Mechanical Properties of Ceramic Composites Exhibiting Tailored Duplex-BimodalMicrostructures

摘要

Distribution of coarse-grain alumina agglomerates within a fine grain alumina-mullite matrix results in substantial T-curve behavior. The T-curve behavior is genuine and not an artifact that may have arisen due to surface cracking add/or lateral cracking effects. In-situ observation or cracks propagating in duplex-bimodal AM revealed three potential T-curve mechanisms: (1) alumina grain bridge formation within alumina agglomerates, (2) elastic-bridge formation and (3) microcracking. The effect of agglomerate volume fraction and size on indentation-strength response suggest the T-curve behavior originates from bridging grains within the alumina agglomerates. However, the level of toughening observed is significantly greater than that expected based on bridging theory. This indicates that there may be some combined contributions from the different mechanisms and/or that bridging in a duplex-bimodal microstructure is more effective than in a monolithic coarse-grain ceramic. (MM).