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将直流电流作用于定向凝固过程中的Ti-48Al-2Cr-2Nb合金,利用OM、XRD、SEM和TEM分析了合金的凝固组织、相组成和片层组织,测试了合金的显微硬度及800℃压缩力学性能。结果表明,电流在一定程度上促进了合金凝固组织的细化及成分的均匀性,减少或消除了片层间偏析。随着电流密度的增大,平均晶粒尺寸和片层厚度呈现先减小后增大的趋势,a2相相对含量先增大而后减小,合金的显微硬度、压缩断裂与屈服强度也呈现先增大后减小的趋势。平均晶粒尺寸最小约0.46 mm,片层间距最小为0.19 mm,分别比未加载电流时降低70%和29%,a2相相对含量从18.5%增至39.4%。片层间距或晶粒尺寸越小,合金的强度越高,变形能力越均匀,塑性也越好。合金的最大显微硬度达542 HV,合金的压缩屈服强度与断裂强度分别达到1200和1365 MPa,与未施加电流时相比均有所提高。加载直流电流引起固-液界面相前沿过冷度减小,可认为是TiAl二元相图中的L→b+L→a+b的包晶反应成分向富Al侧微小偏移,此时初生b相增多,从而造成了TiAl合金室温相组织a2相的相对含量增加。
The direct current was applied to the Ti-48Al-2Cr-2Nb alloy during directional solidification. The solidification microstructure, phase composition and lamellar structure of the alloy were analyzed by OM, XRD, SEM and TEM. ℃ Compressive mechanical properties. The results show that the current to some extent, promote the solidification of alloy thinning and composition uniformity, reduce or eliminate the segregation between layers. With the increase of the current density, the average grain size and the thickness of the lamellae first decreased and then increased, the relative content of the a2 phase first increased and then decreased, and the microhardness, compressive fracture and yield strength of the alloy also appeared First increase and then decrease the trend. The average grain size is about 0.46 mm, the minimum spacing is 0.19 mm, which is 70% and 29% lower than that without current and the relative content of a2 increases from 18.5% to 39.4%. Lamellar spacing or grain size is smaller, the higher the strength of the alloy, the more uniform deformation, plastic, the better. The maximum microhardness of the alloy reached 542 HV. The compressive yield strength and breaking strength of the alloy reached 1200 and 1365 MPa, respectively, which were all higher than those without current. When the DC current is applied, the undercooling of the solid-liquid interface phase decreases. It can be considered that the peritectic reaction component of L → b + L → a + b in the TiAl binary phase diagram is slightly shifted to the Al-rich side, The amount of primary b phase increased, resulting in an increase of the relative content of a2 phase in the room temperature TiAl alloy.