Łyszkowski Radosław, Polkowski Wojciech, Czujko Tomasz
Faculty of Advanced Technology and Chemistry, Military University of Technology, 2 Urbanowicza, 00-908 Warsaw, Poland.
Foundry Research Institute, 73 Zakopiańska, 30-418 Cracow, Poland.
Materials (Basel). 2018 Nov 8;11(11):2214. doi: 10.3390/ma11112214.
A new concept of the cross-channel extrusion (CCE) process under back pressure (BP) was proposed and tested experimentally. The obtained by finite element method (FEM) results showed that a triaxial compression occurred in the central zone, whereas the material was deformed by shearing in the outer zone. This led to the presence of a relatively uniformly deformed outer zone at 1 per pass and a strong deformation of the paraxial zone (3⁻5/pass). An increase in the BP did not substantially affect the accumulated strain but made it more uniform. The FEM results were verified using the physical modeling technique (PMT) by the extrusion of clay billet. The formation of the plane of the strongly flattened, and elongated grains were observed in the extrusion directions. With the increase in the number of passes, the shape of the resulting patterns expanded, indicating an increase in the deformation homogeneity. Finally, these investigations were verified experimentally for Fe-22Al-5Cr (at. %) alloy using of the purposely designed tooling. The effect of the CCE process is the fragmentation of the original material structure by dividing the primary grains. The complexity of the stress state leads to the rapid growth of microshear bands (MSB), grain defragmentation and the nucleation of new dynamically recrystallized grains about 200⁻400 nm size.
提出了一种背压（BP）下的跨通道挤压（CCE）工艺新概念，并进行了实验测试。有限元法（FEM）得到的结果表明，中心区域发生了三轴压缩，而外层区域的材料则通过剪切变形。这导致每道次外层区域存在相对均匀变形，而近轴区域则发生强烈变形（3⁻5道次）。背压的增加对累积应变没有实质性影响，但使应变更加均匀。通过挤压粘土坯料，利用物理模拟技术（PMT）验证了有限元法的结果。在挤压方向上观察到强烈扁平化和拉长晶粒平面的形成。随着道次数量的增加，所得图案的形状扩大，表明变形均匀性增加。最后，使用专门设计的工装对Fe-22Al-5Cr（原子百分比）合金进行了实验验证。CCE工艺的效果是通过分割原始晶粒使原始材料结构破碎。应力状态的复杂性导致微剪切带（MSB）迅速增长、晶粒破碎以及尺寸约为200⁻400 nm的新动态再结晶晶粒形核。
