直流電流對Ti-48Al-2Cr-2Nb合金組織和性能的影響直流電流對Ti-48Al-2Cr-2Nb合金組織和性能的影響Effects of direct current on the microstructure and properties of Ti-48Al-2Cr-2Nb 將直流電流作用于定向凝固過程中的Ti-48Al-2Cr-2Nb合金。并分析了合金的凝固組織、相組成和片層組織，測試了合金的顯微硬度及800℃壓縮力學性能。結果表明，電流在一定程度上促進了合金凝固組織的細化及成分的均勻性，減少或消除了片層間偏析。隨著電流密度的增大，平均晶粒尺寸和片層厚度呈現先減小后增大的趨勢，α2相相對含量先增大而后減小，合金的顯微硬度、壓縮斷裂與屈服強度也呈現先增大后減小的趨勢。平均晶粒尺寸最小約0.46 mm，片層間距最小為0.19 μm，分別比未加載電流時降低70%和29%，α2相相對含量從18.5%增至39.4%。片層間距或晶粒尺寸越小，合金的強度越高并且變形能力愈均勻，塑性也越好。合金的最大顯微硬度值達到542 HV，合金的壓縮屈服強度與斷裂強度分別達到1200 和1365 MPa，與未施加電流時相比均有所提高。加載直流電流引起固-液界面相前沿過冷度減小，可認為是TiAl二元相圖中的L→β+L→α+β的包晶反應成分向富Al側微小偏移，此時初生β相增多，從而造成了TiAl合金室溫相組織α2相的相對含量增加。 TiAl based alloys have been widely used as promising aerospace structural materials, which benefits their unique combination of mechanical properties.However, they yield poor plasticity and low process ability，furthermore restrict their widely applications.This paper proposes an efficient way by which direct electric current was imposed on the solidification process of TiAl-based alloy. Influences of direct current on the microstructure and properties of directionally solidified Ti-48Al-2Cr-2Nb using water cold crucible directional solidification equipment has been investigated. The changes of solidification microstructure, phase structure and composition of the alloy and γ/α2 interlamellar structures were characterized by OM, XRD, SEM as well as TEM. The effect of direct current on the size of eutectoid colony, interlamellar spacing and relative content of α2 phase had been studied by Image Pro Plus. Furthermore, the mechanical properties such as the microhardness and hot compressive property at 800℃ of the directionally solidified Ti-48Al-2Cr-2Nb were performed. The results reveal that the direct current can evidently promote the homogeneity of the solidification component and refiner the structure, as well as the segregation in lamellar colonies can be efficiently reduced or eliminated to a certain extent. With increasing of the current density, the grain size and the lamellar spacing decreased first and then increased, however, the α2 phase content showed a totally different trend. Moreover, the microhardness, compression yield strength and the fracture strength of the alloy also revealed a trend of decrease after the first increase too. With DC current increasing, the average grain size and interlamellar spacing decline to the lowest of 0.46 mm and 0.19 μm, respectively, and the content of α2-phase increased from 18.5% to 39.4%. The microhardness of sample reaches 542HV, the compression yield strength and the fracture strength are remarkably improved, and the maximum values reach 1200MPa and 1365MPa, respectively. In sum, the DC current can cause a reduction of the supercooling in front of the liquid phase during the solidification process. The results can be seen as the peritectic reaction L→β+L→α+β moving a tiny drift to the direction of the Al-rich side in TiAl binary phase diagram, consequently, the primary β-phase has been increased, the α2 phase content microstructure under room temperature increases, evidently.
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