Thermal Expansion Of Al Based Composite Materialsat Elevated Temperatures
Adam Kurzawa, Jacek W. Kaczmar, Andrzej Janus Politechnika Wrocławska, Instytut Technologii Maszyn i Automatyzacji, ul. Łukasiewicza 3/5, 50-371 Wrocław
Annals 1 No. 2, 2001 pages 167-170
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abstract Besides excellent mechanical and development properties of composite materials, thermal expansion and dimensional stability at temperature intervals 20÷450°C play the very important role and effect on practical applications of these materials. There are shown results of dilatometric investigations of composite materials on AK9 matrix strengthened with ceramic preforms made of Saffil fibres. These materials were prepared by pressure infiltration of porous ceramic preforms with liquid AK9 alloy - „squeeze casting”. Composite materials containing 10, 15 and 20 vol.% of ceramic fibres were investigated. Samples of diameter of 5 mm and length of 30 mm made of these materials were heated from ambient temperature (20°C) to 450°C and cooled again to the ambient temperature. For comparison dilatometric investigations applying the same heating and cooling conditions were performed for not strengtened AK9 alloy. Analysis of dilatograms showed, that after 1-st heating and cooling cycle shrinkage of samples was ascertained. For example in the case composite materials containng 15 vol.% of fibres shortening after 1-st heating cycle was 1.3 x 10−3 (Fig. 1) and for composite material containing 20 vol.% of fibres shrinkage was of 1.7 x 10−3 (Fig. 3). Shrinkage of samples was not ascertained in the not strengtened AK9 cast alloy and after 2-nd heating and cooling cycle of composite materials (Fig. 2). On this base it can be ascertained, that after 1-st heating and cooling cycle the composite materials achieved dimensional stability. Achieving of dimensional stability after 1-st cycle of heating and cooling can be explained by the intensive diffusional transport of matter from the matrix to the pores at the interface during heating process. In the future investigations it should be explained which parameters of thermal treatment effects on the thermal stability. Performed investigations showed dependence of thermal expansion coefficients α from the fibres content in the AK9 matrix what is shown at Figs. 4 and 5. Increase of ceramic fibres content in the matrix effects on decrease of thermal expansion coefficients α approximately proportional to the fibres contents. The largest thermal expansion coefficient α was measured for cast AK9 alloy.