W. M. Liu

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (16)24.53 Total impact

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    ABSTRACT: High-quality titanium nitride (TiN) films with nano-structure were prepared at ambient temperature on (111) silicon substrates by filtered cathodic arc plasma (FCAP) technology with an in-plane “S” filter. The effects of substrate bias and argon flux on the crystal grain size, roughness and preferred orientation were systematically investigated. It was found that the substrate bias and argon flux can affect the properties of TiN films effectively. Transmission electron microscope images showed that the crystal grain size was uniform and ranged from 10 nm to 5 nm. The results of X-ray diffraction and electron diffraction indicated that the degree of preferred orientation was more evident under high substrate bias and high argon flux. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Physica Status Solidi (A) Applications and Materials 12/2005; 202(1):95 - 101. · 1.46 Impact Factor
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    ABSTRACT: Microarc oxidation coatings on AM60B magnesium alloy were prepared in phosphate-KOH electrolytes with and without NaAlO2 addition. The effect of NaALO(2) on the characteristic of breakdown voltage in different concentrations of NaAlO2 has been studied. The compositions, structure and morphologies of the oxide coatings formed in different concentrations of NaAlO2 were determined by energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The corrosion resistance of the oxide coatings was evaluated in 3.5 wt.% NaCl solution using potentiodynamic polarization tests. The results showed that the solution conductivity increased while the values of breakdown voltage decreased with the increase of concentration of NaAlO2. In both cases the coatings contained Mg, Al, O and P as well as a trace amount of Na and K, and were mainly composed of MgO and spinel MgAl2O4. The addition of NaAlO2 into the base electrolyte resulted in the increase of spinel MgAl2O4 in the oxide coating. Furthermore, the number and size of micropores on top of the surface decreased with the increasing concentration of NaAlO2, though the surface roughness increased with the NaAlO2 addition. The coating formed in the electrolyte containing 8.0 g/L NaAlO2 exhibited the highest corrosion resistance in NaCl solution. (c) 2005 Elsevier B.V All rights reserved.
    Surface and Coatings Technology 01/2005; 199(2-3):121-126. · 1.94 Impact Factor
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    ABSTRACT: As an interlayer in the gradient layers such as AlN/Ti/TiN/DLC prepared by plasma-based ion implantation (PBII) on 2024 aluminum alloy, titanium layer plays an important role in enhancing adhesion, reducing thermal stress, limiting the crack propagation, etc. A series of dual-layers prepared by PBII with nitrogen then titanium at various sputtering currents of titanium target on 2024 aluminum alloy have been reported in this paper. The composition distributions and the chemical states are analyzed using X-ray photoelectron spectroscopy (XPS). The structures are studied with grazing X-ray diffraction (GXRD). The results show that PBII with titanium strongly depends on the sputtering current. It is found that there exists a critical sputtering current corresponding only to a titanium-implanted layer containing TiAl3. When the sputtering current exceeds the critical value, a titanium-deposited layer rich in α-Ti is formed on a titanium-implanted layer. By controlling the sputtering current an appropriate titanium interlayer can be prepared to meet the requirement of forming a proper gradient layer.
    Applied Surface Science 01/2005; · 2.54 Impact Factor
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    ABSTRACT: DLC films ranging from 5 to 180 nm in thickness have been prepared by plasma-based ion implantation (PBII) with C on Si. The structures of the films were studied with XPS and Raman spectroscopy. The nanohardness and the intrinsic stress of the films were measured. Dry sliding wear experiments have been carried out, using a ball-on-disc tester, to investigate the tribological properties of DLC films against alumina balls, employing various normal applied loads and reciprocating frequencies. For comparison, DLC films prepared by plasma-assisted chemical vapor deposition (PACVD) on Si were also investigated. The results show that the films prepared by PBII exhibit more significant improvement in tribological properties than the films prepared by PACVD because the former present higher sp3/sp2 ratio, higher hardness and lower stress than the latter. The effects of the film thickness, the applied loads and the reciprocating frequencies on the tribological properties are also presented.
