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向TiAl合金中添加C元素反应形成的Ti 2AlC相与Ti 3AlC相分别具有改善TiAl合金塑性和强度的作用. 一般地, 液相烧结过程中会发生L + TiC→Ti 2AlC(Ti 3AlC)的包晶反应, 但在固相烧结过程中Ti 2AlC与Ti 3AlC的形成可能具有不同机制. 本文以多层石墨烯为碳源, 通过1100—1350 ℃的固相烧结获得C与TiAl合金的界面反应组织, 借助微观组织表征与分析, 发现Ti 2AlC与Ti 3AlC生成过程中没有TiC参与. 进一步计算发现TiC/TiAl, Ti 2AlC/TiAl与Ti 3AlC/TiAl的界面能分别约为1.2, 0.87和0.39 J·m 2, 据此得出Ti 2AlC与Ti 3AlC可以不经TiC中间相直接形成. 此外, 研究还发现在1150—1250 ℃几乎只生成Ti 2AlC相, 但1250—1350 ℃界面产物组成为Ti 3AlC + 少量Ti 2AlC相, 原因在于烧结温度对基体α相含量存在影响, 进而影响Ti 2AlC与Ti 3AlC的形成倾向. 在1150—1250 ℃, TiAl合金基体由γ + 少量α相组成, Ti 2AlC具有较高形成倾向; 1250—1350 ℃基体几乎完全转化为α相, α相含量增大对Ti 3AlC的形成具有促进作用. 研究结果表明, 通过控制TiAl合金与多层石墨烯的固相烧结温度, 可以调控Ti 2AlC与Ti 3AlC的相对含量, 进而有望改善TiAl合金的塑性与强度.Ti 2AlC and Ti 3AlC formed by the reaction between C and TiAl alloy can improve the plasticity and strength of TiAl alloy respectively. Generally, the peritectic reaction of L + TiC→Ti 2AlC (Ti 3AlC) occurs in the process of liquid-phase sintering, but different formation mechanisms of Ti 2AlC and Ti 3AlC may exist in the solid-state sintering. In this work, multilayer graphene is employed to fabricate the reaction interface with TiAl alloy under 1100–1350 ℃, which is the common solid-state sintering temperature of TiAl alloy. According to the microstructure characterization and analysis, Ti 2AlC and Ti 3AlC are verified to contain no TiC. The interface energy values of TiC/TiAl, Ti 2AlC/TiAl and Ti 3AlC/TiAl are calculated to be about 1.2, 0.87 and 0.39 J·m 2, respectively, indicating that Ti 2AlC and Ti 3AlC can be formed directly without TiC mesophase. Besides, only Ti 2AlC is observed to be formed at 1150–1250 ℃, while the interface products at 1250–1350 ℃ change into Ti 3AlC with a small amount of Ti 2AlC. The mechanism that the sintering temperature affects the formation tendency of Ti 2AlC and Ti 3AlC can be ascribed to the content of α phase. The TiAl alloy matrix is composed of γ and a few α phases at 1150–1250℃, but almost completely transforms into α phase at 1250–1350 ℃, and the increase in the α content can promote the formation of Ti 3AlC. The above results demonstrate the possibility of regulating the relative content of Ti 2AlC and Ti 3AlC through controlling the sintering temperature, which provides a promising method to improve the plasticity and strength of TiAl alloy.
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化合物 摩尔生成自由能 ${\varDelta _{\text{f} } }G_{\text{m} }$/(kJ·mol–1) TiAl3 0.06522T– 289.37 TiAl 0.02224T– 91.078 Ti3Al 0.01678T– 109.75 TiC 0.01522T– 189.07 Ti2AlC 0.03045T– 387.13 Ti3AlC 0.1208T– 583.45 
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摩尔反应自由能 温度/℃ 1150 1250 $ \Delta {G_1} $ –3.72 –3.69 $ \Delta {G_2} $ –5.52 –5.50 $ \Delta {G_3} $ –6.88 –6.68 下载:
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序号 晶体 空间群 晶格常数 a TiAl ${ { {{Pm} }\bar 3 m} }$ a=b= 4.0051 Å,c= 4.0707 Å b Ti3Al ${{P63/mmc} }$ a=b= 5.764 Å,c= 4.664 Å c TiC ${ { {{Fm} }\bar 3 m} }$ a=b=c= 4.328 Å d Ti3AlC ${ { {{Pm} }\bar 3 m} }$ a=b=c= 4.156 Å e Ti2AlC ${{P63/mmc} }$ a=b= 3.063 Å,c= 13.668 Å 下载:
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相 TiAl Ti3Al TiC Ti2AlC Ti3AlC 弹性模量
G/GPa70 56 182 115 83 泊松比ν 0.23 0.28 0.228 0.164 0.25 线膨胀系数
α/10–612—14.5 12—14.5 7.74 9.62 10.1 下载:
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温度/
℃$ {\sigma _{{\text{γ /TiC}}}} $/
(J·m2)$ {\sigma _{{\text{γ /H}}}} $/
(J·m2)$ {\sigma _{{\text{α /H}}}} $/
(J·m2)$ {\sigma _{{\text{γ /P}}}} $/
(J·m2)$ {\sigma _{^{{\text{α /P}}}}} $/
(J·m2)1150 1.243 0.879 0.831 0.396 0.308 1200 1.230 0.872 0.827 0.390 0.303 1250 1.223 0.868 0.821 0.385 0.288 1300 1.220 0.866 0.819 0.384 0.288 1350 1.217 0.864 0.819 0.383 0.287 下载:
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