【作者】 蔡大勇；

【导师】 姚枚； 刘文昌； 陈宗霖；

【作者基本信息】 燕山大学 ， 材料学， 2003， 博士

【摘要】 在对GH169（Inconel718）合金及其析出相电化学特性分析的基础上，通过电解液及电解条件的选择，实现了(γ″+γ′)、δ及NbC相的电解分离及定量分析，验证了GH169合金X射线衍射(XRD)定量相分析方法的可行性，相对误差低于10%。根据合金元素在γ″与γ′相之间的分配关系，计算了γ″及γ′相含量（Wγ′ 及Wγ″）的关系，发现Wγ″与Wγ′ 的比值约为3；利用该结果对XRD定量相分析方法进行了修正。通过定量相分析及组织观察，研究了GH169合金中δ相的溶解行为。对于本试验中δ相初始含量为8.4wt%的合金，在980℃保温30min后，δ相接近于溶解平衡，其含量约为3.0wt%；1000℃保温时，经过6h后接近溶解平衡，其含量约为0.6wt%；在1020℃保温1h后，δ相几乎完全溶解。建立了GH169合金中δ相溶解的动力学模型，并揭示了溶解过程的控制环节。溶解初期主要表现为针状δ相长轴方向的溶断，后期主要为短棒状及颗粒状δ相尺寸的减小。δ相的溶解不受Nb或Ni原子的长程扩散过程控制，而受界面反应过程控制，溶解初期及后期分别满足收缩未反应芯模型及三级反应模型。据此，确定了δ相溶解的动力学方程。研究了GH169合金δ相溶解处理对其强度、塑性及缺口敏感性的影响。确定了δ相含量对合金缺口敏感性影响的定量关系，当其含量高于0.62wt%时，合金对缺口不敏感；而当其含量为0.33wt%时，合金已表现为严重的缺口敏感。研究了喷丸处理对GH169合金缺口敏感性的影响。对于1020℃×1h回溶处理的缺口敏感试样；双时效前喷丸处理可使其持久寿命提高10倍以上，合金对缺口不敏感。据此提出了改进GH169合金热加工工艺的建议，在最终双时效前，采用本文给出的XRD定量相分析方法测定合金中δ相的含量，如果其含量低于0.62wt%，则对合金进行高强喷丸处理，然后进行双时效；该工艺可有效避免GH169缺口敏感的发生，减少废品。用Gleeble3500热模拟机系统研究了热轧态GH696（ЭИ696）合金的热变形行为。GH696合金的热变形激活能为499kJ/mol，确定了热变形方程，给出了不同应变量、变形温度及应变速率下的应变速率敏感性指数及能量消耗效率，建立了GH696合金的热加工图(Processing map)。不同真应变下的热加工图相似，随着变形温度的升高及应变速率的降低，能量消耗效率逐渐升高。真应变为0.7时，在变形温度1150℃左右、应变速率为0.001/s-1时，能量消耗效率η达到峰值，约为40-48%，η值大于40%的区域为完全再结晶区。该结果为GH696合金热变形工艺优化提供了理论依据。研究了固溶处理温度对GH696（ЭИ696）合金力学性能的影响。当固溶温度超过1050℃时，合金强塑性下降。断口及组织分析表明，GH696合金晶界处析出的片状间隙相TiC是导致其强塑性下降的主要原因。用差热分析法（DSC）研究了冷却速度对TiC相析出过程的影响，当冷却速度为1℃/min时，未发现TiC的析出，但当冷却速度大于10℃/min时，<WP=5>却发现了TiC的析出。明确了TiC晶界相的形成是由于固溶后快冷过程中溶质原子非平衡偏聚的结果。更多还原

【Abstract】 On the basis of the electrochemistry analysis of GH169 (Inconel718) superalloy and its precipitates, a respective extraction technique of (γ″+γ′), δ and NbC phases was employed, and their quantitative analysis was successfully fulfilled. The quantitative phase analysis results are in good agreement with those obtained through the X-ray diffraction (XRD) quantitative phase analysis method previously proposed. According to the distribution relationship of alloy elements in γ″ to γ′ phase, the ratio of weight fraction of γ″ to γ′ phase is calculated and is believed to be a constant equal to 3. This result is adopted for the correction of the XRD quantitative phase analysis method. Dissolution kinetics and microstructure evolution of δ phase in GH169 during holding at 980℃, 1000℃ and 1020℃ were analyzed using XRD and scanning electron microscopy (SEM). For the specimens with initial content of δ phase of 8.4wt%, a dynamic equilibrium state reaches after holding at 980℃ for more than 30 minutes and at 1000℃ for more than 2 hours, and the equilibrium contents are 3.0wt% and 0.6wt% respectively. Nearly all δ phase dissolves into the austenitic matrix at 1020℃ for more than 1 hours. Dissolution models of δ phase were established and the controlling step was revealed. Dissolution process of needle-like δ phase can be divided into two stages, the initial stage is mainly characterized as the fracture from long needle shape to short bars or particles and the following stage is the decrease in size for the short bars or particles. The whole dissolution process is governed by the interface reaction mechanism, but not by the long-distance diffusion of Nb or Ni atoms in the austenite matrix. The dissolution kinetics equations are established by applying the reaction shrinking core model and the third order reaction model for the initial and final stage of δ phase dissolution, respectively.Influences of δ phase dissolution treatment on the mechanical properties and notch sensitivity of GH169 were studied. Quantitative relationship between the notch sensitivity and the content of δ phase is established. GH169 alloy is not sensitive to notch when the content of δ phase is higher than 0.62wt%. By contrast, seriously notch sensitivity is observed when the content of δ phase is 0.33wt%. The influence of shot peening on the notch sensitivity of GH169 was studied. For the notch sensitive specimens having been heated at 1020℃ for 1h, stress rupture life can be improved for 10 times and failure occurs at the smooth region when shot peening is performed before double ageing. Based on the above results, an advice for the hot working technology of GH169 is proposed. Quantitative analysis of δ phase using the XRD method should be performed before the double ageing treatment and shot peenig should be performed, if the content of δ phase is lower than 0.62wt%. In this case, notch sensitivity can be <WP=7>effectively avoided.Hot deformation behavior of hot-rolled GH696 (ЭИ696) was investigated by the use of Gleeble 3500 simulator. Hot deformation equation is given to characterized the dependence of peak stress on the temperature and strain rate. The apparent activation energy is about 499kJ/mol. The strain rate sensitivity and efficiency of power dissipation is determined under different hot deformation conditions. Processing maps are established and interpreted on the basis of microstructure observation. The maps obtained at true strains range from 0.1 to 0.7 are essentially similar, and efficiency of power dissipation increases gradually with the increase of temperature and decrease of strain rate. A domain with its peak efficiency about 40-48% appears at about 1150℃ and 0.001/s-1, and is correspondent to dynamic recrystallization (DRX) for the true strain of 0.7.Influence of solid solution treatment temperature (range from 1000℃ to 1150℃) on the mechanical properties of GH696 was studied. Strength and plasticity decrease with the increase of solution temperature. Fractography and microstructure analys更多还原