An innovative method for the microstructural modification of TiAl alloy solidified via direct electric current application

• 来源期刊: 材料科学技术（英文版）
• 年，卷（期）: 2019,（1）
• 页码范围: 23-28
• 页数: 6页
• 语种: 英文

摘要

Ti-48Al-2Cr-2Nb alloy solidified with the application of direct electric current has a refined and homogeneous microstructure without segregation.We observed an initial decrease followed by a subsequent increase in grain size and lamellar spacing,with the increase in current density.Similar trend can also be obtained by varying the amount ofα2-phase (Ti3Al).Using a directional solidification processing method,the columnar crystal microstructure transforms into an equiaxed crystal microstructure at a current density of 32-64 mA/mm2.High dislocation density is also introduced with a minimum cross-sectional grain size of 460 μm at a current density of 64 mA/mm2.The application of electric current alters the free energy of the critical nucleus and temperature via joule heating,causing a transformation from a columnar grain microstructure into an equiaxed grain microstructure.The increase in current density leads to a rise of the nucleation rate,and a resulting undercooling combined with temperature gradient contribute to growth of the primary phase,which finally results in grain coarsening at a critical current density of 96 mA/mm2.The climb and cross-slip of dislocation and the migration of grain boundary ultimately create variable lamellae spacing of TiAl alloy.