Microstructure and microhardness of Ti3Al/TiAl/Al2O3 composites sintered under high pressure
Anna Świderska-Środa*, Zbigniew Witczak*, Adam Presz*, Dariusz Oleszak** *Centrum Badań Wysokociśnieniowych PAN, ul. Sokołowska 29/37, 01-142 Warszawa **Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa
Annals 4 No. 11, 2004 pages 269-273
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abstract Ti3Al/TiAl - based fine grained intermetallic matrix composites reinforced with alumina were studied. Two-phase alloy with chemical composition Ti-48Al-2Cr (at.%) exhibiting a lamellar structure (Fig. 1) was obtained by a conventional casting. Next, the alloy was crushed and subjected to mechanical milling in a laboratory ball mill. The resulting powder was mixed with a commercial alumina powder (10 and 20 wt.%) and milled again (Fig. 2). After that, the powders were sintered at 960°C under the pressure of 3 GPa. The samples without Al2O3 showed uniform microstructure with a band-like distribution of intermetallic compounds (Fig. 5). The microstructure of the samples containing alumina was more refined comparing to two-phase sinter (Fig. 6). The alumina powder was located inside the grains of intermetallics as a dispersive particles. However, single-phase areas of Al2O3 were also observed. For higher alumina content the homogeneity of microstructure was smaller. The measured microhardness for all sintered samples was at least two times bigger if compared to the as-cast sample (Tab. 1). The hardness of the composites, despite of the various alumina content, was the same within experimental error and only 10% higher than for two-phase sintered sample. Key words: intermetallic phases Ti-Al, composite structure, high-pressure sintering