W.-M. Liu

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (109)118.66 Total impact

  • S.-S. Xu · X.-M. Gao · M. Hu · J.-Y. Sun · L.-J. Weng · W.-M. Liu
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    ABSTRACT: WSx films on Si(100) wafer and 9Cr18 steel substrates were deposited by medium frequency magnetron sputtering. The structure of the films was characterized by X-ray diffraction, field emission scanning electron microscope, atomic force microscope and X-ray photoelectron spectroscope. The mechanical and tribological properties were investigated using triboindenter and vacuum ball-on-disk tribometer, respectively. The results show that the S/W ratio raised with increasing working pressure, and increased firstly and then decreased with increase in sputtering power density, that was ascribed to the different oxidation degree of the deposited films and the selective sputtering. When the S/W ratio was low, the films were compact and hard, but exhibited high friction and wear due to the high content of W. As the S/W ratio was raised, the films showed an increase in WS2 content, along with a lower and more stable friction and better wear resistance.
    No preview · Article · Sep 2013 · Mocaxue Xuebao/Tribology
  • M. Hu · X.-M. Gao · L.-P. Zhang · Y.-L. Fu · J. Yang · L.-J. Weng · W.-M. Liu
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    ABSTRACT: The ZrN/α-SiNx nanoscaled multilayer films were deposited under different substrate bias voltage by reactive magnetron sputtering. The microstructures of these films were analyzed using high resolution transmission electron microscope(HRTEM). The mechanical and tribological properties of these films were comparatively investigated by nanoindenter and ball-on-disc tribometer in vacuum condition, respectively. The results reveal that lower bias condition may result ZrN layers characterized with amorphous (or amorphous-like) microstructrue in multilayer films. And the higher bias voltage condition may result mixing of interfaces between ZrN layers and SiNx layers in multilayer films. The transformation from crystal to amorphous microstructure of ZrN layers and interface mixing in multilayer films may both degrade the mechanical and tribological properties of the ZrN/α-SiNx nanoscaled multilayer films. The appropriate bias voltage (-80 V) favors the formation of the sharp coherent interfaces between the crystalline ZrN layers and amorphous SiNx layers. As a result, the ZrN/α-SiNx nanoscaled multilayer film prepared under -80 V shows better mechanical and tribological properties.
    No preview · Article · Jan 2013 · Mocaxue Xuebao/Tribology
  • J.-Y. Hao · L.-J. Weng · J.-Y. Sun · W.-M. Liu
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    ABSTRACT: The use of space satellites for communication and navigation is ever increasing in both military and commercial applications. High costs for both constructing and launching satellites are driving the need to extend the useful lifetime of these satellites. Improving lubrication of the mechanical systems is one of the key issues for prolonged service lifetime of satellite or spacecraft. MoS2-based film was prepared by rf-sputtering. Lubricants, i.e. trifluorinated-butyl with methyl terminated silicon oil (code as 115# oil) and the related grease formulated by PTFE powders (code as KK-5 grease) were synthesized at laboratory. Friction and wear properties of the MoS2 film, MoS2 film coated with 115# oil or KK-5 were investigated on a UMT-2MT tribo-meter. The effects of load and speed on friction and wear were also investigated. The worn surfaces of the MoS2 and its counterpart AISI 52100 steel balls were observed by scanning electron microscopy (SEM). It was found that the friction coefficient and wear lifetime of MoS2 dry-film were about 0.11 and 1.0 × 105 revolution, respectively. The friction and wear properties of solid lubricating film/oil or grease complex lubrication system were much better than that of MoS2 dry-film. The friction coefficient and wear lifetime of the MoS2 film lubricated with KK-5 grease were about 0.09 and 2.1 × 105 revolution, respectively. The complex lubrication system, MoS2+115# oil, exhibited excellent friction and wear properties. Its friction coefficient was about 0.07 and its wear lifetime exceeded 8.0 × 105 revolution.
