Analysis of phase transformation in plasma sprayed alumina coatings using Rietveld refinement

During plasma spraying of alumina with the stable α phase in the starting powder, metastable phases tend to form in the final coating. This is attributed to the rapid quenching associated with the process. In this paper the weight fraction of metastable phase formed, i.e., stable phase retained, and has been estimated using Rietveld refinement of X-ray diffraction data. This weight fraction depends on the process parameters like standoff distance, primary and secondary gas flow rate, nozzle size, etc., which in turn control particle melting. Under favourable melting conditions the weight fraction of the metastable phases approaches 1.