偏晶合金凝固過程及微合金化的影響
發(fā)布時間：2019-05-28 02:14
【摘要】：偏晶合金十分廣泛,其主要特點是,單一均勻的偏晶合金熔體在冷卻過程中將發(fā)生液-液相變,生成兩個互不混溶的液相。如凝固形成少量相以微小粒子形式彌散分布于基體中的復合材料,則許多偏晶合金具有優(yōu)異性能,在工業(yè)上擁有廣闊的應用前景。然而,偏晶合金液-液相變過程十分復雜,影響因素繁多,在常規(guī)的凝固條件下,極易形成相偏析嚴重乃至兩相分層的凝固組織。這限制了該類合金的工業(yè)開發(fā)與應用。開展偏晶合金凝固過程及其組織控制研究對推動偏晶合金材料工業(yè)應用具有重要意義。微合金化對金屬和合金凝固過程與組織具有重要影響,但迄今為止,有關微合金化條件下偏晶合金凝固行為的研究鮮有報道,本論文采用實驗與模擬計算相結合的研究方法,研究微合金化條件下偏晶合金凝固行為,探索微合金化對偏晶合金凝固組織的影響及用微合金化法控制偏晶合金凝固過程及組織的可行性。主要研究工作及成果如下:實驗研究了微量元素對偏晶合金凝固組織的影響,考察了微量元素Bi對Al-Pb合金、微量元素Sn對Al-Pb(Bi)合金凝固組織的影響。發(fā)現微量元素Bi、Sn可以顯著細化Al-Pb(Bi)偏晶合金凝固組織;隨著微量元素添加量的增加,彌散相液滴的平均尺寸呈現先減小后保持不變的規(guī)律;彌散相體積分數越大,微量表面活性元素對偏晶合金中彌散相粒子的細化效果就越好,表明微量元素Bi可以作為Al-Pb合金的表面活性元素,微量元素Sn可以作為Al-Pb(Bi)合金的表面活性元素。建立了微量表面活性元素作用下偏晶合金連續(xù)凝固組織演變過程模型,并結合實驗開展了模擬研究,揭示了微量表面活性元素對偏晶合金連續(xù)凝固組織的影響機理。結果表明,表面活性元素富集于基體液相與彌散相液滴界面處,降低偏晶合金液-液相變過程中兩液相間的界面能,從而提高彌散相液滴的形核率,降低彌散相液滴的Marangoni速率,促進偏晶合金形成彌散型凝固組織。提出了在氟鹽反應法中采用納米碳管(CNT)作為碳源制備Al-Ti-C中間合金的新思路,制備出了 TiC顆粒彌散度高的Al-Ti-C中間合金,分析了 CNT作為碳源時Al-Ti-C中間合金凝固組織的形成過程,結果表明,Al-Ti-C中間合金制備過程中,TiC顆粒是通過固態(tài)C與溶質Ti反應生成,而不是通過溶質C與溶質Ti反應生成;CNT尺寸小,比表面積大,能夠增加鋁熔體與CNT間的接觸面積,同時,CNT結構中存在大量的缺陷和空位,使CNT具有較高的化學活性,這些均有利于促進CNT與溶質Ti之間的反應,促進TiC顆粒高度彌散分布于基體中的Al-Ti-C中間合金的形成。以Al-Pb(Bi)偏晶合金為對象,實驗研究了微量化合物TiC對偏晶合金凝固組織的影響。發(fā)現微量化合物TiC可以顯著細化Al-Pb(Bi)偏晶合金凝固組織;隨著TiC顆粒添加量的逐漸增加,彌散相液滴的平均尺寸呈現先保持不變、增大、減小再保持不變的趨勢;彌散相體積分數越大,微量化合物TiC對彌散相粒子的細化效果就越好,表明TiC顆�？梢宰鳛锳l-Pb(Bi)偏晶合金液-液相變過程中彌散相液滴的有效異質形核質點,能大幅度提高彌散相液滴形核率,促進彌散型偏晶合金凝固組織的形成。建立了 TiC顆粒在偏晶合金熔體中的動力學行為模型及微量化合物TiC作用下偏晶合金凝固組織演變過程模型,模擬計算與實驗研究相結合,分析了 TiC顆粒在合金熔體中的動力學行為及其對偏晶合金凝固組織的影響,闡明了微量化合物TiC對偏晶合金凝固組織形成過程的影響機理。結果表明,TiC顆粒自加入偏晶合金熔體后會發(fā)生溶解、粗化及冷卻時沉淀析出過程,這一過程對偏晶合金凝固組織影響重大,TiC顆粒對彌散相液滴的細化效果主要取決于液-液相變開始溫度時熔體中存在的TiC顆粒的數量密度。當TiC顆粒添加量較小,冷卻至液-液相變開始溫度時熔體中存在的TiC顆粒的數量密度不足時,微量化合物的添加會粗化彌散相液滴;只有當TiC顆粒添加量較大,冷卻至液-液相變開始溫度時熔體中存在的TiC顆粒的數量密度足量時,微量化合物的添加才會細化彌散相液滴,促使彌散型偏晶合金凝固組織的形成。
[Abstract]:The partial crystal alloy is very wide, and its main characteristics are that a single, homogeneous, monotectic alloy melt will take place in the cooling process to a liquid-liquid phase to form two immiscible liquid phases. If a small amount of the composite material dispersed in the matrix is dispersed in the form of small particles, many of the partial crystal alloys have excellent properties and have a wide application prospect in the industry. However, the process of the liquid-liquid phase transformation of the partial-crystal alloy is very complicated, and the influence factors are various. Under the conventional solidification condition, the solidification structure with serious phase segregation and even two-phase stratification can be easily formed. This limits the industrial development and application of such alloys. It is of great significance to carry out the solidification process of the partial crystal alloy and the research of its structure control. The micro-alloying has an important influence on the solidification process and the microstructure of the metal and the alloy, but so far, the research on the solidification behavior of the partial-crystal alloy under the condition of micro-alloying is rarely reported. The effect of microalloying on the solidification structure of the partial-crystal alloy and the feasibility of controlling the solidification process and the microstructure of the partial-crystal alloy were investigated by microalloying. The main research work and results are as follows: The effect of trace elements on the solidification structure of the metacrystal alloy is studied. The effect of trace element Bi on the solidification structure of Al-Pb (Bi) alloy is investigated. When the trace elements Bi and Sn are found, the solidification structure of the Al-Pb (Bi) partial crystal alloy can be obviously refined; with the increase of the addition of the trace elements, the average size of the dispersed phase liquid drops is kept constant; the larger the volume fraction of the dispersion phase, The better the fine effect of the trace surface active element on the dispersion phase particles