高洁净度TiAl合金及其纳米复合材料的制备，组织和力学性能

发布时间：2018-05-21 20:31

本文选题：高铌TiAl合金 + 真空磁悬浮熔炼　；参考：《北京科技大学》2015年博士论文

【摘要】：TiAl合金的潜在应用领域主要为高温和循环载荷下的结构部件,比如航空发动机低压涡轮叶片、汽车增压涡轮器等。随着Ti-48Al-2Cr-2Nb(除特殊标注外,全文都为原子分数)合金在美国波音787客机GenX发动机的应用,国内外对于TiAl合金的研究和应用又产生了新一轮的热潮。无论是开发新型的铸造TiAl合金还是变形TiAl合金,提高合金的洁净度都有着重要意义。因此,本文的主要研究内容针对高洁净度熔炼高铌TiAl合金的真空磁悬浮熔炼过程进行了系统的研究,包括制备工艺、成分-组织均匀性和力学性能；还借助于真空磁悬浮熔炼的电磁搅拌作用以搅拌-铸造法制备了TiAl基纳米复合材料,并研究了纳米颗粒对TiAl合金组织和力学性能的影响。本文的主要结论和创新点如下：(1)在真空磁悬浮熔炼高铌TiAl合金时,不当的布料方式会导致原料搭桥和热爆损失,影响熔炼过程以及合金成分的准确性。通过坩埚内Al上Ti下的布料方式可以有效避免原料搭桥的产生。热爆的产生是由于气体和Al蒸气的压力大于原料静压力而导致的,通过减少坩埚内海绵钛的质量和提高炉内压力可以有效抑制热爆的产生。(2)通过优化的真空磁悬浮两次熔炼工艺,高铌TiAl合金铸锭的成分组织均匀。在第二次熔炼中采取了抽真空-熔化-充氩气-熔炼的工艺制度使合金含O量降低到300ppm。(3)在真空熔炼高铌TiAl合金时,合金的烧损主要来源于海绵钛的飞溅损失。尽管Al具有较高的蒸气压,但足通过充Ar使炉内达到500Pa以上可以有效降低Al的挥发损失。(4)通过对锭型的优化设计,促进了高铌TiAl合金在锭型内的顺序凝吲。铸锭中集中缩孔分布在冒口处,气缩孔基本消除,有效地减小了分散缩孔的体积。通过铸锭温度温度场的模拟设计出最佳的锭型尺寸为：锭型壁厚20mm、锭身斜度4.2。、锭身高径比3.3、冒口斜度30。。(5)经过真空悬浮熔炼并浇注的高铌TiAl合金铸锭,其组织为均匀的等轴近片层组织。降低Al含量和添加B元素都使片层团尺寸减小。虽然B细化作用最为显著,然而大量硼化物的析出损害了材料的室温拉伸力学性能。(6)当高铌TiAl-B合金在α单相区进行热处理时,铸锭中出现了粗晶环。粗品环的形成与B的含量(0.5%)和铸锭凝固时的冷却速率有关。降低B含量和提高铸锭的冷却速率都会使粗品环的宽度增大。粗晶环的形成是因为B含量大于某一临界值时凝固前沿B导致的成分过冷和温度过冷共同作用使整个铸锭硼化物的分布密度不同,使得α单相区热处理时硼化物对α晶粒的钉扎作用不同。并且高温时弯曲板条状的硼化物转变为针状的硼化物,这种转变也削弱了对α晶粒的钉扎作用,这两种硼化物都富集了Nb元素并且都具有相同的B27正交结构。(7)通过搅拌-铸造法成功制备了TiAl基纳米复合材料,试验的纳米陶瓷颗粒有α-Al2O3、γ-Al2O3、TiO2、Y2O3、TiC,纳米金属颗粒有W和Mo。其中α-Al2O3、TiO2、TiC和W纳米颗粒在经过电磁搅拌后都可以在TiAl基体中实现均匀分散的分布,根据其分布判断出这几种颗粒的润湿性大小为：WTiO2TiCα-Al203。(8)纳米颗粒在TiAl合金凝固中起到了异质核心的作用,因此细化了初生β枝晶,然而纳米氧化物陶瓷颗粒却使片层团组织粗化,其主要原因是O的溶解稳定了高温α相,促进了α晶粒的快速生长,进而转变为粗大的片层团。当纳米TiC的添加量大于1wt.%时,基体中有Ti2AlC的析出并细化了片层团组织,同时C的溶解减小了7和a2片层间距。(9)纳米颗粒的添加使TiAl合金的室温和高温维氏硬度都有一定提高,硬度提高最显著的是纳米TiC和纳米W,然而TiC却损害了材料的室温断裂韧性,只有纳米W颗粒的添加即提高了基体的室温和高温硬度又提高了基体的断裂韧性,达到40MPa/m1/2。
[Abstract]:The potential applications of TiAl alloys are the structural components under high temperature and cyclic loading, such as aero engine low pressure turbine blades, automotive turbocharger, and so on. The application of Ti-48Al-2Cr-2Nb (the full text for atomic fraction) alloy to the GenX engine of the Boeing 787 aircraft in the United States and the study of TiAl alloys at home and abroad. There is a new round of upsurge of application and application. It is of great significance to develop new cast TiAl alloy or deformed TiAl alloy to improve the cleanliness of the alloy. Therefore, the main research content of this paper is to systematically study the vacuum magnetic levitation process of Gao Jie's pure melting high niobium TiAl alloy, including the preparation process, The composition homogeneity and mechanical properties of TiAl based nanocomposites were also prepared by the stirring casting process in vacuum magnetic suspension melting. The effects of nanoparticles on the microstructure and mechanical properties of TiAl alloys were studied. The main conclusions and innovations of this paper were as follows: (1) high niobium TiAl in vacuum maglev smelting. In gold, improper material will lead to bridge and thermal explosion loss, influence melting process and the accuracy of alloy composition. Through the material under Al Ti in the crucible, the production of bridge can be avoided effectively. The thermal explosion is caused by the pressure of gas and Al steam greater than the static pressure of the raw material, by reducing the crucible inside the crucible. The quality of the titanium sponge and the increase of the pressure in the furnace can effectively suppress the thermal explosion. (2) the composition of the high niobium TiAl alloy ingot is homogeneous through the optimized two smelting process of vacuum magnetic levitation. In the second smelting process, the vacuum melting, argon filling and melting process system has been adopted to reduce the content of O to 300ppm. (3) in vacuum smelting. When high niobium TiAl alloy, the