扩散型固态相变动力学与热力学研究
发布时间：2018-09-07 12:31
【摘要】：扩散型固态相变动力学与热力学研究属于材料科学与加工领域的重要基础理论研究,其形核和生长过程直接决定着材料的最终结构与性能。在现今复杂的材料相变过程中,传统经典理论的应用存在着诸多矛盾和偏离。因而,实现固态相变热力学、动力学甚至力学之间交互作用的精确理论描述,不仅意味着微观结构形成机制的精确洞察,还意味着材料新结构与新性能的开发,具有极为深远的科学和实际意义。 本论文以非晶态合金晶化、过饱和Al-Si合金Si的析出以及纯Fe或Fe基合金γ/α相变三个典型的扩散型形核-生长类固态相变为研究对象,从公式简单的极端非平衡忽略热力学因素影响的纯动力学过程入手,到遵循热力学局域平衡的纯扩散控制生长动力学过程,再到考虑热力学因素近平衡条件下的相变过程,通过逐步松弛传统动力学理论模型假设,并进一步耦合化学和机械驱动力等热力学因素,建立一套包括从转变分数和最大转变速率分析中确定相变动力学机制的方法、各向异性生长理论以及同软碰撞的交互、扩散控制相变可加性原理和等动力学概念的扩展、转变固有错配应变及扩散诱导应变弹塑性调节同界面控制相变和混合模式控制相变的交互等理论体系,旨在将扩散型形核-生长类固态相变推向更深的理论层次。本文主要结论如下： (1)基于固态相变动力学解析模型,对等温和非等温相变过程中转变分数和转变速率峰值进行了分析研究。借助动力学参数如Avrami指数n和总有效激活能Q同温度T或转变分数f的演化规律,提出了能够直接从转变分数和转变峰值分析中确定相变形核、生长和碰撞方式以及相关动力学参数的技巧和方法。包括基于等动力学和可加性原理的非等温相变向等温相变的转化以及单独的形核和生长激活能的确定。这些方法成功用于评价DSC测量得到的非晶Mg-Cu-Y等温晶化和非晶Pd-Ni-P-Cu等时晶化的动力学机制等信息。 (2)基于经典JMAK(Johnson-Mehl-Avrami-Kolmogorov)理论对形核-生长过程的统计学处理,对随机取向各向异性颗粒生长过程中所遭遇的阻碍效应进行了随机分析,解析给出了颗粒遭遇1次阻碍、k次阻碍以及无穷多次阻碍的固态相变动力学解析模型。首次证明传统唯象碰撞模型f=1-[1+(ξ-1)xe]-ξ1仅仅对应于各向异性颗粒遭遇无穷多次阻碍这一极端情况,并成功揭示了碰撞因子ξ的物理意义。阻碍效应不仅取决于阻碍级数k,还取决于非阻碍因子γ。它将导致Avrami指数的减小,转变中期最为剧烈,而转变初期和末期比较缓和,但却不影响相变过程中的有效激活能。该模型成功用于描述非晶态Fe33Zr67合金薄带的等温晶化过程。 （3）针对扩散控制固态相变，假设位置饱和形核、1维扩散控制生长和溶质扩散场线性近似，考虑相邻晶粒间的各向异性生长和溶质扩散场的重叠，基于两阶段生长理论和各向异性晶粒形状保持不变的生长尺寸分布规律，从晶核随机分布的概率密度入手，建立了一个能够综合考虑晶粒各向异性效应和软碰撞效应的扩散控制固态相变动力学解析模型。该模型成功用于解释Fe-0.17wt.%C合金γ→α相变中晶界铁素体半厚同经典抛物线生长理论的偏离以及描述0.37C-1.45Mn-0.11V微合金钢中晶界铁素体的体积分数。 （4）以过饱和Al-Si二元合金中纯Si的扩散控制析出为例，基于等温和非等温扩散控制生长的精确解，分析了传统可加性原理和经典等动力学假设在平衡或近平衡动力学过程中失效的原因。通过引入一个同温度历史相关的函数，得到了一个广义化的可加性原理和等动力学概念，以兼容同温度历史相关的瞬时转变速率。 （5）基于球形夹杂、无限小变形理论以及界面处位移连续，在不同转变阶段构建对应不同弹塑性区域的位移、应力和应变等变形状态，分析和描述了固态相变体积错配应变的弹塑性调节同相变过程的交互作用，提出了一个能够耦合化学和机械驱动力的固态相变动力学解析模型。利用纯Fe块状γ→α相变对上述模型进行了分析和讨论，转变错配应变能可以通过塑性变形得到一定程度的松弛。机械驱动力随f单调递增，转变前期阻碍转变进行，转变后期反而促进转变。模型成功用于纯Fe连续冷却γ→α相变的热膨胀实验。此外分析和讨论了转变错配弹塑性调节给γ/α相亚稳平衡温度所带来的影响。 （6）以Fe-C合金中的近平衡γ→α混合模式控制相变为研究对象，综合考虑转变错配应变和扩散应变，基于同转变分数相关的错配应变能模型、应力作用下的扩散方程以及热力学计算等，建立了γ/α相界面迁移、溶质组元扩散以及错配应变弹塑性调节三者交互作用的理论模型，分析和讨论了有限母相尺寸效应下转变错配应变及扩散应变的弹塑性调节给两相热力学平衡，，包括亚稳平衡温度、成分和相分数，以及等温和非等温混合模式控制相变动力学所带来的影响。错配应变的弹塑性调节不仅会影响动力学过程，还会从根本上影响热力学。错配应变能可以通过弹塑性应力/应变场和溶质扩散场等多场耦合得到更进一步的松弛。
[Abstract]:Dynamics and thermodynamics of diffusive solid-state phase transition (DSPCT) is an important basic theory in the field of material science and processing. Its nucleation and growth directly determine the final structure and properties of materials. Accurate theoretical descriptions of the interactions among variable thermodynamics, dynamics and even mechanics mean not only an accurate insight into the formation mechanism of microstructure, but also the development of new structures and properties of materials, which have far-reaching scientific and practical significance.
