Additive manufacturing of fatigue resistant materials: Challenges and opportunities

This overview focuses on the current state of knowledge pertaining to the mechanical characteristics of metallic parts fabricated via additive manufacturing (AM), as well as the ongoing challenges and imminent opportunities in fabricating materials with increased fatigue resistance. Current experimental evidence suggests that the mechanical properties of laboratory AM specimens may not be representative of those associated with parts, due primarily to differences in geometry/size which influence the thermal histories experienced during fabrication, and consequently, microstructural features, surface roughness, and more. In addition, standards for mechanical testing methods, specimen design procedures, post-manufacturing treatments, etc., may need to be revised for AM parts. Standardizing the AM process may only be accomplished by strengthening the current understanding of the relationships among process parameters, thermal history, solidification, resultant microstructure, and mechanical behavior of the part. Having the ability to predict variations in mechanical behavior based on resultant microstructure, or matching the best conceivable properties of a part in accordance with the loading critical plane, are some possible solutions for making AM a more reliable means for producing functional parts. Developing microstructure-property models is arguably the first necessary step toward design optimization and the more efficient, accurate estimation of the structural integrity of AM parts.