    No preview · Article · Mar 2010 · Mocaxue Xuebao/Tribology
  • M. Zhang · X.-B. Wang · X.-S. Fu · W.-M. Liu
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    ABSTRACT: A UMT-2 tribometer was performed to measured the Electrical contact resistance (ECR) between tribo-pairs lubricated by base oil and base oil containing nano-LaF 3 (NLa), nano-Ag (NA), nano-SiO 2 ( NS) and nano-A1 2O 3 (NAl) particles. ECR measuring technique was used to verify the formation of tribo-film generated by nanoparticulate oil additive. The test was done in a reciprocating ball-on-disk mode under boundary lubricated condition at frequency of 15 Hz and normal load of 5 N. Variation of electrical contact resistance between tribo-pairs was observed during the first 250 s when it was lubricated by base oil, then a drop of base oil containing 2% NLa, NA, NS or NA1 was added. ECR was recorded continuously, thus a curve of the ECR versus time was obtained. Because the interface film generated by nanoparticulate oil additive acted as either an insulating barrier or electrical layer for electrical current, ECR was used to visualize the formation of interface film. The formation of tribo-films was further proved by surface analysis on wear scar using XPS. ECR measuring technique provided real-time information about the formation of surface films. The chemical state change of nanoparticles did not happen during rubbing, but its capability of forming a film were different. The deposit velocity and the protective film thickness of NLa and NA were larger than that of NS and NAl. Friction test performed in the presence of NLa or NA was characterised with the formation of an interface film which was strongly bonded to worn surface.
    No preview · Article · Nov 2007 · Mocaxue Xuebao/Tribology
  • X.-M. Gao · J.-Y. Sun · M. Hu · L.-J. Weng · W.-M. Liu
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    ABSTRACT: Cu films were deposited on carbon steel substrates at low temperatures (LT, 164 K-115 K) and room temperature (RT) by ion plating. The crystal structure and morphology of the Cu films were analyzed by X-ray diffraction and scanning electron microscopy. The friction and wear properties were tested by home-made ball-on-disk vacuum tribometer. The adhesive critical load (Lc) between Cu film and substrate was also measured by scratch tester. The results show that substrate temperature significantly affected the preferred orientation of ion-plated Cu films. At -600 bias voltages, the LT Cu films showed (111) preferred orientation, while the RT Cu films showed (200) preferred orientation. In compared with the RT Cu films, the LT Cu films exhibited smoother surface morphology and better adhesion between the film and substrate. Wear rates of the LT Cu films were significantly lower than that of the RT Cu films in vacuum. The friction and wear properties were discussed in terms of structure and mechanical properties of the Cu films.
    No preview · Article · Jul 2007 · Mocaxue Xuebao/Tribology
  • B. Yu · Y.-M. Liang · W.-M. Liu
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    ABSTRACT: Potassium stearate films doped with ionic liquid were prepared by dip-coating on hydroxyl silicon substrates. The tribological property of the composite films sliding against AISI-52100 steel ball was investigated with dynamic static friction coefficient measurement apparatus in ball-on-plate configuration. The morphologies of the wear tracks of the various films and the counterparts were examined using a scanning electron microscope equipped with an energy-dispersive X-ray analyzer attachment. It was found that the composite films on the hydroxyl-terminated silicon substrate showed better tribological properties than potassium stearate films under relative lower sliding velocity. At the load of 1.0 N, the composite potassium steartate film containing 40.0%wt ionic liquid slid 5000 cycles without failure, while the pure potassium stearate film only lasted 100 cycles. Transfer film was more easily formed on the counterpart steel ball with increasing the concentration of ionic liquid in the composite film. As a result, the tribological performance of the composite film was improved.
    No preview · Article · Mar 2007 · Mocaxue Xuebao/Tribology
  • B. Yu · F. Zhou · B. Wang · G. Liu · Y.-M. Liang · W.-M. Liu
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    ABSTRACT: Potassium stearate films on hydroxyl silicon substrates were prepared by dip-coating. The tribological properties of the films sliding against AISI-52100 steel ball and Si3N4 ceramic ball were investigated with dynamic static friction coefficient measurement apparatus and universal micro-tribometer in ball-on-plate configuration. The morphologies of the wear tracks of the potassium stearate films and the counterparts were examined using a scanning electron microscope equipped with an energy-dispersive X-ray analyzer attachment. The potassium stearate films on the hydroxyl-terminated substrate showed better tribological properties under relative higher sliding velocity or sliding against Si3N4 ceramic ball. Because of the different chemical nature and larger surface roughness of steel ball and Si3N4 ball, transfer film of potassium stearate is more easily formed on ceramic ball, resulting in lower friction coefficient and longer wear life as compared to that of steel ball.
