微纳米ZrB2p/Al复合材料的原位合成机制和组织特征

采用Al--KBF4--K2ZrF6组元通过熔体直接反应法制备了ZrB2颗粒增强铝基复合材料,优化的初始合成温度范围为850～870℃,反应时间为25～30 min.扫描电镜观察结果显示：ZrB2颗粒尺寸为300～400 nm,颗粒间距200 nm左右,有团簇现象,团簇体尺寸为30～40μm.当颗粒理论体积分数为3%时,单位熔体体积内ZrB2颗粒形核数量为6.68×1017 m-3,平均线长大速率为47.3nm.s-1.分析团簇原因认为：大量细小高熔点ZrB2增加了熔体黏度,颗粒扩散阻力大,限制了颗粒迁移位移;ZrB2颗粒因密度大具有较高的沉降速率.原位反应过程分析表明：通过Al3Zr--AlB2间的分子化合及Zr]--B]间的原子化合得到ZrB2颗粒,是高温稳定相.

In situ fabrication and microstructure of micro-nano ZrB2p/Al composites

Aluminum matrix composites reinforced by ZrB2 particles were fabricated with Al-KBF4-K2ZrF6 components via a melt direct reaction method.The suitable synthesizing temperature and reaction time are 850 to 870 ℃ and 25 to 30 min,respectively.Scanning electron microscopy observations indicate that the size of the particles is 300 to 400 nm and the interval between them is about 200 nm.Some of the particles stick together,leading to clusters with a size of 30 to 40 μm.When the theoretical volume fraction of the particles is 3%,the nucleation amount is 6.68×1017m-3,and the average linear growth velocity is 47.3 nm· s-1.The reason for clustering is that abundant fine and infusible ZrB2 particles increase the viscosity of the composite melt.High diffusion resistance prohibits the particles from migrating.Thus the particles have higher density and sedimentation velocity,which make them cluster easily.In situ reaction analysis shows that the particles can be obtained by molecular combination between Al3Zr and AlB2 or atomic combination between Zr and B atoms,and they are stable at high temperature.