纳米颗粒增强铝基复合材料的制备及其半固态模锻成形研究

发布时间：2018-01-20 11:26

本文关键词： 纳米颗粒金属基复合材料固/液界面动力学本构模型半固态模锻成形　出处：《南昌大学》2016年博士论文　论文类型：学位论文

【摘要】：分别借助分段多频超声振动及分段多频超声振动复合界面润湿反应制备了纳米颗粒增强铝基复合材料。研究了纳米颗粒含量对复合材料的组织及力学性能的影响。分析了纳米颗粒分散机制、晶粒细化机制及复合材料强化机制。对润湿反应进行热力学分析,并研究了超声时间及超声温度对复合材料组织的影响。相对于传统技术,通过这些新颖的方法,纳米颗粒能够有效地分散在基体内。微观研究结果显示,纳米颗粒的加入导致了基体晶粒细化,复合材料最终的微观组织依赖于纳米颗粒聚集的程度及聚集体的主要尺寸。热力学计算结果揭示了润湿反应在本实验条件下可以自发进行。超声分散及其产生的疲劳破坏是引起纳米颗粒有效分散的主要原因。而润湿剂的加入促进了纳米颗粒与基体熔体的润湿,进而改善纳米颗粒在熔体内的分散。晶粒细化主要归因于颗粒推移机制及异质形核行为。相对于基体合金,在加入1.5 wt.%纳米颗粒及1.0 wt.%润湿剂,800°C下制备的复合材料的拉伸、抗压及硬度有很大的提高。TEM分析显示,在晶粒内存在高密度位错及洁净纳米颗粒/基体界面,意味着复合材料力学性能的改善与基体合金的位错型强化及载荷在颗粒/基体界面的有效传递有关。除此之为,对复合材料的拉伸、压缩断口进行了研究。在颗粒增强复合材料的凝固过程中,凝固前沿与悬浮颗粒发生相互作用。纳米颗粒被凝固前沿吞没或被推移至固/液界面。通过实施铸造实验,研究了纳米颗粒在基体中的分散及聚集程度与合金微观结构的关系。建立了一个用于计算界面推移纳米颗粒的临界界面速率的流体动力学模型。除此之外,讨论了分布在固/液界面前沿的纳米颗粒对界面形貌的影响。微观组织分析结果显示,复合材料晶粒的大小与纳米颗粒及纳米颗粒团聚体在基体内的分布有关。基于建立的流体动力学模型发现,对于颗粒尺寸小于颗粒临界尺寸的36%(r0.36r*=0.9973μm)的纳米颗粒,其颗粒推移的临界界面速率要比稳态推移微米颗粒所需的临界界面速率低4个数量级,意味着越小的纳米颗粒更容易被界面吞没,而非推移。实验数据与模型完全吻合。结果显示,局部溶体的成分过冷及颗粒后的溶质堆积导致了胞状界面的生成。对于半固态模锻成形,具有适当液相份数且含有细小球状晶粒的微观组织是必需的。在本研究中,采用超声振动和颗粒诱发技术制备了适合短流程半固态模锻成形的复合材料半固态浆料。通过这个技术,纳米颗粒有效地分散在基体内,同时能够获得细小且分布均匀的球状半固态组织。研究了冷却速率、超声温度范围及超声功率对复合材料半固态组织的影响。同时也分析了第二相对微观组织的影响。微观结构分析揭示,通过以10°C/min的冷却速率,在700°C-620°C范围内施加1 k W的超声振动能够获得良好的半固态组织,其中固相率、固相颗粒的平均尺寸及外形因素分别为0.715、73μm和0.84。超声振动诱发的成分均匀性及润湿剂的引入导致了纳米尺寸Al7Cu2Fe及Mg Al2O4相的生成。基于TEM分析及物相晶体结构,结果发现,这些硬质相与α-Al有良好的晶体学取向关系,意味着合金中强化了异质形核行为,进而诱发初生α-Al晶粒过早析出。同时,讨论了半固态组织的演变机制。采用Gleeble-3500热模拟试验机,对纳米颗粒增强铝基复合材料进行半固态等温压缩实验,研究了变形温度、应变速率及纳米颗粒对复合材料等温压缩力学行为的影响。对复合材料压缩断口进行研究,并讨论了复合材料的变形机制。建立了纳米颗粒增强铝基复合材料半固态模锻成形的本构模型。基于压缩实验数据,采用多元线性回归法对本构模型的系数进行求解。结果发现,随着变形温度的提高及应变速率的减少,峰值及稳态应力减少。固相颗粒间液相的润滑作用是导致变形抗力减少的主要原因。随着纳米颗粒含量的增加及粒径的减少,峰值及稳态应力增大,细小且均匀分布的纳米颗粒的增强效应显著。断口分析表明,高温或高应变速率能够促使液相沿晶界连续分布,进而在固相颗粒表面形成一薄层液相膜,最终导致润滑作用改善。在变形过程中,试样经历了强化、软化及稳态三个阶段,分别为液相流、固液协同流动及固相塑性变形机制。结果表明,通过本构模型获得的理论数据与实验数据拟合程度较好。基于复合材料的本构方程,对其半固态模锻成形进行了数值模拟。分析了半固态坯料的量、成形温度及成形速率对等效应变、应力场的影响。同时成功地实施了十字轴零件的短流程半固态模锻成形。讨论了成形温度、下模移动速率及保压时间对零件充型行为的影响。基于数值模拟结果发现,较高的成形速率及成形温度下,坯料能够获得均匀分布的等效应力应变场及较低的最大成形力,而适量的半固态坯料有利于提高成形件的完全充型能力。半固态模锻成形结果表明,较高的成形温度和下模移动速率有利于改善半固态浆料的充型能力,而较长的保压时间能够充满型腔,压实锻件。纳米颗粒的含量及粒径对零件的力学性能产生影响。随着纳米颗粒含量的增加及颗粒尺寸的减少,零件的强度增大,同时材料的塑性也有所提高。晶粒细化,微观组织均匀化、纳米颗粒的Orowan效应及颗粒在晶界处的钉扎作用是导致零件力学性能改善的主要原因。除此之外,对半固态模锻零件热处理后拉伸断裂面进行了分析。
[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.

【学位授予单位】：南昌大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TB333;TG316.3

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