Formation of chainlike structures in an Mn-89.7 wt%Sb alloy during isothermal annealing process in the semisolid state i
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This study is concerned with the investigation of the structural evolution occurring during isothermal annealing of an Mn-89.7 wt%Sb alloy in a high magnetic field in the semisolid state. The alloy specimens were isothermally annealed without and with an 11.5-T magnetic field for various annealing times. With the application of the magnetic field, the average characteristic radius of the primary MnSb particles increased with increasing annealing time. The primary MnSb particles were oriented with their c-plane parallel to the imposed field direction. Furthermore, the primary MnSb particles were found to align along the field direction and form chainlike structures eventually. These phenomena were attributed to the attraction and coalescence of the particles induced by the dipole–dipole interactions among them. I. INTRODUCTION
The control of the microstructure is essential in the development of high-performance materials, because the microstructure is known to be strongly relative to the properties of materials.1 In recent years, the effects of high magnetic fields on the crystallographic orientation of crystals and macrostructural alignment of phases in materials have been the object of great attention because the oriented or aligned structures are potential to enhance and tailor the physical and mechanical properties of these materials.2,3 Depending on their lattice structure, crystalline materials with noncubic structure are more or less anisotropic in their magnetic properties. The anisotropy energy originating from the magnetic anisotropy may induce the orientation of crystals in a magnetic field. Generally, ferromagnetic materials have high anisotropic magnetic properties, providing highly possibilities of orientation of these materials by magnetic fields. Some crystal-oriented ferromagnetic materials have been successfully prepared using magnetic orientation even in high viscosity resins at low temperature, which is below their Curie temperatures.4,5 Recently, this approach has been extended to nonmagnetic materials, such as paramagnetic materials, whose magnetic properties exhibit significant decreases in comparison with those of the ferromagnetic ones. Farrel et al.6 showed that the anisotropy energy associated with the paramagnetic state of superconducting YBa2Cu3O7-d was strong enough at room temperature to induce the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0262 J. Mater. Res., Vol. 24, No. 7, Jul 2009
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alignment of small crystals in a 9.4-T magnetic field. Based on their study, some other researchers7–9 also obtained crystallographically oriented structures in various superconducting compounds using magnetic fields with a large range of intensities. Furthermore, using the slip casting method in a high magnetic field followed by a sintering step, some crystal-oriented ceramics were fabricated at room temperature by initially dispersing the small particles in low viscosity slurries.10,11 With
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