Ti-Al合金扩散连接工艺及机理研究

发布时间：2018-04-02 18:12

  本文选题：高铌TiAl合金　切入点：Ti_2AlNb合金　出处：《哈尔滨工业大学》2017年硕士论文

【摘要】：高铌TiAl合金和Ti_2AlNb合金作为新兴轻质高温Ti-Al合金,是航空航天等领域应用的理想材料。本文对高铌TiAl合金自身以及高铌TiAl与Ti_2AlNb合金进行直接扩散连接,研究了扩散连接工艺对接头微观组织和力学性能的影响,获得最佳连接工艺参数,分析了接头的断裂位置和断口形貌,综合探究了接头组织,力学性能,断裂位置以及断口形貌之间的联系,阐述了扩散连接接头的形成机理。对高铌TiAl合金进行直接扩散连接连接,连接界面处主要为再结晶的转变,随着连接温度的升高及保温时间的延长,将其分为六个阶段。孔洞闭合阶段,随着原子不断扩散,孔洞消失;再结晶形核前期,随着位错在连接界面处不断堆积,畸变程度小的一侧的晶粒边界向大的一侧延伸;再结晶形核后期,随着位错的进一步堆积,边界向畸变程度小的一侧延伸,再结晶形核完成;再结晶长大阶段,随着连接温度的升高或保温时间的延长,再结晶晶粒不断长大,位错不断减少;连续动态再结晶发生及物相转化阶段,当达到一定温度时,连接界面处发生连续动态再结晶。当连接温度达到1125°C时,母材及接头内部出现物相转化,造成连接界面处α2相增多,不利于接头性能提高;接头完全形成阶段,连接界面处再结晶晶粒尺寸不断增大,数量不断增多,此时接头剪切强度达最大值为154.3MPa。保温时间和压力对再结晶的影响与温度有相似之处,但过大的压力,会抑制再结晶晶粒的长大。不同连接工艺参数下,断裂形式以脆性断裂为主。在高铌TiAl合金和Ti_2AlNb合金直接扩散连接过程中,随着连接温度的升高或者保温时间延长,连接界面处主要表现为物相的转化,其可分为四个阶段。孔洞闭合阶段,两侧母材原子扩散更加充分,连接界面处孔洞消失;(Al(Ti,Nb)_2+Ti_3Al)混合层以及Ti_3Al层形成阶段,由于Nb原子在连接界面处的积累及Al原子的扩散,在连接界面处生成Al(Ti,Nb)_2相和Ti_3Al相,此时界面结构为Ti_2AlNb合金/Al(Ti,Nb)_2+Ti_3Al/Ti_3Al/高铌TiAl合金;O相形成阶段,Al原子穿过混合层进入Ti_2AlNb母材中,致使O相形成,此时界面结构为Ti_2AlNb合金/Ti_2AlNb/O/Al(Ti,Nb)_2+Ti_3Al/Ti_3Al/高铌TiAl合金形成;Ti_3Al过渡层形成阶段,随着原子进一步扩散,Al(Ti,Nb)_2相逐渐消失,O相层变为不连续状态,连接界面处形成Ti_3Al过渡层,界面结构为Ti_2AlNb合金/Ti_3Al/高铌TiAl合金,此时接头强度达到最大值为66.1MPa。不同连接工艺参数下接头的断裂形式均为脆性断裂。
[Abstract]:High niobium TiAl alloy and Ti_2AlNb alloy as new lightweight high temperature Ti-Al alloys are ideal materials for aerospace applications.In this paper, the direct diffusion bonding of high niobium TiAl alloy and high niobium TiAl and Ti_2AlNb alloy is carried out. The effect of diffusion bonding process on the microstructure and mechanical properties of the joint is studied, and the optimum bonding process parameters are obtained.The fracture location and fracture morphology of the joint were analyzed. The relationship among the microstructure, mechanical properties, fracture location and fracture morphology of the joint was investigated. The formation mechanism of the diffusion joint was described.In the direct diffusion bonding of high niobium TiAl alloy, the interfacial transition is mainly recrystallization. With the increase of bonding temperature and the prolongation of holding time, it is divided into six stages.In the closing stage of the cavity, the cavity disappears with the diffusion of atoms, and in the early stage of recrystallization, the grain boundary of the side with small distortion extends to the larger side as the dislocation accumulates at the junction interface, and the later stage of recrystallization nucleation,With the further accumulation of dislocation, the boundary extends to the side with small distortion degree, and the recrystallization nucleation is completed, at the stage of recrystallization, the recrystallization grain grows and the dislocation decreases with the increase of joining temperature or the prolongation of holding time.Continuous dynamic recrystallization occurs in the phase of phase transformation. When the temperature reaches a certain temperature, continuous dynamic recrystallization occurs at the interface.When the bonding temperature is up to 1125 掳C, there is a phase transformation between the base metal and the joint, which results in the increase of 伪 _ 2 phase at the interface, which is not conducive to the improvement of the joint properties, and the recrystallization grain size at the interface increases continuously at the stage of the complete formation of the joint.The maximum shear strength of the joint is 154.3 MPA.The effect of holding time and pressure on recrystallization is similar to that of temperature, but excessive pressure will inhibit recrystallization grain growth.Brittle fracture is the main fracture form under different connection parameters.In the process of direct diffusion bonding between high niobium TiAl alloy and Ti_2AlNb alloy, with the increase of bonding temperature or the prolongation of holding time, the interfacial transition of the interface is mainly material-phase transformation, which can be divided into four stages.In the closing stage of the cavity, the diffusion of the base metal atoms on both sides is more complete, and the holes disappear at the connection interface, and the mixed layer of NbTiTiTi2Ti3Aland the formation stage of the Ti_3Al layer are formed, due to the accumulation of NB atoms at the junction interface and the diffusion of Al atoms.Ti_3Al phase and Ti_3Al phase are formed at the junction interface. At this time, the interface structure is Ti_2AlNb alloy / AlTiTiTiNbTi2 Ti_3Al/Ti_3Al/ high niobium TiAl alloy O phase formation stage, the Al atom passes through the mixing layer into the Ti_2AlNb base metal, resulting in O phase formation.At this point, the interface structure is Ti_2AlNb alloy Ti2AlNb / O / AlTiNb / Ti_3Al/Ti_3Al/ Ti_3Al/Ti_3Al/ high niobium TiAl alloy to form Ti3Al transition layer. With the further diffusion of atoms, the O phase layer gradually disappears and the O phase layer becomes discontinuous, and the Ti_3Al transition layer is formed at the junction interface.The interface structure is Ti_2AlNb alloy / Ti3Al / high niobium TiAl alloy, and the maximum strength of the joint is 66.1 MPA.The fracture form of the joint is brittle fracture under different process parameters.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.1
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本文编号：1701528