    No preview · Article · Sep 2006 · Mocaxue Xuebao/Tribology
  • ZG Guo · WM Liu
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    ABSTRACT: Biomimic super-hydrophobic surface has been considered as a new research field in mimicing biological systems with chemistry. The super-hydrophobic phenomena of lotus etc. give such model of preparations of biomimic super-hydrophobic surfaces on many substrates. The studies on super-hydrophobic properties and micro-structures of lotus and the research progress in biomimicing of super-hydrophobic surface are reviewed. The author's opinions with respect to the future development of this research field are proposed.
    No preview · Article · Jun 2006 · Progress in Chemistry -Beijing-
  • Z.-G. Guo · F. Zhou · W.-M. Liu
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    ABSTRACT: A superhydrophobic silica film was prepared by means of sol-gel and self-assembly techniques, with a very high water contact angle (155°-157°) and a small sliding angle (3°-5°), making water droplet move readily on the surface. The film surface morphologies were observed with scanning electron microscope, and the elements on surface were determined by X-ray photoelectron spectroscopy. It was found that there were many microconvexities with binary structure uniformly distributed on the surface atop of the film with the average diameter of about 0.2 μm and nanoconvexities on the lower surface layer of the film with the average diameter of about 13 nm, and the film surface structure was similar to that of lotus surface. Many elements such as F and Cl were observed on the film surface, which could make the film surface energy decreased dramatically. The possible reason of leading to superhydrophobic properties on the as-prepared film is due to form an appropriate surface roughness after sol-gel method, and its surface energy will be further decreased after being modified with perfluorooctyltrichloromethoxysilane (FOTMS). These two formed conditions of surface roughness and low surface energy on the film will make the film formed on silicon exhibit good superhydrophobic properties.
    No preview · Article · Apr 2006 · Acta Chimica Sinica -Chinese Edition-
  • L. Shi · C. F. Sun · P. Gao · F. Zhou · W. M. Liu
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    ABSTRACT: Ni–Co–carbon nanotubes composite coatings were prepared by electrodeposition in a Ni–Co plating bath containing carbon nanotubes (CNTs) to be co-deposited. The polarization behavior of the composite plating bath was examined on a PAR-273A potentiostat/galvanostat device. The friction and wear behaviors of the Ni–Co–CNTs composite coatings were evaluated on a UMT-2MT test rig in a ball-on-disk contact mode. The morphologies of the original and worn surfaces of the composite coatings were observed on an atom force microscope (AFM) and scanning electron microscope. It was found that the introduction of the carbon nanotubes in the electrolyte caused the shift towards larger negatives of the reduction potential of the Ni–Co alloy coating, and the co-deposited CNTs had no significant effect on the electrodeposition process of the Ni–Co alloy coating. However, the co-deposited CNTs led to changes in the composition and structure of the composite coatings as well. Namely, the peak width of the Ni–Co solid solution for the composite coating is broader than that of the Ni–Co alloy coating and the composite coating possess higher microhardness and elastic modulus than Ni–Co alloy coating. The co-deposited CNTs were uniformly distributed in the Ni–Co matrix and contributed to greatly increase the microhardness and tribological properties of the Ni–Co alloy coating.
    No preview · Article · Apr 2006 · Surface and Coatings Technology
  • Z.-G. Guo · W.-M. Liu
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    ABSTRACT: A new kind of molybdenum coordination compound (MCC) without sulfur and phosphorus was prepared and evaluated as a promising lubricant additive for steel-steel contact. Tribological behavior of synthetic MCC as a lubrication additive for a steel-steel contact was comparatively investigated on SRV test rig with (ball-on-disc configuration), using paraffin as a comparison. The worn steel surfaces lubricated with paraffin and 1% MCC + paraffin under different loads were observed by scanning electron microscope, and the chemical states of some typical elements on the worn surfaces were analyzed by X-ray photoelectron spectroscopy. It was found that the synthesized MCC in the paraffin base oil significantly reduced friction coefficient and wear rate. Paraffin containing 1wt% MCC additive showed better friction-reducing and anti-wear abilities compared with paraffin without additives. Meanwhile hardness on worn surface, when lubricated with 1% MCC + paraffin, increased during friction and wear process, which contributed to reducing friction and wear of both tribo-pairs. Significant improvement of friction and wear, is due to action of the boundary layer and MCC deposited on the worn steel surface which prevent direct steel-steel contact from severe adhesion, scuffing, and seizure.
