發(fā)布時(shí)間：2018-01-20 11:26

  本文關(guān)鍵詞： 納米顆粒 金屬基復(fù)合材料 固/液界面動(dòng)力學(xué) 本構(gòu)模型 半固態(tài)模鍛成形　出處：《南昌大學(xué)》2016年博士論文　論文類(lèi)型：學(xué)位論文

【摘要】：分別借助分段多頻超聲振動(dòng)及分段多頻超聲振動(dòng)復(fù)合界面潤(rùn)濕反應(yīng)制備了納米顆粒增強(qiáng)鋁基復(fù)合材料。研究了納米顆粒含量對(duì)復(fù)合材料的組織及力學(xué)性能的影響。分析了納米顆粒分散機(jī)制、晶粒細(xì)化機(jī)制及復(fù)合材料強(qiáng)化機(jī)制。對(duì)潤(rùn)濕反應(yīng)進(jìn)行熱力學(xué)分析,并研究了超聲時(shí)間及超聲溫度對(duì)復(fù)合材料組織的影響。相對(duì)于傳統(tǒng)技術(shù),通過(guò)這些新穎的方法,納米顆粒能夠有效地分散在基體內(nèi)。微觀研究結(jié)果顯示,納米顆粒的加入導(dǎo)致了基體晶粒細(xì)化,復(fù)合材料最終的微觀組織依賴(lài)于納米顆粒聚集的程度及聚集體的主要尺寸。熱力學(xué)計(jì)算結(jié)果揭示了潤(rùn)濕反應(yīng)在本實(shí)驗(yàn)條件下可以自發(fā)進(jìn)行。超聲分散及其產(chǎn)生的疲勞破壞是引起納米顆粒有效分散的主要原因。而潤(rùn)濕劑的加入促進(jìn)了納米顆粒與基體熔體的潤(rùn)濕,進(jìn)而改善納米顆粒在熔體內(nèi)的分散。晶粒細(xì)化主要?dú)w因于顆粒推移機(jī)制及異質(zhì)形核行為。相對(duì)于基體合金,在加入1.5 wt.%納米顆粒及1.0 wt.%潤(rùn)濕劑,800°C下制備的復(fù)合材料的拉伸、抗壓及硬度有很大的提高。TEM分析顯示,在晶粒內(nèi)存在高密度位錯(cuò)及潔凈納米顆粒/基體界面,意味著復(fù)合材料力學(xué)性能的改善與基體合金的位錯(cuò)型強(qiáng)化及載荷在顆粒/基體界面的有效傳遞有關(guān)。除此之為,對(duì)復(fù)合材料的拉伸、壓縮斷口進(jìn)行了研究。在顆粒增強(qiáng)復(fù)合材料的凝固過(guò)程中,凝固前沿與懸浮顆粒發(fā)生相互作用。納米顆粒被凝固前沿吞沒(méi)或被推移至固/液界面。通過(guò)實(shí)施鑄造實(shí)驗(yàn),研究了納米顆粒在基體中的分散及聚集程度與合金微觀結(jié)構(gòu)的關(guān)系。建立了一個(gè)用于計(jì)算界面推移納米顆粒的臨界界面速率的流體動(dòng)力學(xué)模型。除此之外,討論了分布在固/液界面前沿的納米顆粒對(duì)界面形貌的影響。微觀組織分析結(jié)果顯示,復(fù)合材料晶粒的大小與納米顆粒及納米顆粒團(tuán)聚體在基體內(nèi)的分布有關(guān)�；诮⒌牧黧w動(dòng)力學(xué)模型發(fā)現(xiàn),對(duì)于顆粒尺寸小于顆粒臨界尺寸的36%(r0.36r*=0.9973μm)的納米顆粒,其顆粒推移的臨界界面速率要比穩(wěn)態(tài)推移微米顆粒所需的臨界界面速率低4個(gè)數(shù)量級(jí),意味著越小的納米顆粒更容易被界面吞沒(méi),而非推移。實(shí)驗(yàn)數(shù)據(jù)與模型完全吻合。結(jié)果顯示,局部溶體的成分過(guò)冷及顆粒后的溶質(zhì)堆積導(dǎo)致了胞狀界面的生成。對(duì)于半固態(tài)模鍛成形,具有適當(dāng)液相份數(shù)且含有細(xì)小球狀晶粒的微觀組織是必需的。在本研究中,采用超聲振動(dòng)和顆粒誘發(fā)技術(shù)制備了適合短流程半固態(tài)模鍛成形的復(fù)合材料半固態(tài)漿料。通過(guò)這個(gè)技術(shù),納米顆粒有效地分散在基體內(nèi),同時(shí)能夠獲得細(xì)小且分布均勻的球狀半固態(tài)組織。研究了冷卻速率、超聲溫度范圍及超聲功率對(duì)復(fù)合材料半固態(tài)組織的影響。同時(shí)也分析了第二相對(duì)微觀組織的影響。微觀結(jié)構(gòu)分析揭示,通過(guò)以10°C/min的冷卻速率,在700°C-620°C范圍內(nèi)施加1 k W的超聲振動(dòng)能夠獲得良好的半固態(tài)組織,其中固相率、固相顆粒的平均尺寸及外形因素分別為0.715、73μm和0.84。超聲振動(dòng)誘發(fā)的成分均勻性及潤(rùn)濕劑的引入導(dǎo)致了納米尺寸Al7Cu2Fe及Mg Al2O4相的生成�；赥EM分析及物相晶體結(jié)構(gòu),結(jié)果發(fā)現(xiàn),這些硬質(zhì)相與α-Al有良好的晶體學(xué)取向關(guān)系,意味著合金中強(qiáng)化了異質(zhì)形核行為,進(jìn)而誘發(fā)初生α-Al晶粒過(guò)早析出。同時(shí),討論了半固態(tài)組織的演變機(jī)制。采用Gleeble-3500熱模擬試驗(yàn)機(jī),對(duì)納米顆粒增強(qiáng)鋁基復(fù)合材料進(jìn)行半固態(tài)等溫壓縮實(shí)驗(yàn),研究了變形溫度、應(yīng)變速率及納米顆粒對(duì)復(fù)合材料等溫壓縮力學(xué)行為的影響。對(duì)復(fù)合材料壓縮斷口進(jìn)行研究,并討論了復(fù)合材料的變形機(jī)制。建立了納米顆粒增強(qiáng)鋁基復(fù)合材料半固態(tài)模鍛成形的本構(gòu)模型�；趬嚎s實(shí)驗(yàn)數(shù)據(jù),采用多元線性回歸法對(duì)本構(gòu)模型的系數(shù)進(jìn)行求解。結(jié)果發(fā)現(xiàn),隨著變形溫度的提高及應(yīng)變速率的減少,峰值及穩(wěn)態(tài)應(yīng)力減少。固相顆粒間液相的潤(rùn)滑作用是導(dǎo)致變形抗力減少的主要原因。隨著納米顆粒含量的增加及粒徑的減少,峰值及穩(wěn)態(tài)應(yīng)力增大,細(xì)小且均勻分布的納米顆粒的增強(qiáng)效應(yīng)顯著。斷口分析表明,高溫或高應(yīng)變速率能夠促使液相沿晶界連續(xù)分布,進(jìn)而在固相顆粒表面形成一薄層液相膜,最終導(dǎo)致潤(rùn)滑作用改善。在變形過(guò)程中,試樣經(jīng)歷了強(qiáng)化、軟化及穩(wěn)態(tài)三個(gè)階段,分別為液相流、固液協(xié)同流動(dòng)及固相塑性變形機(jī)制。