Chapter 5 - Microstructure and properties of additive manufacturing builds

Abstract

In this chapter, the roles of physical defects, microstructure evolution, and resulting properties with reference to metal additive manufacturing (AM) processes are discussed. Mechanisms related to defect formation are correlated to melt bead instability, surface roughness, and volumetric porosity, as well as, macro- and microcracking. In the first part of the chapter, microstructure evolutions in fusion-based AM processes are discussed based on ensuing phase transitions, including solidification and solid-state transformations due to multiple thermal cycles. Furthermore, the role of spatially varying chemical compositions on microstructure evolution is presented. These spatial variations of defect and microstructural distributions are then correlated to property scatter. Tensile, fatigue, and creep properties are discussed in detail based on published case studies. In the second part of the chapter, microstructure evolutions during solid-state AM processes are introduced. Case studies based on binder jet and ultrasonic additive manufacturing are presented to outline the underlying mechanisms. Some of the emerging solid-state manufacturing processes that are based on intense plastic deformations are introduced. Finally, the need to describe the spatial variations of microstructure and properties toward qualification of AM components for critical applications is justified.