abstract
This paper studies attained microstructures and reactive mechanisms involved in vacuum infiltration of copper aluminate preforms with liquid aluminium. At high temperatures, under vacuum, the inherent alumina film enveloping the metal is overcome, and aluminium is expected to reduce copper aluminate, rendering alumina and copper. Under this approach, copper aluminate toils as a controlled infiltration path for aluminium, resulting in reactive wetting and infiltration of the preforms. Ceramic preforms containing a mixture of Al2O3 and CuAl2O4 were infiltrated with aluminium under distinct vacuum levels and temperatures, and the resulting reaction and infiltration behaviour is discussed. Copper aluminates stability ranges depend on vacuum level and oxygen partial pressure, which determine both CuAl2O4 and CuAlO2 ability for liquid aluminium infiltration. At 1100 degrees C and 0.76 atm vacuum level CuAl2O4 is stable, indicating pO(2) above 0.11 atm. Reactive infiltration is achieved via reaction between aluminium and CuAl2O4; however, fast formation of an alumina film blocking liquid aluminium wicking results in incipient infiltration. At 1000 C and 3.8 x 10(-7) atm vacuum level, CuAl2O2 decomposes to Cu and Al2O3 indicating a pO(2) below 6.0 x 10(-7) atm; infiltration of the ceramic is hindered by the non-wetting behaviour of the resulting metal alloy. At 1000 degrees C and 1.9 x 10(-6) atm vacuum level CuAlO2 is stable, indicating pO(2) above 6.0 x 10(-7) atm. Extensive infiltration is achieved via redox reaction between aluminium and CuAlO2, rendering a microstructure characterised by uniform distribution of alumina particles amid an aluminium matrix. This work evidences that liquid aluminium infiltration upon copper aluminate-rich preforms is a feasible route to produce Al-matrix alumina-reinforced composites. The associated reduction reaction renders alumina, as fine particulate composite reinforcements, and copper, which dissolves in liquid aluminium contributing as a matrix strengthener. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
keywords
MATRIX COMPOSITES; ALLOYS; WETTABILITY; CARBON; SYSTEM; MICROSTRUCTURE; INTERFACES; METAL
subject category
Materials Science
authors
Guedes, M; Ferreira, JMF; Rocha, LA; Ferro, AC
our authors
José Maria da Fonte Ferreira
Retired Professoracknowledgements
The authors are grateful to Teresa Marcelo (LNEG) for helpful discussions and use of lab facilities, and to Paulo Machado (EST/IPS) for assistance in experimental issues. MG acknowledges FCT for financial support under contract SFRH/BD/25711/2005.