結(jié)果表明,通過(guò)本構(gòu)模型獲得的理論數(shù)據(jù)與實(shí)驗(yàn)數(shù)據(jù)擬合程度較好�；趶�(fù)合材料的本構(gòu)方程,對(duì)其半固態(tài)模鍛成形進(jìn)行了數(shù)值模擬。分析了半固態(tài)坯料的量、成形溫度及成形速率對(duì)等效應(yīng)變、應(yīng)力場(chǎng)的影響。同時(shí)成功地實(shí)施了十字軸零件的短流程半固態(tài)模鍛成形。討論了成形溫度、下模移動(dòng)速率及保壓時(shí)間對(duì)零件充型行為的影響�；跀�(shù)值模擬結(jié)果發(fā)現(xiàn),較高的成形速率及成形溫度下,坯料能夠獲得均勻分布的等效應(yīng)力應(yīng)變場(chǎng)及較低的最大成形力,而適量的半固態(tài)坯料有利于提高成形件的完全充型能力。半固態(tài)模鍛成形結(jié)果表明,較高的成形溫度和下模移動(dòng)速率有利于改善半固態(tài)漿料的充型能力,而較長(zhǎng)的保壓時(shí)間能夠充滿(mǎn)型腔,壓實(shí)鍛件。納米顆粒的含量及粒徑對(duì)零件的力學(xué)性能產(chǎn)生影響。隨著納米顆粒含量的增加及顆粒尺寸的減少,零件的強(qiáng)度增大,同時(shí)材料的塑性也有所提高。晶粒細(xì)化,微觀組織均勻化、納米顆粒的Orowan效應(yīng)及顆粒在晶界處的釘扎作用是導(dǎo)致零件力學(xué)性能改善的主要原因。除此之外,對(duì)半固態(tài)模鍛零件熱處理后拉伸斷裂面進(jìn)行了分析。
[Abstract]:Respectively by means of multi frequency ultrasonic vibration and piecewise piecewise multi frequency ultrasonic wetting reaction to prepare the nano particle reinforced aluminum matrix composites. The microstructure and mechanical effects of nano particles content on the properties of composite materials. The nanoparticles dispersed mechanism analysis, grain refining mechanism and strengthening mechanism of composite materials. The thermodynamics analysis on the wetting reaction, and studied the effects of ultrasonic temperature and ultrasonic time on the microstructure of composites. Compared with the traditional technology, through these novel methods, nano particles can be effectively dispersed in the matrix. The microscopic research results show that the addition of the nano particles leads to the grain refinement of the matrix, the size of the main microstructure of the composites depends on and the degree of aggregation of nano particles in aggregates. Thermodynamic calculation results reveal the wetting reaction can occur spontaneously at the experimental conditions. The sound and the spread of fatigue damage is mainly caused by nano particles dispersed effectively. And the wetting agent accelerate the wetting of particle and matrix melt, thereby improving the dispersion of nano particles in the melt. The grain refinement is mainly attributed to the particle pushing mechanism and heterogeneous nucleation behavior. Compared with the matrix alloy, the addition of 1.5 wt.% wt.% 1 nano particles and wetting agent, 800 C prepared under the tensile, compressive strength and hardness have greatly improved.TEM analysis showed that, in the grain of memory in high density dislocations and clean nano particle / matrix interface, mean dislocation type to improve the mechanical properties of composites and matrix alloy strengthening and load the particle / matrix interface transfer. Besides, the tensile of the composite, compression fracture were studied. In the solidification process of particle reinforced composite material, the solidification front along Interact with suspended particles. Particles engulfed by the solidification front or is pushed to the solid / liquid interface. Through the implementation of casting experiment, study the relationship between nano particle