Effect Of B And La And Ce On Structure And Mechanical Properties Of Ti44Al6Nb Alloys

In this study, different Ti44Al6Nb based alloys botton ingots were prepared byadding different elements, such as B, La and Ce , with a non consumable vacuum arcsmelting furnace. The structure and mechanical properties of these ingots were studied.The rules of effect of B, La and Ce on the structure and mechanical properties of theseingots were concluded, the mechanism of these were revealed. An optimumcomposition of TiAlNb alloys with excellent structure and mechanical properties wasobtained finially.The surface quality of the B added TiAlNb alloys is the best, that of the Ce addedTiAlNb alloys is the better. However, the element of La decreases the surface quality,the more content of La, the worse of the surface quality.The results show that the Ti44Al6Nb ingot is composed of fine equiaxed grains andfully lamellar colonies. The grains of Ti44Al6Nb alloys are refined by adding B element,and the grain size decreases from 1143 m to 88 m with increasing the content of Bfrom 0.1% (at.%) to 1.2% (at.%) , the grains are equiaxed at the same time. The grainsare refind by adding B element throught heterogeneous nucleation. The microstructureof Ti44Al6Nb alloys with addition of La is composed of fine equiaxed grains too, thegrains are the smallest when the content of La is 0.9% (at.%), that means the refiningeffect is the best at this composition for La added Ti44Al6Nb. The grains of Ti44Al6Nballoys are refined when Ce element is added, and the grain size decreases from142 m to648 m with increasing the content of Ce from 0.05% (at.%) to 2.0% (at.%). Theelements of La and Ce in the alloys depress the growing of the grains by increasingnucleation through forming constitutional supercooling. The grains of Ti44Al6Nb alloysare refined when both La and B are added, the more content of La and B, the finer of thegrains. The grains Ti44Al6Nb alloys will be refined when the content of La and Ce areless than 0.9% and 0.15% respectively, whereas the grains coarse when the compositionis Ti44Al6Nb1.2La0.2Ce. Among the three elements, the refining effect of B element isthe best.The compressive properties of these TiAlNb ingots were tested, the results showthat the additon of B or La can improve the ultimate compressive strength(UCS) and thecompressibility, especially for B added alloys, the UCS can reach 2030.50 MP, the compressibility is 30%. However, the element of Ce has little effect on the compressiveproperties. Scanning electron microscopy observation indicated that the fracture modeof B or La added TiAlNb alloys is mainly transgranular fracture, that of Ce addedTiAlNb alloys is mainly cleavage fracture.