擴散型固態(tài)相變動力學(xué)與熱力學(xué)研究
發(fā)布時間：2018-09-07 12:31
【摘要】：擴散型固態(tài)相變動力學(xué)與熱力學(xué)研究屬于材料科學(xué)與加工領(lǐng)域的重要基礎(chǔ)理論研究,其形核和生長過程直接決定著材料的最終結(jié)構(gòu)與性能。在現(xiàn)今復(fù)雜的材料相變過程中,傳統(tǒng)經(jīng)典理論的應(yīng)用存在著諸多矛盾和偏離。因而,實現(xiàn)固態(tài)相變熱力學(xué)、動力學(xué)甚至力學(xué)之間交互作用的精確理論描述,不僅意味著微觀結(jié)構(gòu)形成機制的精確洞察,還意味著材料新結(jié)構(gòu)與新性能的開發(fā),具有極為深遠的科學(xué)和實際意義。 本論文以非晶態(tài)合金晶化、過飽和Al-Si合金Si的析出以及純Fe或Fe基合金γ/α相變?nèi)齻�典型的擴散型形核-生長類固態(tài)相變?yōu)檠芯繉ο?從公式簡單的極端非平衡忽略熱力學(xué)因素影響的純動力學(xué)過程入手,到遵循熱力學(xué)局域平衡的純擴散控制生長動力學(xué)過程,再到考慮熱力學(xué)因素近平衡條件下的相變過程,通過逐步松弛傳統(tǒng)動力學(xué)理論模型假設(shè),并進一步耦合化學(xué)和機械驅(qū)動力等熱力學(xué)因素,建立一套包括從轉(zhuǎn)變分數(shù)和最大轉(zhuǎn)變速率分析中確定相變動力學(xué)機制的方法、各向異性生長理論以及同軟碰撞的交互、擴散控制相變可加性原理和等動力學(xué)概念的擴展、轉(zhuǎn)變固有錯配應(yīng)變及擴散誘導(dǎo)應(yīng)變彈塑性調(diào)節(jié)同界面控制相變和混合模式控制相變的交互等理論體系,旨在將擴散型形核-生長類固態(tài)相變推向更深的理論層次。本文主要結(jié)論如下： (1)基于固態(tài)相變動力學(xué)解析模型,對等溫和非等溫相變過程中轉(zhuǎn)變分數(shù)和轉(zhuǎn)變速率峰值進行了分析研究。借助動力學(xué)參數(shù)如Avrami指數(shù)n和總有效激活能Q同溫度T或轉(zhuǎn)變分數(shù)f的演化規(guī)律,提出了能夠直接從轉(zhuǎn)變分數(shù)和轉(zhuǎn)變峰值分析中確定相變形核、生長和碰撞方式以及相關(guān)動力學(xué)參數(shù)的技巧和方法。包括基于等動力學(xué)和可加性原理的非等溫相變向等溫相變的轉(zhuǎn)化以及單獨的形核和生長激活能的確定。這些方法成功用于評價DSC測量得到的非晶Mg-Cu-Y等溫晶化和非晶Pd-Ni-P-Cu等時晶化的動力學(xué)機制等信息。 (2)基于經(jīng)典JMAK(Johnson-Mehl-Avrami-Kolmogorov)理論對形核-生長過程的統(tǒng)計學(xué)處理,對隨機取向各向異性顆粒生長過程中所遭遇的阻礙效應(yīng)進行了隨機分析,解析給出了顆粒遭遇1次阻礙、k次阻礙以及無窮多次阻礙的固態(tài)相變動力學(xué)解析模型。首次證明傳統(tǒng)唯象碰撞模型f=1-[1+(ξ-1)xe]-ξ1僅僅對應(yīng)于各向異性顆粒遭遇無窮多次阻礙這一極端情況,并成功揭示了碰撞因子ξ的物理意義。阻礙效應(yīng)不僅取決于阻礙級數(shù)k,還取決于非阻礙因子γ。它將導(dǎo)致Avrami指數(shù)的減小,轉(zhuǎn)變中期最為劇烈,而轉(zhuǎn)變初期和末期比較緩和,但卻不影響相變過程中的有效激活能。該模型成功用于描述非晶態(tài)Fe33Zr67合金薄帶的等溫晶化過程。 （3）針對擴散控制固態(tài)相變，假設(shè)位置飽和形核、1維擴散控制生長和溶質(zhì)擴散場線性近似，考慮相鄰晶粒間的各向異性生長和溶質(zhì)擴散場的重疊，基于兩階段生長理論和各向異性晶粒形狀保持不變的生長尺寸分布規(guī)律，從晶核隨機分布的概率密度入手，建立了一個能夠綜合考慮晶粒各向異性效應(yīng)和軟碰撞效應(yīng)的擴散控制固態(tài)相變動力學(xué)解析模型。該模型成功用于解釋Fe-0.17wt.%C合金γ→α相變中晶界鐵素體半厚同經(jīng)典拋物線生長理論的偏離以及描述0.37C-1.45Mn-0.11V微合金鋼中晶界鐵素體的體積分數(shù)。 （4）以過飽和Al-Si二元合金中純Si的擴散控制析出為例，基于等溫和非等溫擴散控制生長的精確解，分析了傳統(tǒng)可加性原理和經(jīng)典等動力學(xué)假設(shè)在平衡或近平衡動力學(xué)過程中失效的原因。通過引入一個同溫度歷史相關(guān)的函數(shù)，得到了一個廣義化的可加性原理和等動力學(xué)概念，以兼容同溫度歷史相關(guān)的瞬時轉(zhuǎn)變速率。 （5）基于球形夾雜、無限小變形理論以及界面處位移連續(xù)，在不同轉(zhuǎn)變階段構(gòu)建對應(yīng)不同彈塑性區(qū)域的位移、應(yīng)力和應(yīng)變等變形狀態(tài)，分析和描述了固態(tài)相變體積錯配應(yīng)變的彈塑性調(diào)節(jié)同相變過程的交互作用，提出了一個能夠耦合化學(xué)和機械驅(qū)動力的固態(tài)相變動力學(xué)解析模型。利用純Fe塊狀γ→α相變對上述模型進行了分析和討論，轉(zhuǎn)變錯配應(yīng)變能可以通過塑性變形得到一定程度的松弛。機械驅(qū)動力隨f單調(diào)遞增，轉(zhuǎn)變前期阻礙轉(zhuǎn)變進行，轉(zhuǎn)變后期反而促進轉(zhuǎn)變。模型成功用于純Fe連續(xù)冷卻γ→α相變的熱膨脹實驗。此外分析和討論了轉(zhuǎn)變錯配彈塑性調(diào)節(jié)給γ/α相亞穩(wěn)平衡溫度所帶來的影響。 （6）以Fe-C合金中的近平衡γ→α混合模式控制相變?yōu)檠芯繉ο螅C合考慮轉(zhuǎn)變錯配應(yīng)變和擴散應(yīng)變，基于同轉(zhuǎn)變分數(shù)相關(guān)的錯配應(yīng)變能模型、應(yīng)力作用下的擴散方程以及熱力學(xué)計算等，建立了γ/α相界面遷移、溶質(zhì)組元擴散以及錯配應(yīng)變彈塑性調(diào)節(jié)三者交互作用的理論模型，分析和討論了有限母相尺寸效應(yīng)下轉(zhuǎn)變錯配應(yīng)變及擴散應(yīng)變的彈塑性調(diào)節(jié)給兩相熱力學(xué)平衡，，包括亞穩(wěn)平衡溫度、成分和相分數(shù)，以及等溫和非等溫混合模式控制相變動力學(xué)所帶來的影響。錯配應(yīng)變的彈塑性調(diào)節(jié)不僅會影響動力學(xué)過程，還會從根本上影響熱力學(xué)。錯配應(yīng)變能可以通過彈塑性應(yīng)力/應(yīng)變場和溶質(zhì)擴散場等多場耦合得到更進一步的松弛。
[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.
【學(xué)位授予單位】：西北工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：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.
【學(xué)位授予單位】：西北工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG111
【參考文獻】
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