In this paper, three typical diffusion-type nucleation-growth solid-state phase transitions, i.e. crystallization of amorphous alloys, precipitation of supersaturated Al-Si alloys and gamma/a phase transitions of pure Fe or Fe-based alloys, have been studied. The pure kinetic process, in which the influence of thermodynamic factors is neglected and the extreme non-equilibrium is simplified, is proceeded with, and the pure diffusion follows the thermodynamic local equilibrium is followed. Controlling the growth kinetics process and then the phase transition process under the near-equilibrium condition considering the thermodynamic factors, a set of formulas including the determination of the phase transition kinetics mechanism from the analysis of the transition fraction and the maximum transition rate is established by gradually relaxing the assumptions of the traditional kinetic model and further coupling the thermodynamic factors such as chemical and mechanical driving forces. METHOD, ANISOTROPIC GROWTH THEORY, INTERACTION WITH SOFT COLLISION, ADDITIVE PRINCIPLE OF DIFFUSION-CONTROLLED PHASE TRANSFORMATION AND EXTENSION OF EQUIVALENT KINETIC CONCEPTS, TRANSFORMATION OF INTRINSITIAL Mismatch STRAIN, DIFFUSION-INDUCED STRAIN ELASTOPLASTIC ADJUSION Push forward to a deeper theoretical level. The main conclusions of this paper are as follows:
(1) Based on the analytical model of solid-state phase transition kinetics, the transition fraction and the peak value of transition rate in isothermal and non-isothermal phase transition processes are analyzed and studied. Techniques and methods for nucleation, growth and collision modes, and related kinetic parameters, including transition from non-isothermal to isothermal based on isokinetic and additive principles, and determination of individual nucleation and growth activation energies, have been successfully used to evaluate the isothermal crystallization of amorphous Mg-Cu-Y and amorphous P measured by DSC. D-Ni-P-Cu isochronous crystallization kinetics mechanism and other information.
(2) Based on the classical JMAK (Johnson-Mehl-Avrami-Kolmogorov) theory, the stochastic analysis of the hindrance effect on the growth of randomly oriented anisotropic particles is carried out. The analytical model of solid-state phase transition kinetics with one hindrance, K hindrance and infinite hindrance is given. For the first time, it is proved that the traditional phenomenological collision model f = 1 - [1 + (zeta-1) xe] - zeta 1 only corresponds to the extreme case that the anisotropic particles encounter infinite multiple blockages, and the physical significance of the collision factor zeta is successfully revealed. The model has been successfully used to describe the isothermal crystallization process of amorphous Fe33Zr67 alloy ribbons.
