Gasar多孔铜（合金）的气孔结构及其力学性能研究

【作者】 李再久；

【导师】 周荣；

【作者基本信息】 昆明理工大学 ， 材料加工工程， 2014， 博士

【摘要】 Gasar,也被称为金属-气体共晶定向凝固,是一种基于气体在金属固／液两相中的溶解度差而发展起来的制备多孔金属的新工艺。相比于烧结,发泡等传统方法制备的多孔金属,Gasar多孔金属由于其内部气孔呈圆柱形且沿凝固方向定向排列,使其除具有传统多孔金属小比重、高刚度、减震性能好等特点外,还具有自己特殊的综合性能优势,如优异的力学性能、热交换性能,因而其具有重要的潜在应用价值。结构参数是影响Gasar多孔金属性能的重要因素。为达到对多孔金属气孔结构的定量控制,以满足其在不同领域的应用背景,前期研究者开展了其各自的研究工作。但在现有的文献报道中,并未深入分析气泡生长的动力学(形核和长大)对Gasar气孔结构的影响机制；也未从金属-气体共晶定向凝固热力学基础理论分析的角度,建立起一个相对简易的气孔结构预测模型；同时缺少合金化对Gasar气孔结构影响的深入研究；此外,对多气孔结构参数复合作用下的Gasar多孔金属力学行为特征等方面的研究也较少。本文从Gasar多孔金属的制备方法出发,针对以上四个方面内容逐一展开研究。依托课题组自行开发研制的Gasar定向凝固装置,利用简单模铸法制备了不同结构参数的Gasar多孔Cu试样。根据(溶质)质量守恒定律,推导得出能准确预测多孔Cu气孔率的公式。此外,通过对气泡形核和长大过程的深入分析,明晰了气体压力及过热度等工艺参数对Gasar气孔结构的影响机制。在简单模铸法实验研究结果的基础上,为实现对Gasar多孔金属气孔结构的定量控制,通过连续铸造法制备得到不同拉速及气压下的多孔Cu试样。通过对金属-氢共晶定向凝固过程的热力学分析,建立了一个用来描述Gasar工艺中工艺参数对气孔直径及气孔间距影响的理论模型；并用该模型与连铸实验数据进行比较。结果表明,理论计算结果与相应实验结果总体吻合良好；低下拉速率下,气孔结构与模型假设理想结构的偏离,以及固/液界面附近的熔体对流,是造成理论计算值与实验值存在一定的偏差的主要原因。采用连续铸造法,拉制出横截面分别为Φ15mm和80×12mm的Gasar多孔Cu、Cu-Zn及Cu-Ni合金试样,并研究了合金元素含量对多孔Cu气孔结构和形貌的影响。结果表明：随Zn、Ni含量增加,固／液界面前沿“糊状区”宽度的增加,以及固／液界面凝固模式的改变(平面---胞状---柱状枝晶---等轴枝晶),是造成Gasar多孔合金气孔结构规则性和均匀性逐渐恶化的主要原因。在多气孔结构参数的复合作用下,研究了Gasar多孔Cu室温下的力学行为及各向异性性能。结果表明,气孔率及加载方向等结构参数是影响多孔金属力学性能的主要因素。更多还原

【Abstract】 Gasar, also called "unidirectional solidification of metal-gas eutectic", which is based on the gap of gas solubility between liquid and solid metals, is a revolutionary process for fabricating porous metal. Compared with the randomly distributed pore structure of traditional sintered or frothed porous metals, the pores in Gasar porous metals are aligned one direction. This resulted in an unique combinations of physical and mechanical properties such as higher mechanical property and superior capacity of heat transmission for Gasar porous metals. Therefore, this kind of porous metal has important potential applications. The pore structure parameter is significant factor that impact the porous metals properties. In order to quantitative control the pore structures, the appropriate studies have been carried out by many researchers. Few researches are systematically made on the pore nucleation and growth processes and their impact on the pore structures, and no researches have been made on the prediction model obtained from the thermodynamic analysis on directional solidification of metal-hydrogen eutectic. The other is that the influence of alloying on pore structure of Gasar porous metal has not been further researched. In addition, the research concerned the mechanical behavior of Gasar porous metal under the recombination action of pore structure and loading direction is still deficient. This thesis will be concentrated on these three aspects.By use of the developed Gasar mould casting apparatus, porous Cu samples with different pore structure parameters have been fabricated. Based on the law of mass conservation, a theoretical formula was proposed for calculating the porosity in Gasar porous Cu. Furthermore, through a deep analysis of the process of pore nucleation and growth, find out the mechanism of how the process parameters (gas pressure and degree of superheat) influence the pore structure.In order to quantitative control the pore structures of Gasar porous metal, a Gasar continuous casting technique was developed to fabricate porous metal. A lot of porous Cu samples were fabricated under different hydrogen pressures and withdraw rates. With the thermodynamic analysis on directional solidification of metal-hydrogen eutectic, a theoretical model was developed to predict the effect of the Gasar processing parameters on the pore diameter and inter-pore spacing. The model can predict the overall tendency of the experimental results. The deviation between the calculated and experimental values in the case of lower withdrawal rate is considered to be associated with the difference between the real pore structure and ideal pore structure, and the melt convection in the vicinity of solid/liquid interface.Gasar porous Cu, Cu-Zn and Cu-Ni samples with different cross-sections (φ15mm and80×12mm) have been fabricated by using the continuous casting technique under a hydrogen press of0.6MPa at various withdraw rates. The influences of Zn and Ni contents on the pore structure and morphology were investigated. The change of pore structure and morphology of porous alloy samples is primarily dependent on the solidification mode (planar, cellular, columnar dendritic, equiaxed dendritic) and the width of mushy zone, which are controlled by the alloying element contents.The anisotropic mechanical properties of Gasar porous Cu under the recombination action of pore structure and loading direction was studied. The results shows the mechanical behaviors depend on the porosity and the loading directions.更多还原