Shellmould Fabrication For The Investment Casting Of Titanium Aluminides

Titanium aluminides alloys are emerging as potential light-weight, high-temperature structural materials and possess wide capacities of engineeringapplications in aeronautics, space and automobile industries because of their lowdensity, high specific strength and specific modulus, good oxidation-resistanceand creep-resistance. Investment casting is regarded as an economical processingtechnologyfor complex titanium aluminnides-based net-shape components.In this paper, ZrO2 was selected as face-coat refractory throughcomprehensive analysis of metal-mold interfacial reaction and the measurementof microhardness and element distributing SEM analysis for investment castingof titanium aluminides using different refractory powder such as Y2O3, CaO,Al2O3, ZrO2 and the blend of Al2O3 and ZrO2(the ration is 1:1). The coating,dewaxing and baking parameters of the mold were optimized through theresearch of the influence of S/L, the content of fine powders and bakingtemperature on face-coat strength. The fabrication technology is finallydetermined.A method adding high polymer and water based latex was suggested toimprove the deformability of the mold. The inner part appears to many holes andthe bending strength is reduced after the mold baked. When the addition is0.02~0.03%(wt%) in investment casting of titanium aluminides, thedeformability is greatly improved. The dewaxing pressure and time are 7kg/cm2and 5 minutes. The baking process is determined as following: 200℃retaining 1hour, 400℃1 hour, 1150℃2 hours. The sound"I"style titanium aluminideswere obtained using the mold prepared above.A nominal composition Ti-43Al-9V-0.3Y(at%) has been prepared by LinnV-3,3-TITAN high-frequency centrifugal casting machine. The influence ofcasting size, pouring temperature, preheating temperature of the mold and rotatespeed to the interfacial reaction was investigated.The measurement of microhardness and element distributing SEM analysisindicate: with the increase of pouring and preheating temperature, the reactionlayer become thicker while rotate speed gets no obvious influence to reaction layer but higher rotate speed gets increased coarseness. X-ray diffraction analysisconfirmed the formation of new phase Y2(Zr0.45Ti0.55)2O7, and the interfacialreaction mechanism was investigated.