Wenzhuang Lu

Microstructure and tribological properties of REs borided TC21 alloy

Abstract The hard titanium boride layers are produced on titanium alloy TC21 using rare earth (RE) additions boriding technique. The microstructural evolution and phase transformations of the boride layers are examined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy and X-ray diffraction. Moreover, the friction and wear behaviour of boride layers under dry sliding conditions are evaluated using an HT-1000 friction and wear tester, and the microstructures of worn surfaces are also characterised by SEM. The results show that the boron concentrations in the surface layer during surface boriding have been improved with a small amount of RE additions, coupled with enhanced surface hardness and coating layer thickness. Moreover, all of the borided alloys appear to have better wear resistance and lower friction coefficient than as received alloy; furthermore, the RE borided samples show higher hardness and better wear resistance than conventional one, without RE additions.

Effect of rare earth (RE) on pack boronising process of titanium alloy

Abstract The pack boronising experiments were carried out on the TC21 titanium alloy using monomer boron powder as the boriding agent with and without rare earth oxide CeO2 respectively. The friction and wear behaviour of boride coated TC21 samples were evaluated using a pin on disc friction tester. The boride layers were investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, SEM and optical microscopy. The results show that the boride layers grown on TC21 consist of continuous top layer TiB2 and sublayer TiB whiskers; with the addition of CeO2 in the boriding agent, the grain size of boride layers is refined, the diffusion efficiency is increased and more TiB changes to TiB2; the microhardness of the top layer is ∼3200 HV(10 g); without CeO2, the friction coefficient of boride coated TC21 sample is ∼0·56, while with the addition of CeO2, it is <0·2. The boride coated TC21 samples show a much better wear resistance than the TC21 substrate.

Effects of rare earth additions during surface boriding on microstructure and properties of titanium alloy TC21

Abstract In the present paper, the effects of rare earth (RE) additions to the solid state boriding of titanium alloy TC21 have been studied. The microstructural evolution and phase transformations of the borided layers were examined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction. Moreover, the microhardness for the borided layer was also determined by Vickers hardness test. The results showed that the addition of a small amount of RE elements in the boriding process can lead to an increased boron concentration in the surface layer coupled with the improved surface hardness and coating layer thickness. Furthermore, the presence of trace quantities of RE oxide (Ce2O3) in boride layers indicated that the RE elements as catalysts could not only influence but also accelerate boriding process.

A novel rare earth-salt bath nitriding of TC21-DT titanium alloy

ABSTRACT A novel rare earth (RE)-salt bath nitriding of TC21-DT titanium alloy was primarily developed by adding certain amount of RE cerium oxide (CeO2) in KNO3 and NaNO3 salt bath, heated to temperatures in the range 590–650°C for periods up to 5 h in an ambient furnace atmosphere. The results showed that Ti phases and titanium nitride phase were formed on the surface of RE added samples; while no titanium nitride phases formed on the surface of conventional one, without RE addition. Furthermore, the surface hardness of nitrided samples, incorporated with RE addition, was about two times higher than that of conventional one (340HV0.01). The main improvement mechanism was analysed as well.

Influence of film thickness on structural and optical-switching properties of vanadium pentoxide films

Vanadium oxide films were deposited at different sputtering times on sapphire substrates by radio frequency reactive magnetron sputtering. The effects of thickness on the surface structural, morphology and optical-switching properties of the films were studied comprehensively. X-ray diffraction results show that all the prepared films are polycrystalline vanadium pentoxide films (V2O5) on (001) preferred orientation. Both root-mean-square roughness and average surface grain size decrease with the increase of thickness. With the thickness reduction, the closing time decreases first and then increases at the turning point of 350 nm, and the maximum and the minimum are 2.7 ms at 600 nm and 1.7 ms at 350 nm, respectively. The recovery time decreases rapidly with the reduction of the film, which varies from 40 ms at 600 nm to 27 ms at 150 nm. More concerning, the dynamic range of transmittance varies greatly from thickness, and the transmittance ratio before and after the phase transition covers from 3.75 at 150 nm to the maximum of 7.3 at 600 nm under a continuous probe light of 1064 nm.