    Surface & Coatings Technology - SURF COAT TECH. 01/2005; 191(1):90-95.
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    ABSTRACT: High-quality TiN films were successfully deposited on silicon and stainless-steel substrates at low temperature using an improved filtered cathode arc plasma technique developed in our lab. Atomic force microscope, x-ray diffractometer, x-ray photoelectron spectroscopy, and a nanoindenter were employed to characterize the TiN thin films. The microhardness of the TiN films have a high value up to 41 GPa, which is far higher than that of TiN compounds deposited by conventional chemical vapor deposition and physical vapor deposition methods (20 Gpa or so). The films are of a stronger preferred crystalline orientation, very smooth surface, and high reflectivity. The effects of the negative substrate bias on the preferred crystalline orientation, surface roughness, deposition rate, and microhardness of Tin thin films are discussed in detail.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 11/2004; 22(6):2419-2423. · 1.43 Impact Factor
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    ABSTRACT: Using plasma-based ion implantation, two types of gradient layers have been prepared on 2024 Al alloy. One is prepared by N-implantation then C-deposition, the other adds an interlayer composed of a Ti layer and a Ti–N layer between N-implantation and C-deposition. C-deposition is carried out at various implanting voltages or C2H2/H2 ratios. The composition depth profiles of these layers were characterized by x-ray photoelectron spectroscopy. The structure, morphologies and microstructure of the C layers were studied using Raman spectroscopy, atomic force microscope and transmission electron microscope, respectively. The surface hardness was measured with a Knoop tester and a mechanical property microprobe. The dry ball-on-disc wear tests were performed in ambient air. The gradient layer without interlayer is composed of an N-implanted layer rich in AlN and a diamond-like carbon (DLC) layer (film), and the two layers are connected with a C–Al transition layer containing Al4C3. The Ti layer rich in α -Ti and the N-implanted layer are connected by a Ti–Al transition layer containing TiAl3, while the Ti–N layer rich in TiN and the DLC film are connected by a C–Ti transition layer containing TiC, TiCN, etc. Thus, the gradient layer with interlayers has optimized the gradient structure. DLC films are compact and amorphous, contain high sp3/sp2 ratios and depend on the implanting voltage and the C2H2/H2 ratio. Similarly, these gradient layers exhibit significant improvement in morphologies, surface hardness and tribological properties; the interlayer, the implanting voltage and the C2H2/H2 ratio all have prominent effects on these properties.
    Journal of Physics D Applied Physics 01/2004; 37(3):392. · 2.53 Impact Factor
  • J.X. Liao, W.M. Liu, T. Xu, Q.J. Xue
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    ABSTRACT: Four carbon nanometer films ranging from 5 to 60 nm have been prepared by plasma-based ion implantation (PBII) with C on Si (1 0 0) wafers. Raman spectra and X-ray photoelectron spectroscopy (XPS) indicate these films are diamond-like carbon (DLC) films with high sp3/sp2 bonds ratio. Atomic force microscopy shows that their appearances are smooth and compact, and improved to some extent. Meanwhile, XPS displays that they are naturally connected with the Si substrate by a C–Si transition layer where the implanted C+ ions react with Si to form SiCx. Infrared spectra reveal they contain some hydrogen, and hydrogen mainly combines with carbon to form sp3 CH, CH2 and CH3 bonds. Proper DLC films will be obtained and used as the qualified candidates in some particular engineering applications by actively optimizing PBII parameters.
    Applied Surface Science 01/2004; · 2.54 Impact Factor
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    P. Liu, W.M. Liu, Q.J. Xue
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    ABSTRACT: The in situ radical transfer addition polymerization of styrene from silica nanoparticles was carried out by the free radical polymerized of styrene in the presence of mercaptopropyl-modified silica nanoparticles as chain-transfer agent. The effects of the amount of the initiator, polymerizing temperature and polymerizing time on the convention of styrene (C) and the percentage of grafting were investigated. Results of elemental analysis, IR, X-ray photoelectron spectrometer and transmission electron microscope demonstrated that the desired polymer chains have been covalently bonded to the surface of the silica nanoparticles. A C of 42.56% and a PG of 38.10% could be achieved with the optimal condition. The polystyrene grafted silica nanoparticles could be separated and used as nanofiller for polymers.
