Papers by Keyword: Coefficient of Thermal Expansion

Abstract: Miniaturisation of electronic chips which have increasing functionality within the same package size has induced significant increases in requirements for extraction of heat from the integrated circuit (IC). Packaging materials therefore have to be capable to conduct heat efficiently and at the same time have low coefficient of thermal expansion (CTE) to minimize the thermal stress and warping. In the present study, copper silicon carbide was selected with an aim to solve thermal management problem presented by current IC systems. Powder metallurgy routes were chosen to fabricate the MMC based on this materials system. Copper and silicon carbide powders were mixed together in a planetary ball mill, and the green articles were then compacted and sintered to produce the final product of CuSiC. The sintering parameters were investigated for their effects towards the thermal conductivity of the composite. Sintering parameters investigated included temperature, heating duration and the gaseous environment. Upon sintering, the CuSiC particle bond to one another giving a higher strength and a possibility in attaining desirable density. Thus to achieve good thermal conductivity, the recommended sintering parameter suggests that the CuSiC composite should be sintered at 950°C for 7 hours in nitrogen gas.

Abstract: In this paper, MCrAlY bonding layer was prepared through high velocity-oxygen fuel spray on the AZ91 magnesium alloy surface. 8wt%YSZ ceramic layer was deposited on the surface of bonding layer through atmospheric plasma spraying. The coatings were characterized by XRD and SEM. The hardness of the coating was tested. The coefficients of thermal expansion of the coating were measured through TMA. It was found that there were un-melted 8YSZ particles surrounded by melted particles layer by layer. Parts of ZrO₂ transited from cubic to tetragonal. The microhardness of the YSZ coating and bonding layer were 832.1Hv_0.3 and 700.3Hv0.3, respectively. The coefficients of thermal expansion of the magnesium alloy, MCrAlY layer and YSZ coating were 42.46 ×10^-6·k^-1, 15.26 ×10^-6·k^-1, 9.28 ×10^-6·k^-1, respectively. The bonding coat matched the magnesium alloy substrate and the YSZ coating well. The dimension of AZ91 magnesium alloy sample was very stabilized before and after coating deposition.

Abstract: Abstract: In order to study the effect of WC size on the thermal expansion coefficient of WC/Cu composites after anneal, WC/Cu composites with different WC particle size were prepared by powder metallurgy method. In this paper the thermal expansion coefficient of WC/Cu composites were measured by digital image correlation method. The results show that the thermal expansion coefficient increased with the increasing of temperature and the particle size.

Abstract: Thermodynamic properties of the heavy metal germanium tellurite (NZPGT) core and cladding glasses have been investigated. Coefficient of thermal expansion (CTE) and softening temperature (Ts) of the Er³⁺⁄Yb³⁺ codoped NZPGT core glasses were identified to be 1.89×10^–5 °C^–1 and 343 °C, respectively. Glass transition temperature (Tg), onset crystallization temperature (^Tx), peak temperature of crystallization (Tc), temperature difference value (ΔT) and thermal stability parameter (H) of the core glasses were solved to be 290 °C, 412 °C, 470 °C, 122 °C and 0.42, respectively, and the corresponding vaules of cladding glasses were derived to be 290 °C, 391 °C, 400 °C, 101 °C and 0.35. The investigation results indicate optical fiber drawing of Er³⁺⁄Yb³⁺ codoped medium-low phonon energy NZPGT glasses can be achieved in the temperature range 345—380 °C, which provides a valuable temperature reference for further high-quality optical fibers drawing in developing optical devices.

Abstract: Milled form of mesophase pitch-based graphite fibers were coated with a chromium layer using chemical vapor deposition technique, and Cr-coated graphite fiber/Cu composite with 50 vol.% fibers was fabricated by hot-pressing. The composite was characterized with scanning/transmission electron microscopies and by measuring thermal properties, including thermal conductivity and coefficient of thermal expansion (CTE). The results showed that the milled fibers were preferentially oriented in a plane perpendicular to the pressing direction, leading to anisotropic thermal properties of the composite. The Cr coating reacted with graphite fiber and formed to a continuous and uniform Cr₃C₂ layer. This carbide layer established a good metallurgical interfacial bonding in the composite, which can improve the thermal properties effectively. The in-plane thermal conductivity and CTE of the composite reached to 392 W/mK and 6.5 ppm/K respectively, making the composite suitable for being electronic packaging materials.

Abstract: AlN/epoxy (AlN/EP) composites were fabricated by casting method. The effects of the AlN content on microstructure, thermal conductivity and thermal expansion properties of composites were investigated. The results indicate that with the AlN content increasing, the thermal conductivity increase, while the coefficient of thermal expansion (CTE) decreases. When the volume fraction of AlN is 25%, the thermal conductivity is 0.507 W/m•K, which is about 2.5 times higher than that of the epoxy matrix, while the coefficient of thermal expansion is 53.7 ppm/°C. The thermal conductivity results obtained were also analyzed using the Maxwell-Eucken model to explain the effect of AlN fillers on the formation of thermal conductive networks.

Abstract: Short carbon fiber reinforced AZ91 magnesium alloy matrix composites have been made by stir casting technique. The microstructure and the fibre matrix interfacial region of the composites characterized using optical and scanning electron microscopes reveal uniform distribution of fiber in the matrix and good interfacial bonding respectively. Increase in compressive strength values are observed with increase in fiber content where as the room and high temperature (150°C) strength properties are found to decrease marginally. The microfractograph of the tensile fractured surface reveals mixed type of fracture.

Abstract: The top of COREX-C3000 gasifier was simulated with a finite element analysis technique. It is studied of the influence of thermal expansion coefficient of the refractories on the temperature field and stress field and the function discipline with different parameters. The results of the simulation indicated that when the coefficient of thermal expansion of working lining and permanent lining are respectively 3.5×10^-6/K and 4.5×10^-6/K, the distortion and initial stress of the gasifier top are much less.

Abstract: High Nb containing TiAl based alloys exhibit excellent corrosion resistance to molten zinc. They are expected to serve as the potential coating materials of corrosion resistance to molten zinc. Four TiAl-Nb alloys of good oxidation resistance and their powders were prepared by arc-melting and ball milling, respectively. The Microstructure, Hardness, Coefficient of thermal expansion, and grain size distribution of four as-cast TiAl-Nb alloys and their powders were investigated. In addition, EPMA analysis was employed to further examine the existential state of element Y in as-cast TiAl-Nb alloys. It was found that element Y existed in the form of YAl2 phase in the grain boundaries and triple junctions. Higher content of Al in TiAl-Nb alloy results in bigger Coefficient of thermal expansion. Lamellar microstructures and fine grains exert a positive influence on hardness. Powders prepared by ball milling displayed angular and irregular morphology.

Abstract: In this study, SiC particles reinforced aluminum matrix composite was successfully fabricated using powder metallurgy technique followed by hot extrusion. The phases were identified by XRD and the microstructures were observed by SEM. The results showed that only Al and SiC phases existed in the composite, SiC particulates were well distributed in the aluminum matrix and the interface between Al and SiC was clean and well combined. Meanwhile, thermal conductivity and coefficient of thermal expansion of the composite were investigated, the research showed that thermal conductivity decreased as SiC_p content increased because of poor thermal conductivity of SiC_p and increased crystal defects forming during the fabrication process. And the same to thermal conductivity, coefficient of thermal expansion of the composite decreased as SiC_p content increased because SiC_p can acted as obstacles to the motion of dislocations, which can hinder the hot movement of electronics.