【作者】 朱冬冬；

【导师】 朱兆军；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2009， 硕士

【摘要】 本文采用非自耗真空氩弧熔炼炉熔炼合金,研究了冷却速度对Ti-48Al、Ti-48Al-0.2B、Ti-52Al、Ti-52Al-0.2B合金显微组织的影响;利用六面顶压机分别在2GPa和4GPa高压下制备Ti-48Al凝固试样;利用X射线衍射对不同冷却速度下的TiAl金属间化合物及高压下凝固的TiAl金属间化合物相组成进行了分析;采用光学显微镜、扫描电子显微镜、能谱分析仪等分析测试手段分别对常压、高压下合金凝固组织形貌进行了观察。X射线衍射分析表明,随着冷却速度的增加,Ti-48Al合金中γ相晶格参数a有减小的趋势,而c值的变化并无规律;使用铜和石墨模具吸铸的Ti-48Al和Ti-48Al0.2B合金试样,其原始α晶粒特别细小,块状转变完全,无α2/γ片层组织或α2单相组织,吸铸后只产生γ单相。随着冷却速度的增加,Ti-52Al和Ti-52Al-0.2B合金晶粒尺寸均有减小的趋势,微量B元素的加入致使片层组织间距变小,且B的细化效果减弱。高压下凝固的Ti-48Al合金由α2-Ti3Al和γ-TiAl相组成,随着凝固压力的增大,α2-Ti3Al相含量及片层组织均增多,偏析γ-TiAl相减少,且片层组织中Al含量升高。在不同压力下凝固时,圆形试样边缘的组织和心部的组织均有较大的差异,2GPa下凝固时,边缘部位和心部均为双态组织,但心部偏析γ-TiAl相较边缘部位多;而4GPa下凝固时,试样边缘组织为全片层状组织,心部为双态组织。文中最后讨论了压力对Ti-Al合金偏析的影响,随着压力的增大溶质偏析变小。更多还原

【Abstract】 In this paper, Ti-48Al、Ti-48Al-0.2B、Ti-52Al、Ti-52Al-0.2B alloys were prepared by vacuum non-consumble arc-melting method. The effect of three different kinds of cooling rate on the microstructures of these alloys have been studied. In addition, the samples of Ti-48Al alloys were prepared by solidifying under 2GPa and 4GPa by high pressure cubic press. The phase constitution of the TiAl intermetallics solidified under different cooling rates and high pressure is characterized by X-ray diffraction (XRD). By means of optical microscope, scanning electron microscopy (SEM), energy dispersive X-ray spectroscope (EDX), characters of microstructure and phase composition of alloys, effects of high pressure on solidification processing of alloys solidified under normal and high pressure were investigated respectively.X-ray diffraction indicates that with the increasing of cooling rates, crystal parameters (a) ofγ-TiAl phase have the tendency of decreasing, but no definite relation of the change of crystal parameters (c). After solidification in graphite and cuprum mold, the grain size of primaryαin Ti-48Al and Ti-48Al-0.2B is very fine, and it all transforms toγ. After the massive transformation there is no lamellar microstructure orα2-Ti3Al. Wth the increasing of cooling rates, the grain size of Ti-52Al based alloys decreased. And the addition of trace boron leads to the lamellar microstructure increased .When cooling rate increases, the refining effect of B is less evident.The microstructure of Ti-48Al solidified under high pressure consists ofα2-Ti3Al andγ-TiAl phase. With the increasing of pressure, the fraction ofα2-Ti3Al phase and lamellar microstructure increasing,γ-TiAl phase decreasing. There exists great discrepancy in the periphertal and core zone of the round samples solidified under pressure. The microstructures of the periphertal and core zone are also duplex when solidified under 2GPa. When the pressure is 4GPa, the periphertal zone is full lamellar microstructure, the core zone duplex microstructure.Meanwhile the effect of pressure on the microsegregation of TiAl alloys were analyzed. With the increasing of pressure, the microsegregation decreases. .更多还原