    European Polymer Journal 01/2004; 40(2):267-271. · 2.56 Impact Factor
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    J. X. Liao, W. M. Liu, T. Xu, Q. J. Xue
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    ABSTRACT: A series of carbon films have been prepared by plasma-based ion implantation (PBII) with C on pure Al and Si. Emphasis has been placed on the effect of implanting voltage on the characteristics of these films. The structures of the films were analyzed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The morphologies were observed by atomic force microscope (AFM). Surface hardness and electrical resistivity were also measured. The results indicate that the characteristics of these films are strongly dependent on the implanting voltage. An implanting voltage threshold value ranging from 3 to 5 kV starts to form a C-substrate transition layer owing to C+ ions implanted into the substrate. The transition layer exhibits a gradual change in composition and structure and effectively connects the carbon film and the substrate. Also, an implanting voltage threshold value ranging from 5 to 10 kV starts to form diamond-like carbon (DLC) films. An increasing voltage causes the resultant DLC films to be smoother and more compact. Moreover, Raman spectrum, chemical state of C1s, surface hardness and electrical resistivity all prove an optimum voltage of approximately 30 kV corresponding to the lowest ratio of sp2/sp3.
    Carbon. 01/2004; 42(2):387-393.
  • P. Liu, W. M. Liu, Q. J. Xue
    Journal of Materials Science 01/2004; 39:3825-3827. · 2.16 Impact Factor
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    ABSTRACT: The N-pre-implanted 2024 aluminum alloy was implanted with Ti and N, or implanted with Ti, and then with Ti and N by plasma-based ion implantation (PBII) to form two gradient layers, respectively. The composition depth profiles of the gradient layers were characterized by X-ray photoelectron spectroscopy. A series of ball-on-disk wear experiments have been carried out in ambient air, to investigate the tribological behavior of the gradient layer against steel ball under dry and un-lubricated conditions, employing various applied loads and a constant sliding speed. The results revealed that tribological properties of the gradient layers were improved markedly in contrast with those of the unmodified sample, and strongly dependent on their composition depth profiles. The gradient layer implanted with Ti, and then with Ti and N was much thicker and contains higher N, thus it corresponded to higher hardness which slowly decrease from surface to substrate and the optimal tribological properties including higher load carrying capacity. As load was increasing, the tribological properties decreased, and the adhesive degree increased since the gradient layer became thinner rapidly. Of course, more proper gradient layers will be obtained as the qualified candidates in some particular engineering applications by optimizing PBII parameters.
    Wear. 01/2004; 256(7):840-845.
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    ABSTRACT: DLC films can play an important role in tribological properties of Al-alloys. A gradient layer of AlN/Ti/TiN/DLC film has been prepared by plasma-based ion implanted N, followed by Ti, and N and Ti, and finally C on 2024 Al-alloy. Emphasis has been placed on the tribological properties of the gradient layer. Its composition depth profile and chemical structure were characterized using X-ray photoelectron spectroscopy (XPS), the surface C-layer and the wear tracks were analyzed by laser Raman spectroscopy. The morphologies of the C-layer were observed by atomic force microscopy (AFM), the hardness of the gradient layer was measured with the mechanical property microprobe and the dry wear tests against AISI steel ball at different sliding loads were performed with a ball-on-disk wear tester in ambient environment. The results indicate that the gradient layer shows a gradual change in hardness, compact surface appearance and good tribological properties owing to the gradient structure. As the number of the sliding cycles or the load is increasing, the tribological properties decrease due to the graphitization of the DLC films. Meanwhile, the gradient layer can be controlled by PBII processing parameters, thus an optimized gradient layer can be obtained to offer the possibility of making aluminum alloys and other soft alloys qualified candidates for particular engineering applications.
