Yanchao Dai

Correlation between microstructures and mechanical properties in Ni-rich Ni–Mn–Ga high-temperature shape-memory alloys

ABSTRACT Microstructures and mechanical properties of polycrystalline and single-crystalline Ni55+xMn25Ga20−x (x = 1, 2, 3) alloys are investigated. The alloys exhibit a single martensite phase for x = 1, and two phases containing tetragonal martensite phase and face-centered γ phase for x = 2 and 3. The appearance of γ phase can apparently raise the strength and plasticity of the alloys. Moreover, single crystals show better mechanical properties compared with the polycrystals with the same composition. Furthermore, a kind of net-like γ phase is observed in directionally solidified Ni58Mn25Ga17 single crystal. This alloy exhibits excellent plasticity due to that the crack propagation is seriously hindered by the plastic net-like γ phase.

Effect of a transverse magnetic field on primary-Si distribution during directional solidification in hypereutectic Al-Si alloy

The effect of a transverse magnetic field on the distribution of the primary Si in a directionally solidified Al-21 wt.% Si alloy is investigated. The results reveal that the application of the magnetic field leads to the appearance of banded structures of primary Si. Furthermore, the inclination of the banded structure decreases with the increase of magnetic-field intensity. The in situ measurement results of the Seebeck signal confirm the existence of a thermoelectric power difference between the solid phase and the liquid phase at the solid/liquid interface in the directionally solidified Al-21 wt.% Si alloy. Thus, the formation of the banded structures should be attributed to the thermoelectric magnetic convection (TEMC) and the resultant force of the primary Si, i.e., gravity force and thermoelectric magnetic force (TEMF). The migration of the primary Si toward the lower left side of the sample is induced by the resultant force, which leads to the formation of banded structures. Moreover, the increase of magnetic-field intensity increases the resultant force of the primary Si, resulting in a decrease of the inclination of banded structure.

Control of dendrite growth by a magnetic field during directional solidification

In this work, the alignment behavior of three kinds of dendrites (Al3Ni, alpha-Al and Al2Cu dendrites) with a remarkable crystalline anisotropy during directional solidification under an axial magnetic field is studied by the EBSD technology. Experimental results reveal that the magnetic field is capable of tailoring the dendrite alignment during directional solidification. Further, based on the crystalline anisotropy, a method to control the dendrite alignment by adjusting the angle between the magnetic field and the solidification direction is proposed. Copyright (C) EPLA, 2016