Vacuum infiltration of copper aluminate by liquid aluminium

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 Al 2O 3 and CuAl 2O 4 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 CuAl 2O 4 and CuAlO 2 ability for liquid aluminium infiltration. At 1100 °C and 0.76 atm vacuum level CuAl 2O 4 is stable, indicating pO 2 above 0.11 atm. Reactive infiltration is achieved via reaction between aluminium and CuAl 2O 4; however, fast formation of an alumina film blocking liquid aluminium wicking results in incipient infiltration. At 1000 °C and 3.8 × 10 −7 atm vacuum level, CuAlO 2 decomposes to Cu and Al 2O 3 indicating a pO 2 below 6.0 × 10 −7 atm; infiltration of the ceramic is hindered by the non-wetting behaviour of the resulting metal alloy. At 1000 °C and 1.9 × 10 −6 atm vacuum level CuAlO 2 is stable, indicating pO 2 above 6.0 × 10 −7 atm. Extensive infiltration is achieved via redox reaction between aluminium and CuAlO 2, 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.