The Effect of Heat Treatment on the Microstructure and Tensile Properties of Laser Powder Bed Fused (L-PBF)

Abstract

The as-fabricated microstructure of Haynes 214 by laser powder bed fusion (L-PBF) is dendritic due to the high cooling rates, which is generally considered undesirable and removed via heat treatments. In this study, the effects of various heat treatments on the microstructure and tensile properties of laser powder bed fused Haynes 214 are investigated. Test specimens were fabricated on a L-PBF system in the vertical orientation. Multi-step heat treatments were performed including stress-relief, hot isostatic pressing, solution annealing and ageing. Examining the microstructures revealed columnar grains in the non-heat treated (NHT) condition with grain growth occurring after stress relief. Room temperature tensile tests showed the lowest strengths in the NHT condition. The highest strengths were seen in the aged condition which was attributed to gamma prime precipitation hardening. Finally, the tensile fracture surfaces indicated ductile failure mode in both the NHT and heat treated conditions with the measured elongation being the highest for NHT and lowest in the aged condition.