Scanning Electron Microscopy


Scanning electron fractography is an inherent part of investigations of factors which determine the mechanical properties of materials and their failure. Transition bcc metals show the widest variety of fracture mechanisms under uniaxial tension.

Brittle fracture is affected by cleavage from various defects - stress concentrators.

In brittle-ductile transition, fracture starts by a "tough" mode but finishes by a brittle one - by cleavage. A fracture mechanism changes after the "tough" crack has reached some critical length. Mechanisms of subcritical growth are of cleavage with relaxation, inter-granular fracture and dimpled ones.

Dimples are observed in ductile fracture. Cleavage is absent. The dimples are nucleated as a result of both failure of particles and their interfaces and delamination of structure elements.

All varieties of observed fracture surface may be described as a result of actions of the following mechanisms - cleavage, cleavage with relaxation, pore coalescence, brittle intergranular or intercellular fracture.

Fractographical analysis allows one to obtain information not only about the fracture mechanisms but also such characteristics as: fracture toughness, brittle-ductile transition limits, structure transformations preceding fracture.

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