Fatigue Evaluation of Type 316 Stainless Steel Using Positron Annihilation Lineshape Analysis and β+-γ Coincidence Positron Lifetime Measurement

In order to non-destructively evaluate the degree of fatigue damage in type 316 stainless steel, frequently used in the primary system of nuclear power plants, positron annihilation lineshape analysis and β + -γ coincidence positron lifetime measurement were applied. In positron annihilation lineshape analysis, an energy spread of annihilation gamma ray peak was measured and expressed as the S-parameter. In positron lifetime measurement, mean lifetime analysis and two-component analysis were conducted. As a result, the S-parameter and the mean lifetime increased monotonously with fatigue life ratio. Strain-controlled fatigue increased more at the early stage of fatigue than stress-controlled fatigue. The S-parameter in the both stress- and strain-controlled fatigue reached almost the same value at the end of fatigue, and also the mean lifetime in the both stress- and strain-controlled fatigue reached almost the same value at the end of fatigue. In two-component analysis of positron lifetime measurement, the positron lifetime of the defect component did not change during fatigue, and the relative intensity of the defect component increased with fatigue life ratio. At the early stage, the relative intensity of defect component in the strain-controlled fatigue was larger than in stress-controlled fatigue, and both intensities reached almost the same value at the end of fatigue.