Abstract
Corrosion fatigue studies have been conducted on martensitic Type 403 turbine blade alloy in air, deaerated distilled water, and deaerated 0·01 and 1M NaCl solutions at pH 2, 7, and 10 at 100°C. At the same value of applied stress, the fatigue life in distilled water was almost the same as that obtained in air, while in chloride solutions the fatigue life was drastically reduced. The difference in fatigue life was attributed to the influence of chloride induced corrosion pits on crack initiation and to the effects on crack propagation of the change in solution chemistry at the tips of growing fatigue cracks. In 1M chloride solution at pH 10, the application of cyclic stressing promoted the development of corrosion pits, which did not form in unstressed material. A morphological investigation of crack initiation has shown that branched cracks and debonded regions developed at non-metallic inclusions in specimens fatigued in air. In contrast, cracks initiated in a transgranular mode in distilled water. Cracks initiated from corrosion pits were observed in all chloride solutions, except 0·01 M chloride solution at pH 10 where cracks initiated by an intrusion-extrusion mechanism.
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