Simultaneous regulation of strength and ductility of laser powder bed fusion manufactured Haynes 230 alloy

Abstract

Haynes 230 alloy is widely used in aero-engines with high strength, fatigue resistance, oxidation resistance and other properties. However, the powder metallurgy process limits its application due to hot cracks and low strength. In this work, crack inhibition and mechanical properties improvement of the laser powder bed fusion (L-PBF) manufactured Haynes 230 alloy using 25 groups of different laser energy densities and scanning strategies were investigated. Results show that the high density, nearly crack-free, fine microstructure, and excellent strength and ductility were achieved by a laser energy density of 59.4 J/mm3 and rotation angle of 90° for the L-PBF manufactured Haynes 230 alloy. The microstructure was composed of γ matrix, carbides (M6C, M23C6), and La2O3 nanoparticles. Interestingly, many carbides were found to be mainly uniformly distributed at the grain or sub-grain boundaries with the following orientation relation: [011]γ//[011]M23C6. Simultaneously, by adjusting laser energy density and scanning strategy, the liquid film, low-melting eutectic phase, hot stress concentration, and high-angle grain boundaries (HAGBs) were suppressed, and the hot cracks were reduced. In addition, yield strength and ultimate tensile strength enhancement of the L-PBF manufactured Haynes 230 alloy was attributed to the synergistic effect of solid solution strengthening, dislocation strengthening, Orowan strengthening, and grain refinement. Whereas ductility enhancement was the main effect of defect inhibition, grain refinement, and nanoprecipitate. This work has verified the feasibility of crack inhibition and mechanical properties improvement of the L-PBF manufactured Haynes 230 alloy by various laser energy densities and scanning strategies.