【作者】 张森；

【导师】 王俊；

【作者基本信息】 上海交通大学 ， 材料学， 2012， 硕士

【摘要】 本文以高纯铝、海绵Ti和B4C为反应原料,按照Al-5Ti-1B4C的成分配比,分别采用低温高能超声处理工艺和高温感应熔炼工艺,研究了新型Al-Ti-B-C四元中间合金的制备工艺。利用X射线衍射仪、扫描电子显微镜和能谱仪等材料分析测试设备,对中间合金的物相和组织形貌进行了分析。研究了不同工艺参数对中间合金中TiAl3、TiB₂和TiC相尺寸形貌的影响;计算并分析了Al-5Ti-1B4C体系的反应热力学与动力学机制;同时研究了不同工艺下制备的中间合金对工业纯铝的细化行为,并就Al-Ti-B-C四元中间合金的细化机制进行了探讨。主要取得了以下研究结果:⑴热力学计算结果表明,Al-5Ti-1B4C反应体系中3Ti + B4C = 2TiB₂ + TiC的反应焓变ΔrH0和吉布斯自由能变化ΔrG0最低,反应自发进行的倾向最大。⑵本文实验参数下的高能超声处理工艺无法在850℃促进Ti与B4C的反应,在该温度下制备的中间合金中仅含有Al和TiAl3相。显微组织研究发现,该类中间合金中的TiAl3相为团块状,尺寸一般在20μm以下;随着超声处理次数和时间的增加,块状的TiAl3相趋于均匀分散,同时有向球状转化的趋势。⑶通过提高反应温度,可以显著改善Al/B4C界面润湿性。利用感应熔炼法在1400℃和1600℃下制备的Al-Ti-B-C中间合金中含有Al、TiAl3、TiB₂和TiC相。其中,TiB₂为20μm左右的短片状,而颗粒状TiC则为团聚分布且尺寸跨度较大,从2μm到亚微米不等;片状TiAl3的长度则随反应温度的升高而增加。Al/B4C界面处的反应3[Ti]+B4C=TiB₂+TiC是生成TiB₂和TiC异质形核质点的控制环节。⑷仅含有TiAl3相的中间合金对工业纯铝的细化效果一般;而同时含有TiAl3、TiB₂和TiC相的Al-Ti-B-C四元中间合金则具有优良的细化性能。在0.2wt%的添加量下,由感应熔炼法在1400℃和1600℃下制备的Al-Ti-B-C中间合金可以分别将工业纯铝晶粒细化至189μm和192μm;保温静置60min后,仍可以将工业纯铝细化至220μm左右。⑸TiB₂、TiC相的非均匀形核和溶质Ti抑制Al晶粒生长的共同作用是Al-Ti-B-C四元中间合金细化铝及铝合金的主要机制。在形核过程中,中间合金中的TiB₂和TiC相与Al的润湿性好,晶格匹配度高,能够形成良好的非均匀形核界面,α-Al从而在这些质点上形核;而进入晶粒长大阶段后,溶质Ti对α-Al晶粒生长的抑制作用成为主导。因此,可以认为Al-Ti-B-C四元中间合金的细化机制为碳硼化物理论和溶质理论的一种耦合效应。更多还原

【Abstract】 In this thesis, master alloys were prepared by high-energy ultrasound treatment process at low temperature and induction melting process at high temperature respectively. High purity aluminum, sponge Ti and B4C particles were used as reactants, in accordance with the composition ratio of Al-5Ti-1B4C. And the materials analysis facilities, such as X-ray diffractometer, scanning electron microscopy and energy dispersive spectroscopy, were used to observe and identify the existence and morphology of production phases. The effect of different process parameters on the morphology and size distribution of the TiAl3, TiB₂ and TiC particles in master alloys were carefully studied. The thermodynamic and kinetic mechanisms of the Al-5Ti-1B4C reaction system were analyzed by the calculation and experimental results. Finally, the grain refinement performance of the master alloy synthesized by different process were well researched and the refining mechanisms of Al-Ti-B-C master alloy were discussed. The main conclusions can be summarized as follows:⑴The thermodynamic calculations showed that the reaction, 3Ti + B4C = 2TiB₂ + TiC, has the lowest enthalpyΔrH0 and Gibbs free energy changeΔrG0 in the Al-5Ti-1B4C system. So, this reaction may react in the system spontaneously.⑵There was no evidence of the reaction between Ti and B4C in the high energy ultrasound treatment process at 850℃. Such master alloys synthesized by ultrasound treatment are only composed with Al and TiAl3. The block TiAl3 phase has a average size less than 20μm. With the increase of the times and duration of ultrasound treatment, the block TiAl3 tend to be finely dispersed in the matrix, and become a spherical shape.⑶The wettability of Al/B4C interface is improved significantly by rising reaction temperature. The Al-Ti-B-C quaternary master alloys prepared by induction melting process at 1400℃and 1600℃are composed with Al, TiAl3, TiB₂ and TiC phases. The TiB₂ has plate-like shape with a length of 20μm, the TiC size spans from 2μm to submicron level, and the length of flake TiAl3 increased with the rising reaction temperature. The Al/B4C interface reaction, 3[Ti] + B4C =2TiB₂ + TiC, is the key mechanism to generate TiB₂ and TiC nucleating substrates.⑷The Al-Ti-B-C quaternary master alloys containing TiAl3, TiB₂ and TiC had an excellent refining performance on commercial pure aluminum, compared with the master alloys only containing TiAl3. The mean grain sizes of commercial pure aluminum were diminished to 189μm and 192μm separately by adding 0.2wt% master alloys synthesized by induction melting process at 1400℃and 1600℃. After holding for 60 min, the diameter of commercial pure aluminum grain was stable around 220μm.⑸The combination effect of heterogeneous nucleation caused by TiB₂ and TiC particles and the grain growth restriction caused by solute Ti is the main grain refinement mechanism of the quaternary Al-Ti-B-C master alloy. In the nucleating process,α-Al starts to form at the surface of TiB₂ and TiC substrates which have a good wettability and lattice match with Al. In the later grain growth stage, the growth inhibition ofα-Al caused by solute Ti is the dominant effect. So, the refinement mechanism of Al-Ti-B-C mater alloy is a coupling effect of the carbon-boride theory and the solute theory.更多还原