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Report No.

Positron microscopic analysis of crack failure in stainless steels

Yu, R.; Maekawa, Masaki; Miwa, Yukio; Hirade, Tetsuya ; Nishimura, Akihiko ; Kawasuso, Atsuo

Employing a positron beam with lateral resolution of about 30 micometer, we performed one and two dimensional scan of crack tips in mechanically fatigued as well as stress corrosion cracked (SCC) stainless steels. Results suggest the existence of quite different crack failure mechanisms in the two types of specimen. In agreement with normal crack propagation principal, creation of dislocations and vacancies close to a crack in the mechanically fatigued sample lead to an expected narrowing of the positron annihilation 511 keV Doppler broadening $$gamma$$-ray peak (S(crack)/S(bulk)=1.01). Contrarily, widening of the Doppler broadening peak was observed for the SCC specimen (S(crack)/S(bulk)=0.97). Such phenomenon was ascribed to the micro-compositional and micro-structural differences between the studied samples.



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