液相原位反应制备纳米氧化钇弥散强化铜基复合材料的机理及其性能研究

Yttria is believed to be an attractive candidate for the dispersion strengthening agents of oxide-dispersion-strengthened copper-based composites owing to its high thermodynamic stability. More importantly, yttria has fluorite-related structure and would inherently form different interfaces with copper matrix. Thus, yttria offers interesting opportunity to explore the role of the dispersion/matrix interface. The major hindrance to developing yttria-dispersion-strengthened copper-based composites is the very small solubility of yttrium in copper, which negates direct precipitation of yttria dispersions from solution. In this project, yttria nanoparticles dispersion distributed in copper matrix will be prepared by the interaction between the in-situ oxidation of yttrium atoms in molten Cu-Y alloy at liquid phase line temperature and the solidification of molten Cu-Y alloy. The in-situ oxidation mechanism of yttria nanoparticles at liquid phase line temperature will be studied by analyzing the suppressing roles of the solidification of molten Cu-Y alloy in the growth and segregation of yttria nanoparticles. The particle size and volume fraction of yttria dispersions will be controlled by adjusting the oxygen solubility and yttrium content in molten Cu-Y alloy. The isothermal solidification mechanism of molten Cu-Y alloy at liquid phase line temperature resulted from the in-situ oxidation of yttria nanoparticles will be studied by analyzing the effects of the in-situ oxidation of yttria nanoparticles on the solidification nucleation free energy and undercooling of molten Cu-Y alloy. The grain size of copper matrix will be refined by adjusting the particle size and volume fraction of yttria dispersions. The strengthening mechanisms of yttria-dispersion-strengthened copper-based composites at different temperatures will be studied by analyzing the effects of the particle size and volume fraction of yttria dispersions on the coherent precipitate strengthening of the coherent interfaces between yttria dispersions and copper matrix and the effect of the grain size of copper matrix on the fine grain strengthening. Yttria-dispersion-strengthened copper-based composites with high strength and excellent resistance to high temperature softening will be prepared.

氧化钇因高的热力学稳定性和与铜有共格关系而被认为是铜基复合材料最合适的弥散强化相，但钇在铜中极少的固溶度满足不了固相反应生成弥散强化粒子的要求。本项目利用铜钇熔液中的钇原子在液相线温度的原位氧化反应和熔液凝固的相互作用生成了弥散分布于铜基体上的纳米氧化钇粒子。通过研究熔液凝固抑制氧化钇粒子长大和防止其偏聚的作用，理解纳米氧化钇粒子在液相线温度的原位生成机制，改变氧溶解度和钇含量控制氧化钇粒子的颗粒尺寸和体积分数；通过研究氧化钇的原位生成对熔液凝固的形核自由能和过冷度的影响，理解氧化钇的原位生成引起的铜钇熔液在液相线温度等温凝固的机理，控制氧化钇粒子的颗粒尺寸和体积分数细化铜基体的晶粒尺寸；通过研究不同温度时氧化钇颗粒尺寸和体积分数对共格界面引起的沉淀强化的影响及铜基体的晶粒尺寸对细晶强化的影响，理解不同温度的强化机制，制备出兼有高强度和优良抗高温软化能力的纳米氧化钇弥散强化铜基复合材料。

氧化钇因高的热力学稳定性和与铜有共格关系而被认为是铜基复合材料最合适的弥散强化相，但钇在铜中极少的固溶度满足不了固相反应生成弥散强化粒子的要求。本项目利用铜钇熔液中的钇原子在液相线温度的原位氧化反应和熔液凝固的相互作用生成了弥散分布于铜基体上的纳米氧化钇粒子。研究内容包括氧化钇粒子在液相原位反应中的形成机理、铜钇熔液在原位反应作用下的凝固机理、纳米氧化钇弥散强化铜基复合材料的强化机制、纳米氧化钇弥散强化铜基复合材料的导电机制等4方面。.（1）Cu–Y合金的原位氧化从热力学上来讲为择优氧化，温度和氧分压是控制择优氧化的关键因素，液相原位反应将根据反应温度来选择合适的氧分压；工业氮气符合热力学计算得到的氧分压范围，且氧分压可调，可持续供氧，因此被选择作为液相原位反应的供氧剂。Y2O3颗粒均匀弥散地分布于铜基体上，粒子形貌多为球状、椭球状。Y2O3颗粒细小，最大不超过14 nm，粒子尺寸均呈单峰分布，随着Y含量的增加Y2O3颗粒尺寸有降低的趋势。Y2O3颗粒的晶面取向与铜基体明显的一致，颗粒与基体具有完全共格的界面关系。.（2）在液相原位反应过程中，当没有氧原子存在时，Cu–Y熔液由于存在动态平衡不会凝固。当有氧原子进入熔液中时，Y优先与O反应生成Y2O3粒子，在Y2O3粒子附近的局部区域将会由于贫Y而产生过冷。且Y2O3粒子作为形核剂能加速熔液的不均匀形核，在过冷度和形核剂的共同作用下，熔液发生等温凝固。在等温凝固条件下，Y2O3粒子周围的熔液一旦凝固，Y2O3粒子的长大过程就由液相扩散变为固相扩散，长大速度会大幅降低，最终得到均匀分布的纳米Y2O3弥散强化铜基复合材料。.（3）Cu–Y2O3复合材料的抗拉强度随着Y2O3体积含量的增加而升高，其延伸率都能保持在30%以上，其断口形貌为明显的韧性断裂的特征。Cu–Y2O3复合材料的强化机制主要为弥散颗粒强化，而且强化方式为切割机制和绕过机制共同强化。位错能够切过的共格析出相的最大尺寸为2.4 nm，尺寸大于2.4 nm的Y2O3颗粒将以绕过机制来强化基体。对临界应力的分析表明Cu–Y2O3复合材料具有良好的高温强度。.（4）随着Y2O3含量的增加，Cu–Y2O3复合材料的导电率呈下降趋势。Cu–0.9vol%Y2O3复合材料的导电率为98 %IACS，高于美国SCM公司生产的Cu–Al2O3复合材料。