【作者】 徐斌；

【导师】 曾卫东；

【作者基本信息】 西北工业大学 ， 材料加工工程， 2007， 硕士

【摘要】 Ti₂AlNb基合金是针对我国新型航空航天发动机的发展需求而研制的一种新型的高比强度钛铝金属间化合物，其名义成份为Ti-22Al-25Nb。全面、系统地认识热机械处理条件下Ti₂AlNb基合金的高温变形机制及组织演变规律是将其应用于航空领域迫切需要解决的重要问题。本文以××高性能发动机工程应用为背景，研究了Ti₂AlNb基合金在热变形过程中高温变形机制、不同热处理条件下的组织演变规律及其对力学性能的影响。研究的主要结果如下： 研究揭示了Ti₂AlNb基合金热变形过程中变形温度、应变速率对流动应力的影响规律，建立了合金在三相区以及三相区以上的本构关系模型以及在1060-1100℃时的晶粒长大模型。 采用等温恒应变速率压缩实验研究，发现在低温或高温、高应变速率下出现明显的流动应力软化现象，温度越低，应变速率越高，流动软化现象越明显；高应变速率(10s^-1)时易发生不连续屈服现象，应变速率和温度越高，峰值流动应力下降幅度越大。不连续屈服现象与晶界突然增殖大量可动位错有关，与固溶原子的钉扎无关。 基于动态材料模型（DMM）理论，建立了Ti-22Al-25Nb合金的热加工图，分析了热成形过程中的功率耗散规律和塑性失稳条件，揭示了Ti-22Al-25Nb合金在各种热变形条件下的组织演变规律和热变形机理。 以Prasad塑性失稳准则为依据，建立了Ti₂AlNb基合金塑性失稳条件。发现在温度940-970℃、应变速率0.4-10s^-1和温度970-1060℃、应变速率1-10s^-1范围为流动失稳区，前者主要发生绝热剪切和45°剪切开裂，功率耗散率达到最小值；后者以局部塑性流动和纵向开裂为主，功率耗散率小于33％。 研究了塑性加工“安全区”的变形机制，发现在940-970℃、应变速率0.001-0.4s^-1范围，以α₂／O相板条球化为主；在970-1030℃、应变速率0.001-1s^-1范围，功率耗散率为35-45％，呈现连续再结晶特征。在1030-1060℃、应变速率0.001-0.1s^-1范围，功率耗散率为45-66％，连续再结晶晶粒长大。 研究了Ti₂AlNb基合金中各相之间的转变关系，发现在三相区和两相区对材料进行二次锻造，并在（α₂+O+B2）三相区和（O+B2）两相区进行合适的热处理，可以在细化原始组织的前提下得到适量的O相、α2相和B2转变组织，从而获得优越的综合性能。更多还原

【Abstract】 Ti₂AlNb-based alloy is a new type of high specific strength titanium aluminum intermetallic compounds designed for new aeroengine development. It’s nominal composition is Ti-22Al-25Nb. Study of the hot deformation mechanisms and microstructure evolvtion is meaningful for the safety designing of components used in airplane. Considering the application background of some special high performance areoengines, this investigation is focused on the hot deformation characteristics of Ti2AlNb-based alloy at different hot deformation conditions. The relationships between microstructure and performance are analyzed. A brief introduction to the project and the main achievements are as follows:The influence of deformation temperature, strain rate and flow stress in hot deformation process are disclosed. A constitutive relationship of this alloy is formulated at three-phase region and above it. A relational expression of the grain growth is established at 1060-1100 ℃.Based on the hot compression experimental study at isothermal constant strain rate, the flow curves of this alloy exhibits obvious flow softening at low temperature with all strain rates tested or at high temperature with high strain rates. The flow stress drop increases with temperature decreasing or strain rate increasing. This phenomenon is attributed to microstructure changes of this alloy. Discontinuous yielding easily occurs at higher strain rate (10s^-1). The peak flow stress drop increases with the strain rate and the temperature increasing. It is considered that discontinuous yielding is associated with the generation of new mobile dislocations from grain boundary sources, but independent of solute-pinning.Using processing maps developed on the basis of dynamic material model （DMM）. The results show that this alloy exhibit a wide instability regime due to cracking or shear band formation at a strain rate greater than 1s^-1. At lower temperatures （940-970℃）, the instability was characterized by shear cracking along 45° orientation with respect to the compression axis and adiabatic shear band formation. At higher temperatures （970-1060℃）, the instability was attributed to longitudinal cracking or flow localization. The others were safe regimes characterized by recrystallization.更多还原