burning loss of the alloy is mainly due to the spatter loss of titanium sponge. Although Al has high vapor pressure, it can effectively reduce the volatilization loss of Al by filling up to 500Pa in the furnace by filling Ar. (4) through the optimum design of the ingot type, the sequential indation in the ingot type of high niobium TiAl gold is promoted. The concentrated shrinkage of the ingot is concentrated. In the riser, the air shrinkage cavity is basically eliminated and the volume of the dispersed shrinkage cavity is effectively reduced. The optimum ingot size is designed by the simulation of the temperature and temperature field of ingot. The ingot thickness 20mm, the ingot body slope 4.2., the ingot height ratio 3.3, the riser slope 30.. (5) through the vacuum suspension melting and pouring of the high niobium alloy ingot are uniform. The reduction of Al content and the addition of B elements reduce the size of the lamellar mass. Although the B refinement is the most significant, the precipitation of a large number of boride damages the tensile mechanical properties of the material at room temperature. (6) when the high niobium TiAl-B alloy has been heat-treated in the alpha single-phase region, the coarse ring is formed in the ingot. The formation of the coarse ring and B The content (0.5%) is related to the cooling rate of the ingot solidification. Reducing the B content and increasing the cooling rate of the ingot will increase the width of the ring. The formation of the roughing ring is due to the combination of the component overcooling and the temperature overcooling caused by the B content greater than a critical value in the solidification front B, which makes the distribution density of the boride in the whole ingot different. The boride has different pinning effects on the alpha grain during the heat treatment of the alpha single phase region. And at high temperature, the boride of the strip shape of the curved plate turns into a needle like boride, which also weakens the pinning effect on the alpha grain. These two borates have enriched the Nb elements and all have the same B27 orthogonal structure. (7) success by the agitation casting method. TiAl based nanocomposites have been prepared. The tested nano ceramic particles are alpha -Al2O3, gamma -Al2O3, TiO2, Y2O3, TiC. The nano particles have W and Mo. in which the alpha -Al2O3, TiO2, TiC and W nanoparticles can be distributed uniformly in the matrix after electromagnetic stirring, and the wettability of these particles is judged according to their distribution. WTiO2TiC alpha -Al203. (8) nanoparticles play the role of heterogeneous core in the solidification of TiAl alloy, thus refining the primary beta dendrites. However, the nano oxide ceramic particles make the lamellar tissue coarser. The main reason is that the dissolution of O has stabilized the high temperature alpha phase and promoted the rapid growth of the alpha grain, and then changed into a coarse lamellar mass. When the addition of nano TiC is greater than 1wt.%, the matrix is precipitated by Ti2AlC and the lamellar tissue is refined. At the same time, the dissolution of C is reduced by 7 and A2 layer spacing. (9) the addition of nano particles makes the hardness of the TiAl alloy at room temperature and high temperature Vivtorinox to a certain extent, and the most notable is the nano TiC and nano W. However, TiC has damaged the material. At room temperature fracture toughness, only nano W particles increased the hardness of the substrate at room temperature and high temperature, and increased the fracture toughness of the matrix, reaching 40MPa/m1/2.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.2;TB33

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