Associate Professor, Condensed Matter Science and Technology Institute, College of Science, Harbin Institute of Technology, China.

Speech Title: New concepts for tailoring mechanical properties of alumina composites designed with compressive residual stresses
Abstract: Multilayer composites are an increasingly important concept for the design of structural ceramics requiring improved fracture toughness, strength, and mechanical reliability. In this work, a new class of alumina-based microstructural composites combining equiaxed and textured layers were fabricated to explore the effects of texture fraction, residual stress, and stress location on crack propagation behaviour and mechanical properties in a multilayer structure. Due to the thermal expansion differences between the textured layers and equiaxed layers, residual compressive stresses as high as 740 MPa were achieved in the embedded textured layers, which are very effective to arrest cracks in the composites. Besides, the interface between the basal planes of highly oriented alumina grains causes cracks to deflect within the textured layers due to the weak bonding. The coupling of these two mechanisms results in significant enhancements in both fracture toughness and work of fracture, about 3 times and 50 times higher than those of equiaxed alumina monolith. We believe that embedding textured layers with compressive stresses in the composites represent an important strategy for designing flaw-tolerant materials with pronounced crack growth resistance and a high work of fracture.
References
[1] Y. Chang, R. Bermejo, G. L. Messing, J. Am. Ceram. Soc., 97 (2014) 3643-3651.
[2] Y. Chang, O. Sevecek, R. Bermejo, G. L. Messing, J.Eur. Ceram. Soc., 35 (2015) 631-640.