Preparation Of Large Fe₃Al Based Bulk Nanocrystalline Alloys By Aluminothermic Reaction And The Microstructural Formation And Evolution

This paper mainly reviews the structural models,performance,applications and preparation methods of bulk nanocrystalline materials and the progress of intermetallic compounds Fe₃Al. Large bulk nanocrystalline Fe₃Al materials added Cr were prepared by aluminothermic reaction,and the microstructures of different regions were studied. Moreover,formation mechanism of microstructure was proposed. Annealing was adopted to optimize the microstructure of the large bulk nanocrystalline Fe₃Al based materials. Meanwhile,effect of the annealing and content of Cr on the microstructure were studied. Finally,mechanism of microstructural formation was proposed. All the contents can be summarized as follows:1. Prepared Fe₃Al-10%Cr large bulk nanocrystalline material is mainly composed of disordered nanocrystalline of bcc structure,some amorphous and micro-level Cr-rich precipitates,in which the nanocrystalline produced as homogeneous nucleation. A big difference of mean grain size exited in radial direction and height direction,and minmum of mean grain size can be obtained at subcentral position in radial direction. As in height direction,the mean grain size increased from top to bottom.2. The annealings of different temperatures and different times revealed that the annealing had no effection on the crystal structure of the nanocrystalline material. However,it influenced the average grain size and Cr-rich precipitates greatly.The content of Cr-rich precipitates increased and the precipitated phase coarsened after annealing.3. Large bulk nanocrystalline Fe₃Al materials with different Cr content were prepared by aluminothermic reaction. It is found that the disordered nanocrystalline of bcc structure are dominant in the microstructure of large bulk nanocrystalline Fe₃Al materials with different Cr content,as the microstructure was testified as a multiphase structure. And the nanocrystalline produced as homogeneous nucleation as well. The average grain size of Fe₃Al-5%Cr nanocrystalline material reached the maximum (30.46nm). With the increase of Cr content,the average grain size decreased to 27.8 nm, and the content of Cr-rich precipitates increased and the precipitated phase coarsened as well.4. The annealing on Fe₃Al-5%Cr and Fe₃Al-15%Cr unaffected the crystal structure of the large bulk nanocrystalline materials,but it influenced Cr-rich precipitates and the average grain size in different levels. Basically,element distribution in Fe₃Al-5%Cr large bulk nanocrystalline materials was insensitive to the annealing.It was different from the element distribution in the Fe₃Al-15%Cr bulk nanocrystalline, in which Cr precipitated obviously with a large size.