Cheng Biao Wang

Comparative Study on Ni-Zn Ferrites by One-Step Synthesis and Conventional Two-Step Synthesis

The magnetic hysteresis parameters like coercivity (Hc) and saturation magnetization (Ms), and dielectric parameters like dielectric constant (ε΄) and dielectric loss (ε΄΄/ε΄) of Ni0.5Zn0.5Fe2O4 prepared by “one-step synthesis” and conventional two-step synthesis methods, respectively, were comparatively investigated. It was observed that the saturation magnetization, dielectric constant and dielectric loss for samples prepared by “one-step synthesis” method are lower than those of ferrite samples prepared by conventional synthesis method. However, the coercivity of the former is higher due to its smaller grain size. The low dielectric loss makes these samples especially attractive for use at high frequencies.

Influence of titanium ion implantation on nucleation of diamond films on tungsten carbide

Abstract Diamond film has been deposited on substrate of cobalt cemented tungsten carbide (WC–Co). An exploration is carried out to reveal effect of Ti ion implantation and ion implantation energy on the diamond nucleation and growth on tungsten carbide. Diamond nucleation density is enhanced with Ti ion implantation and a dense nucleation belongs to a sample at 35 kV. A diamond film growing subsequently consists of oriented diamond crystals with columnar structure and such crystals uniformly distribute and grow well on tungsten carbide.

W-Doped DLC Films by IBD and MS

W-doped DLC films were synthesized from ethyne and tungsten by ion beam deposition and magnetron sputtering, and the influence of W target current on the structures and the properties of W-doped DLC films were studied. There exist some defects smaller than 3micron in W-doped DLC films and the influence of W target current on the defects is unobvious. The W content in the films is tardily increased with W target current below 3.5A, and then acutely rises with W target current. When target current is below 3.5A, the ratio of sp3-C to sp2-C is first decreased and then increased with the rise of target current, and the ratio of WC-C to sp2-C is close to 0; but when the target is above 3.5A, the ratio of sp3-C to sp2-C is decreased and the ratio of WC-C to sp2-C is augmented with further increasing target current. The hardness and the modulus is first decreased with target current and the minimum value is reached for the W-doped DLC films deposited with a target current of 2.6A. The W-doped DLC films deposited with a target current of 2.6A exhibit the best film-substrate adhesion. The W-doped DLC films deposited with a low target current exhibit a friction coefficient while the wear resistance of the W-doped DLC films deposited with a medium target current of 2.6A is best.

Cr-Doped DLC Multilayered Thin Films Deposited Using Cathodic Vacuum Arc- and DC Magnetron-Assisted Ion Beam Sputtering

A series of graded films of Cr/CrN/ CrNC/CrC/(Cr-DLC)/[(Cr-(Cr-DLC))×10] were deposited on Si(100) wafer and 4135 alloy structural steel using cathodic vacuum arc technique and direct current magnetron sputtering method combined with ion beam sputtering. The surface morphology, microstructure, nano-hardness, adhesion and wear properties of the films were investigated using 3-dimensional white-light interfering surface profiler, scanning electron microscopy, nanoindentation, scratch adhesion test, ball-on-disc test, etc. It was measured that the as-prepared Cr-doped DLC multilayered thin films have a strong adhesion to the substrates with a critical load exceeding 80 N, and the average friction coefficient during 30 min test in air was 0.23. This film will be promising in application against wear.

Roles of Dopants in Sintering Behavior of ZnO-Based Varistor

Three series of ZnO-based materials with different doping levels were prepared. The correlation between the composition and microstructure, and the roles of main dopants, Bi2O3 and Sb2O3, in the sintering behaviors were proposed. Both Bi2O3 and Sb2O3 evaporated at 1115°C, but the amount of them, in which bismuth is the majority, is not significant. Bi2O3 functioned mainly as liquid during sintering to promote the sintering of ZnO, but it doesn’t mean the materials will be denser. The bismuth-rich phase retracted into small pores during cooling, leaving the big pores as voids at room temperature. More Bi2O3 added would result in less increase in material densities and dramatic decrease in relative densities, and a little bit increase in grain sizes of matrix ZnO. Sb2O3 would react with ZnO matrix into spinel, Zn7Sb2O12, which will pin at the grain boundary of ZnO to control the ZnO grain growth. The more Sb2O3 added, the smaller the grain sizes of ZnO. Appropriate amount of Sb2O3 added will yield denser materials.

