Mechanical and elastic properties of modified thick thermal barrier coatings

Mechanical and elastic properties of the phosphate sealed and laser-glazed 8Y2O3–ZrO2 and 22MgO–ZrO2 thick thermal barrier coatings (TBCs) were studied. Mechanical properties were determined by erosion and abrasion experiments and the elastic properties were evaluated by four-point bending (4PB) tests. Phosphate based sealing treatments improved significantly the erosion and abrasion resistance of the coatings and also increased the coating microhardness, bending strength and stiffness. The improvements of mechanical properties in the phosphate sealed coatings were caused by the lamellae bonding, due to the sealant. The effect of laser-glazing on the mechanical and elastic properties varied between the studied materials. The melted surface layer of the laser-glazed 8Y2O3–ZrO2 coating was very hard and dense and had excellent resistance against mechanical wear. At the same time the vertical segmentation crack network in the coating structure lowered the bending strength and stiffness. In laser-glazed 22MgO–ZrO2 coating the melted layer was also very hard, but most of the segmentation cracks were curved and branched and under mechanical loads they had tendency to coalesce. For this reason the laser-glazed 22MgO–ZrO2 coating had poor mechanical properties.