Microstructure and mechanical properties of Haynes 188 alloy manufactured by laser powder bed fusion

Haynes 188 alloy with a combination of strength and ductility is of significance in aircraft engines and recent development in additive manufacturing significantly increases potential applications of this material. However, understanding the microstructure and tensile properties of Laser Powder Bed Fusion (LPBF) Haynes 188 alloy is limited. Here, a crack-free Haynes 188 alloy is successfully fabricated. The LPBF specimens are observed in two different directions: perpendicular and parallel to the building direction, referred to as “LPBF-H" and “LPBF-V" sections, respectively. To investigate the anisotropy of LPBF specimens, tensile tests were conducted on LPBF Haynes 188 alloy with different observed sections. The vertical sections show lower yield strength than the horizontal sections due largely to an elongated columnar structure. The effects of solute, grain size and dislocation on the strengthening mechanism are discussed thoroughly. The synergy effects of the grain size and the dislocation increase the strength of the LPBF alloys compared to wrought and casting equivalents. For LPBF specimens, the dislocation cellular structure is particularly investigated. To better understand the plasticity, the fracture morphology is also analyzed. The developed understanding on the microstructure and mechanical properties of Haynes 188 alloys in this work could also be applicable to other Co-based superalloys.