TOUGHENING OF BRITTLE MATERIALS BY GRAIN BOUNDARY DESIGN AND CONTROL

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The grain boundary character distribution (GBCD) was investigated on three different types of brittle polycrystalline materials produced by different processing methods: refractory metal molybdenum, directionally solidified Ni_3Al and rapidly solidified Fe-50%Co alloy ribbon.It has been found that the grain boundary character distribution (GBCD) condition of processing and subsequent heat treatments. It has been reveal ed that intergranular brittleness can be controlled by enhancement of the frequency of low-energy boundaries which are resistant to intergranular fracture, or conversely by reduction of the frequency of high-energy random boundaries which are prone to intergranular fracture.Other microstructural factors associated intergranular brittleness have been investigated: The grain boundary correlation number and the grain boundary triple junction character have been proposed and experimentally studied for real polycrystalline materials.The modelling of fracture processes and characteristics in polycrystals has made clear that the fracture toughness and brittle-ductile transition strongly depend on the grain boundary character distribution (GBCD) and geometrical arrangements of grain boundaries. This finding has provided a strong support to the basic concept of toughening of brittle materials by grain boundary design and control achieved in this investigation. The result obtained from this work may be applied to ceramics.