Determination of fracture toughness for small-sized specimens with ultrafine grain structure

The results of changing the fracture toughness of materials are given for the VT6 titanium alloy. Its coarse grain structure was reduced down to ultrafine structure by forging. The specific energy of fracture γ for the small-sized chevron-notched specimens was found thanks to the new technique. It is shown that severe plastic deformation reduces γ at room temperature. The structure of the surface fracture of the VT6 alloy's ultrafine grain structure can be conceived as local zones of strong deformed material with a high concentration of pores. Such kind of structure cannot be formed only by means of crystallographic shears along close-packed planes. That fact proves the cardinal role of rotational modes of deformation in the origination and formation of a crack at various scale levels.