锻态Ti-6Al-7Nb合金高温热变形行为研究.pdf

分类号 TH142 10710-2012025006 博 士 学 位 论 文 锻态 Ti-6Al-7Nb 合金高温热变形行为研究 张晓琳 导师姓名职称谷立臣 教授 申请学位类别博士学科专业名称机械电子工程 论文提交日期 2021 年 3 月 10 日 论文答辩日期 2021 年 5 月 30 日 学位授予单位长安大学 Study on Hot Deation Behavior of Forged Ti-6Al-7Nb Alloy ADissertation ted for the Degree of Doctor CandidateZhang Xiaolin Supervisor Prof.Gu Lichen Chang’an University, Xi’an, China I 摘要 Ti-6Al-7Nb 合金是继 Ti-6Al-4V 钛合金材料之后的一种新型钛合金材料，该钛合金 综合力学性能表现优异， 是目前国内外钛合金领域的研制热点之一， 可广泛应用于航天、 航空、军事设备、民用设备及生物工程设备中的关键构件。金属材料热成型工艺是 Ti-6Al-7Nb 合金构件制备技术的重要环节，决定着 Ti-6Al-7Nb 合金构件的综合力学性 能、 设备可靠性及使用寿命等。 为了获得综合性能优异的 Ti-6Al-7Nb 合金塑性成形构件， 需对该材料的变形行为进行研究，结合基础的材料试验及工艺仿真模拟技术，从宏观和 微观角度对 Ti-6Al-7Nb 合金的热塑性成形工艺展开探索， 为获取高质量的钛合金构件提 供技术支撑。 本文采用试验研究及有限元数值模拟仿真技术相结合的研究方法，以 Ti-6Al-7Nb 合金的热塑性变形工艺研究为主线，在等温热压缩试验的基础之上，研究了 Ti-6Al-7Nb 合金的四种热塑性变形本构方程关系，获得了不同理论基础的能耗图、失稳图及热加工 图， 并对本构关系及热加工图精度和适用性进行了对比和评价， 揭示 Ti-6Al-7Nb 合金的 热压缩变形的宏微观变化规律。 同时， 研究了不同变形条件下 Ti-6Al-7Nb 合金的微观组 织演变规律，分析了该钛合金材料的流变特征和形变强化特征，并对该钛合金的动态再 结晶行为进行研究，获取了 Ti-6Al-7Nb 合金动态再结晶临界条件。最后，结合有限元仿 真模拟， 对典型 Ti-6Al-7Nb 合金圆盘类零件进行了塑性成形仿真， 分析了变形工艺参数 对成形性能的影响， 获取了能够稳定、 高效和高质量充型的 Ti-6Al-7Nb 合金盘件零件等 温模锻成型工艺参数。主要研究结果如下 利用 Gleeble-3500 热模拟压缩试验机对变形温度在 750～1173K 范围、应变速率在 0.005～10s-1范围、变形量为 60时的 Ti-6Al-7Nb 合金进行等温恒应变速率压缩试验， 获取了该钛合金的流动应力应变数据， 发现变形温度与应变速率对该钛合金的流动应 力曲线变化影响较大，而且该钛合金的热塑性变形过程中存在形变强化和流动软化现 象，变形温度与应变速率对 Ti-6Al-7Nb 合金的形变强化和流动软化作用具有较复杂影 响。 基于 Ti-6Al-7Nb 合金的流动应力应变数据，建立了 Arrhenius、Zerilli-Armstrong、 Johnson-Cook 和人工神经网络热变形塑性本构方程模型， 发现四种本构方程模型的预测 II 能力存有显著差异，特此，引入相关系数 R 与相对误差绝对值平均 ARRE 对本构模型 的预测精度进行量化评价。人工神经网络模型在预测精度及线性相关性中均具有较佳精 度。不同本构模型关系对 Ti-6Al-7Nb 合金流变应力预测的适用范围不同，Arrhenius 本 构方程模型适用于高应变速率、低温和高温形变条件；Zerilli-Armstrong 本构方程模型 适用于高应变速率、低变形温度条件；Johnson-Cook 本构方程模型适用于高应变速率或 较低和较高变形温度条件。通过建立 Ti-6Al-7Nb 合金热塑性变形的 Murty 及 Prasad 能 量耗散图，并绘制出了不同失稳判据下的失稳图，最终确定出 Prasad、Murty 和 Malas 理论的热加工图。通过对不同热加工图的研究及分析，发现应变速率和变形温度对于失 稳区域的分布状况影响显著，采用不同失稳准则而获得的热加工图失稳区域差异性较 大，综合来看三种热加工图的精确度顺序为Murty＞Malas＞Prasad。 利用应变速率敏感性指数 m、温度敏感性指数 s 和应变硬化指数 n1对 Ti-6Al-7Nb 合金的塑性流变和形变强化进行量化表征，发现材料在不同变形条件下的流变能力、流 动软化及形变强化具有显著差异。研究了变形温度和应变速率对微观组织的影响规律， 阐明了 Ti-6Al-7Nb 合金微观组织演变规律及热变形后的物相状态， 同时应用动态再结晶 临界条件，对该钛合金动态再结晶临界应变进行分析，确定该钛合金在热塑性变形时的 动态再结晶临界应变条件。 通过仿真模拟与试验结果比对， 发现有限元仿真能够较精确实现 Ti-6Al-7Nb 合金热 加工过程的预测，另外，对典型的 Ti-6Al-7Nb 合金圆盘类零件进行有限元仿真建模，分 析并探讨工艺参数对该钛合金变形的应力状况、材料体积与形状变化能力的影响，综合 分析知坯料高径比为 1.754、温度 1073K、变形速度为 1.0mm/s 及摩擦因子为 0.4 时， 可实现该钛合金圆盘类构件的稳定、高效和高质量充型。 关键词Ti-6Al-7Nb 合金；高温本构模型；热加工图；微观组织演变；有限元仿真模拟 III Abstract Ti-6Al-7Nb titanium alloy is a new type of titanium alloy engineering material after Ti-6Al-4V titanium alloy material. The titanium alloy has excellent comprehensive mechanical properties. It is one of the hot spots in the field of titanium alloy at home and abroad. It can be widely used in aerospace, aviation, military equipment, civil equipment and bioengineering equipment key components. The thermoplastic molding process of metal materials is an important link in the preparation of Ti-6Al-7Nb titanium alloy components, which determines the comprehensive mechanical properties, equipment reliability and service life of the key components of Ti-6Al-7Nb titanium alloy. To obtain a Ti-6Al-7Nb titanium alloy plastic ing member with excellent comprehensive properties, it is necessary to analyze and study the deation ability of the material, combined with the basic material test and process simulation technology. The thermoplastic ing process of Ti-6Al-7Nb titanium alloy is studied from macro and micro angles to provide technical support for obtaining high quality titanium alloy components. On the basis of isothermal compression test, the four constitutive equations of Ti-6Al-7Nb alloy are studied by combining experimental research, theoretical calculation and finite element numerical simulation, and the accuracy and applicability of different constitutive relations and hot working diagrams are compared and uated to reveal the macroscopic and microscopic changes of hot-pressing deation of Ti-6Al-7Nb alloy. The microstructure evolution of Ti-6Al-7Nb alloy under different deation conditions is studied, the rheological and deation strengthening characteristics of the titanium alloy are analyzed, and the dynamic recrystallization behavior of the titanium alloy is studied. The critical ination of dynamic recrystallization of Ti-6Al-7Nb alloy is obtained. Moreover, the plastic ing simulation Ti-6Al-7Nb typical alloy disc parts is carried out with finite element simulation, and the influence of deation process parameters on is analyzed. Finally, the isothermal forging process parameters of Ti-6Al-7Nb alloy disc parts with stable, high efficiency and high-quality filling are obtained. The main results are as follows IV Based on the flow stress-strain data of Ti-6Al-7Nb titanium alloys, A constitutive equation model for thermal deation of Arrhenius、Zerilli-Armstrong、Johnson-Cook and artificial neural networks was established, It is found that there are significant differences in the prediction ability of the four constitutive equation