Spark Plasma Sintered WC-Ni Cemented Carbides with Various Contents of ZrC Nano-Powder

WC-10Ni cemented carbides with various contents (0-9 wt.%) of ZrC nanopowder were fabricated by spark plasma sintering at 1350 °C with a pressure of 50 MPa. The phase composition, microstructure and mechanical properties of the as-prepared samples were investigated. X-ray diffraction analysis revealed that excepting WC hard phase, a solid solution phase Ni (W,Zr) with different amounts of individual metal was formed with increasing ZrC nanopowder content. Scanning electron microscopy examination indicated that a proper addition content of ZrC can suppress the abnormal growth of WC grains and improve the relative density of WC-Ni cemented carbides. However, with further increase in the content of ZrC (more than 7 wt.%), the agglomeration of ZrC became more and more serious. The samples with 5 wt.% ZrC nanopowder possess a relative higher flexural strength (~1750 MPa) among all the investigated samples. When the addition content of ZrC nanopowder was 3 wt.%, the Vickers hardness of the samples reached its maximum value (~1810 HV10).

Ultrafine WC-Ni-SiCw Cemented Carbides Fabricated by Spark Plasma Sintering

Ultrafine WC-Ni cemented carbides with addition of SiC whisker (SiCw) were fabricated by spark plasma sintering. The microstructure and mechanical properties of the fabricated cemented carbides were investigated. It was found that the addition of SiC whisker had no obvious influence on the phase compositions of the cemented carbides, but the mean grain size of the cemented carbides decreased as the addition fraction of SiC whisker increased. The fabricated WC-Ni cemented carbides presented the highest hardness when 0.75 wt% SiC whisker was added. However, the addition of SiC whisker was detrimental to the flexural strength of the cemented carbides because of the formation of inhomogeneous microstructure in the WC-Ni cemented carbides.

Synergistic Effect of Cr-Doped DLC Coatings and Lubricant Additives

The combination of diamond-like carbon (DLC) coatings and fluid lubrication is an efficacious method to improve the performance and service life of the friction-pairs working under the severe conditions, but the synergistic effect of DLC coatings and lubricant additives have not been clearly unveiled. The synergistic effect of Cr-doped DLC coatings with different Cr content and the lubricant additives of ZDDP, MoDTC, and T307 on the wear of DLC-coated stainless steel sample was studied, and it was found that the wear resistance of DLC-coated stainless steel sample can be further improve by the combination of DLC coatings and fluid lubrication; doping DLC coatings with Cr at an optimum level is beneficial for the wear resistance of DLC-coated stainless steel sample lubricated by PAO, PAO+ZDDP or PAO + MoDTC, but DLC coatings with a moderate Cr content is harmful to the wear resistance of DLC-coated stainless steel sample lubricated by PAO+T307. The synergistic effect of T307 and undoped DLC coatings or Cr-doped DLC coatings with a Cr content of 23.3 % is the best, while the three studied lubricant additives are harmful for the wear resistance of DLC coatings with a Cr content of 2.4 %.

Structure and Tribological Behaviors of Synthetic MoS2 Film Prepared by a Novel Compound Method

In this paper, the structure and tribological properties of synthetic MoS2 film prepared by a novel compound technology—combining magnetron sputtering with low temperature ion sulfurizing were investigated. X-ray diffraction (XRD) pattern for the MoS2 film implies that the film mainly consists of Mo and MoS2 phases. The hardness of the synthetic MoS2 film was 7.44 GPa which was higher than that of the FeS film. The sliding tribological behavior of the MoS2 film was studied by ball-on-disc tests. The results showed that the synthetic MoS2 film possessed excellent friction-reducing and wear-resisting properties. In addition, the tribological behaviors of the MoS2 film were superior to those of the FeS film and original 1045 steel.

Preparation and Characterization of FeS Film by Low Temperature Ion Sulfurizing Technique

In this article, solid lubrication FeS film was prepared on the surface of AISI 1045 steel by means of low temperature ion sulfurizing process. Scanning electron microscopy (SEM) was utilized to observe the surface and cross-section morphologies of the sulfurized layer. The element distribution of the sulfurized layer surface was analyzed by X-ray energy spectrometer. The crystalline phases were determined by X-ray diffraction (XRD). X-ray stress determinator was utilized to measure the residual stress in the sulfurized layer. The nano-hardness and elastic modulus of the sulfurized layer were surveyed by a nano-indentation tester. The results showed that the surface of the FeS film was composed of many minute spherical particles with homogeneous grain size and distribution. The texture of the film was very loose with lots of micro-pores, and the crystallinity was well. There was compressive stress in the FeS film, and the stress value measured is -150 MPa. The average value of nano-hardness and elastic modulus were 4.02 GPa and 157.36 GPa respectively.