dispersion and aggregation degree and microstructure was established. A computational fluid dynamics model for interface moving nanoparticles critical interface velocity. In addition, the paper discusses distribution effects at the solid / liquid interface in front of nanoparticles on interface morphology. The microstructure analysis showed that the size and distribution of nano particles and nano particles composite grains in the matrix. The fluid is established based on the dynamic model for the particle size is smaller than the critical size of particles 36% (r0.36r*=0.9973 m) of the nano particles, the particles on the critical interface velocity than required by steady micron particle critical interface velocity low 4 The number of level, means that the increase of particle size are more likely to be swallowed up and goes on. The interface, experimental data and model fit. The results showed that the soluble solute composition of local undercooling and the accumulation of particles leads to the formation of cellular interface. For semi-solid forging, with appropriate liquid phase micro parts the number of organizations and contains fine spherical grains is required. In this study, using ultrasonic vibration and particle induced preparation technology for short process of semi solid forging composite semi solid slurry. Through this technology, nano particles are effectively dispersed in the matrix, and can obtain fine and uniform distribution of semi-solid microstructure the ball was studied. The cooling rate, effects of ultrasonic temperature range and ultrasonic power on Semi-solid Microstructure of composite materials. The authors also analyze the effect of the second phase microstructure. The microstructure analysis reveals, through The cooling rate of 10 ~ C/min, ultrasonic vibration applied 1 K W at 700 DEG C-620 DEG C range can obtain good semi-solid microstructure, solid phase rate, average size and shape factors of solid particles were 0.715,73 m and 0.84. ultrasonic vibration induced by uniform composition and wetting agent into the lead nanometer size Al7Cu2Fe Mg and the formation of Al2O4. The results showed that TEM crystal phase and structure analysis, based on a crystallographic orientation relationship of their good hard phase and alpha -Al, means that the alloy strengthening heterogeneous nucleation behavior, and then induced primary alpha -Al grain early precipitation. At the same time, discussed the evolution mechanism of semi-solid microstructure. Using the Gleeble-3500 thermal simulation testing machine, the nano particle reinforced aluminum matrix composites by semi-solid isothermal compression experiment, the deformation temperature on the strain rate and the nano particles on the composite mechanics for isothermal compression For the influence of composite compression fracture were studied, and discussed the deformation mechanism of composite material. A nano particle reinforced aluminum