Mullite/ZrO2 coatings produced by flame spraying

Mullite/ZrO2 coatings of the eutectic composition (80/20% (v/v) mullite/ZrO2) have been flame sprayed on both ceramic and metal substrates. Being as-sprayed coatings mostly amorphous, thermal treatments at temperatures in the range of 1000–1300 °C promote crystallization leading to an increase of the hardness and elastic modulus. By in situ heating of the coatings, using the oxyacetylene torch, uncracked crystallised coatings having good mechanical properties are readily produced. The information supplied by the Al2O3–ZrO2–SiO2 phase equilibrium diagram provides insight into the complex microstructure observed in the coatings.