models, Hereby, The prediction accuracy of constitutive model is quantitatively uated by introducing correlation coefficient R and relative error absolute average ARRE. BP artificial neural network model has excellent accuracy in prediction accuracy and linear correlation. Different constitutive models are applicable to the prediction of rheological stress of Ti-6Al-7Nb titanium alloys, Arrhenius constitutive equation model is suitable for high strain rate, low temperature and high temperature deation conditions; Zerilli-Armstrong constitutive equation model is suitable for high strain rate and low deation temperature condition; Johnson-Cook constitutive equation model is suitable for high strain rate or lower and higher deation temperature conditions. Through the establishment of Ti-6Al-7Nb Murty and Prasad energy dissipation diagram of thermoplastic deation of titanium alloy, And draw the instability map under different instability criteria, The hot working drawing of Prasad、Murty and Malas theory is finally determined. Through the study and analysis of different hot working charts, it is found that strain rate and deation temperature have a significant effect on the distribution of unstable regions, And the instability region of hot working map obtained by different instability criteria is quite different. According to the comprehensive analysis, the accuracy order of the three hot working drawings is MurtyMalasPrasad. Using strain rate sensitivity index m、 temperature sensitivity index s and strain hardening index n1, the plastic rheology and deation strengthening of Ti-6Al-7Nb titanium alloy were quantitatively characterized. The influence of deation temperature and strain rate on microstructure is studied, and the evolution law of microstructure and phase state of Ti-6Al-7Nb titanium alloy after thermal deation are expounded. The critical strain of dynamic recrystallization of Ti-6Al-7Nb titanium alloy is analyzed, and the critical strain ination of dynamic recrystallization of titanium alloy during thermoplastic deation is determined. V Through comparison of simulation results with test samples, it is found that finite element simulation can accurately predict the hot working process of Ti-6Al-7Nb alloys. In addition, the finite element simulation modeling of typical Ti-6Al-7Nb alloy disc parts is carried out, The influence of deation process parameters on the stress condition, material volume and shape change ability of the titanium alloy is discussed. The stability, high efficiency and high quality filling can be realized when the ratio of height to diameter is 1.754, the temperature is 1073K, the deation speed is 1.0 mm/s and the friction factor is 0.4. Keywords Ti-6Al-7Nb titanium alloy; High temperature constitutive model; Thermal processing diagram; Microstructure evolution; Finite element simulation VII 目目录录 第一章绪 论...........................................................................................................................1 1.1 钛合金的研究与应用...................................................................................................1 1.2 热变形行为的国内外研究现状...................................................................................9 1.3 Ti-6Al-7Nb 合金的研究现状......................................................................................13 1.4 选题背景及研究意义.................................................................................................17 1.5 主要研究内容与思路.................................................................................................18 1.5.1主要研究内容.................................................................................................18 1.5.2主要研究技术路线.........................................................................................19 第二章基础理论和方法.......................................................................................................21 2.1 有限元模拟基础.........................................................................................................21 2.2 试验研究方法.............................................................................................................23 2.2.1 试验材料及试样...............................................................................................23 2.2.2 热模拟压缩试验...............................................................................................23 2.3.1 Johnson-Cook 本构方程................................................................................... 24 2.3.2 Zerilli-Armstrong 本构方程..............................................................................25 2.3.3Arrhenius 本构方程...........................................................................................26 2.3.4 人工神经网络模型...........................................................................................27 2.4 DMM 加工图理论基础...............................................................................................27 2.5 