Shubin Ren

Wettability and pressureless infiltration mechanism in SiC-Cu systems

Abstract The wetting behavior of copper alloys on SiC substrates was studied by a sessile drop technique. The microstructure of SiCp/Cu composites and the pressureless infiltration mechanism were analyzed. The results indicate that Ti and Cr are effective elements to improve the wettability, while Ni, Fe, and Al have minor influence on the improvement of wettability. Non-wetting to wetting transition occurs at 1210 and 1190°C for Cu-3Al-3Ni-9Si and Cu-3Si-2Al-1Ti, respectively. All the copper alloys react with SiC at the interface forming a reaction layer except for Cu-3Al-3Ni-9Si. High Si content favors the suppression of interfacial reaction. The infiltration mechanism during pressureless infiltration is attributed to the decomposition of SiC. The beneficial effect of Fe, Ni, and Al is to favor the dissolution of SiC. The real active element during pressureless infiltration is Si.

Influence of binder composition on the rheological behavior of injection-molded microsized SiC suspensions

The influence of four kinds of binders consisting of paraffin wax (PW), random-polypropylene (RPP), high-density polyethylene (HDPE), and stearic acid (SA) on the rheological behavior of injection-molded SiC feedstocks was investigated over a temperature range of 150°C to 180°C and a shear rate range of 4 s−1 to 1259 s−1. The results showed that all the feedstocks exhibited pseudoplastic flow behavior. The wax-based binder of multipolymer components (PW-RPP-HDPE) exhibited better comprehensive rheological properties compared with the binder of monopolymer components (PW-RPP or PW-HDPE). The addition of 5wt% SA to the binder could reduce the viscosity of the feedstock but enhance the rheological stability by improving the wettability between the binder and the SiC powder. The binder of 65wt% PW + 15wt% HDPE + 15wt% RPP + 5wt% SA was found to be a better binder for microsized SiC injection molding.

Effects of Sintering Process on Microstructure and Properties of Flake Graphite-Diamond/Copper Composites

Flake graphite-diamond/Cu–Cr–Zr composites with good two-dimensional thermophysical properties were prepared by vacuum hot-pressing technology. The influence and working mechanism of the hot-pressing temperature on the relative density and thermal conductivity of the composites were studied to obtain the optimum sintering process. The results showed that with a pressing pressure of 10 ∼ 20 MPa, the relative density and thermal conductivity of the composite materials increased as the sintering temperature increased from 950 to 1010°C. When the temperature rose to 1010 ∼ 1040°C, a near fully dense composite material was obtained and thermal conductivity reached maxima of 410 and 119 W/m K parallel and perpendicular to the graphite planes, respectively, both of which are close to the theoretical value. However, relative density and thermal conductivity drastically decreased as the temperature continued to increase beyond 1070°C. This is attributed to the combined effect of sintering temperature and wettability between the matrix and the reinforcements.

Effect of Graphite as Forming Additive on Wear Properties of (SiCp+Al2O3f)/Al Composites Prepared by Pressure Infiltration

The 2024Al matrix composites reinforced by 30 vol% SiCp and 10 vol% Al2O3f as wear-resistant materials are prepared by pressure infiltration. The graphite powders are added during the preparation of the preform to support shaping. In this article, the effect of the size of the graphite powder on the friction and wear properties of the composites is researched. The results showed that at a given conditions, namely, the size of the SiCp is 14 µm and the diameter of the Al2O3 fiber is 4–5 µm, the composites made from 5 ∼ 30 µm have a more stable friction coefficience and lower wear rate than those from 30 ∼ 50 µm and 50 ∼ 70 µm graphite because the diameter of the generated pores in the corresponding preforms is smaller and more concentrated, resulting in a uniform distribution of the reinforcements in the matrix. The detailed effect mechanisms of different graphite sizes on wear and friction properties of the composites as well as the porosity of the corresponding preforms are also discussed.

