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Al-Si-C系合金中多尺度SiCp的原位合成机制与强化行为的研究

发布时间:2019-01-11 08:29  文章来源:笔耕文化传播
【摘要】:本文基于液-固多相反应原理,采用碳质体法在Al-Si合金熔体中原位合成了多尺度β-SiCp,并以此制备出SiCp增强铝基复合材料。首先,对Al-Si-C体系的热力学和动力学分析,研究了铝熔体中SiCp合成工艺条件,提出了多尺度SiCp的渐进式合成机制。其次,研究了铝熔体中碳质体对SiCp形貌演变的遗传影响,提出了原位合成SiCp的平行层状生长和定向吸附堆垛机制,并采用基于密度泛函理论的第一性原理方法,计算分析了Al掺杂对SiC晶体结构和电子密度分布的影响,揭示了掺杂型SiCp化学键合与硬度的相关性。最后,基于对复合材料力学性能的分析,提出了原位合成多尺度SiCp增强Al-Si基复合材料的协同强化机制以及高温骨架强化机制。具体来讲,本文的主要研究内容有:(1)铝熔体中多尺度SiCp原位合成机制本文系统研究了铝熔体中Si浓度、碳含量、反应温度以及保温时间等因素对Al-Si-C反应体系中β-SiCp合成的影响,研究了原位合成SiCp的临界反应条件。提出了原位合成多尺度SiCp的反应机制:即以Al4C3为中间过渡相的渐进式反应,由于受到Al4C3遗传效应的影响,由此获得的SiCp多为微米或亚微米尺度;另一种直接反应机制,即通过铝熔体中溶解态[Si]与[C]的直接反应,合成纳米尺度SiCp=对于反应体系中Cu等第三组元的影响进行研究,结果表明,Cu的添加使体系的固相线和液相线均降低,导致SiCp的原位合成温度由约750℃降低至700℃左右,也使SiCp尺寸明显减小,并能有效地提高复合材料的力学性能。另外,还研究了以α-SiO2作为Si源的Al-Si-SiO2-C反应体系的合成机理,并制备出原位SiCp和Al203复合增强铝合金复合材料。(2)铝熔体中掺杂型SiCp生长机制与化学结构的研究系统研究了Al-Si-C体系中SiCp形貌的演变规律,即随着保温时间的延长,SiCp由六角薄片状逐渐演变成六棱台状,最终演变成不规则的多面体状。晶体结构分析表明,SiC三个晶面的生长速率依次为:V{110}V{100}V{111},其平衡晶体形貌为表面自由能较低的六角薄片状,Si与C原子优先沿110和100晶向进行堆垛,其生长速率较快,而111晶向的生长速率最慢,最终被保留下来。铝熔体中SiCp采用平行层状生长和定向吸附堆垛的机制进行生长。随着SiC中Al含量的降低,SiCp增强铝基复合材料的布氏硬度由88.8HBW增加至109.2HBW,质量磨损率由0.371 mg/min降低至0.272mg/min。采用第一性原理理论计算了不同Al掺杂量时SiCp的化学结构,研究发现,随着SiCp中Al掺杂量的增加,其(011)晶面中原子排布发生变化,导致SiCp中共价键成分降低,碳原子周围的电子云密度减小,掺杂型SiCp的硬度降低,建立了Al掺杂型SiC中化学键合与硬度之间的相关性。研究了碳质体的尺寸与种类对SiCp形貌的遗传效应,结果表明,碳质体尺寸减小,有助于加快体系的反应速率,使其形貌更趋近于多面体形态;碳质体的形貌能够在一定程度上对合成SiCp形貌产生遗传影响。(3)原位合成SiCp对Al-Si系合金复合材料强化行为的研究本文采用特种碳质体制备了多尺度SiCp增强铝合金复合材料,并测试了其洛氏硬度、耐磨性能以及热膨胀性能,提出了多尺度SiCp的协同强化机制。采用热等静压技术对复合材料进行改进,由此制备出组织致密的SiCp/ZL111复合材料,其硬度和高温强度均提高较大。采用合金型碳质体制备了SiCp/Al-Si系合金复合材料,研究了热处理态和热挤压态的高温拉伸性能,结果发现:热处理态SiCp复合材料在350℃的拉伸强度可达132MPa,并对其高温强化机制进行了研究;热挤压处理破坏了复合材料中SiCp与金属间化合物共同构筑的耐热网状骨架结构,大幅降低复合材料的高温拉伸强度。
[Abstract]:In this paper, based on the principle of liquid-solid multi-phase reaction, multi-scale Al-SiCp is synthesized in the melt of Al-Si alloy by using a carbon-mass method, and the SiCp reinforced aluminum-based composite is prepared. First, the thermodynamic and kinetic analysis of the Al-Si-C system is analyzed, and the process conditions of SiCp synthesis in the aluminum melt are studied, and the progressive synthesis mechanism of multi-scale SiCp is put forward. Secondly, the genetic influence of the carbon mass in the aluminum melt on the evolution of the SiCp morphology was studied. The parallel layered growth and the directional adsorption stacking mechanism of SiCp synthesized in situ were put forward, and the first principle method based on the density functional theory was used. The effect of Al doping on the crystal structure and electron density distribution of SiC is calculated and the correlation between the chemical bond and hardness of the doped SiCp is revealed. Finally, based on the analysis of the mechanical properties of the composite, a synergistic strengthening mechanism and a high-temperature framework strengthening mechanism for the in-situ synthesis of the multi-scale SiCp-reinforced Al-Si-based composite are put forward. In particular, the main research contents of this paper are as follows: (1) In-situ synthesis of multi-scale SiCp in aluminum melt, the effect of Si concentration, carbon content, reaction temperature and heat preservation time on the synthesis of Al-SiCp in Al-Si-C reaction system is studied in this paper. The critical reaction conditions of in-situ synthesis of SiCp are studied. In this paper, the reaction mechanism of in-situ synthesis of multi-scale SiCp is put forward, that is, the gradual reaction of Al4C3 as the intermediate transition phase, because of the influence of the genetic effect of Al4C3, the obtained SiCp is in the micron or submicron scale, and the other is a direct reaction mechanism. In