多层石墨烯与TiAl合金复合材料固相烧结过程中Ti_(2)AlC与Ti_(3)AlC的形成机制

Formation mechanisms of Ti_(2)AlC and Ti_(3)AlC during solidstate sintering between multilayer graphene and TiAl alloy composite

向TiAl合金中添加C元素反应形成的Ti_(2)AlC相与Ti_(3)AlC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_(2)AlC(Ti_(3)AlC)的包晶反应,但在固相烧结过程中Ti_(2)AlC与Ti_(3)AlC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_(2)AlC与Ti_(3)AlC生成过程中没有TiC参与.进一步计算发现TiC/TiAl,Ti_(2)AlC/TiAl与Ti_(3)AlC/TiAl的界面能分别约为1.2,0.87和0.39 J·m^(2),据此得出Ti_(2)AlC与Ti_(3)AlC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_(2)AlC相,但1250-1350℃界面产物组成为Ti_(3)AlC+少量Ti_(2)AlC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_(2)AlC与Ti_(3)AlC的形成倾向.在1150-1250℃,TiAl合金基体由γ+少量α相组成,Ti_(2)AlC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_(3)AlC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_(2)AlC与Ti_(3)AlC的相对含量,进而有望改善TiAl合金的塑性与强度.

Ti_(2)AlC and Ti_(3)AlC 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_(2)AlC(Ti_(3)AlC)occurs in the process of liquid-phase sintering,but different formation mechanisms of Ti_(2)AlC and Ti_(3)AlC 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_(2)AlC and Ti_(3)AlC are verified to contain no TiC.The interface energy values of TiC/TiAl,Ti_(2)AlC/TiAl and Ti_(3)AlC/TiAl are calculated to be about 1.2,0.87 and 0.39 J·m2,respectively,indicating that Ti_(2)AlC and Ti_(3)AlC can be formed directly without TiC mesophase.Besides,only Ti_(2)AlC is observed to be formed at 1150-1250℃,while the interface products at 1250-1350℃change into Ti_(3)AlC with a small amount of Ti_(2)AlC.The mechanism that the sintering temperature affects the formation tendency of Ti_(2)AlC and Ti_(3)AlC 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_(3)AlC.The above results demonstrate the possibility of regulating the relative content of Ti_(2)AlC and Ti_(3)AlC through controlling the sintering temperature,which provides a promising method to improve the plasticity and strength of TiAl alloy.