氢对TiAl基合金铸造性能及熔模铸造界面反应的影响

发布时间：2018-06-10 00:07

本文选题：TiAl合金 + 液态置氢　；参考：《华中科技大学》2015年硕士论文

【摘要】：TiAl基合金具有良好的高温强度、抗蠕变性及抗氧化性等优点,是航空航天工业中潜在的轻质高温结构材料,但其严重的室温脆性及塑性加工工艺性差限制了其进一步应用。熔模铸造技术可以避免其塑性成形困难的问题,同时节约成本,但合金熔体较差的铸造充型性能及严重的界面反应限制了铸件的质量。热氢处理技术是将氢元素在合金的成形或热处理阶段引入,可以提高合金的高温加工性能并改善组织,但在铸造工艺中研究较少。本文通过在氢气氛下电弧熔炼TiAl基合金完成液态置氢过程,并浇注到石墨铸型及氧化钇陶瓷型壳,分别研究氢对TiAl基合金铸造性能及界面反应过程的影响。通过螺旋形石墨模具研究了氢对TiAl基合金流动性的影响,随熔炼气氛中氢分压的提高,合金流动性增加,当氢分压提高到15kPa时,流动长度比氢分压为0kPa时提高了209%,当氢分压大于15kPa时,流动性增加趋于平稳。氢降低了TiAl基合金原子之间的键合作用,降低了合金熔体的粘度及表面张力,同时降低了液相线,相对地提高了过热度,缩小了结晶温度范围。通过薄壁多孔石墨模具研究了氢对TiAl基合金浇注复杂铸件时铸造性能的影响,随着氢分压的提高,合金充型体积分数提高,当氢分压为20kPa时,充型体积提高了约25%。由于石墨铸型的退让性差及合金熔体充型时的紊流状态,铸件存在少量裂纹及气孔,氢对铸件裂纹及气孔的数量及分布没有明显影响。通过Y2O3陶瓷型壳浇注TiAl基合金研究了氢对界面反应过程的影响,界面反应生成了氧化物Ti3O、TiO、TiO2及Al2O3,新相Y2(Ti2O7)及Y3Al2(AlO4)3,在反应层中O元素及Y元素扩散距离比较短。氢原子与氧原子在界面处反应生成了水分子,并在反应层表面形成了气孔形貌,减少了在反应层中氧元素的含量及扩散趋势。当氢分压提高时,反应层表面中氧含量减少,当氢分压为7.5kPa时,氧含量比氢分压为0kPa时的氧含量减少了34%。
[Abstract]:Tial based alloys have the advantages of good high temperature strength, creep resistance and oxidation resistance, and are potential lightweight high temperature structural materials in aerospace industry. However, their serious room temperature brittleness and poor processing technology limit their further application. Investment casting technology can avoid the difficulty of plastic forming and save cost, but the poor mold filling performance and serious interface reaction of alloy melt limit the quality of casting. The hot hydrogen treatment technology is the introduction of hydrogen element in the forming or heat treatment stage of the alloy, which can improve the high temperature working property and the microstructure of the alloy, but it is less studied in the casting process. The effect of hydrogen on casting properties and interfacial reaction process of tial based alloys was studied by arc melting in hydrogen atmosphere and pouring into graphite mold and yttrium oxide ceramic shell. The effect of hydrogen on the fluidity of tial based alloy was studied by spiral graphite mould. With the increase of hydrogen partial pressure in melting atmosphere, the alloy fluidity increased, and when hydrogen partial pressure increased to 15 KPA, The flow length is increased by 209 when the hydrogen partial pressure is 0 KPA, and when the hydrogen partial pressure is greater than 15 KPA, the fluidity increases steadily. Hydrogen reduces bond cooperation between tial alloy atoms, decreases the viscosity and surface tension of alloy melt, decreases the liquid phase line, increases the superheat, and reduces the crystallization temperature range. The effect of hydrogen on casting properties of TiAl-based alloy casting complex castings was studied by means of thin wall porous graphite mould. With the increase of hydrogen partial pressure, the filling volume fraction of alloy increased. When hydrogen partial pressure was 20 KPA, the filling volume increased by about 25%. Due to the low yield of graphite mold and the turbulent state of alloy melt filling, there are a few cracks and pores in the casting, but hydrogen has no obvious effect on the quantity and distribution of the cracks and pores in the casting. The effect of hydrogen on the interfacial reaction was studied by pouring TiAl-based alloy with Y _ 2O _ 3 ceramic shell. The interfacial reaction resulted in the formation of oxides Ti _ 3O _ 2O _ 2 and Al _ 2O _ 3, new phase Y _ 2o _ 2O _ 7) and Y _ 3AL _ 2o _ 4O _ 4C _ 3. The diffusion distance between O element and Y element in the reaction layer was relatively short. Hydrogen atoms react with oxygen atoms to form water molecules at the interface, and the pore morphology is formed on the surface of the reaction layer, which reduces the content and diffusion trend of oxygen elements in the reaction layer. When the hydrogen partial pressure increases, the oxygen content in the reaction layer decreases, and when the hydrogen partial pressure is 7.5 KPA, the oxygen content decreases by 34% compared with the hydrogen partial pressure at 0 KPA.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG292

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