Effect of sintering on the relative density of Cr-coated diamond/Cu composites prepared by spark plasma sintering

Cr-coated diamond/Cu composites were prepared by spark plasma sintering. The effects of sintering pressure, sintering temperature, sintering duration, and Cu powder particle size on the relative density and thermal conductivity of the composites were investigated in this paper. The influence of these parameters on the properties and microstructures of the composites was also discussed. The results show that the relative density of Cr-coated diamond/Cu reaches ~100% when the composite is gradually compressed to 30 MPa during the heating process. The densification temperature increases from 880 to 915°C when the diamond content is increased from 45vol% to 60vol%. The densification temperature does not increase further when the content reaches 65vol%. Cu powder particles in larger size are beneficial for increasing the relative density of the composite.

Effect of graphite powder as a forming filler on the mechanical properties of SiCp/Al composites by pressure infiltration

Abstract(38vol% SiCp + 2vol% Al2O3f)/2024 Al composites were fabricated by pressure infiltration. Graphite powder was introduced as a forming filler in preform preparation, and the effects of the powder size on the microstructures and mechanical properties of the final composites were investigated. The results showed that the composite with 15 μm graphite powder as a forming filler had the maximum tensile strength of 506 MPa, maximum yield strength of 489 MPa, and maximum elongation of 1.2%, which decreased to 490 MPa, 430 MPa, and 0.4%, respectively, on increasing the graphite powder size from 15 to 60 μm. The composite with 60 μm graphite powder showed the highest elastic modulus, and the value decreased from 129 to 113 GPa on decreasing the graphite powder size from 60 to 15 μm. The differences between these properties are related to the different microstructures of the corresponding composites, which determine their failure modes.

Sintering behavior and thermal conductivity of nickel-coated graphite flake/copper composites fabricated by spark plasma sintering

Nickel-coated graphite flakes/copper (GN/Cu) composites were fabricated by spark plasma sintering with the surface of graphite flakes (GFs) being modified by Ni–P electroless plating. The effects of the phase transition of the amorphous Ni–P plating and of Ni diffusion into the Cu matrix on the densification behavior, interfacial microstructure, and thermal conductivity (TC) of the GN/Cu composites were systematically investigated. The introduction of Ni–P electroless plating efficiently reduced the densification temperature of uncoated GF/Cu composites from 850 to 650°C and slightly increased the TC of the X–Y basal plane of the GF/Cu composites with 20vol%–30vol% graphite flakes. However, when the graphite flake content was greater than 30vol%, the TC of the GF/Cu composites decreased with the introduction of Ni–P plating as a result of the combined effect of the improved heat-transfer interface with the transition layer, P generated at the interface, and the diffusion of Ni into the matrix. Given the effect of the Ni content on the TC of the Cu matrix and on the interface thermal resistance, a modified effective medium approximation model was used to predict the TC of the prepared GF/Cu composites.

Effect of Al 2 O 3sf addition on the friction and wear properties of (SiC p +Al 2 O 3sf )/Al2024 composites fabricated by pressure infiltration

Aluminum (Al) 2024 matrix composites reinforced with alumina short fibers (Al2O3sf) and silicon carbide particles (SiCp) as wear-resistant materials were prepared by pressure infiltration in this study. Further, the effect of Al2O3sf on the friction and wear properties of the as-synthesized composites was systematically investigated, and the relationship between volume fraction and wear mechanism was discussed. The results showed that the addition of Al2O3sf, characterized by the ratio of Al2O3sf to SiCp, significantly affected the properties of the composites and resulted in changes in wear mechanisms. When the volume ratio of Al2O3sf to SiCp was increased from 0 to 1, the rate of wear mass loss (Km) and coefficients of friction (COFs) of the composites decreased, and the wear mechanisms were abrasive wear and furrow wear. When the volume ratio was increased from 1 to 3, the COF decreased continuously; however, the Km increased rapidly and the wear mechanism became adhesive wear.