Abstract
The effect of additional deformation on crack growth resistance by mechanical (bending) and cyclic thermal loading on silicon nitride specimens was investigated. Cracks initiated primary by Vickers indenter were formed in the corners of impression. Secondary impressions induced localized deformation at the crack tips. The influence of introduced deformation on indentation crack growth was not the same for bending and thermal cycling. Localized deformation resulted in the half of the specimens in small increase, and in the other half in small degradation of the fracture forces during mechanical loading. In contrary, the suppression of the indentation crack growth was observed in 80 % of the specimens after thermal cycling. The ambiguity of attained results can be explained by the interaction of primary and secondary indentation cracks. The effect of localized deformation on the suppression of indentation crack growth overlaps with the effect of secondary cracks formation.

Key words
Si₃N₄, deformation, bending testing

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