材料塑性失稳判断准则.............................................................................................29 2.6 本章小结.....................................................................................................................32 第三章Ti-6Al-7Nb 合金热变形本构方程研究...................................................................33 3.1 热模拟压缩试验.........................................................................................................33 3.2 热压缩变形行为分析.................................................................................................34 3.3 本构方程描述.............................................................................................................36 3.3.1 Zerilli-Armstrong 本构方程模型描述..............................................................36 3.3.2 Johnson-Cook 本构方程模型描述................................................................... 40 3.3.3Arrhenius 本构方程模型描述...........................................................................44 VIII 3.3.4 人工神经网络模型描述...................................................................................49 3.4 本构模型对比分析.....................................................................................................51 3.5 本章小结.....................................................................................................................54 第四章Ti-6Al-7Nb 合金热加工图研究...........................................................................................56 4.1 Ti-6Al-7Nb 合金流变特征..........................................................................................56 4.2 Ti-6Al-7Nb 合金功率耗散图建立..............................................................................60 4.2.1 基于 Prasad 理论的能量耗散图......................................................................61 4.2.2 基于 Murty 理论的能量耗散图.......................................................................63 4.2.3 两种理论的能量耗散图对比分析...................................................................65 4.3 Ti-6Al-7Nb 合金塑性热加工图建立..........................................................................66 4.3.1 塑性失稳判据的理论计算...............................................................................66 4.3.2 不同失稳判据下的加工图...............................................................................71 4.4 本章小结.....................................................................................................................75 第五章Ti-6Al-7Nb 合金组织演变与变形分析............................................................................. 77 5.1 Ti-6Al-7Nb 合金热变形微观组织演变规律..............................................................77 5.1.1 变形温度确定时的微观组织演变...................................................................77 5.1.2 应变速率确定时的微观组织演变...................................................................79 5.2 Ti-6Al-7Nb 合金变形特征分析..................................................................................82 5.3 热变形组织的 EBSD 分析........................................................................................85 5.3.1 晶粒取向差分析...............................................................................................85 5.3.2 大小角度晶界及晶粒度分析...........................................................................87 5.3.3 晶界位相差.......................................................................................................88 5.3.4 试样组织织构分析...........................................................................................89 5.4 动态再结晶临界应变.................................................................................................91 5.4.1 动态再结晶临界应变理论基础.......................................................................91 5.4.2 动态再结晶临界应变的分析...........................................................................93 5.4.3 动态再结晶 Z 参数..........................................................................................96 5.5 本章小结.....................................................................................................................98 IX 第六章典型 Ti-6Al-7Nb 合金零件成形仿真研究........................................................................99 6.1 热模拟压缩试验模拟分析.........................................................................................99 6.2 盘件等温模锻有限元分析模型的建立...................................................................103 6.2.1 仿真模拟模型的创建.....................................................................................103 6.2.2 仿真模拟条件设置.........................................................................................105 6.3 锻坯初始高径比对盘件等温模锻的影响分析.......................................................106 6.4 变形温度对盘件等温模锻的影响分析...................................................................110 6.5 变形速率对盘件等温模锻的影响分析...................................................................113 6.6 摩擦因子对盘件等温模锻的影响分析...................................................................117 6.7 等温模锻工艺参数影响分析...................................................................................121 6.8 本章小结...........................................................................................