铸态Ti-47Al(W,Si)合金组织演化及力学性能研究

Microstructure Evolution and Mechanical Properties of As-cast Ti-47Al(W,Si)Alloys

采用ISM熔炼制备了Ti-47Al和Ti-47Al-1.0W-0.5Si两种合金铸锭,分析了合金铸锭的宏微观组织演化规律。结果表明,铸锭组织为铸型壁与铸型底部双激冷柱状晶组织,柱状晶的生长方向为其择优取向<0001>晶向,其片层取向均与柱状晶的生长方向垂直。少量Si元素的加入在合金中形成了共晶Ti_5Si_3相,W元素起固溶强化作用,但W元素的加入以及铸型较快的冷却速率使室温组织中有少量的B_2相,并且合金元素的加入细化了Ti-47Al合金的片层组织。室温压缩试验表明,W、Si元素的加入显著提高了合金的综合力学性能,Ti-47Al(W,Si)合金压缩应变时,当应力方向与片层界面平行时具有较大的压缩屈服强度,合金断裂时裂纹以沿着α_2/γ片层界面的方式断裂。压应力方向与片层界面垂直时,具有较大的抗压强度和压缩应变量,断裂方式以裂纹穿过α_2/γ片层界面扩展断裂。

Intermetallic Ti-47Al（in atomic fraction）and Ti-47Al-1W-0.5Si（in atomic fraction）alloys were produced by ISM method.Macro-and microstructure evolution was investigated by optical microscopy（OM）and scanning electron microscopy（SEM）.The macrostructure of ingot is composed of two different direction columnar grains due to the chilling of side wall and bottom in steel mould.The growth direction of the columnar grains is the preferred direction〈0001〉.The all lamellar orientation in columnar grains is perpendicular to the growth direction for the determined relationship of the solidstate phase transformation.A small amount of Si element added in the alloy can generate eutectic Ti5Si3 particle phase,and a little of B2 phase can be observed in Ti-47Al-1W-0.5Si alloy because of the addition of W as solid strengthening effects and the faster cooling rate.The addition of W and Si can refine the lamellar structure and improve mechanical properties of the Ti-47 Al alloy.The alloys have the high yield stress when the compression stress is parallel to the lamellar interface,and alloy crack is propagated alongα2/γlamellar interface,while alloys have the higher compression stress and strain when the stress is perpendicular to the lamellar interface,and fracture mode is characterized by crack crossingα2/γlamellar interface.