In situ synthesis of composite MTiO3–Al2O3 coatings via laser zone melting

Laser zone melting was employed in this work to prepare MTiO₃ based coatings over commercial, polycrystalline Al₂O₃ substrates, using the corresponding mixtures of powdered alkaline earth carbonates and TiO₂ as starting materials. In situ synthesis of the series M = Ca, Sr, Ba was studied using a CO₂ laser as the heating source, emitting at 10.6 μm, following substrate preheating to a temperature of 750 °C and sample displacement speed of 500 mm h⁻¹. Microstructure (SEM) and phase composition (XRD) demonstrated in situ formation of crystalline MTiO₃ perovskite (M = Ca, Sr), MAl₂O₄ (M = Ca), MAl₁₂O₁₉ magnetoplumbite type (M = Sr) and MAl₁₄O₂₂ β-alumina type (M = Ba) phases. Substantial interaction with the substrate resulted in stable, 50–150 μm thick, composite coatings.