SEDL / STP / STP955-EB / STP33824S

Oxygen Effects on Void Stabilization in Stainless Steel

Seitzman, LE
Research assistant, professor, and professor, University of Wisconsin, Madison, WI

Kulcinski, GL
Research assistant, professor, and professor, University of Wisconsin, Madison, WI

Dodd, RA
Research assistant, professor, and professor, University of Wisconsin, Madison, WI

Pages: 7    Published: Jan 1987

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Abstract

Void nucleation theories often require surface energies significantly lower than established values in order to properly model cavity formation in metals. Surface impurities can cause the necessary decrease in surface energy and oxygen, which can interact readily with surfaces, is an abundant impurity in many metals. This study indicates that oxygen is especially effective in stabilizing voids. The amount of oxygen necessary to stabilize void formation in ion-irradiated Type 316 stainless steel is calculated as a function of temperature. Voids can be stabilized by reducing the surface energy such that the void becomes the most energetically stable vacancy cluster defect up to a size of 100 vacancies (D = 1.3 nm in steel). In austenitic steel, voids are stabilized when the surface energy decreases from 2.2 to 1.0 J/m². This level of reduction in surface energy could be accomplished by the chemisorption of oxygen, initially in solution, on void embryos that are formed in the early stages of irradiation. Calculations for a Type 316 stainless steel reveal that the required amount of free oxygen initially in solution to nucleate voids is a minimum of 4 appm at 550°C.