况以及探测器内部温升对靶面成像的二次热辐射干扰情况;采用热弹性力学模型仿真计算探测器内部的热应力和热变形情况。结果表明:探测器受到1.06μm激光照射,矫正镜激光辐照度在50 W/cm²时,靶面受到二次热辐照度在0.6 s时达到100μW/cm²的量级,使红外探测器达到饱和;探测器受激光辐照后系统最高温度出现在矫正镜中心处,拟合得到系统最高温度与受照时间函数关系,可预测探测器升温结构破坏;最大热变形出现在矫正镜背面中心处,由外向内形成不等附加光程差,干扰探测器的成像效果;最大热应力出现在矫正镜前面中心处,得到最大热应力与激光辐照度间的线性关系曲线,为矫正镜热应力破坏提供预测参数。     

Vacuum anodic discharge as source of ionized fluxes of coating material

Cathodic and anodic discharges are effective sources of coating material ionized fluxes. Of special interest is the use of anodic discharges, particularly discharges with a thermoelectronic cathode. The discharge forms fluxes in high vacuum with regulated ionization and the absence of micro liquid droplets. The initiation conditions and characteristics of the discharge in the voltage range from 50 to 500 V with currents up to 5 A were investigated. The dependence of vacuum, interelectrode distance, and cathode heating temperature were considered. Conditions for the production of coating material fluxes with maximum ionization were established.