| Ti Al based alloy has low density, relatively large specific strength and specific modulus, excellent oxidation resistance and high temperature performance, then becomes a superior candidate of structural materials used in aerospace and other fields to take the place of Ni based super alloy with high density and Ti alloy whose work temperature is relatively low. However, the low room temperature(RM) plasticity and low fracture toughness of Ti Al based alloy present in its actual application, and more and more attention is paid to searching for new approaches to overcome these problems. Although alloying is a traditional method, it’s relatively simple and useful, is one of important methods of alloy development. Since rare earth elements have unique physical and chemical properties, they can be used to refine the microstructure and purify the alloy melt of Ti Al based alloys, and then improve the RM plasticity and facture toughness, consequently, the alloying of rare earth elements is very meaningful in theory and practice t o the application of Ti Al based alloy.In this paper, by adding Er element to Ti-47Al-(2,6,10)Nb alloys, button ingots with different content of Er were prepared by non-consumable tungsten electrode vacuum arc melting furnace, the effect of Er on the refinement of solidifying microstructure was investigated. The formation heat, activity and activity coefficient of each components of the button ingots were calculated using the Miedema model of the formation heat of alloys, the constituent phases probably exi sting in the alloy were predicted, and in the means of scanning electron microscopy(SEM) and energy dispersive spectrometer(EDS), the microstructure morphology and the distribution of alloy elements and precipitated phases of the button ingots of Ti-47Al-(2,6,10)Nb-x Er(x=0.2, 0.4, 0.8, 1.0) were researched. By the mechanical tests of compression, Vickers hardness and fracture toughness, the influence of Er on the mechanical properties of Ti-47Al-(2,6,10)Nb alloy was analysed.With the increase of Er content, the coarse columnar dendritic grains of Ti-47Al-(2,6,10)Nb change into smaller and more compact, and have the trend of changing into equiaxed grains, in general, the primary dendrite arm spacing of the three alloys with different Nb decreases with the increase of Er content, in the meanwhile, the secondary dendrite microstructure become more developed. With respect to the Ti-47Al-2Nb alloy, when the content of Er is 0.2 at.%, the primary dendrite arm spacing decreases sharply, the effect of refinement is very prominent.Although the content of Er is different,the morphology of the precipitated phases in Ti-47Al-(2,6,10)Nb alloy is similar, all precipitated phases present little rounding particles, rods, strips and irregular polygons, and distribute in g rains or around gains dispersedly. These little rounding particles are mainly Er2O3, the bright granular,strip,bar and so on,combining with spectroscopy and XRD analysis precipitated the phase were Er2O3 and Al3 Er compounds.Compression test results show that Er content has remarkable effect on the compression properties of the alloy, Ti-47Al-2Nb-0.2Er alloy has high compressive strength and large compressive strain; keep the same Nb content, the microhardness of the alloy are along with the increase of the content of Er rises first and fall later;when Er content increased from 0 to 0.8 at.%, the fracture toughness of alloy presents a gradually increasing trend, when Er content from 0.8at.% increase to 1.0 at.%, the fracture toughness of alloy has a sharply drop trend, comparing the compression performance, microhardness as well as the mechanical properties such as fracture toughness, we can draw a conclusion in Ti-47Al-(2~10)Nb-x Er(x=0,0.2,0.4,0.8,1.0) alloy, Ti-47Al-2Nb-0.2Er alloy has better comprehensive mechanical properties.Cr element is added to the Ti-47Al-2Nb-0.2Er composition,and for directional solidification experiments.Relative to the directional solidification of Ti- 47Al-2Nb-2Cr alloy, the mechanical properties of Ti-47Al-2Cr-2Nb-0.2Er alloy was improved, and the fracture toughness reach to 29 MPa·m1/2. |
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