Exp-ECAP工艺对钛铝双金属复合棒材界面组织及性能的影响

Influence of Exp-ECAP Process on the Interface Microstructure and Properties of Ti/Al Bimetallic Composite Rods

提出一种耦合镦、剪、挤等多种变形于一体的膨胀-等通道转角挤压工艺(expansion-equal channel angular pressing,Exp-ECAP)。450℃下采用单道次Exp-ECAP挤压结合退火热处理成功制备钛铝双金属复合棒材。利用SEM、EDS、XRD、EBSD和剪切试验研究了钛铝双金属复合棒材界面微观组织和结合性能。结果表明,在Exp-ECAP变形剧烈剪切应力和退火高温条件下,钛铝双金属复合棒材获得了良好的界面结合,钛、铝2种基体元素通过相互扩散形成了厚度约为1.27μm的冶金结合层,界面层内生成的新相以金属间化合物TiAl为主,并含有少量不均匀分布的Ti_(3)Al(靠近钛侧)和TiAl_(3)(靠近铝侧)。Ti/Al界面层金属通过发生相变反应和部分再结晶产生了大量等轴、细小的超细晶组织,晶粒随机生长,无明显的择优取向。钛铝双金属复合棒材平均剪切强度为66.29 MPa,剪切破坏主要发生在TiAl相层,表现出脆性断裂的特征。

A novel process,expansion-equal channel angular pressing(Exp-ECAP)which couples multiple forms of deformation such as upsetting,shearing,and extrusion into one was proposed.Ti/Al bimetallic composite rod was fabricated by a single pass of Exp-ECAP process at 450℃combined with post annealing heat treatment.The interface microstructure and bonding properties of Ti/Al bimetallic composite rod were investigated using SEM,EDS,XRD,EBSD and shear test.The results show that under the severe shear stress of Exp-ECAP process and the high-temperature annealing conditions,the Ti/Al bimetallic composite rod achieves good interfacial bonding quality,and a metallurgical bonding layer of approximately 1.27μm thickness forms through mutual diffusion of the titanium and aluminum matrix elements.New phases generated in the bonding interface layer are mainly intermetallic compound TiAl,and there are a small amount of inhomogeneous distributed Ti3Al(near the Ti side)and TiAl_(3)(near the Al side).Moreover,a large number of equiaxed ultrafine grains are obtained in the Ti/Al interface bonding layer through phase transformation reactions and partial recrystallization,and the grains grow randomly without obvious preferred orientation.The shear strength of Ti/Al bimetallic composite rod is about 66.29 MPa,and shear failure mainly occurs in the TiAl phase layer,exhibiting brittle fracture characteristics.