| Investment casting is an important process of manufacturing TiAl alloy component. In this paper, the effects of B and Y on the microstructure and mechanical properties of cast TiAl alloys have been investigated; the effects of heat treatment on the microstructure and mechanical properties of TiAl alloys which contain B and Y have been investigated; unique ceramic mould surface material for investment casting of TiAl alloys, numerical simulation and practical casting experiment have also been studied.Y intrinsic oxidation can reduce content of O atom in TiAl alloy. Content of Oxygen dropped to 460 ppm in Ti-45Al-5Nb-0.08 Y alloy from 740 ppm in Ti-45Al-5Nb alloy. The interlamellar spacing of α2/γ lamellar could be refined from 580 nm to 200 nm by the addition of trace Y in Ti-45Al-5Nb alloy. But the addition of trace Y has no influence on the size of grain size. The Y-rich phases are Y2O3, YAl O3, and Al Y in Ti-45Al-5Nb alloy. The phases adopt the orientation relationship: 1213]YAl O3//[101]Y2O3. Y can improve mechanical properties of as-cast Ti-45Al-5Nb alloy at room temperature.The microstructure of Ti-45Al-5Nb alloy could be refine by adding B and the effective addition levels are intended higher than 0.4at.%. The ribbons consist of an intimate nanoscale mixture of boride flakes and metallic laths in Ti-45Al-5Nb alloy, and the phases adopt the orientation relationship: [001]Bf//[001]D7b//[001]B2. Constitutional undercooling mechanism was established for the explaining of grain refinement. The as-cast Ti-45Al-5Nb-0.4B alloy show best mechanical properties at room temperature.In Ti-45Al-5Nb-0.4B-x Y(x=0.02, 0.04, 0.06, 0.08, at.%) alloys, the ribbons consist of Bf and YBO3, and the phases adopt the orientation relationship: [001]Bf//[010]YBO3. The growth mechanism of Bf and YBO3 is perpendicular to each other and had a consistent growth direction. Y2O3 has been consumed by the growth of YBO3 ribbon. The residual Y-rich phases are Al Y and Al2 Y. The as-cast Ti-45Al-5Nb-0.4B-0.06 Y alloy show best mechanical properties at room temperature.TiAl alloys which contain B and Y have been full lamellar heat treated. Ti-45Al-5Nb-0.4B-0.06 Y alloy show best mechanical properties at room temperature, whose tensile strength and elongation were improved to 709 MPa and 0.63% at room temperature. TiAl alloys contain B and Y have been duplex heat treated. Ti-45Al-5Nb-0.4B-0.06 Y alloy show best mechanical properties at room temperature, whose tensile strength and elongation were improved to 706 MPa and 0.67% at room temperature.Crystallization mechanism of binders were studied, the calcination temperature of ACZ, AMT, and Y-sol should be 950°C, Al-sol should be 1100°C. The interfacial reaction between TiAl alloys and moulds were investigated respectively. The microstructure and phase composition of interfacial layers were studied. Considering the extent of the reaction interface, the compactness of adhering sand, invasion depth of TiAl alloy, whether the refractory particles mixed in TiAl alloy, thickness of interfacial reaction, thickness of adhering sand, hardness of the casting surface, thickness of hardened layer and other factors, Al-Sol + Al2O3 was the best face coat in all twelve kinds of moulds, and thickness of interfacial reaction is just 2 μm, and sand adhesion free.Finite element simulation software Pro CAST was used to analyze the casting process and optimize the process parameters for test casting. The test casting was produced by VIM with optimized process parameters. TiAl alloy testing casting show homogeneous microstructure, from the inner circle to the outer edge. Shrinkage porosity are dispersed in the disk which are in good agreement with the simulation results. Based on the result of testing casting, an optimized design was developed for the manufacturing of TiAl grating casting(Φ580×10 mm) with sharp edges, good internal and high quality. |
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