摘要
为改善Ni_3Al合金的室温塑性,研究了不同电流强度的直流电场对冷坩埚定向凝固Ni_3Al合金微观组织的影响。结果表明,在直流电场作用下,随着电流强度的增加,Ni_3Al合金的定向凝固组织的一次枝晶间距变小,凝固界面变得平直。未施加直流电流时,凝固组织由L12型结构的Ni_3Al基体和B2型结构的Ni Al析出相两相组成。当定向凝固过程中施加直流电流时,凝固组织中析出相由B2型NiAl相转变为呈薄层状、晶面对称的孪晶马氏体NiAl相。
Due to their excellent high-temperature strength, and good oxidation resistance, Ni3Al- based alloys have long attracted considerable interest as a class of high-temperature structural material. These properties, combined with their unique high thermal conductivity, make them ideal for special appli- cations, such as blades in gas turbines and jet engines. However, polycrystalline Ni3Al alloys show almost no ductility and extremely low fracture resistance at ambient temperatures. Ni3Al alloys with the high duc- Ulity at room-temperature can be adjusted by the microstructure through directional solidification （DS） and matching. It has been shown that the electric field can refine the solidification structure, reduce the den- drite spacing, promote the diffusion and change the solute redistribution in the solidification process. In or- der to improve the room temperature ductility of Ni3AI alloy, the effect of current intensity on microstruc- ture of DS Ni-25Al alloy is investigated. In this work, the effects of constant current intensity and NiAI phase on the microstructura are researched. The results show that in the DC electric field, as the result of the aggregation of current along dendrite tip and the Joule heat at the tip of dendrite, the primary dendrit- ic spacing （Z） decreases with the increasing of current intensity. And the solid-liquid interface tends to be straight resulting from the Joule heat and Peltier effect caused by the segregation of current and the dif- ference in conductivity between solid and liquid interface. When no direct current is applied the DS sam-pies contain the L12 structure of Ni3AI matrix and B2 structure of NiAI precipitate phase. The microstruc- ture is a duplex structure which consist of gray Ni3AI matrix and black NiAI precipitates. NiAI precipitates with regular shape and has obvious orientation along with the growth direction. When the DC current is applied, NiAI precipitates is irregular and dispersion and has no obvious directionality, due to Joule heat effect generated by the current effect, the undercooling increased and the precipitated NiAI phase trans- formed into thin martensite NiAI phase with twin crystal symmetry from the NiAI-B2 type structure.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2017年第11期1461-1468,共8页
Acta Metallurgica Sinica
基金
国家自然科学基金项目No.51471062~~
关键词
NI
Al
金属间化合物
直流电场
定向凝固
微观组织
Ni3Al, intermetallics, DC electric field, directional solidification, microstructure
