Influence of Casting Defects on S–N Fatigue Behavior of Ni-Al Bronze

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2015-02, Vol.46 (2), p.708-725
• Main Authors: Sarkar, Aritra, Chakrabarti, Abhishek, Nagesha, A., Saravanan, T., Arunmuthu, K., Sandhya, R., Philip, John, Mathew, M. D., Jayakumar, T.
• Format: Article
• Language: English
• Subjects: Alloys; ALUMINUM BRONZES (CASTING); BRONZES; CASTING; Casting defects; Characterization and Evaluation of Materials; Chemistry and Materials Science; CORROSION PROTECTION; Corrosion resistance; Defects; Fatigue (materials); FATIGUE PROPERTIES; High cycle fatigue; Intermetallic compounds; Materials Science; Mechanical properties; Metal fatigue; Metallic Materials; Metallurgy; Nanotechnology; PROPELLERS; Proximity; S N diagrams; STRESS; Stresses; Structural Materials; Surfaces and Interfaces; Thin Films
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-014-2668-4

Nickel-aluminum bronze (NAB) alloys have been used extensively in marine applications such as propellers, couplings, pump casings, and pump impellers due to their good mechanical properties such as tensile strength, creep resistance, and corrosion resistance. However, there have been several instances of in-service failure of the alloy due to high cycle fatigue (HCF). The present paper aims at characterizing the casting defects in this alloy through X-ray radiography and X-ray computed tomography into distinct defect groups having particular defect size and location. HCF tests were carried out on each defect group of as-cast NAB at room temperature by varying the mean stress. A significant decrease in the HCF life was observed with an increase in the tensile mean stress, irrespective of the defect size. Further, a considerable drop in the HCF life was observed with an increase in the size of defects and proximity of the defects to the surface. However, the surface proximity indicated by location of the defect in the sample was seen to override the influence of defect size and maximum cyclic stress. This leads to huge scatter in S – N curve. For a detailed quantitative analysis of defect size and location, an empirical model is developed which was able to minimize the scatter to a significant extent. Further, a concept of critical distance is proposed, beyond which the defect would not have a deleterious consequence on the fatigue behavior. Such an approach was found to be suitable for generating S – N curves for cast NAB.