Effect of the type of reinforcing phase on the stress of plastic flow in aluminium-based MMCs
Edward Fraś, Andrzej Kolbus, Andrzej Janas Akademia Górniczo-Hutnicza, Wydział Odlewnictwa, ul. Reymonta 23, 30-059 Kraków
Annals 3 No. 6, 2003 pages 120-124
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abstract Aluminium-based metal matrix composites are a very attractive material for constructions, characterised by high tribological and mechanical properties, effectively combined with a very advantageous strength-to-density ratio. The utilisation properties of these composites depend on the type, size and volume fraction of particles of a reinforcing phase, and also on the choice of the matrix type and the method of fabrication. In a traditional way, MMCs are fabricated by an ex situ process, i.e. preparing in a separate process the reinforcing phase, which is next introduced to the composite matrix by, e.g., mixing. In the in situ process, the reinforcing phase is formed as a result of chemical reactions which proceed between the alloy constituents in metal bath. An improved variant of the SHS process has been selected, i.e. the SHSB process - self-propagating high temperature synthesis in metal bath [1, 2]. The method has been applied in fabrication of in situ Al+TiC and Al+TiB2 composites. From pure powdered materials, like titanium, aluminium, boron and carbon, briquettes of stochiometric composition, ensuring the synthesis of TiC and TiB2, respectively, were prepared. The briquettes were next introduced to molten alloy. The composite synthesis was performed in vacuum; the ready materials were cast in a steel die. In the second part of the experiment, the traditional, DURALCAN type, ex situ composites reinforced by SiC particles were fabricated. From thus prepared composite castings, specimens were cut out for metallographic and structural examinations, and for mechanical testing. The structure was examined by X-raying; the mechanical properties were tested in isothermal compression test at both standard temperature of 293 K and elevated temperature of 623 K. Basing on the obtained results it has been proved that Al+TiC composites are characterised by mechanical properties higher than the DURALCAN type composites and Al+TiB2 composites. Key words: composite ex situ, composite in situ, titanium carbide, silicon carbide, titanium boride, exothermic reaction, process SHSB