Temperature dependent tensile behavior of additively manufactured HAYNES® 214: A comparative study between laser powder bed fusion and laser powder directed energy deposition

Abstract

In this study, the tensile behaviors of laser powder bed fused (L-PBF) and laser powder directed energy deposited (LP-DED) HAYNES® 214 were investigated at a wide range of test temperatures (−195, 25, 425, 650, 870 and 980 °C). Specimens fabricated in the vertical orientation were subjected to a three-step heat treatment including stress relief, hot isostatic pressing, and solution treatment. The non-heat treated microstructures of L-PBF and LP-DED specimens were dendritic and columnar, oriented in the build direction. Recrystallization occurred after solution annealing, with the nucleation and growth of equiaxed grains. Tensile results revealed higher strength for the L-PBF specimens compared to LP-DED up to 650 °C, attributed to their finer grain size. The highest strengths were recorded at cryogenic temperatures, where diminished dislocation mobility and deformation twinning provided increased resistance to plastic deformation. From room temperature to 425 °C, a gradual decrease in strength was ascribed to the increase in dislocation motion with temperature. Ductility was measured to be similar for both processes up to 650 °C, and fracture surface analysis showed transgranular failure at these temperatures. A ductility dip was observed between temperatures of 650–870 °C due to the activation of grain boundary sliding resulting in intergranular cracking. The heterogeneous grain size distribution in both L-PBF and LP-DED specimens led to the ductility being comparable for both processes. The highest test temperature of 980 °C introduced sufficient thermal energy to promote significant grain boundary sliding which resulted in intergranular fracture in the L-PBF and LP-DED specimens.

Keywords

• Additive manufacturing
• HAYNES® 214
• Microstructure
• Tensile properties
• Temperature effects