摘要
本文运用放热弥散反应法(XD法)合成Al-ZrO_2和Al-ZrO_2-B系铝基复合材料。根据热力学基本理论对反应过程进行热力学分析;采用金相显微镜、SEM和XRD等现代手段分析反应产物及其微观组织;结合DSC(Differential Scanning Calorimetry)曲线对反应过程进行动力学分析;研究不同工艺参数对反应过程及其结果的影响;并测试材料的常温力学性能,探讨其强化机理和断裂机制。
机理研究表明:在Al-ZrO_2系中,随着温度的增加,Al液化并与ZrO_2形成液—固界面,当温度升至830℃左右时,界面处反应生成热力学稳定的α-Al_2O_3和活性Zr原子,α-Al_2O_3与液态Al润湿性差,偏聚于反应界面,阻碍Zr原子的扩散;Zr原子在反应热和浓度梯度的作用下扩散进入Al基体,反应生成Al_3Zr。Al-ZrO_2-B反应系中,加入的B首先与Al在700℃结合生成AlB_2,升温至840℃左右时,与ZrO_2结合反应生成α-Al_2O_3和ZrB_2,抑制Al_3Zr形成,B/ZrO_2摩尔比为2时,Al_3Zr基本消失,反应产物仅由α-Al_2O_3和ZrB_2组成;由升温速率分别为10℃/min、20℃/min和30℃/min的DSC曲线和Kissinger方程,计得Al-ZrO_2的反应活化能为358 kJ/mol,B/ZrO_2摩尔比为1时,反应活化能升至393 kJ/mol。
性能研究表明:增强相体积分数为20%和30%的复合材料,随着B/ZrO_2摩尔比由0增至1和2时,拉伸强度先降后升,分别由135MPa和186MPa降至130MPa和163MPa后又升至189MPa和209MPa。延伸率却随之先增后降,分别从4.7%和14.9%增至10.3%和16.1%后降至8.1%和12.3%。Al-ZrO_2,Al-ZrO_2-B系复合材料的强化机理为弥散强化、细晶强化、位错强化,断裂机制有位错机制和空位形核机制。
In this article,Al-ZrO_2 and Al-ZrO_2-B systems aluminum matrix composites were fabricated by means of exothermic dispersion(XD).Thermodynamic analysis of reaction process was carried out.The reaction products and microstructures of composites were analysed by modern means such as optical microscope(OM),scanning electron microscopy (SEM),and X-Ray diffraction(XRD).The kinetics of the reaction process was investigated based on DSC and the influence of different technical parameters on the reaction process and results;the normal temperature mechanical performance was tested and its strengthening mechanism and fracture mechanism were explored.
The study of mechanism shows that:with the raise of temperature,Al liquefied and formed fluid-solid interface with ZrO_2;when the temperature reached 830℃,α-Al_2O_3,which has stable thermodynamic properties,and active Zr atoms were produced.In Al liquation, owing to its poor wettability,α-Al_2O_3 particles were prone to segregate at the interface and hindered Zr atoms' dispersion;however,with the effect of concentration gradient and heat,Zr atoms diffused into Al matrix and then Al_3Zr generated.In Al-ZrO_2-B system,firstly B reacted with Al at 700℃to form AlB_2;as warming up to 840℃,AlB_2 reacted with ZrO_2 to generateα-Al_2O_3 and ZrB_2,which inhibited the formation of Al_3Zr.When B/ZrO_2 molar ratio was 2,Al_3Zr basically disappeared in the matrix;the reaction product only consists ofα-Al_2O_3 and ZrB_2.The activation energy value of Al-ZrO_2 system calculated from DSC curves with different heating rates and the Kissenger equation was shown to be 358 kJ/mol. When B/ZrO_2 molar ratio is 1,the activation energy rise to 393 kJ/mol.
The research of mechanical properties shows that:as B/ZrO_2 molar ratio grew from 0 to 1,further to 2,the tensile strength of the composites whose reinforcement volume fraction were 20%and 30%firstly decrease from 135MPa and 186MPa to 130MPa and 163MPa respectively,but then rose to 189MPa and 209MPa.However,the elongation rate varied in the opposite way,increasing from 4.7%and 14.9%to 10.3%and 16.1%at first,and then falling to 8.1%and 12.3%.The strengthening mechanism of Al-ZrO_2 and Al-ZrO_2-B systems composites can be interpreted by dispersion strengthening,fine grain strengthening, dislocation strengthening;the fracture mechanism include dislocation nucleation mechanism and the vacancy mechanism.
引文
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