Study Of Electromagnetic Cold Crucible Continuous Casting Ti-Al-Nb Alloy

Ti Al-based alloys have a very excellent integrated performance of lower density, high specific stiffness and specific strength, high temperature properties including good high temperature strength, oxidation resistance and creep resistance. Therefore Ti Albased alloys have attracted more and more attention and application in aerospace and other fields. However, when it comes to the room temperature, the low room temperature plastic and fracture toughness limit their applications. Ti Al-based alloys have four kinds of typical microstructure. In particular, the fully lamellar organization with two-phase alloys consisting of Ti Al(γ) and Ti3Al(α2), has a good balance of room temperature plastic and fracture toughness. Due to the higher chemical activity of the titanium, at the same time to control Ti Al-based alloys organization and avoid pollution, our study group makes use of directional solidification technology inventing the electromagnetic cold crucible directional solidification technique equipment. And we conduct the electromagnetic continuous casting experiments and the directional solidification experiments to make the alloy samples with the directional solidification organization.In this topic study, we first use the German ALD water cooled copper crucible vacuum induction melting furnace(ISM) to melt raw material Ti44 Al alloy ingot and Ti48 Al alloy ingot. Then use the electromagnetic cold crucible to take the electromagnetic continuous casting experiments and the directional solidification experiments of Ti Al alloy with high purity Nb wires.In this topic, we control Ti44Al(Nb) the power(temperature gradient) parameter, and controls Ti48Al(Nb) the draw speed(solidification rate) parameter. The results show that the Ti44Al(Nb) has a good directional solidification organization, and with the increase of input power, the morphology is changing from branched- dendritic Cellular- cellular transformation, the lamellar spacing decreasing, the angles between the growth direction with the lamellar direction are also reducing; but for the Ti48Al(Nb), the situation is different, the directional solidification effect is not very good, it has the CET transformation. The reasons are that there are lots of particle nucleation in the front of the S/L interface and enough time to grow because of the high purity Nb wire existing. At the same time through the analysis of the respective regions of the ingot component, we found that the ingot’s homogeneity is better, consistent with the pre-designed components.Meanwhile we measure the comprehensive properties of the experimental samples of the(Ti, Al, Nb) ternary alloy and the cast ingot. We found that the compressive properties and the tensile properties of Ti44Al(Nb) have improved a bit comparing to the cast ingot, which reach 1770 MPa and 455 MPa. But the bending strength, the bending deflection and the fracture toughness have changed a lot obviously, which can reach 994.5MPa, 0.6mm and 23.5MPa·m1/2. But as to the Ti48Al(Nb), the regularity is not obvious due to the bad directional solidification effect. Though the compressive properties and the tensile properties have also improved a bit, the fracture toughness also improve a little. The reasons we have analyzed are that the difference between the compressive properties and the tensile properties of equiaxed grains and columnar grains fully lamellar microstructure is not very obvious. But for the bending strength and the fracture toughness, the columnar grains fully lamellar microstructure have obvious advantages. At high temperatures with the increase of strain rate, the compressive stress also increase, but the temperature increases, the compressive stress decreases. The alloys with the directional microstructures behave better than the cast equiaxed grains in the high temperature compressive stress. By observing and analyzing the fractographs of tensile, bending and fracture, we found that the propagation of cracks is perpendicular to the lamellar and parallel to the lamellar, there exist river shape patterns, which are the typical cleavage fracture characteristics. Though it has changed the properties a lot, the tensile fracture mode also belongs to the totally brittle fracture.