Phase compositions and depth-profiling of calcium aluminates in a functionally-graded alumina/calcium-hexaluminate composite

The phase developments, abundances and depth-profiling of various calcium aluminates (i.e. CA, CA2 and CA6) in a functionally-graded alumina/calcium-hexaluminate material (FGM) at temperatures ranging 1000–1650°C have been systematically analysed by X-ray diffraction (XRD) and synchrotron radiation diffraction (SRD). Results show that CA and CA2 formed at approximately 1000 and 1300°C, respectively, remained stable even at 1400°C, but eventually transformed fully to CA6 at 1650°C. XRD of the FGM shows the presence of corundum in the alumina layer and a mixture of CA6 and corundum in the graded region. Qualitative depth-profiles of phase contents within the FGM show that the abundance of CA6 in the graded layer decreased gradually with increasing depths towards the alumina layer.