Search

The microstructure, orientation and magnetostrictive properties of a Fe81Ga19 polycrystal grown by Bridgman method were investigated. A big central single crystal surrounded by some small crystals was observed. Laue X-ray back-reflection confirmed the <001> orientation of the central crystal and deviation from the <001> direction for the edge crystals. Subgrain boundaries were monitored in the crystal. It was confirmed that orientations of all the subgrains were very close to the <001> direction. Measurement of the magnetostriction in different crystals indicated the strong anisotropy of the magnetostrictive properties. This work opens the possibility of preparing large-sized single crystal of FeGa alloys by using the Bridgman method. [ABSTRACT FROM AUTHOR]

<100>-, <112>- and <149>-oriented single crystals of Fe75.5Ga24.5 alloy were prepared by optical float zone melting method. The pseudoelasticity behavior and elastocaloric effect of the single crystals were investigated, as well as the associate microstructures. D03 phase structure was realized by solution treatment at 800 °C and annealed at 600 °C for 10 h. The compressive deformation behavior exhibits significant dependence on the crystalline directions. Excellent pseudoelasticity with recoverable strain up to 5% is obtained by compression along <149> direction. The pseudoelasticity disappears after five deformation cycles. Adiabatic temperature change is simultaneously detected during the pseudoelasticity, especially during loading process. [ABSTRACT FROM AUTHOR]

Ni50.5Mn25Ga24.5 alloy with cellular microstructure was fabricated. The effect of the cellular microstructure on the internal friction (IF) behavior associated with martensitic transformation (MT), premartensitic transformation (PMT) and twin boundary motion (TBM) was investigated. Compared with conventional Ni–Mn–Ga alloys, the temperature span of the IFMT peak is significantly expanded, the IFPMT is weakened, and no IFTBM is detected. Both IFMT and IFPMT in the cellular microstructure exhibit unique frequency dispersion feature which has never been observed in conventional Ni–Mn–Ga alloys. The effect of point defects associated with the cellular microstructure is considered to understand the observed results. [ABSTRACT FROM AUTHOR]

Studies on Co-doped Ni–Mn–Ga ferromagnetic shape memory alloys (FSMAs) have been quite active topics in recent years. Unlike previous reports where the amount of Co doping was generally less than 8 at%, in this work Ni55−xCoxMn20Ga25 (8.5 ≤ x ≤ 11.0) alloys were studied with high Co doping. Unusual effects of both composition and magnetic field on phase transitions were observed. With the increase in substitution of Co for Ni, the magnetic transition temperatures increase gradually but the martensitic transformation temperature decreases quite sharply. In particular, the average decrease in the martensitic transformation temperatures is up to 100 K which is nearly twice that in the case of Co content of less than 8 at%. Further, under an applied magnetic field ranging from 0.03 to 0.60 T, abnormal stabilization of a martensite phase with lower magnetization was monitored. Magnetic entropy change of 1.6 J·kg−1·K−1 was induced at the martensitic transformation of Ni46.5Co8.5Mn20Ga25 alloy by an applied field of 1 T. The magnetic contributions, including the magnetocrystalline anisotropy and the Zeeman energy, to the thermodynamics of the martensitic transformation are considered to understand the observed unusual phenomena. This work results in new insights into the understanding of Co-doped Ni–Mn-based ferromagnetic shape memory alloys. [ABSTRACT FROM AUTHOR]