【作者】 金华；

【导师】 王国峰；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2009， 硕士

【摘要】 纳米材料由于其具有特殊和优异的物理和力学性能,成为材料领域的研究热点之一。脉冲电沉积非常简单,并可以制备高密度、无孔洞、组织可控的纳米材料和复合材料,是超塑性研究中的理想模型材料,但是在变形时纳米纯金属的晶粒由于晶界缺乏钉扎元素而容易长大,在一定程度上损失了材料良好的纳米效应。纳米增强相的加入可以细化基体晶粒,并起到阻碍晶粒长大的作用,达到在变形过程中稳定材料组织的目的。本文采用脉冲电沉积方法制备了含不同Al2O3颗粒的Al2O3/Ni-Co纳米复合材料,研究添加剂、Al2O3颗粒对材料组织、力学性能和热稳定性的影响,通过超塑单向拉伸实验研究Al2O3/Ni-Co纳米复合材料的超塑性。采用脉冲电沉积的方法制备了Al2O3/Ni-Co纳米复合材料,并对不同成分制备所得材料的基本性能进行了分析。平均电流密度为2A/dm2,温度为50℃时,以1,4丁炔二醇为添加剂制得材料晶粒为180nm;以糖精为添加剂,加入20nm、50nm、100nm Al2O3颗粒所得材料晶粒分别为35nm、25nm、40nm,大部分晶粒呈等轴状。糖精的细化效果明显优于1,4丁炔二醇,Al2O3对材料也有明显的细化效果。借助DSC和SEM,对Al2O3/Ni-Co纳米复合材料的热稳定性能进行了研究。实验表明晶粒长大推迟,说明材料有较高的热稳定性,但经过热处理的材料晶粒仍然不可避免地出现了长大现象。通过拉伸实验研究Al2O3/Ni-Co纳米复合材料和Ni-Co纳米材料的超塑性。拉伸实验温度分别为450℃、500℃、550℃,应变速率范围为8.33×10-4s-1,1.67×10-3s-1和1.67×10-2s-1,基于实验结果和分析,含50nm Al2O3颗粒材料低温超塑性最优,在550℃得到的最佳材料的的延伸率达到632%。通过SEM分析Al2O3/Ni-Co纳米复合材料和Ni-Co纳米材料在超塑拉伸时的断口,分析其断裂特征、晶粒运动特征以及位错、硫元素偏析对超塑变形的协调作用。温度是诱发超塑变形时晶粒长大的主要因素。Al2O3/Ni-Co纳米复合材料的晶粒长大现象远不如Ni-Co纳米材料明显。更多还原

【Abstract】 Nanocrystalline materials possess unique physical and mechanical properties and are among the most interesting topic in the materials research. Pulse electrodeposition is not only simple but it can also produce pure nanocrystalline materials and composites free of porosity. Recently nanocrystalline materials produced by electrodeposition are used as perfect models for superplasticity, however, because nanocrystalline pure metal is lack in the pinning effect on the grain boundaries during deformation, the grain growth becomes rapidly, resulting the reduced superplasticity. Nano reinforced particles can refine matrix crystal and nail the growth of the crystal grains, they are helpful for superplasticity since they enhance the structural stability of nanocrystalline materials. Al2O3/Ni-Co nanocomposite containing various Al2O3 particles were produced by pulse electrodeposition. We research on the effect of additive and Al2O3 particles on material structure, mechanical properties and thermal stability. This paper studies superplasticity of Al2O3/Ni-Co nanocomposite through the way of superplaticity tensile tests.Al2O3/Ni-Co nanocomposite were produced by pulse electrodeposition. This paper analyses the materials properties produced by various components. At the condition of 2A/dm2 as average current density and 50℃as experiment temperature, the grain size is 180nm when 1,4-butynediol as an additive; and the grains size are 35nm, 25nm and 40nm respectively when benzosulfimide as an additive, joining 20nm Al2O3 particles, 50nm Al2O3 particles and 100nm Al2O3 particles. Most grains remained in equiaxed shape. Refining effectiveness of benzosulfimide is better than that of 1,4-butynediol, the refining effectiveness of Al2O3 is also obviously.The thernam stability of Al2O3/Ni-Co nanocomposite are studied with the method of DSC and SEM. The experimental results indicate that the growth of crystal grains are postponed. But grains after annealing appeared to grow up to some inevitable level.Tensile tests were carried out to study the superplasticity of Al2O3/Ni-Co nanocomposite and Ni-Co nanocomposite. Temperatures of these tensile tests are 450℃,500℃and 550℃.Strain rate ranges from 8.33×10-4s-1 , 1.67×10-3s-1 to 1.67×10-2s-1.On the basis of results and analyses, the low temperature superplasticity of 50nm Al2O3 particles is the best, the elongation of optimal material obtained at 550℃is up to 632%.Francture surface of Al2O3/Ni-Co nanocomposite and Ni-Co nanophase materials during superplastic tensile test were analyzed by SEM. Based on the observed results, the fracture behavior and grain motion were explained, and the accommodation processed of dislocation, S segregation were also discussed. Grain growth during superplastic deformation was maninly attributed to the effect of temperature. Comparing with nanocrystalline Ni-Co, the grains of Al2O3/Ni-Co nanocomposite grew slowly, which is the key reason for the enhanced superplasticity of nanocompsite.更多还原