matrix composites semi-solid forging forming. Compression constitutive model based on experimental data, using multiple linear regression method is used to calculate the coefficient of constitutive model. The results showed that with increasing deformation temperature the increase and decrease of strain rate, peak and steady-state stress reduced. Lubrication liquid solid particles is a major cause of deformation resistance decreased with decreasing diameter. Increase the content of nano particles and particle, the peak value and the steady state stress increases and the enhancement effect of nano particles is fine and uniform distribution significantly. The fracture analysis indicated that high temperature and high strain rate can promote the continuous distribution of liquid phase along the grain boundary, and then a thin liquid film is formed on the solid surface, resulting in improved lubrication in deformation. In the process, the sample undergoes a hardening, softening and steady in three stages, including the liquid phase flow, liquid flow and solid phase coordination mechanism of plastic deformation. The results show that the constitutive good theoretical data and experimental data fitting degree model. The constitutive equations of composite materials based on the semi-solid forging process the numerical simulation analysis. The semi-solid billet, forming temperature and forming rate of the equivalent strain, stress field. At the same time, the successful implementation of the short process of semi-solid forging cross shaft parts forming. The forming temperature, lower die moving rate and holding time effect on the filling behavior of parts the results of numerical simulation. Based on that, the higher the rate of forming and the forming temperature of billet can be obtained equivalent uniform distribution of stress and strain field and the maximum forming force is low, and the amount of semi solid billet is beneficial to improving the forming Complete filling capacity of semi-solid forging parts. The results show that the higher the forming temperature and lower die moving rate is conducive to the filling capacity of semi-solid slurry to improve, and the longer time pressure to fill the cavity, compaction forging. Nanoparticle content and particle size on the mechanical properties of parts of the impact. With the increase of the content of nano particles and reduce the particle size, increase the strength of the parts of the plastic material, at the same time also increased. Grain refinement, microstructure homogenization, Orowan effect and particle is the main cause to improve the mechanical properties of the parts in the grain boundary pinning effect. In addition, the semi solid state forging parts after heat treatment the tensile fracture surface was analyzed.

【學(xué)位授予單位】：南昌大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類(lèi)號(hào)】：TB333;TG316.3

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