Structure of the Al-(TiB2+Al2O3)p composites produced by IN SITU method
Andrzej Zyska*, Katarzyna N. Braszczyńska-Malik** *Politechnika Częstochowska, Katedra Odlewnictwa, al. Armii Krajowej 19, 42-200 Częstochowa **Politechnika Częstochowska, Instytut Inżynierii Materiałowej, al. Armii Krajowej 19, 42-200 Częstochowa
Annals 4 No. 11, 2004 pages 336-340
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abstract The results of structural and X-ray examination of aluminium composites produced of powder mixes with the reinforcing phase synthetized of oxides have been presented. The TiB2 and Al2O3 reinforcement has been generated by using three types of reactive powder mixes: Al-TiO2-B2O3 , Al-TiO2-B, Al-Ti-B2O3. Thermodynamic calculations concerning the free enthalpy change (Δ 0 ) GT for chemical reactions possible to proceed in these systems have been performed (Table 1, Fig. 1) and the composition of individual mixes has been estimated on the basis of the predicted reaction courses (Table 2). The in situ composites with the same percentage of the reinforcing phase (15 wt.%) have been produced in the temperature of 1323 K, then subjected to mechanical mixing at 973 K and next to the applied pressure of 50 MPa. Structural and X-ray analyses have revealed that the process of the reinforcing phase generation have not been fully realized in two of the reactive sysytems i.e. where Al-TiO2-B2O3, Al-TiO2-B mixes have been applied. Large inclusions of unprocessed B2O3 substrate have been found along with Al3Ti phase (Fig. 2, 3) in the stucture of composite made of the Al-TiO2-B2O3 mix. Despite the fact, the reinforcement achieved in this composite is relatively evenly distributed in the matrix volume, and the size of the reinforcing particles is of the order 1÷3 μm. The composite obtained from the Al-TiO2-B system is characterized by a small quantity of the reinforcing particles and the presence of intermediate phases Al3Ti and AlB2 (Figs. 4, 5). The reinforcement is dispersed throughout the matrix volume and found mainly inside the grains of aluminium phase. The proper reaction course for generating TiB2 and Al2O3 particles has been stated for Al-Ti-B2O3 system. Only the desired reinforcing phases evenly distributed throughout the matrix volume have been obtained, their particle size being of the order of 1÷5 μm (Figs. 6, 7). Key words: metal matrix composites, ceramic particles, in situ method, microstructure