Research On The Microstructure And Property Of Directionally Solidified Mn-Sb Composites

Mn-Sb alloy is an important magnetic material, which has so many characters such as magneto-optical effect, magnetocaloric effect, magnetostrictive effect etc. Materials containing Mn and Sb elements have wide prospects in piezoelectric ceramic, magnetic refrigeration and magneto-optical recording areas. In this paper, the directionally solidified Mn-Sb in situ composites are investigated with liquid metal cooling directional solidification technology by adopting proper alloy compositions(eutectic, hypoeutectic, hypereutectic). Microstructure of directionally solidified Mn-Sb in situ composites with different compositions and their magnetic properties are investigated by the help of metallograph, scanning electron micrograph, X-ray diffraction and other analysis test methods.Microstructure of the directionally solidified eutectic Mn-Sb in situ composite with different growth velocities is investigated. Rodlike eutectic is obtained when the growth velocity is in the range of 3μm/s to 9μm/s, the interrod spacing and the diameter of MnSb phase decrease. Rodlike eutectic changes into cellular eutectic at the growth velocity of 20μm/s and 25μm/s, the cellular microstructure is refined as the growth velocity increases. The orientation of MnSb is approached by means of X-ray diffraction, which reveals that MnSb phases are oriented gradually with their c axes parallel to the growth direction, when the growth velocity is in the range of 3μm/s to 20μm/s.The c axis of MnSb deviates from the growth direction at the growth velocity of 25μm/s. The directionally solidified eutectic Mn-Sb alloy has magnetic anisotropy. The saturation magnetization has little change as the growth velocity increases. The magnetizing velocity in the direction perpendicular to the directional solidification and the magnetic anisotropy increase with the increase of the growth velocity first and then reduce.For the component of hypoeutectic alloy, the primary MnSb of the directionally solidified alloy grew in dendrite. With the increasing of growth velocity, the primary dendritic spacing of the primary MnSb is refined, the secondary and tertiary dendritic arm spacings are restrained. The dendrites grow gradually along the directional solidification. The hypoeutectic Mn-Sb alloy has magnetic anisotropy. With the increasing of the growth velocity, the saturation magnetization decreases slightly. The magnetizing velocity in the direction perpendicular to the directional solidification has little change. There is no obvious variation of the magnetic anisotrophy.Based on the research of hypereutectic Mn-Sb alloy, the primary Sb appears in dendrite, and shows the behavior of faceted growth. With the increasing of the growth velocity, the primary dendritic spacing is refined, the density of the primary Sb increases. The hypereutectic Mn-Sb alloy has weak magnetic anisotropy. As the growth velocity increases, the saturation magnetization shows little change. In the direction perpendicular to the directional solidification, there is no obvious variation of the magnetizing velocity when the growth velocity ranging from 3μm/s to 20μm/s, however, the magnetizing velocity reduces as the growth velocity increases to 25μm/s. The magnetic anisotrophy has little change.The experimental results indicate that Mn-Sb composites with directionally solidified microstructure can be obtained by controlling the solidification parameters when using the directional solidification method.