【摘要】 利用OM和TEM研究了脉冲电流作用下Ti-48Al-2Cr-2Nb合金的凝固组织,并分析了其微观组织演变及形成机理。结果表明,脉冲电流细化了TiAl合金的一次枝晶臂间距、柱状晶尺寸和片层间距。未加载电流的TiAl合金凝固的初生相为α相,TiAl合金的片层取向与柱状晶生长方向夹角较大,甚至垂直于生长方向。脉冲电流作用导致枝晶发生熔断和破碎,促进了β枝晶相的析出及增多,片层取向与晶体生长方向夹角较小或成45°生长的片层进一步增多。脉冲电流降低了固-液相之间的自由能及原子扩散激活能,减少形核位垒及晶核的形核功,从而在一定程度上促进原子扩散,增大了形核率,细化一次枝晶臂间距及柱状晶;初生相的转变析出及其特殊的位向关系是片层取向变化的主要原因。更多还原

【Abstract】 As a new type of lightweight and high temperature structural material, Ti Al 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-2 Nb 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-2 Nb 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.更多还原