Processing of ceramic-metal interpenetrating composites

Interpenetrating composites consist of 3-dimensionally interpenetrating matrices of two different phases; in the present work they were alumina and aluminium-magnesium alloys and were produced by infiltrating ceramic foams with molten alloys. The foams were made by mechanically agitating ceramic suspensions to entrain gases and then setting the structure via the in-situ polymerisation of organic monomers, a process known as gel casting. This resulted in the foams having a very open and interconnected structure that could be easily infiltrated by the molten metals. Previous composites have been produced at Loughborough University using squeeze casting; however, whilst infiltration was usually accomplished in a matter of seconds, the resulting size and shape of the composite was limited. Hence the present work has focused on investigating the potential for using gravity-fed infiltration. Whilst this was much slower, often taking several minutes, when optimised it is believed it will offer the potential for the production of large and complex-shaped pieces. The composites were produced at atmospheric pressure by infiltrating 2-10 wt.% magnesium content Al-Mg alloys into 20% dense Al2O3 foams with highly interconnected porosity. The processing parameters of temperature, ≥ 900°C, and atmosphere, flowing N2- Ar, were investigated to determine the processing window and infiltration kinetics. In-situ observation of the process shows that infiltration is faster at higher temperatures, Mg contents and N2 partial pressures. Both optical and scanning electron microscopy (SEM) have been used to characterize the composites.