含硼金属包覆膜的物相结构与含硼金刚石的生成

使用以FeB为硼源的含硼粉末冶金铁基触媒，在六面顶压机上高温高压合成含硼金刚石单晶。金相观察发现，金刚石金属包覆膜由粗大的板条状渗碳体和细密的莱氏体共晶组织构成。X射线衍射（XRD）发现，金属包覆膜的物相组成为（Fe，Ni）3C、（Fe，Ni）3（C，B）、石墨（Gr）以及γ-（Fe，Ni）（A）。使用透射电镜（TEM）在包覆膜中发现了颗粒状的Fe3（C，B），条状的γ-（Fe，Ni）和颗粒状的Fe23（C，B）6。电子探针分析（EPMA）结果表明，硼元素在包覆膜中存在浓度梯度，越接近含硼金刚石，硼元素的含量越高。分析认为，高温高压下硼是以铁-碳-硼化合物的形式通过金属包覆膜向金刚石晶体扩散的，Fe3（C，B）或（Fe，Ni）3（C，B）极有可能是含硼金刚石生长的直接碳源和硼源。

Boride phase-structure in metallic film and the formation of boron-doped diamond single crystal

The boron-doped diamond single crystal was synthesized at high temperature and high pressure （HTHP） in cubic apparatus with iron-based catalyst made by powder metallurgy using FeB as boron source. The phase and microstructure of the metallic film surrounding diamond crystal were investigated by means of metallographic microscope, XRD, TEM and EPMA. The metallographic microstructure of the film is composed of coarse lathy original cementite and compact eutectic ledeburite. There are （Fe, Ni）3C, （Fe,Ni）3（C,B）, graphite and γ-（Fe,Ni） in the film observed by XRD. The results of TEM indicate that the phase of the film nearby the diamond includes granular Fe3（C,B）, lathy γ- （Fe,Ni） and grainy Fe23 （C,B）6. By exploring EPMA, the concentration gradient of boron in the film is revealed. With closing the diamond crystal, the content of boron in the film increases. Basis of the results above, a conclusion can be draw that the boron diffuses across the film by combining with iron and carbon. In general, it is very possible that the Fe3（C,B） or （Fe,Ni）3（C,B） in film is the direct carbon and boron source of diamond.