Yu Min Zhang

High Speed Lapping of SiC Ceramic Material with Fixed Abrasive

An experimental investigation is carried out to machine SiC ceramic material through method of high speed plane lapping with fixed abrasive. The results show that the material removal mechanism and the surface roughness are chiefly related to the granularity of abrasive and the lapping pressure for the brittle materials such as SiC ceramic. It is easily realized to machine SiC ceramic material in ductile mode with a high efficiency and a low cost using W3.5 grit under a lapping pressure of 0.1MPa and then a smooth surface with surface roughness of Ra 2.4nm can be achieved.

Study on ZrC-20vol.%SiCw Ultrahigh Temperature Ceramics by Hot Pressing

The ZrC-20vol.%SiCw ultrahigh temperature ceramics with relative density of 99.2% can be prepared by hot pressing at 1900 oC and 30MPa for 60 min. The mechanical properties and microstructure of the composite were studied. The flexural strength and fracture toughness reaches up to 626.17MPa, 5.03 MPa•m1/2, respectively. SEM analysis shows the microstructure of the ZrC-20vol.%SiCw is homogeneous and SiC whiskers are uniformly distributed around the ZrC grains, which inhibit the ZrC grain growth during sintering. The fracture surface of ZrC-20vol.%SiCw reveals a mixture of intergranular and transgranular failure, and SiC whiskers play a remarkable role in improving the strength and toughness of ZrC matrix. The toughening mechanism of the composite is mainly fine-grain strengthening and whisker pull-out.

Characterization of Silicon Carbide Grown on RB-SiC by Chemical Vapor Deposition

Silicon carbide is one of the best materials for satellite mirror and chemical vapor deposition (CVD) is an effective method of preparing SiC whiskers and films. In this paper, SiC whiskers or films were deposited on substrates of RB-SiC in an upright chemical vapor deposition furnace of Φ150mm × 450 mm with methyltrichloride silicane (MTS) as precursor gas and H2 as carrier gas under dilute gases of different H2/Ar ratio and different deposition temperature between 1050°C and 1150°C. The morphology and composition of the CVD-SiC grown on RB-SiC substrate were determined by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. As a result, whisker-like, worm-like or ball-like SiC can be respectively obtained dependent on different deposition conditions such as H2/Ar ratio and deposition temperature, and the composition of the productions are determined as β-SiC by XRD. Furthermore, the deposition mechanisms of different morphologies of SiC are introduced.

The Fabrication of Co-Continuous SiC/P20 Steel Composites

The network SiC ceramics was fabricated by combining organic foam impregnation and presureless sintering method. The co-continuous interpenetrating SiC/P20 steel composites were fabricated by means of pressureless infiltration technique. The results showed that coarse surface of SiC ceramics with three-dimensional network structure was obtained and observed, which was halpful for the reaction of metal alloy during the impregnation process. The continuous interface could be detected in the SiC/P20 steel composites.

Oxidation Behavior Research of the SiC/B4C Multiphase Ceramics

Inthis investigation, the rare-earth oxide Yb2O3 combined with Al2O3served as sintering additives and SiC and B4C powder were applied to fabricate SiC/B4C multiphase ceramics composites by pressureless sintering. The results proved thatcombination of Al2O3 and Yb2O3 sinter additives were effective fordensification of SiC/B4C composites. The influence of oxidation time onthe phase constitution, micro-structure and oxidation behavior of SiC/B4C composites was investigated.Theformation of eutectic phase Yb2Si2O7 phase waswrapped on the SiC surface and it reduced further oxidation of SiC particles.The oxidation kineticcurves followed a parabolic rule.

Influence of EDTA-2Na Concertration on the Microstructure and Corrosion Behaviors of Mg-Al-Y Alloy

In this paper,the micro-arc oxidation technology were utilized to fabricated the oxidation coating in order to resolve the corrosion resistance of the Mg-Al-Y alloy. The EDTA-2Na solution was introduced into the electrolyte solution for improving the coating corrosion properties.After the micro-arc oxidation process, phase structural, surface morphology and corrosion resistance of the MAO coating of Mg-Al-Y alloy were performed by XRD, SEM and Potentiodynamic polarisation measurements. The introduce of EDTA-2Na in the electrolyte solution improve the positive potential and reduced the corrosion current, which would improve the corrosion resistance properties of the Mg-Al-Y alloy.

Influence of Reaction Temperature on the Densification Behavior of the SiC/B4C Composites

In this investigation, the rare-earth oxide La2O3 combined with Al2O3 served as sintering additives and commercial α-SiC and B4C powder were applied to fabricate SiC/B4C composites by pressureless sintering. The results proved that combination of Al2O3 and La2O3 sinter additives were effective for densification of SiC/B4C composites. The influence of sinter temperature on the phase constitution, micro-structure and densification behavior of SiC/B4C composites was investigated.

Pop-In Events and Elastic Deformation of Sapphire Single Crystal during Nanoindentation

Sapphire single crystal is widely used in many fields because of its excellent properties, as a focus of mechanical test, nanoindentation on sapphire is paid a great deal of attention by researchers. In this manuscript, the maximum load, depth and loading rate effects on the first pop-in event during nanoindentation of sapphire single crystal were discussed, the results indicated that these factors had no effect on the load at which the first pop-in occurred and the extension width of pop-in; the deformation below the first pop-in event was discussed and it could be roughly considered as purely elastic deformation through analyzing.

The Research of Micro Arc Oxidation Behavior of the Magnesium Alloy

The ceramics coating hadobtained by the micro arc oxidation technology in order to resolve thecorrosion resistance of the Mg alloy.The phase composition, surface morphology,gained weight and polarization behavior of the micro arc oxidation coating wasinvestigated in details. After the introduce of the sodiumcitrate in the electrolyte solution, thespecimen had high relatively positive potential and low corrosion current, sodoped sodium citratewould improve the corrosion resistance properties of the Mg alloy .

The Effect of the C4O6H4KNa Concentration on the MAO Coating of the Mg-Sr-Al-Y Alloy

In order to resolve the corrosion resistance of the Mg-Sr-Al-Y alloy, the micro arc oxidation technology were utilized to fabricated the oxidation coating in this paper. The potassium sodium tartrate (C4O6H4KNa) solution was introduced into the electrolyte solution for improving the coating properties. The effect of the C4O6H4KNa content on the phase composition, surface morphology and potentiodynamic polarization behavior was investigated. Compared with the Mg-Sr-Al-Y matrix alloy, the specimen with sodium citrate had high relatively positive potential and low corrosion current , so it proved that the introduce of the doped C4O6H4KNa would improved the corrosion resistance properties. Key words: Micro arc oxidation, Potassium sodium tartrate (C4O6H4KNa), Polarization behavior, Corrosion resistance properties.