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Abstract
This research focuses on the infiltration of two porous structures. In the first, two different silicon sources were used to infiltrate structures derived from different Canadian pine, beech and maple species for the production of silicon carbide (SiC). This allows the use of a precursor structure that is already available, thus saving time, energy and cost of manufacturing. Carbonized wood species measuring 15 mm x 11 mm x 13 mm were used as precursors for the production of silicon carbide (SiC) using two silicon sources (sol and powder) in order to produce a porous SiC structure mimicking that of wood. The liquid sol was vacuum infiltrated into the pyrolyzed wood species, dried and reacted at 1575 °C under a 70 L/h flow of argon. Scanning electron microscopy (SEM) showed SiC grains formed on the interior of the tracheid walls and a high density of SiC whiskers were discovered in certain tracheids of pine and vessels of beech and maple. Both cyclic and repeated infiltration processes were undertaken. In addition, infiltration of carbonized pine wood with molten silicon was carried out in order to obtain a porous SiC structure. Infiltration was based on capillary forces within the preform and the infiltration depth was measured. Optical microscope, SEM, EDS and XRD were used for microstructure characterization and phase identification.
In the second part of this work, a liquid A356 aluminum alloy was infiltrated into a porous silicon carbide foam structure. Three dimensional silicon carbide (SiC) ceramic foams were employed as reinforcement for producing an aluminum alloy metal matrix composite with potential as a base plate material in electronic packaging. These are commonly manufactured with aluminum/silicon carbide (Al/SiC) particulate materials, nickel-iron and copper alloys. A base plate provides mechanical strength to the integrated circuit design, as well as aids in transfering the heat from the chip to the heat sink. Packaging base plate materials are required to have low coefficient of thermal expansion (CTE), high thermal conductivity, and low density. A356 aluminum alloy was vacuum infiltrated into a 100 PPI (pores per inch), silicon carbide (SiC) foam network, at 775°C using an in-house built apparatus. It has been shown that this metal matrix composite has similar properties to traditional packaging materials with the added benefit of a lower density. CTE and thermal conductivity are within the range of commercially available materials, with porosity levels of 7%, using this method. Flexural strength and Young's modulus of the composite provide reasonable values as a result of the low reinforcement concentration employed. Secondary Electron Microscopy (SEM) was used to investigate the fractured surfaces of the Charpy, flexural strength and compression tests. In the Charpy and flexural strength samples, the A356 aluminum-silicon alloy matrix shows signs of mixed fracture; cleavage regions and some dimpling. In the network structure, the majority of the failure is from SiC layers debonding from the aluminum matrix with some SiC layer peeling (inter-delamination). Compressive loading showed internal damage in the form of failed SiC struts. X-ray Diffraction (XRD) analysis did not detect any brittle aluminum carbide at the Al/SiC interface. The Rule of Mixtures (ROM) is used for a first rough estimate of certain mechanical and thermal properties.