    No preview · Article · Mar 2006 · Mocaxue Xuebao/Tribology
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    ABSTRACT: The preparation of bulk naocrystalline Fe3Al-based material by aluminothermic reaction was described. Ferric sesquioxide and aluminum powders were weighed according to the stoichiometry of the aluminothermic reaction. Metallographic investigations and chemical analysis of the polished cross sections of the Fe3Al product are performed on an electron probe microanalyzer. EPMA examination revealed that the bright phase consists of Fe and Al elements and the black phase consists of Mn, Al, and S elements.
    No preview · Article · Feb 2006 · Advanced Materials
  • M. Zhang · X.-B. Wang · X.-S. Fu · W.-M. Liu
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    ABSTRACT: Oil-soluble nano-Cu additives were synthesized in laboratory. 1% nano-Cu particle was dispersed in SJ 15W/40 gasoline engine oil (NC) and SJ 15W/40 gasoline engine oil (SJ) was used for comparing. Its self-repair properties as lubricating oil additives were investigated by SRV oscillating friction and wear tester. Test conditions are room temperature, frequency 25 Hz, stroke 1 mm. Self-repair properties of nano-Cu additives in connection with distance and load were, investigated in terms of variation in friction coefficient arid wear volume loss with time and load. Regardless of time and load, friction coefficient and wear volume lubricated by NC are all lower relative to SJ 15W/40 oil. When load was 400 N, experiment time was as longer as 1.5 h instead of 0.5 h, also when load more than 500 N wear volume will minish than foregoing. These phenomena represent wear self-repair effect evidently. Analytical tools such as profilometer, micro-sclerometer, scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyse worn surface of steel discs. Profilometer and micro-sclerometer analysis results show that 1% nano-Cu additives contained in SJ 15W/40 lubricating oil have very good self-repair performance to steel-steel rubbing relative to SJ 15W/40 lubricating oil, it can level off and mend the worn surface. Analyses of scanning electron microscopy, X-ray photoelectron spectroscopy indicate that nano-Cu additive take place in situ tribochemistry reaction and built a self-repair deposit soft film composed of copper on the steel discs surface. The film has lower shear intensity and significant reduced friction coefficient, at the same time it can compensate wear loss of rubbing.
    No preview · Article · Nov 2005 · Mocaxue Xuebao/Tribology
  • X.-H. Li · Q.-H. Li · Z.-J. Zhang · H.-X. Dang · W.-M. Liu
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    ABSTRACT: Silica nanoparticles modified with organic compound containing double bonds was synthesized by surface modifying in situ and the structure was characterized by transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy and chemistry analysis. Dispersivity of the nanoparticle was studied by measuring light transmittance, and friction reducing and anti-wear behavior of the silica used as additive in lubricant were analyzed on wear tester. Worn steel surface and typical elemental distribution were analyzed by scanning electron microscopy and energy dispersive spectroscopy. As a result, nano-SiO2 well dispersed in lubricating oil, that contributed to apparently improvement on anti-wear and friction reducing ability of gas mobile oil, and nano-SiO2 can repair worn surface to a certain degree due to forming nano-coextruded films on rubbing surface.
    No preview · Article · Nov 2005 · Mocaxue Xuebao/Tribology
  • D.-P. Feng · L.-J. Weng · W.-M. Liu
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    ABSTRACT: Perfluoropolyether (PFPE) oil has been used as lubricant for aerospace, magnetic recording system and so on for decades. A review was given on synthetic method, physical and tribological properties, lubrication and degradation mechanism of PFPE, especially in aerospace and magnetic recording system. Compared to hydrocarbon lubricant, PFPE has wider temperature range, lower vapor pressure, but usually much more wear, and it is easily degraded by catalysis, eletron beam and ion beam. It is proposed that more chemical stability, better antiwear ability lubricants for aerospace should be developed.
    No preview · Article · Nov 2005 · Mocaxue Xuebao/Tribology
  • Jun Liang · B. G. Guo · Jun Tian · H. W. Liu · J. F. Zhou · W. M. Liu · Tao Xu
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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.
    No preview · Article · Sep 2005 · Surface and Coatings Technology
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    ABSTRACT: Surface modified SiO2 nanoparticles were synthesized. A four-ball machine was used to investigate the tribological behavior of SiO2 nanoparticles as additive in lithium grease. The worn surfaces of steel balls were analyzed by means of scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Analytical results indicate that SiO2 nanoparticles as additive can increase antiwear ability and load-carrying capacity of lithium grease. The reason is that SiO2 nanoparticles can deposited in boundary film play the role of self-replenish in the worn surface.