in the partial crystal alloy, the better the trace element Bi can be used as the surface active element of the Al-Pb alloy, and the trace element Sn can be used as the surface active element of the Al-Pb (Bi) alloy. The evolution process model of the partial-crystal alloy continuous solidification structure under the action of micro-surface-active elements is established, and the simulation research is carried out in combination with the experiment, and the influence mechanism of the trace surface-active element on the continuous solidification structure of the partial-crystal alloy is disclosed. The results show that the surface-active element is enriched in the interface of the liquid phase of the matrix and the dispersed phase drop, and the interfacial energy between the two liquid phases in the liquid-liquid phase of the partial-crystal alloy is reduced, so that the nucleation rate of the dispersed phase liquid drops is improved, the Marangoni rate of the dispersed phase liquid drops is reduced, And the dispersion type solidification structure is formed by promoting the partial crystal alloy. A new method for preparing Al-Ti-C intermediate alloy by using carbon nanotubes (CNT) as a carbon source in the fluorine salt reaction method is proposed, and the Al-Ti-C intermediate alloy with high TiC particle dispersion is prepared, and the forming process of the solidification structure of the Al-Ti-C intermediate alloy when the CNT is used as a carbon source is analyzed, the results show that, in the preparation process of the Al-Ti-C intermediate alloy, the TiC particles are generated by the reaction of the solid state C and the solute Ti, not by the reaction of the solute C and the solute Ti; the CNT size is small, the specific surface area is large, the contact area between the aluminum melt and the CNT can be increased, and meanwhile, The CNT structure has a large number of defects and vacancies, so that the CNTs have higher chemical activity, which are beneficial to promoting the reaction between the CNTs and the solute Ti, and promoting the formation of the Al-Ti-C intermediate alloy in the matrix. The effect of the micro-compound TiC on the solidification structure of the Al-Pb (Bi) alloy is studied in this paper. It is found that the micro-compound TiC can refine the solidification structure of the Al-Pb (Bi) alloy, with the increasing of the amount of the TiC particles, the average size of the dispersed phase droplets will remain unchanged, increase, and reduce the tendency to remain unchanged; the larger the volume fraction of the dispersion phase, The better the fine effect of the micro-compound TiC on the dispersion phase particles, the better the TiC particles can be used as the effective heterogeneous nucleation points of the dispersed phase droplets in the liquid-liquid phase transformation of the Al-Pb (Bi) partial crystal alloy liquid-liquid phase transformation, and can greatly improve the dispersion phase liquid drop shape nuclear rate and promote the formation of the dispersion type partial crystal alloy solidification structure. The dynamic behavior model of TiC particles in the melt of the partial-crystal alloy and the evolution process model of the solidification structure of the partial-crystal alloy under the action of the micro-compound TiC are established, and the simulation calculation is combined with the experimental research. The dynamic behavior of TiC particles in the alloy melt and its influence on the solidification structure of the partial-crystal alloy are analyzed, and the influence mechanism of the micro-compound TiC on the formation process of the solidification structure of the partial-crystal alloy is illustrated. The results show that TiC particles can be dissolved, coarsened and cooled in the process of precipitation and precipitation, which has a significant influence on the solidification structure of the partial-crystal alloy. The effect of TiC