Zhi Qiang Fu

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.

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.

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 %.

Tribological Behaviors of W-Doped DLC Films

W-doped DLC films were synthesized from CH4 and W by ion beam deposition and magnetron sputtering, and the influence of W target current on the surface morphology and the mechanical properties of W-doped DLC films deposited were studied. The W-doped DLC films in the study have a smooth dense surface with several particles of about 2micron. The hardness, the modulus, and the film-substrate adhesion of the films are increased with the rise of W target current and the critical load of the scratch test for all the W-doped DLC films is above 70N. The friction coefficient of W-doped DLC films is increased with the increase of W target current while the lowest wear rate is obtained when W target current is 1A.

W Gradedly-Doped Diamond-Like Carbon Thin Films

W gradedly-doped diamond-like carbon films were deposited on silicon and stainless steel by a hybrid technique combining ion beam deposition with magnetron sputtering. The structure, mechanical performance, friction coefficient, and wear loss were investigated. With increasing W target current applied, the structure of the as-prepared films changed from amorphous DLC to a composite of metal-containing DLC and metal carbides; the content of sp3 structure decreased from 31.26% to 22.3%; the nanohardness increased from 12 GPa to 28 GPa; the elastic modulus increased from 170 GPa to 310 GPa; and the critical loads were in the range of 80~100 N. The comprehensive tribological property of the as-prepared samples was improved after W doping.

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

Mn-Zn ferrites doped with Cr3+ were prepared by “one-step synthesis” and conventional two-step synthesis methods, respectively. Their phase compositions and microstructures were characterized by X-ray diffraction and scanning electron microscopy, respectively. And their magnetic magnetic performance, such as saturation magnetization (Ms), magnetic hysteresis, initial permeability μi and power loss were comparatively investigated by vibrating sample magnetometer. It was observed that the difference of magnetic performance of the samples prepared by both methods is little. The similar performance of both methods makes the “one-step synthesis” especially attractive for application when considering energy economization.

Phase Composition and Microstructure of Binderless WC-ZrC Cemented Carbides Fabricated by Spark Plasma Sintering

Binderless WC-based cemented carbides with different fractions (0-9 wt.%) of ZrC nanopowder were fabricated through spark plasma sintering at 1600 °C under a uniaxial pressure of 50 MPa. The addition effect of ZrC nanopowder on the phase composition and microstructure of the fabricated materials were explored with the help of X-ray diffraction and scanning electron microscope. The results indicated that W2C phase was detected in the samples with 0-3 wt.% ZrC nanopowder, but with further increase in ZrC added fraction, ZrO2 phase instead of W2C phase was detected. The apparent density decreased gradually with the increase in added fraction of ZrC nanopowder, while the relative density increased initially and then decreased, reaching its maximum of about 98.2% when the added fraction of ZrC nanopowder was about 3 wt.%, indicating that appropriate added fraction of ZrC nanopowder can improve the densification of binderless WC cemented carbides. Without ZrC nanopowder, the coarsening and abnormal growth of WC grains were serious, resulting in many large prismatic WC grains in the samples. However, Such phenomena could be suppressed by adding ZrC nanopowder, resulting in much finer and more homogenous microstructure after 1-3 wt.% ZrC nanopowder was added. When the added fraction of ZrC nanopowder was higher than 3 wt.%, the agglomeration of ZrC nanopowder became more and more serious.