Evaluation of Zr- and Ti-containing Aluminum-Boron Carbide composites as materials for elevated temperature performance in engineering applications

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The constant need to enhance the performance of critical components used in the automotive, aerospace and other industries has been the driving force behind the development of improved high-performance structural materials. Metal matrix composites (MMCs) have emerged as a promising group of materials for such applications. Two commonly used metal matrices are those of Al and Ti, which have low densities and are available in a variety of alloy forms. However, the high cost of Ti alloys limits their application to those cases where performance is the main goal irrespective of cost. The reinforcements added to produce the composite are carbides, oxides and nitrides, selected for their excellent combinations of specific strength and stiffness at ambient and elevated temperatures. Aluminum MMCs provide both light weight, courtesy of the Al matrix, and enhanced strength, stiffness and wear resistance through the reinforcement. While SiC and Al2O3 have been more commonly used as the reinforcement, the more recently introduced B4C is both the lightest and the hardest of the three, making it a viable choice with respect to the reduced weight criterion so prevalent in today’s industry. The enhanced elevated-temperature strength and favorable neutron absorption characteristics of Al-B4C composites are strong points which justify investigating their suitability for use in both current and emerging applications. For successful commercialization of any developed product, cost-effectiveness and affordability are important factors to consider. Keeping this point in mind, and based on the applicant’s extensive expertise in the study of SiC and Al2O3 particulate-reinforced Al MMCs, together with experience gained from recent studies on the behavior of Al alloys containing Zr, Ti and Sc additions, the proposed study aims to investigate Al-B4C MMCs containing Zr and Ti additions as potential materials for use in engineering applications requiring stable high temperature performance. A range of Al-B4C composite alloys will be prepared using a) pure Al and b) 6061 alloy as the matrix, with Ti and Zr additions, employing the molten metal processing route; the 6061 alloy was selected for evaluating the feasibility of rolling these materials into sheets for use in car body applications, etc. A powder injection technique will be used to inject the reinforcement particulate into the molten metal. This technique was invented and successfully applied by the applicant in 1990. The fluidity of these composites at various melt temperatures will be characterized and analyzed in terms of the interfacial reactions (i.e. wettability) between reinforcement and matrix, using extensive transmission electron microscopy. The high temperature performance will be studied by monitoring the precipitation behavior in heat-treated samples using TEM for examining the nano-sized strengthening Al-Zr/Ti precipitates. Other important properties, such as hardness and impact toughness, will also be investigated for a complete characterization of these materials. The experimental data obtained will provide valuable input for modeling the microstructure/property relations in such composite materials. An equally important component of this undertaking will be the training of high qualified personnel in this specialized area of research. The fundamental, scientific and technological aspects of data generated by this project will impact both academic and industrial sectors and thereby the Canadian economy as a result.