particles on the dispersion phase droplets depends mainly on the amount and density of TiC particles present in the melt at the beginning of the liquid-liquid phase change. when the amount of the TiC particles in the melt is less than the amount of the TiC particles present in the melt when the amount of the TiC particles is small, the dispersion phase liquid drops are coarsened by the addition of the trace compound; only when the amount of the TiC particles is large, When the quantity and density of the TiC particles present in the melt at the beginning of cooling to the liquid-liquid phase change are sufficient, the addition of the micro-compound can refine the dispersion phase liquid droplets and promote the formation of the diffusion-type partial crystal alloy solidification structure.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG146.21
本文編號：2486644
[Abstract]:The partial crystal alloy is very wide, and its main characteristics are that a single, homogeneous, monotectic alloy melt will take place in the cooling process to a liquid-liquid phase to form two immiscible liquid phases. If a small amount of the composite material dispersed in the matrix is dispersed in the form of small particles, many of the partial crystal alloys have excellent properties and have a wide application prospect in the industry. However, the process of the liquid-liquid phase transformation of the partial-crystal alloy is very complicated, and the influence factors are various. Under the conventional solidification condition, the solidification structure with serious phase segregation and even two-phase stratification can be easily formed. This limits the industrial development and application of such alloys. It is of great significance to carry out the solidification process of the partial crystal alloy and the research of its structure control. The micro-alloying has an important influence on the solidification process and the microstructure of the metal and the alloy, but so far, the research on the solidification behavior of the partial-crystal alloy under the condition of micro-alloying is rarely reported. The effect of microalloying on the solidification structure of the partial-crystal alloy and the feasibility of controlling the solidification process and the microstructure of the partial-crystal alloy were investigated by microalloying. The main research work and results are as follows: The effect of trace elements on the solidification structure of the metacrystal alloy is studied. The effect of trace element Bi on the solidification structure of Al-Pb (Bi) alloy is investigated. When the trace elements Bi and Sn are found, the solidification structure of the Al-Pb (Bi) partial crystal alloy can be obviously refined; with the increase of the addition of the trace elements, the average size of the dispersed phase liquid drops is kept constant; the larger the volume fraction of the dispersion phase, The better the fine effect of the trace surface active element on the dispersion phase particles in the partial crystal alloy, the better the trace element Bi can be used as the surface active element of the Al-Pb alloy, and the trace element Sn can be used as the surface active element of the Al-Pb (Bi) alloy. The evolution process model of the partial-crystal alloy continuous solidification structure under the action of micro-surface-active elements is established, and the simulation research is carried out in combination with the experiment, and the influence mechanism of the trace surface-active element on the continuous solidification structure of the partial-crystal alloy is disclosed. The results show that the surface-active element is enriched in the interface of the liquid phase of the matrix and the dispersed phase drop, and the interfacial energy between the two liquid phases in the liquid-liquid phase of the partial-crystal alloy is reduced, so that the nucleation rate of the dispersed