基于解析模型的形核—长大型固态相变动力学研究

发布时间：2018-05-28 15:35

本文选题：非晶晶化 + 多晶型转变　；参考：《西北工业大学》2015年博士论文

【摘要】：高性能金属材料制备过程中，基于固态相变原理的热处理技术是不可或缺的关键手段。随着金属材料制备技术的革新，其固态相变动力学行为已无法用传统理论来描述。固态相变动力学过程直接影响材料的微观组织和结构，进而决定其性质和服役性能。因此，开展固态相变动力学研究不仅具有重要的科学意义，而且蕴含着潜在的工程应用前景。本文研究了两种常见的金属固态相变过程：非晶晶化和多晶型转变。理论上，通过分析不同条件下影响固态相变动力学的因素，松弛传统理论假设，提出一般性动力学理论模型。实验上，借助热分析技术(DSC和DIL)获得固态相变转变动力学曲线，结合相分析和组织分析判断转变机制，最终实现对理论模型的验证。主要结论如下： 1基于解析模型，提出了动力学分析新方法。从总的有效激活能表达式出发，提出获取形核和生长激活能的线性回归分析方法；从转变分数归一化处理出发，得到判断等温模型迭代方法。据此获得了多种非晶合金晶化过程的动力学参数。 2将一般形式温度积分和初始温度引入到解析模型中，拓展了模型应用范围。根据激活能数值，选择最优温度积分组合以保证模型精度；当转变初始温度不可忽略时，模型仍精确预测出动力学参数和转变分数。该模型可成功描述Ti50Cu42Ni8非晶合金晶化动力学过程。 3拓展了解析模型中和积转化概念，提出了同步及非同步多机制相变动力学模型。该模型可为诸多动力学现象提供合理解释：消耗新相的子过程会导致有效生长指数逐渐降低；Avrami形核机制是由多个子过程叠加所致；无限多个非同步位置饱和子过程的综合作用与连续形核机制等效；异常的转变速率及Avrami指数均源自于孕育期；等。根据非同步多机制相变模型，成功分析了Mg-Cu-Y和Zr-Cu-Al非晶合金晶化动力学行为。 4针对界面控制生长固态相变，提出了普适的扩展解析模型。在独立描述形核和生长动力学时引入热力学因素，模型可用于描述近平衡和极端非平衡状态下的相变过程。采用特殊的温度积分处理，模型可同时适用于连续加热和连续冷却过程。利用热膨胀仪定量表征了二元Fe基置换固溶体的奥氏体/铁素体非等温相变动力学行为，扩展解析模型可精确描述其全转变动力学过程。 5从经典速率方程出发，，引入不同的热力学驱动力，得到用于描述等温和等时相变动力学过程的热-动力学模型。该模型可预测完全等温相变温度区间，解释等温相变后期迟缓阶段及非等温相变中异常转变等动力学行为。基于该模型成功分析了Fe-3Mn和Fe-2Co合金奥氏体/铁素体相变动力学行为。 6基于脆性熔体Vogel-Fulcher-Tammann关系，将随温度变化的激活能耦合到固态相变动力学中，得到了描述非晶在过冷液相区晶化的一般性模型。根据该模型，提出了直接由晶化动力学实验数据获取熔体性质信息的分析方法。该模型成功描述了Zr-Cu-Al-Ni合金系的等温和非等温晶化动力学。
[Abstract]:During the preparation of high performance metal materials, the heat treatment technology based on the principle of solid phase transformation is an indispensable key means. With the innovation of the metal material preparation technology, the dynamic behavior of the solid phase transformation can not be described by the traditional theory. The solid state phase transformation kinetics process directly affects the microstructure and structure of the material, and then decides on it. Properties and service properties. Therefore, it is not only of important scientific significance to carry out the study of solid phase transition kinetics, but also contains potential engineering applications. In this paper, two kinds of common solid state phase transition processes: amorphous and polycrystalline transformation. In theory, the analysis of the factors affecting the kinetics of solid phase transition under different conditions is theoretically analyzed. In the experiment, the kinetic curve of the transformation of solid phase transition is obtained by thermal analysis (DSC and DIL), and the transformation mechanism is judged by phase analysis and tissue analysis, and the final verification of the theoretical model is realized. The main conclusions are as follows:
1 based on the analytical model, a new method of dynamic analysis is proposed. From the general effective activation energy expression, the linear regression analysis method for obtaining the nucleation and growth activation energy is proposed. From the transformation of the fractional normalization treatment, the iterative method of determining the isothermal model is obtained. Accordingly, the kinetic parameters of the crystallization process of various amorphous alloys are obtained.
2 the general form of temperature integral and initial temperature are introduced into the analytical model, and the application range of the model is extended. According to the activation energy value, the optimal temperature integral combination is selected to ensure the model accuracy. When the initial temperature can not be ignored, the model can predict the dynamic parameters and the transition fraction accurately. The model can describe the Ti50Cu42Ni8 successfully. Crystallization kinetics of amorphous alloys.
3 extended the concept of analytic model neutralization and transformation, and proposed a dynamic model of synchronous and asynchronous multi mechanism phase transformation. This model can provide a reasonable explanation for many dynamic phenomena: the subprocess of consumption of new phase leads to the gradual decrease of the effective growth index; the Avrami nucleation mechanism is caused by the superposition of a number of sub processes; The synthetic effect of the step position saturation process is equivalent to the continuous nucleation mechanism, and the abnormal transition rate and Avrami index are all derived from the inoculation period, and so on. The crystallization kinetics of Mg-Cu-Y and Zr-Cu-Al amorphous alloys have been successfully analyzed according to the model of the asynchronous multi mechanism phase transition.
4 a universal analytical model is proposed for the growth of solid phase transition in the interface control. The thermodynamic factors are introduced to describe the nucleation and growth kinetics independently. The model can be used to describe the phase transition process under the state of near equilibrium and extreme non equilibrium. The special temperature integral treatment can be used for continuous heating and continuous cooling. A thermal expansion instrument was used to quantitatively characterize the non isothermal phase transition kinetics of the austenite / ferrite of two element Fe base displaced solid solution. The extended analytical model can accurately describe the full transformation kinetics.
5 from the classical rate equation, the thermal dynamic model used to describe the isothermal and isothermal phase transition kinetics is obtained by introducing different thermodynamic driving forces. The model can predict the complete isothermal phase transition temperature range, explain the dynamic behavior of the delay phase in the later phase of isothermal phase transition and the abnormal transition in the non isothermal phase transition. Based on the model, the model is successful The kinetics of austenite / ferrite transformation in Fe-3Mn and Fe-2Co alloys was analyzed.
6 based on the Vogel-Fulcher-Tammann relationship of brittle melt, a general model for describing the crystallization of the amorphous phase in the supercooled liquid phase is obtained by coupling the activation energy with the change of temperature to the solid-state phase transition kinetics. Based on this model, an analytical method for obtaining the information of the melt properties directly from the experimental data of crystallization kinetics is proposed. The model is successfully described. The isothermal and non isothermal crystallization kinetics of Zr-Cu-Al-Ni alloy system was studied.
【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG111.5

【参考文献】