Dislocation-toughened ceramics

The brittle nature of ceramics limits their application range decisively despite their importance for key technologies. For decades, materials scientists appreciated the high bond strength of ceramics and accepted the absence of a toughness-enhancing plastic zone. Hence, the possibility of toughening ceramics by engineering mobile dislocations to form a plastic zone around crack tips, as it occurs naturally in metals, was hardly considered. This is surprising as dislocations are mobile at room temperature in a whole range of ceramic materials. However, the mere mobility of dislocations does not directly lead to a plastic zone at crack tips which enhances toughness. Here, we extensively investigate the dislocation behavior with a range of methods from dark-field X-ray microscopy and ultra-high voltage electron microscopy to indentation and molecular dynamics culminating in a simple conclusion: plastic zones in ceramics at crack tips are available to toughen ceramics after all; only – a large number of dislocations is required. After introducing a suitable dislocation density, we demonstrate that local plasticity is successfully enabled and provide evidence for toughening ceramics by dislocations. This seemingly simple realization opens up a range of new opportunities far beyond our current imagination. Conventional sintering, the standard densification method for ceramics, actually yields ceramics virtually free of dislocations and dislocation sources. In other words, the brittleness of ceramics appears as merely a consequence of the established conventional production method.