Co-continuous composites for high-temperature applications

The present work demonstrates a new method for creating a high-temperature composite. First, silica is reacted in liquid aluminum. This creates a highly aligned, near single crystal alumina structure that has about 25% open volume that is filled with aluminum. This open space is subsequently re-infiltrated with a refractory metal (NiAl or a nickel alloy), creating an interpenetrating phase or co-continuous composite. Experiments with this material were carried out to assess the degree to which this co-continuous structure (with phases of very different coefficients of thermal expansion) is susceptible to thermal cycling damage. Both the Al–Al2O3 and NiAl–Al2O3 materials were examined and the former case is compared to an axially reinforced Al–Al2O3 composite with a similar alumina volume fraction. The results showed that unlike traditional composites co-continuous composites were quite resistant to thermal cycling damage, and the NiAl–Al2O3 showed no thermal cycling damage as noted by no strength loss or cracking, but the elastic modulus of the composite was related to its environmental history (the composite elastic modulus was observed to change by 25%, and in a reversible way). This is postulated as being due to the role hydrogen may have in controlling interface sliding behavior at the NiAl and Al2O3 interfaces. Overall this work points to a potentially useful processing route and architecture for high-temperature composite materials.