Xin Bo He

Effect of SiC on the Oxidation Resistance Performance of C/ZrC Composite Prepared by Polymer Infiltration and Pyrolysis Process

Stitched carbon fiber cloth reinforced zirconium carbide composite (C/ZrC) was prepared by polymer infiltration and pyrolysis (PIP) process. C/ZrC-SiC composite was obtained by further introduction of SiC with PIP process in order to improve anti-oxidation property. The results show that 1.9vol% SiC addition improves the mechanical and anti-oxidation properties of C/ZrC composite. The flexural strength of C/ZrC is 247.9MPa, while that of C/ZrC-SiC is 273.1MPa. After oxidation in a muffle furnace at 1200°C for 30 minutes, the mass loss rate was reduced from 30.6% (C/ZrC) to 20.1% (C/ZrC-SiC), and the flexural strength and elastic modulus of C/ZrC were 56.7MPa and 5.7GPa, respectively, while those of C/ZrC-SiC were 122.9MPa and 17.2GPa, respectively.

Preparation and Mechanical Properties of C/SiC Joints with Pins or Bolts

C/SiC substrates and M3 bolts were prepared by precursor infiltration and pyrolysis (PIP) process firstly, then the joints with four joining methods (2 φ3mm soft pins, S-A; 2 M3 bolts, S-B; 2 φ3mm soft pins plus 8 φ1mm soft pins, S-C; 2 M3 bolts plus 8 φ1mm soft pins, S-D) were assembled, finally several PIP cycles were continued to finish densification. The influences of different joining methods and PIP cycles (3 or 6) on the stripping properties of C/SiC joints were investigated, and the fracture modes were analyzed. The stripping loads of the joints adopting 6 PIP cycles are almost two to six times the values adopting 3 PIP cycles, and the corresponding fracture modes are pins or bolts rupture and pull-out, respectively. When adopting 3 PIP cycles, the bearing ability of the joints with bolts (S-B and S-D) is about 51% higher than that of joints with pins (S-A and S-C), but when adopting 6 PIP cycles, the values with pins (S-A and S-C) is about 67% higher than that with bolts (S-B and S-D). Besides, the introduction of φ1mm pins enhances the bearing ability of the joints with 3 and 6 PIP cycles about 45% and 14%, respectively.

Effect of Si on the Wettability of SiC/Al System

In this paper, Si was added to the Al alloy to research its effect on the wettability between SiC and Al at 1000°C. The results showed that the contact angle decreased with the increase of Si content in the Al alloys and it droped from 570 to 370 with the Si content from 0 to 12wt% and reached equillibrium with the further addition of Si to 18wt%. The improvement mechanism of Si on the wettabitliy is also discussed in this paper.

Effect of TiC Intermediate Layers on the Thermal Conductivity of Copper/Diamond Composites

TiC intermediate layers were formed on the surface of diamond particle with reaction of Ti powders in mixed molten NaCl-KCl salts. The copper/diamond composites with TiC-coated diamond particles were fabricated by pressure infiltration. Then the microstructure and thermal conductivity of the obtained copper/diamond composites were studied. The results showed the thermal conductivity of the composites with a density of 5.65 g/cm3 reached 514 Wm-1 K-1, which is much higher than with uncoated diamond. The TiC layers synthesized on diamond particles is shown to be an effective way to enhance the thermal conductivity of copper/diamond composite.

Effect of SiC Powder Characteristic on the Rheological Properties of Feedstock

In this study, the effect of SiC powder characteristic on the rheological properties of the feedstock was investigated. It was found that the viscosity of the feedstock decreased with the increase of the particle size. For the binary powder mixtures, the viscosity of the feedstock decreased with the increase of the particle size ratio of the larger particle to finer particle, which is attributed to the increase of the tap density of the powder.

