Understanding Mechanical Property Variability in Laser Powder Bed Fusion Additive Manufacturing through Fractography and Failure Analysis

Laser powder bed fusion (LPBF) is an advanced manufacturing technique that can produce high-density metal components with nearly unlimited complexity. Recognized as a disruptive technology, it is proving capable of overcoming the challenges faced by conventional manufacturing techniques in applications that involve low volume manufacturing, geometrically complex parts, or related to trends associated with glocalization. However, in the adoption of LPBF for the manufacturing of components intended for safety-critical systems, there are some key concerns. Specifically, the reliability of metal LPBF components is under scrutiny, and a thorough understanding of process and corresponding property variability must be achieved before the technique can be widely applied. In previous efforts, large scale statistical evaluations of process variability have been attempted with different degrees of success. While some investigations have been able to observe process variability reflected in the mechanical properties of the metal, they usually fail to ascertain the root causes. Fractography and complementary approaches to failure analysis can provide important details that help elucidate the relationships between process physics and the mechanical behavior of printed parts. The present work describes ongoing efforts in a round robin program to evaluate the mechanical property variability of Grade 5 Ti6Al4V produced via LPBF under static and cyclic loading conditions. Concurrent fractographic evaluations using optical microscopy, scanning electron microscopy, and metallographic techniques are utilized to understand key contributions to the mechanical property variability and to help in the identification of root causes. Details of the findings are presented and the importance to quality control are discussed.