TY - JOUR

T1 - Novel Fe-Mo intermetallic composite synthesized via diffusional-displacive mixed-mode transformation

AU - Varanasi, Rama Sirnivas

AU - Srikakulapu, Kiranbabu

AU - Utsumi, Reina

AU - Saitoh, Hiroyuki

AU - Schnitzer, Ronald

AU - Akiyama, Eiji

AU - Koyama, Motomichi

N1 - Publisher Copyright: © 2024 The Authors

PY - 2024/8/18

Y1 - 2024/8/18

N2 - Transition metal-based intermetallic materials are candidates for high-temperature structural applications. However, they are limited by their low fracture toughness at ambient temperature. Given Fe is a low-cost metal with a low environmental impact, it is necessary to design tough Fe-based intermetallic alloys. We report a novel ferrite-Fe 2Mo intermetallic synthesized through arc melting and quenching of Fe 0.78Mo 0.22 alloy. Diffusional-displacive mixed-mode transformation of the parent ferrite phase resulted in the formation of nanocomposite microstructure. Two distinct microstructure morphologies of the product μ phase were observed: (i) allotriomorphic phase formation at the parent ferrite grain boundaries and (ii) formation of basket-weave Widmanstätten structures at the parent grain interior. Electron probe microanalysis (EPMA) revealed Mo partitioning across ∼800 nm wide Widmanstätten laths, establishing that it is a diffusional-displacive mixed-mode transformation. We performed atom probe tomography (APT) investigations to ascertain the nanoscale Mo solute partitioning. Based on the chemistry of the retained parent ferrite, the Mo partitioning temperature was estimated to be ∼865 °C. Mo partitioned Widmanstätten lath formation is clarified using a shear-assisted diffusional transformation model. APT studies further revealed that the composition of the product μ phase corresponds to stoichiometric Fe 2Mo. It is an anomaly since stoichiometric Fe 2Mo typically corresponds to λ C14 Laves phase. We explain the mechanism of μ phase formation with Fe 2Mo stoichiometry. The nanocomposite exhibits a high hardness (HV 2) of 7.54 GPa and excellent toughness (evidenced by resistance to indentation cracking).

AB - Transition metal-based intermetallic materials are candidates for high-temperature structural applications. However, they are limited by their low fracture toughness at ambient temperature. Given Fe is a low-cost metal with a low environmental impact, it is necessary to design tough Fe-based intermetallic alloys. We report a novel ferrite-Fe 2Mo intermetallic synthesized through arc melting and quenching of Fe 0.78Mo 0.22 alloy. Diffusional-displacive mixed-mode transformation of the parent ferrite phase resulted in the formation of nanocomposite microstructure. Two distinct microstructure morphologies of the product μ phase were observed: (i) allotriomorphic phase formation at the parent ferrite grain boundaries and (ii) formation of basket-weave Widmanstätten structures at the parent grain interior. Electron probe microanalysis (EPMA) revealed Mo partitioning across ∼800 nm wide Widmanstätten laths, establishing that it is a diffusional-displacive mixed-mode transformation. We performed atom probe tomography (APT) investigations to ascertain the nanoscale Mo solute partitioning. Based on the chemistry of the retained parent ferrite, the Mo partitioning temperature was estimated to be ∼865 °C. Mo partitioned Widmanstätten lath formation is clarified using a shear-assisted diffusional transformation model. APT studies further revealed that the composition of the product μ phase corresponds to stoichiometric Fe 2Mo. It is an anomaly since stoichiometric Fe 2Mo typically corresponds to λ C14 Laves phase. We explain the mechanism of μ phase formation with Fe 2Mo stoichiometry. The nanocomposite exhibits a high hardness (HV 2) of 7.54 GPa and excellent toughness (evidenced by resistance to indentation cracking).

KW - Displacive transformation

KW - Fe–Mo alloy

KW - Intermetallic composite

KW - Mixed-mode transformation

KW - Widmanstätten lath

UR - http://www.scopus.com/inward/record.url?scp=85201597082&partnerID=8YFLogxK

U2 - 10.1016/j.matchar.2024.114287

DO - 10.1016/j.matchar.2024.114287

M3 - Article

VL - 216.2024

JO - Materials characterization

JF - Materials characterization

SN - 1044-5803

IS - October

M1 - 114287

ER -