    Surface & Coatings Technology - SURF COAT TECH. 01/2004; 183(2):157-164.
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    ABSTRACT: This article firstly presents results for C45 steel surface modification by post boronizing N þ ion implantation. One boronizing technique, gaseous boronizing with solid boron-yielding agents (GBSA), was employed to make C45 steel boronizing. SEM, XRD, AES, Vicker's microhardness tester and potential dynamic electrochemical were employed to characterize the samples. The properties of the boride layer of C45 steel can be improved by use of post boronizing ion implantation. c-BN compounds can be formed in the boride layer after N þ ion implantation. # 2002 Elsevier Science B.V. All rights reserved.
    Applied Surface Science 08/2002; 195:74-79. · 2.54 Impact Factor
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    ABSTRACT: Silicon–carbon nitride (SiCN) thin films were deposited on Si substrate at room temperature by r.f. reactive sputtering. Fourier transform infrared spectroscopy (FTIR), optical absorption spectra (α(λ)) and electrical conductivity (σ) were studied for the thin films. The effect of the annealing on IR and σ was investigated at different temperatures. IR analysis indicates that Si–H, C–N, Si–C, Si–N, C–N and CN bonds are present in a-SiCN:H films. A shift of the stretching mode for Si–H bond to the high-wavenumber side is observed with increasing the nitrogen flow ratio γN2(=N2/(Ar+H2+N2+CH4)). The shift is from 2000 to 2190cm−1 when γN2=13.7%. The study shows that the film structure and optical and electrical properties are obviously modified readily by controlling the process parameters of deposition. The improvement in the film properties, e.g., good thermal stability, is explained mainly in terms of the cross-linked structure between the Si, C and N atoms.
    Applied Surface Science 01/2002; 185(3):262-266. · 2.54 Impact Factor
  • W.-M Liu, Y.-Q Xia, N Han, Q.-J Xue
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    ABSTRACT: AISI-1045 steel was treated with solid boron permeation, and the interaction between the modified surface layer and the lubricating additive zinc dialkyldithio-phosphate (ZDDP) was examined. The friction and wear behavior of the treated and untreated steel specimens were compared. The phase composition of the boron-permeated layer was examined by means of X-ray diffraction. The chemical states of several typical elements on the worn surfaces of the treated and untreated steel surfaces were examined by means of Auger electron spectroscopy and X-ray photoelectron spectroscopy. Results showed that the wear-resistance of boron-permeated specimens was higher than that of the untreated ones. This was partly attributed to the change in the hardness and phase composition of the steel surfaces after boron permeation. Tribochemical reactions between steel and the active elements of the additive occurred during the sliding of the treated and untreated steel discs against an AISI-52100 steel ball using different lubricants. The resultant surface protective films containing various tribochemical products, together with the adsorbed boundary lubricating film, contributed to the reduction of friction and wear.
    Tribology International 01/2002; 35(8):497-502. · 1.54 Impact Factor
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    ABSTRACT: A coating on carbon steel was fabricated by a self-propagating high temperature synthesis (SHS) casting route. The process is described in detail. The phases in the coating were examined using X-ray diffraction (XRD). The microstructures of the coating and the substrate were analysed using electron probe microanalysis (EPMA) and optical microscopy, respectively. The wear behaviour and microhardness of the coating were determined. The experimental results show that the coating was composed of Ni3 Al and Cr7 C3 phases and had a dense microstructure. Metallurgical bonding had formed between the coating and the substrate. The grain size of the substrate near the interface was coarsened. The wear resistance of the coating is better than that of a bearing steel or a Ni3 Al coating. The microhardness of the coating is higher than that of a Ni3 Al coating or the substrate.
    Materials Science and Technology 12/1999; 16(1):110-114. · 0.75 Impact Factor