Microstructural Evolution and Mechanism of Solidified TiAl Alloy Applied Electric Current Pulse
Zhanxing CHEN,Hongsheng DING(),Ruirun CHEN,Jingjie GUO,Hengzhi FU
1. National Key Laboratory for Precision Hot Processing of Metals, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
Cite this article:
Zhanxing CHEN,Hongsheng DING,Ruirun CHEN,Jingjie GUO,Hengzhi FU. Microstructural Evolution and Mechanism of Solidified TiAl Alloy Applied Electric Current Pulse. Acta Metall Sin, 2019, 55(5): 611-618.
As a new type of lightweight and high temperature structural material, TiAl alloy has become the most ideal candidate in the fields of aerospace, military and civil products, and it has a good perspective in the industrialization. Refining and improving the microstructure of TiAl alloys has higher theoretical significance and engineering value. In this work, the solidified Ti-48Al-2Cr-2Nb alloy applied electric current pulse is studied, and its microstructural evolution and mechanism are analyzed. The results show that the electric current pulse refines the primary dendrite arm spacing, columnar crystal size and interlamellar spacing of the Ti-48Al-2Cr-2Nb alloy. The primary phase is α without electric current pulse, the angle of the Ti-48Al-2Cr-2Nb alloy that between the lamellar orientation and the growth direction is usually bigger, even perpendicular to the growth direction approximately. The applied electric current pulse causes the dendrite to melt and break, and promotes the occurrence and increase of the primary β phase, the lamellae orientation having a small angle or 45° between the growth direction is further increasing. The electric current pulse reduces the solid-liquid phase free energy and atomic diffusion activation energy, reduces the nucleation barrier and the critical nucleation energy, thereby atomic diffusion and the crystallization nucleation is promoted to a certain extent, the primary dendritic spacing and columnar crystals are remarkably refined. The electric current pulse causes the transformation of the primary phase and its corresponding crystal orientation relationship is the main reason for the change of lamellar orientation.
Fund: National Natural Science Foundation of China(51171053);National Natural Science Foundation of China(51471062);National Natural Science Foundation of China(51671072)
Table 1 Parameters of electric current pulse acting on Ti-48Al-2Cr-2Nb alloy
Fig.1 Dendritic morphologies of Ti-48Al-2Cr-2Nb alloy with electric current pulse(a) no current (b) 32 mA/mm2, 100 Hz (c) 64 mA/mm2, 100 Hz(d) 96 mA/mm2, 100 Hz (e) 64 mA/mm2, 50 Hz (f) 64 mA/mm2, 200 Hz
Fig.2 Primary dendritic arm spacing (PDAS) of Ti-48Al-2Cr-2Nb alloy affected by current density (frequency is 100 Hz) (a) and frequency (current density is 64 mA/mm2) (b)
Fig.3 Microstructures of solidified Ti-48Al-2Cr-2Nb alloy with electric current pulse(a) no current (b) 32 mA/mm2, 100 Hz (c) 64 mA/mm2, 100 Hz(d) 96 mA/mm2, 100 Hz (e) 64 mA/mm2, 50 Hz (f) 64 mA/mm2, 200 Hz
Fig.4 Normal frequency distributions of lamellar orientation for solidified Ti-48Al-2Cr-2Nb alloy with different parameters of electric current pulse
Fig.5 Lamellar structures of Ti-48Al-2Cr-2Nb alloy solidified with electric current pulse(a) no current (b) 32 mA/mm2, 100 Hz (c) 64 mA/mm2, 100 Hz(d) 96 mA/mm2, 100 Hz (e) 64 mA/mm2, 50 Hz (f) 64 mA/mm2, 200 Hz
Fig.6 Interlamellar spacing of solidified Ti-48Al-2Cr-2Nb alloy affected by current density (frequency is 100 Hz) (a) and frequency (current density is 64 mA/mm2) (b)
Fig.7 Schematics of the relationship between the lamellar orientation and the growth direction of different primary phasesColor online(a) crystal orientation and lamellar orientation of α phase (b) crystal orientation and lamellar orientation of β phase
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