Study on microstructure of several Nb-Ti-Cr-Al as-cast alloys

Due to low-density, higher elevated temperature strength and good oxidation resistance; the Nb-Ti-Cr-Al alloy was estimated to become a new kind of material used at elevated temperature of next generation. Therefore, it was widely studied by western developed country, but there are still many questions unsolved in this area. In this article, several kinds of Nb-Ti-Cr-Al alloys of different compositions were prepared by arc melting, and analyzed by metallographic method, XRD, SEM and EDS. The results indicated, in Nb-40Ti-15Al alloy, the solidified Structure was typical small equiaxed grains, columnar crystals and common equiaxed crystals. And in Nb-40Ti-10Cr alloy, there is a serious coring segregation of Cr element; it can induce intergranular fracture of ingot. As the content of Cr element increased, constitutional supercooling occurred in solidification process, and the microstruture changed from straight crystal boundary to dendrite, such as Nb-40Ti-20Cr alloy. As for Nb-40Ti-10Cr-10Al alloy, the addition of Al and Cr lead to a great number of sub boundary and precipitated phase, and the microsegregation in alloy are also reduced to a certain degree. To sum up, the content level of Cr and Al is essential to both the microstructure and mechanical performances of Nb-Ti based alloys.