Abstract
To attain fundamental information needed for designing functionally graded thermal barrier coatings, the strength and deformation properties of plasma-sprayed ZrO2-8wt%Y2O3/Ni-20wt%Cr composits with various compositions (0, 25, 50, 75, 100% Ni-20wt%Cr) were investigated from room temperature to 1200°C by means of small punch tests. The room temperature strength decreased rapidly with increasing ceramic content, from>1400MPa for metal to-100MPa for ceramic. The monolithic ceramic and ceramic-rich (75%) composites retained their strength up to 1200°C, whereas the compostions with>50 vol% metal showed lower strength at temperature above 800°C. All the plasma-sprayed materials showed low Young's moduli, being about 20-60% (lower bound for ceramic and upper bound for metal) of the theoretical data for fully dense composites, because of the microstructural features, such as high porosity and microcracks. Connection and propagation of microcracks (process-related defects) were found to occur before the eventual macrofracture of materials, consequently plasma-sprayed materials showed specific fracture behavior; nonlinear load-deflection curves were obtained in spite of brittle nature of the fracture.
