含稀土硬质合金的表面观察

来源期刊：中南大学学报(自然科学版)2003年第5期

论文作者：张立 W.D.Schubert 黄伯云 吴恩熙

文章页码：467 - 471

关键词：硬质合金;稀土; Ce;富集

Key words：cemented carbide; rare earth; cerium; enrichment

摘    要：采用合金烧结表面观察法研究了掺杂稀土在低碳硬质合金中的存在形式与作用机理.掺杂稀土分别以混合稀土(La和Ce为主体成分)-Co(RE-Co)预合金粉形式和La(NO₃)₃的丙酮溶液形式在硬质合金湿磨时直接加入.用扫描电镜和能谱仪对含稀土与不含稀土的低碳硬质合金的烧结表面进行观察与分析.研究结果表明:合金中是否含有稀土以及稀土的掺杂形式对合金的表面结构有很大的影响;以混合稀土-Co预合金粉形式掺杂的硬质合金烧结表面,稀土Ce明显富集,合金表面的稀土形成了含氧的稀土第3相;当稀土以La(NO₃)₃形式掺杂时,合金表面含氧的稀土La第3相的数量明显小于前一种掺杂形式.当稀土以RE-Co预合金粉的形式掺杂时,因Ce与氧具有很强的结合能力,Ce向硬质合金烧结表面富集的驱动力主要来自于合金内部与合金表面氧的浓度差;当稀土以La(NO₃)₃的形式掺杂时,硬质合金烧结表面附近的稀土La向烧结表面聚集的驱动力主要来自于系统自由能的降低.

Abstract: Surface observation method of as-sintered surface is used to study the behavior of rare earth in cemented carbide with low carbon content. The addition forms of rare earth are rare earth(mainly containing lanthanum and cerium )and cobalt pre-alloyed powder and La(NO₃)₃ dissolved in acetone which are added during the wetmilling of cemented carbide. The results by SEM and EDAX show that there are remarkable differences on the surfaces of the as-sintered cemented carbides with and without rare earth, and with different addition forms of rare earth. When rare earth is added into cemented carbide in the form of rare earth-Co pre-alloyed powder, cerium in cemented carbide gets enriched on the sintering surface during sintering, forming a third phase containing oxygen because of its strong affinity to oxygen. When rare earth is added in the form of La(NO₃)₃, both of the amount and the size of the third phase on the surface are smaller than the former, indicating that the addition form of rare earth determines the activity degree of rare earth in cemented carbide during the sintering process and only lanthanum nearby the sintering surface can get together to reduce the free energy of the whole system.