(3) Considering the anisotropic growth between adjacent grains and the overlap of solute diffusion field, assuming the saturated nucleation, the one-dimensional diffusion-controlled growth and the linear approximation of solute diffusion field, based on the two-stage growth theory and the growth size distribution law of anisotropic grains with the same shape, the random distribution is obtained from the nucleus. Based on the probability density, an analytical model of diffusion-controlled solid-state phase transformation is established, which can consider both the anisotropy effect and the soft-collision effect of grain. The model has been successfully used to explain the deviation of half-thickness of grain boundary ferrite from the classical parabolic growth theory in the gamma-alpha phase transformation of Fe-0.17wt.% C alloy and to describe the deviation of 0.37C-1.45Mn-0.11V. Volume fraction of ferrite in MICROTEK alloy microalloyed steel.
(4) Taking the diffusion-controlled precipitation of pure Si in supersaturated Al-Si binary alloys as an example, based on the exact solutions of isothermal and non-isothermal diffusion-controlled growth, the failure reasons of the traditional additivity principle and classical isokinetic hypothesis in equilibrium or near-equilibrium dynamic processes are analyzed. The generalized additivity principle and isokinetic concepts are compatible with the transient transition rates associated with temperature history.
(5) Based on the theory of spherical inclusions, infinitesimal deformation and displacement continuity at the interface, the displacement, stress and strain states corresponding to different elastic-plastic regions are constructed at different transformation stages. The interaction between the elastic-plastic adjustment of volume mismatch strain and the phase transformation process in solid phase transformation is analyzed and described, and a coupling chemistry and strain is proposed. Analytical model of solid-state phase transformation kinetics of mechanical driving force is presented. The above model is analyzed and discussed by means of pure Fe blocky y y_a phase transformation. The transformation mismatch strain energy can be relaxed to a certain extent by plastic deformation. The work has been applied to the thermal expansion experiment of the continuous cooling of pure Fe for the phase transformation from gamma to alpha. In addition, the effect of the mismatched elastoplastic adjustment of the transformation on the metastable equilibrium temperature of the gamma/alpha phase has been analyzed and discussed.
(6) Considering the mismatch strain and diffusion strain, based on the mismatch strain energy model related to the transformation fraction, the diffusion equation under stress and the thermodynamic calculation, the near-equilibrium gamma-alpha mixed mode controlled phase transformation in Fe-C alloy was studied. The interfacial migration of gamma/alpha phase, the diffusion of solute components and the mismatch strain were established. In this paper, the effects of the elastic-plastic adjustment of transition mismatch strain and diffusion strain on the thermodynamic equilibrium of two phases, including metastable equilibrium temperature, composition and phase fraction, and the effect of isothermal and non-isothermal mixed mode on the phase transition kinetics are analyzed and discussed. Mismatched strain energy can be further relaxed by coupling elastic-plastic stress/strain field with solute diffusion field.
【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
[Abstract]:Dynamics and thermodynamics of diffusive solid-state phase transition (DSPCT) is an important basic theory in the field of material science and processing. Its nucleation and growth directly determine the final structure and properties of materials. Accurate theoretical descriptions of the interactions among variable thermodynamics, dynamics and even mechanics mean not only an accurate insight into the formation mechanism of microstructure, but also the development of new structures and properties of materials, which have far-reaching scientific and practical significance.
In this paper, three typical diffusion-type nucleation-growth solid-state phase transitions, i.e. crystallization of amorphous alloys, precipitation of supersaturated Al-Si alloys and gamma/a phase transitions of pure Fe or Fe-based alloys, have been studied. The pure kinetic process, in which the influence of thermodynamic factors is neglected and the extreme non-equilibrium is simplified, is proceeded with, and the pure diffusion follows the thermodynamic local equilibrium is followed. Controlling the growth kinetics process and then the phase transition process under the near-equilibrium condition considering the thermodynamic factors, a set of formulas including the determination of the phase transition kinetics mechanism from the analysis of the transition fraction and the maximum transition rate is established by gradually relaxing the assumptions of the traditional kinetic model and further coupling the thermodynamic factors such as chemical and mechanical driving forces. METHOD, ANISOTROPIC GROWTH THEORY, INTERACTION WITH SOFT COLLISION, ADDITIVE PRINCIPLE OF DIFFUSION-CONTROLLED PHASE TRANSFORMATION AND EXTENSION OF EQUIVALENT KINETIC CONCEPTS, TRANSFORMATION OF INTRINSITIAL Mismatch STRAIN, DIFFUSION-INDUCED STRAIN ELASTOPLASTIC ADJUSION Push forward to a deeper theoretical level. The main conclusions of this paper are as follows:
(1) Based on the analytical model of solid-state phase transition kinetics, the transition fraction and the peak value of transition rate in isothermal and non-isothermal phase transition processes are analyzed and studied. Techniques and methods for nucleation, growth and collision modes, and related kinetic parameters, including transition from non-isothermal to isothermal based on isokinetic and additive principles, and determination of individual nucleation and growth activation energies, have been successfully used to evaluate the isothermal crystallization of amorphous Mg-Cu-Y and amorphous P measured by DSC. D-Ni-P-Cu isochronous crystallization kinetics mechanism and other information.