Microstructural Characterization of Diamond/SiC Composites Fabricated by RVI

Diamond/Si/C porous preform was prepared with phenolic resin, Si, Diamond and graphite. Subsequent reactive vapor infiltration (RVI) of gaseous silicon at 1600 °C for 2 h in vacuum atmosphere resulted in the formation of a compact Diamond/SiC composite. The influence factors of perform porosity were investigated, including process pressure and raw materials. Density and microstructure of Diamond/SiC composites were also discussed. The results showed that the open porosity of preform was mainly influenced by the pressing pressure. It can also be affected by the content, morphology and the particle size of diamond. The preform with open porosity higher than 20% after RVI treatment can obtain Diamond/SiC composites with high density. However, over-high porosity of the perform will cause a mass of unreacted Si exists in the composite which is unfavorable for its application. In order to reduce the content of residual Si, open porosity of preform should be no higher than 40%.

Fabrication of Si3N4 Reinforced 316L Stainless Steel Composites by Powder Injection Moulding

Metal martrix composites, based on 316L stainless steel and reinforced with Si3N4 particles, were manufactured by powder injection moulding. The effect of Si3N4 additions and sintering process on the densification, hardness and phase evolution is investigated. The mechanical properties of the sintered products were measured. Scannning electron microscope was used to examine microstructural changes and fracture surfaces of all samples. Experimental results show that density of all samples, reinforced and unreforced, increases with increasing temperature. The addition of Si3N4 improves the hardness and density.

Preparation and Properties of Porous Diamond Preforms

A binder comprising of 60% PW (paraffin wax), 10% HDPE (high-density polyethylene), 12% PS (polystyrene), 13% PPR (random-polypropylene), and 5% SA (stearic acid) has been selected and successfully employed to fabricate the diamond preforms possessing high strength and well shape retention capability. Various effects of processing methods on the properties of the diamond preforms have been investigated. The results indicate that the binder consisting of PW-HDPE-PS-PPR-SA possesses excellent comprehensive rheological properties and is more appropriate as the organic vehicle for fabricating porous diamond preform. It has been evaluated that the mixing of 140m size diamond particles with 20m size diamond particles in the weight proportion of 3:1 provides the best particle size distribution for preparation of diamond preforms. It is also observed that impregnation of preform with 1.7wt (SiO2)% water glass and subsequently heat-treated in vacuum at 800°C for 40min yields in high strength (with the strength of 7.1 MPa) diamond preform for infiltration. The strengthened preforms have been observed to possess an excellent shape maintaining capability. It is concluded that the diamond-copper composites fabricated by utilizing this high strength preform through hot-press infiltration method have high relative density of 96.4% and thermal conductivity of 300W.m-1.K-1.

Flexural Properties of T700 2D Cf/SiC Composites via Precursor Infiltration and Pyrolysis

2D Cf/SiC composites were prepared by precursor infiltration and pyrolysis (PIP) process with spreaded T700-12K plain weave carbon clothes as the reinforcement. The mechanical properties and microstructures were investigated. The composites are compact with few internal defects since the precursor could infiltrate the preform effectively. CVD-PyC interface modified the surface of T700 carbon fiber, a rough surface is helpful for the interfacial combination and the load transfer. For the Cf/PyC/SiC composites, the flexural strength and flexural modulus were 425±23.2 MPa and 36.3±3.1 GPa, respectively.

Influence of Auxiliary Abrasive on the Resin Bond Used in Diamond Tools

The effects on the mechanical properties for three auxiliary abrasive with different hardness were researched by changing the content of the auxiliary abrasives in the phenolic resin-based bond in this paper. The abrasive tool samples bending strength and Rockwell hardness were tested. It shows that with the increase of TiO2 content, the hardness and strength reduced firstly, but then increased; and when the content of TiO2 was 5%, the Rockwell hardness decreased by 30% and the bending strength fell by 44.98%. As the CeO2 content increases, the hardness of the abrasive tool changed little, while the bending strength decreased more, and when its content was 1%, the bending strength decreased by 25.63%. When the content of SiO2 is 3%, he bending strength decreased by 32.82%; and when its content is 5%, the Rockwell hardness reduced by 24.97%, and then its hardness has a substantial increase.