    No preview · Article · Sep 2005 · Mocaxue Xuebao/Tribology
  • W.-J. Lou · M. Chen · W.-M. Liu · Q.-J. Xue · X.-K. Zhou
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    ABSTRACT: Core-shell CdS nanocrystals, which were modified by different-chain length alkyl thiols, were chemically synthesized by a new liquid-liquid two-phase method. The structure and composition were investigated with UV-Vis absorption spectra, X-ray diffraction, and transmission electron microscopy. The results showed these as-prepared samples consisting of a nano-CdS core and a capped-layer of thiols chemically absorbed on the surface, and the modifiers had a great effect on the size and optical property of the inorganic nano-core. According to further analysis, it was found that the size of CdS nano-core had a quasi-parabola relation with the chain length of the modifiers, which was caused by the competitive result of the surface mobility and self-assembly order of the modifiers in the course of nucleation and growth of CdS nano-core.
    No preview · Article · Jul 2005 · Chemical Journal of Chinese Universities -Chinese Edition-
  • Z.-G. Guo · K.-L. Gu · J.-S. Xu · B. Yu · F. Zhou · W.-M. Liu
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    ABSTRACT: Anti-wear and friction reducing properties of four kinds of lubricant oils, N68, N68MD, Mobil SAE40 and N68ME, were examined with an X-P type pin-on-disk apparatus and a four-ball machine. Relationships between friction coefficient and time were studied and lubrication mechanisms of additives were investigated. Morphology and surface element distribution of the worn surfaces were analyzed by scanning electron microscopy (SEM) and electron dispersion spectrums analysis (EDS) respectively. It is found that friction coefficient of samples lubricated with N68MD decreased with time. Tribo-pairs lubricated with N68MD exhibited lower friction coefficient and lower wear rate. This was probably because N68MD contains elements of S, P and Mo which could form a thin sediment layer on the worn surface of steel ball. Tribo-pairs lubricated with N68ME exhibited good extreme-pressure performance and very low friction coefficient, and with good self-repairing ability. This was probably caused from synergistic action of elements of S, P, Mo, and nano-copper et al contained in the N68ME.
    No preview · Article · Jul 2005 · Mocaxue Xuebao/Tribology
  • Source
    J J Mu · Z Q Liu · W M Liu · Y M Liang · D Y Yang · D J Zhu · Z X Wang
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    ABSTRACT: An investigation of the reductive effect of blood pressure and increment of urinary sodium excretion with calcium and potassium supplementation in children with sodium sensitivity is conducted. In total of 261 school children who had completed a 2-year double-blinded, placebo-controlled trial with calcium and potassium supplementation salt sensitivity, with a salt volume expansion and contraction protocol, was determined. The results showed that in children with salt sensitivity, the increase in blood pressure in the supplementary group was lower by 4.3/4.8 mmHg than that in the placebo group (P<0.05), while no significant change was found between the supplementary group and placebo group in children with nonsalt sensitivity. With calcium and potassium supplementation, the night urinary sodium excretion in children with salt sensitivity was significantly increased (P<0.01), and it is negatively correlated with the increase in blood pressure. It was suggested that a moderate increase of calcium and potassium intake in children with salt sensitivity, through interaction with sodium, can promote urinary sodium excretion and may play contribute to the prevention of hypertension.
    Full-text · Article · Jun 2005 · Journal of Human Hypertension

Publication Stats

1k Citations
118.66 Total Impact Points

Institutions

  • 2001-2006
    • Chinese Academy of Sciences
      • State Key Laboratory of Solid Lubrication
      Peping, Beijing, China
  • 2004
    • Shandong University
      Chi-nan-shih, Shandong Sheng, China
  • 2003-2004
    • Lanzhou University
      Kao-lan-hsien, Gansu Sheng, China
    • Lanzhou Jiaotong University
      Kao-lan-hsien, Gansu Sheng, China
    • Harbin Institute of Technology
      • School of Materials Science and Engineering
      Charbin, Heilongjiang Sheng, China
  • 2002
    • Henan University
      K’ai-feng-shih, Henan Sheng, China