High throughput synthesis of CoCrFeNiTi high entropy alloys via directed energy deposition

Abstract

Blown-powder additive manufacturing process, directed energy deposition (DED) is applicable to scale-up material development with cost-effective elemental powder mixtures. In this paper, the effectiveness of applying DED to the design and synthesis of model CoCrFeNiTi high entropy alloys (HEAs) was demonstrated. Through a careful design of composition and delicate selection of particle size and shape, three CoCrFeNiTi HEAs with different microstructures were in-situ synthesized from premixed elemental powders. Transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction were used for microstructure characterization. H3-Co 24.4 Cr 17.4 Fe 17.5 Ni 24.2 Ti 16.5 in at% (close to Co 1.5 CrFeNi 1.5 Ti) was fabricated with a soft face-centered cubic (FCC)-γ phase structure while hard intermetallic phases such as σ-FeCr, δ-NiTi 2 , and a small amount of Ni 3 Ti 2 were precipitated and uniformed distributed in the FCC matrix for H1-Co 22.2 Cr 16.1 Fe 19 Ni 21.8 Ti 20.9 and H2-Co 25.9 Cr 15 Fe 17 Ni 20.8 Ti 21.3 . With a large percent of the secondary phases, H1 exhibited a hardness value of about 853 HV 0.5 . These HEAs displayed a high oxidation resistance comparable to Inconel 625 superalloy. A detailed evaluation of the composition, microstructure, hardness, oxidation resistance, and wear resistance of these HEAs was conducted as compared with those of a reference HEA and two popular wear-resistant steels. • CoCrFeNiTi high entropy alloys were synthesized via directed energy deposition. • Compositions were controlled by elemental powders with specified size and shape. • A high oxidation resistance comparable to IN625 was obtained. • High fraction of secondary reinforcements led to hardness higher than tool steel.