phase liquid drops is improved, the Marangoni rate of the dispersed phase liquid drops is reduced, And the dispersion type solidification structure is formed by promoting the partial crystal alloy. A new method for preparing Al-Ti-C intermediate alloy by using carbon nanotubes (CNT) as a carbon source in the fluorine salt reaction method is proposed, and the Al-Ti-C intermediate alloy with high TiC particle dispersion is prepared, and the forming process of the solidification structure of the Al-Ti-C intermediate alloy when the CNT is used as a carbon source is analyzed, the results show that, in the preparation process of the Al-Ti-C intermediate alloy, the TiC particles are generated by the reaction of the solid state C and the solute Ti, not by the reaction of the solute C and the solute Ti; the CNT size is small, the specific surface area is large, the contact area between the aluminum melt and the CNT can be increased, and meanwhile, The CNT structure has a large number of defects and vacancies, so that the CNTs have higher chemical activity, which are beneficial to promoting the reaction between the CNTs and the solute Ti, and promoting the formation of the Al-Ti-C intermediate alloy in the matrix. The effect of the micro-compound TiC on the solidification structure of the Al-Pb (Bi) alloy is studied in this paper. It is found that the micro-compound TiC can refine the solidification structure of the Al-Pb (Bi) alloy, with the increasing of the amount of the TiC particles, the average size of the dispersed phase droplets will remain unchanged, increase, and reduce the tendency to remain unchanged; the larger the volume fraction of the dispersion phase, The better the fine effect of the micro-compound TiC on the dispersion phase particles, the better the TiC particles can be used as the effective heterogeneous nucleation points of the dispersed phase droplets in the liquid-liquid phase transformation of the Al-Pb (Bi) partial crystal alloy liquid-liquid phase transformation, and can greatly improve the dispersion phase liquid drop shape nuclear rate and promote the formation of the dispersion type partial crystal alloy solidification structure. The dynamic behavior model of TiC particles in the melt of the partial-crystal alloy and the evolution process model of the solidification structure of the partial-crystal alloy under the action of the micro-compound TiC are established, and the simulation calculation is combined with the experimental research. The dynamic behavior of TiC particles in the alloy melt and its influence on the solidification structure of the partial-crystal alloy are analyzed, and the influence mechanism of the micro-compound TiC on the formation process of the solidification structure of the partial-crystal alloy is illustrated. The results show that TiC particles can be dissolved, coarsened and cooled in the process of precipitation and precipitation, which has a significant influence on the solidification structure of the partial-crystal alloy. The effect of TiC particles on the dispersion phase droplets depends mainly on the amount and density of TiC particles present in the melt at the beginning of the liquid-liquid phase change. when the amount of the TiC particles in the melt is less than the amount of the TiC particles present in the melt when the amount of the TiC particles is small, the dispersion phase liquid drops are coarsened by the addition of the trace compound; only when the amount of the TiC particles is large, When the quantity and density of the TiC particles present in the melt at the beginning of cooling to the liquid-liquid phase change are sufficient, the addition of the micro-compound can refine the dispersion phase liquid droplets and promote the formation of the diffusion-type partial crystal alloy solidification structure.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG146.21
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