15 - Microstructure and mechanical properties of as-built and heat-treated Laser Powder Bed Fusion Al0.3CoCrFeNi High Entropy Alloy

Abstract

High entropy alloys (HEAs) are metallic materials composed of a concentrated mixture of multiple principal elements. The Al0.3CoCrFeNi alloy, produced by arc melting and subsequent thermomechanical treatments, is one of the most studied HEAs due to the wide range of microstructures accessible and the associated high mechanical performances. Thanks to Laser Powder Bed Fusion technology (L-PBF) and the high as-built dislocation density obtained, the room-temperature yield strength of this alloy is largely improved compared to as-cast or wrought counterparts while maintaining significant ductility [1]. This paper highlights the effect of the control of L-PBF process parameters and of heat treatments on the alloy microstructural components (texture, dislocation density, secondary phases) and tensile properties. Analyses were carried out by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT). The hierarchical microstructure is characterized by elongated columnar grains along the building direction (BD), sub-grains, solidification cells, a high dislocation density and a small amount of nano-particles. Two preferential crystallographic orientations <100> and <110> are observed. APT analyses in the as-built FCC supersaturated solid solution revealed a chemical short range ordering via the formation of nanometric NiAl-rich clusters. By increasing the L-PBF Volumetric Energy Density, the melt pool morphology can be controlled, thus the <110> fibre texture along the BD can be favoured. A thermal treatment at 620°C leads to the formation of L12 nano-precipitates. At higher temperature, a needle-shaped B2 phase precipitates. These phases contribute to the alloy hardening. The achieved tensile properties surpass those obtained with the same alloy produced by other processes. The range of tensile properties are the following: YS ≈ 625-780 MPa, UTS ≈ 725-1100 MPa and Elongation ≈ 22-46%. [1] F.Peyrouzet et al., JOM, 71 (10) (2019) 3443-3451

Speaker

Thierry Baffie

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CEA-LITEN, Univ.Grenoble Alpes, Grenoble, France

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Conference

15 - Microstructure and mechanical properties of as-built and heat-treated Laser Powder Bed Fusion Al0.3CoCrFeNi High Entropy Alloy

Date/Time

21/03/2024

4:05 pm -4:25 pm

Location

Room 7