Abstract
This paper introduces the concept of a general approach to the control of grain boundary fracture which is widely recognized as the primary source of the intrinsic brittleness in brittle materials and of extrinsically induced intergranular brittleness by grain boundary segregation, oxidation and wetting of liquid metal. The concept is based on the observations that intergranular brittleness in refractory metals, intermetallics and nanocrystalline materials can be controlled by engineering of grain boundaries, that is, by the elimination of high-energy weak random boundaries or by introduction of a higher fraction of low-energy strong grain boundaries. The transition from brittle to ductile fracture can occur by changing the operating fracture mode from intergranular to transgranular fracture, in both intrinsically and extrinsically brittle materials. Recent achievements of the control of intergranular brittleness by grain boundary engineering are shown to prove the general applicability of the concept for brittle materials with different origins of their brittleness.
