Surface-energy-induced selective growth of (001) grains in magnetostrictive ternary Fe-Ga-based alloys

• Published in: Smart materials and structures 2012-05, Vol.21 (5), p.55024-1-10
• Main Authors: Na, S M, Flatau, A B
• Format: Article
• Language: English
• Subjects: Alloys; Annealing; Atmospheres; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Grains; Magnetic properties and materials; Magnetomechanical and magnetoelectric effects, magnetostriction; Magnetostriction; Materials science; Other heat and thermomechanical treatments; Physics; Segregations; Sulfur; Texture; Treatment of materials and its effects on microstructure and properties
• ISSN: 0964-1726; 1361-665X
• DOI: 10.1088/0964-1726/21/5/055024

Surface-energy-induced selective grain growth has been used to increase the presence of preferred planes in polycrystalline ternary Fe-Ga based alloys and thereby maximize the magnetostrictive performance of these alloys. In this study, alloys were either doped with elemental sulfur or annealed under sulfur atmospheres to control the sulfur concentration on the surface of samples during annealing. We show that the segregation of sulfur, which is known to play an important role in controlling surface energy, can be correlated to the selective growth of {001} grains and an increase in the saturation magnetostriction of the samples. The results show that sulfur atoms are adsorbed (diffused) from the sulfur atmosphere (bulk interior) and segregate on the sample surface. The correlation between surface chemistry, texture development and magnetostriction is presented. The formation of {001} grains occurred under slight surface segregation of sulfur, i.e. at levels of concentration of surface sulfur between 0.5 and 1.35 at.%, for alloys of (Fe0.813Ga0.187)99B1 and (Fe0.813Ga0.187)99.5B0.5 doped with 50 ppm S. In the case of (Fe0.81Ga0.19)99(NbC)1 alloy annealed under a H2S atmosphere, abnormal growth of (001) grains resulted in 88.3% of the sample area being covered with a (001) grain.