Fracture intercrystalline/transcrystalline

In most cases, shear fracture is transcrystalline (through the grains), but, depending on the material state, intercrystalline fracture (fracture along the grain boundaries) may also occur. 

Microstmctural studies on the above samples determined that the addition ofYaOa or MgO caused a transition from a transcrystalline to intercrystalline fracture. This transition was due to softening of the glassy phase, which resulted in slow crack growth at low stress levels. 

As a consequence of the above mentioned effects, but in contrast to many other metallic materials, the fracture toughness of Mo and W is strongly reduced with increasing degree of recrystallization. With increasing plastic deformation, the fracture toughness increases (see Sect. 3.1.9.4), combined with a transition from intercrystalline to transcrystalline cleavage and to a transcrystalline ductile fracture [1.147,158,159]. 

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