Effect of rare earth addition on diffusion kinetics of borided TC21-DT titanium alloy

In this study, the properties and growth kinetics of boride layers, generated on the surface of TC21-DT alloy using appropriate amount of powders of boron carbide (B4C) and rare earth oxide (CeO2) were investigated. By conducting a series of experiments at different temperatures of 1123, 1223 and 1273 K for periods up to 10 h, the effects of rare earth (RE) addition on the growth kinetics of boride layers were studied. The characteristics of the boride layers were examined by scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction and micro-Vickers hardness tester. The results showed that the boron diffusion in boride layers was obviously accelerated by RE addition and the activation energy for RE addition-boriding in TC21-DT alloy was greatly decreased to 58.13kJ/mol, which was approximately 40% lower than that of conventional one, without RE addition.

Temperature Distribution of IFA Polishing Single Silicon Wafer

The ice fixed abrasives (IFA) polishing is a potential polishing process in the semiconductor industry to realize superior surface finish and planarity for semiconductor wafers. The key question in IFA polishing is how to keep suitable ambient temperature and melting rate in production process in order to avoid premature failure of the IFA pad. In this paper, effects of ambient temperature (T), pressure in cylinder (Pc), rotary speed of IFA pad (v) and eccentricity of pressure head (e) on temperature distribution and melting rate of the IFA pad are researched. The results show that T should be kept at about 10 °C in order to control the melting rate of the IFA pad effectively and keep longer polishing time. And suitable Pc, e can be kept at 0.075 MPa or 0.1 MPa and 20 mm or 30 mm, respectively. In order to increase IFA polishing efficiency, the rotary speed of IFA pad can be increased appropriately. All the results provide the basis for choosing suitable processing parameters in IFA polishing.

Study on dispersion property of sub-micro α-Al2O3 powders in water suspension by physical-chemical process

ABSTRACT Sub-micro α-Al2O3 polishing liquid is often used as the slurry in chemical mechanical polishing (CMP). At present, water is usually used as dispersion medium to disperse sub-micro α-Al2O3 powders, but the sub-micro α-Al2O3 powders easily subside in aqueous solution. In previous studies, researchers usually used single method to disperse superfine powders, however, the dispersion effect was non-ideal. In order to solve the difficult problem of sub-micro α-Al2O3 powders dispersed in water suspension, firstly, using physical method, the effects of milling time, ultrasonic time on the dispersion property of sub-micro α-Al2O3 powders in water suspension was studied by single factorial test. Then, using chemical method, the effects of dispersant type, dispersant concentration and pH value on the dispersion property of sub-micro α-Al2O3 powders in water suspension was studied by orthogonal test. Absorbance was used to evaluate the dispersion property of sub-micro α-Al2O3 powders. The results show that the optimal dispersing conditions are milling time 60 min, ultrasonic time 20 min, mass percent concentration of STPP 1% and pH value 9.

Characterization of carbon fiber reinforced resin composites by the nanoindentation technique

The mechanical properties of carbon fiber reinforced resin composites (CFRP) including the epoxy matrix, the carbon fiber and the interface of the carbon fiber/epoxy composites were investigated by means of nanoindentation technique. The hardness, Young’s modulus of the components in CFRP were obtained. The results show that the hardness and Young’s modulus have a gradient variation from the epoxy matrix to carbon fiber.

Micro CVD diamond heat sink

Chemical vapor deposition (CVD) diamond film has broad application prospect as heat sink in microelectronic field for its excellent thermal conductivity. The micro CVD diamond heat sinks with the size of 50μm×100μm×2000μm were prepared using mould copy technique. The micro silicon moulds for deposition of micro CVD diamond heat sinks were fabricated using inductivity coupling plasma (ICP) etching process. Micro CVD diamond heat sinks were synthesized under 2% methane and 98% hydrogen by hot filament CVD (HFCVD) method. The micro CVD diamond heat sinks were investigated by SEM, Raman and photo thermal deflection. The results show that favorable micro CVD heat sinks having a thermal conductivity of 960W·m-1·K-1 can be prepared by mould copy technique.