(2) Based on the classical JMAK (Johnson-Mehl-Avrami-Kolmogorov) theory, the stochastic analysis of the hindrance effect on the growth of randomly oriented anisotropic particles is carried out. The analytical model of solid-state phase transition kinetics with one hindrance, K hindrance and infinite hindrance is given. For the first time, it is proved that the traditional phenomenological collision model f = 1 - [1 + (zeta-1) xe] - zeta 1 only corresponds to the extreme case that the anisotropic particles encounter infinite multiple blockages, and the physical significance of the collision factor zeta is successfully revealed. The model has been successfully used to describe the isothermal crystallization process of amorphous Fe33Zr67 alloy ribbons.
(3) Considering the anisotropic growth between adjacent grains and the overlap of solute diffusion field, assuming the saturated nucleation, the one-dimensional diffusion-controlled growth and the linear approximation of solute diffusion field, based on the two-stage growth theory and the growth size distribution law of anisotropic grains with the same shape, the random distribution is obtained from the nucleus. Based on the probability density, an analytical model of diffusion-controlled solid-state phase transformation is established, which can consider both the anisotropy effect and the soft-collision effect of grain. The model has been successfully used to explain the deviation of half-thickness of grain boundary ferrite from the classical parabolic growth theory in the gamma-alpha phase transformation of Fe-0.17wt.% C alloy and to describe the deviation of 0.37C-1.45Mn-0.11V. Volume fraction of ferrite in MICROTEK alloy microalloyed steel.
(4) Taking the diffusion-controlled precipitation of pure Si in supersaturated Al-Si binary alloys as an example, based on the exact solutions of isothermal and non-isothermal diffusion-controlled growth, the failure reasons of the traditional additivity principle and classical isokinetic hypothesis in equilibrium or near-equilibrium dynamic processes are analyzed. The generalized additivity principle and isokinetic concepts are compatible with the transient transition rates associated with temperature history.
(5) Based on the theory of spherical inclusions, infinitesimal deformation and displacement continuity at the interface, the displacement, stress and strain states corresponding to different elastic-plastic regions are constructed at different transformation stages. The interaction between the elastic-plastic adjustment of volume mismatch strain and the phase transformation process in solid phase transformation is analyzed and described, and a coupling chemistry and strain is proposed. Analytical model of solid-state phase transformation kinetics of mechanical driving force is presented. The above model is analyzed and discussed by means of pure Fe blocky y y_a phase transformation. The transformation mismatch strain energy can be relaxed to a certain extent by plastic deformation. The work has been applied to the thermal expansion experiment of the continuous cooling of pure Fe for the phase transformation from gamma to alpha. In addition, the effect of the mismatched elastoplastic adjustment of the transformation on the metastable equilibrium temperature of the gamma/alpha phase has been analyzed and discussed.
(6) Considering the mismatch strain and diffusion strain, based on the mismatch strain energy model related to the transformation fraction, the diffusion equation under stress and the thermodynamic calculation, the near-equilibrium gamma-alpha mixed mode controlled phase transformation in Fe-C alloy was studied. The interfacial migration of gamma/alpha phase, the diffusion of solute components and the mismatch strain were established. In this paper, the effects of the elastic-plastic adjustment of transition mismatch strain and diffusion strain on the thermodynamic equilibrium of two phases, including metastable equilibrium temperature, composition and phase fraction, and the effect of isothermal and non-isothermal mixed mode on the phase transition kinetics are analyzed and discussed. Mismatched strain energy can be further relaxed by coupling elastic-plastic stress/strain field with solute diffusion field.
【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
【参考文献】
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