other words, by the direct reaction of the dissolved state[Si] and[C] in the aluminum melt, the effect of the nano-scale SiCp = on the third group of elements such as Cu in the reaction system was studied. The results showed that the addition of Cu reduced the solidus and liquidus of the system. the in-situ synthesis temperature of the SiCp is reduced from about 750 DEG C to about 700 DEG C, the size of the SiCp is obviously reduced, and the mechanical property of the composite material can be effectively improved. In addition, the synthesis mechanism of Al-Si-SiO2-C reaction system with Si-SiO2 as Si source was also studied, and the in-situ SiCp and Al203 composite reinforced aluminum alloy composites were prepared. (2) The evolution of SiCp in the Al-Si-C system was studied by the study of the growth mechanism and chemical structure of the doped SiCp in the aluminum melt. The crystal structure analysis shows that the growth rate of the three crystal planes of SiC is: V {110} V {100} V {111}, the balance crystal has a hexagonal sheet shape with lower surface free energy, Si and C atoms take precedence along 110 and 100 crystal, the growth rate is high, and the growth rate of 111 crystal is the slowest. is finally retained. SiCp in the aluminum melt is grown by a mechanism that is parallel to the layered growth and the directional adsorption of the stack. With the decrease of Al content in SiC, the Brinell hardness of SiCp reinforced aluminum-based composite was increased from 81.8HBW to 109.2HBW, and the mass wear rate was reduced from 0.371 mg/ min to 0.272mg/ min. The chemical structure of SiCp in different Al doping levels is calculated by the first principle theory, and it is found that, with the increase of the Al doping amount in SiCp, the atomic arrangement of the (011) crystal plane is changed, which leads to the reduction of the covalent component in the SiCp, and the electron cloud density around the carbon atom is reduced. The hardness of the doped SiCp is reduced, and the correlation between the chemical bond and the hardness in the Al-doped SiC is established. The genetic effect of the size and species of the carbon plastids on the morphology of SiCp is studied. The results show that the reduction of the size of the carbon mass can help to accelerate the reaction rate of the system, and make the morphology of the carbon plastids closer to the shape of the polyhedron. The morphology of the carbon plastids can have a certain degree of genetic influence on the morphology of the synthesized SiCp. (3) In-situ synthesis of SiCp to the reinforced behavior of Al-Si-based alloy composites, a multi-scale SiCp reinforced aluminum alloy composite was prepared by using special carbon plastids, and its Rockwell hardness, wear resistance and thermal expansion performance were tested, and a multi-scale SiCp co-strengthening mechanism was proposed. The composite material was improved by hot isostatic pressing, and the hardness and high temperature strength of the composite SiCp/ ZL111 composite were improved. The high-temperature tensile properties of SiCp/ Al-Si system are studied by using the alloy-type carbon plastids. The results show that the tensile strength of the heat-treated SiCp composite at 350.degree. C. can reach 132MPa, and the high-temperature strengthening mechanism is studied. the hot extrusion treatment destroys the heat-resistant net-like framework structure which is constructed by the SiCp and the intermetallic compound in the composite material, and greatly reduces the high-temperature tensile strength of the composite material.
【学位授予单位】:山东大学
【学位级别】:博士
【学位授予年份】:2016
【分类号】:TG146.21

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