金刚石单晶,聚晶与多晶如何识别

有这么几方面区别：

1. 生产方法上：单晶金刚石是石墨经六面顶压机合成；多晶金刚石是经过爆炸法合成；聚晶金刚石只是把单晶金刚石与结合剂在高温高压下烧结而成的金刚石聚合物。

2. 从微观结构上看：多晶金刚石比单晶金刚石有更多的晶棱和磨削面，在抛光过程中每条晶棱都具有磨削力，并且粗颗粒在磨削过程中会破碎成更小的颗粒脱落，这样既可以保持持续的磨削力，又不易造成划伤。

3. 多晶金刚石所具备的结构优势，使其可以广泛应用于蓝宝石衬底、光学晶体、电子行业等的研磨抛光。

金刚石是自然界中最硬的晶体材料，近几十年来，人们一直在为进一步提高金刚石材料的硬度而不断努力。研究表明，晶粒尺寸为10-30 nm的纳米金刚石努氏硬度高达110-140 GPa，明显高于单晶金刚石。平均孪晶厚度为5-8 nm的纳米孪晶金刚石的维氏硬度可达175-200 GPa，是单晶金刚石硬度的两倍，打破了已知超硬材料的硬度极限。能否进一步提高金刚石材料的硬度就成为新型超硬材料设计和制备的一个重要科学问题。

来自燕山大学田永君院士团队的温斌教授等，与美国芝加哥大学的王雁宾教授合作，提出了一种新型的交织纳米孪晶金刚石结构。通过分析交织纳米孪晶界对位错滑移临界分切应力的影响，利用Sachs模型，计算了交织纳米孪晶金刚石的硬度。结果表明，交织纳米孪晶界比一般纳米孪晶更能提高金刚石的硬度。其硬化机理是由于交织孪晶界阻碍了更多滑移面上的位错移动，进而增加了位错滑移的临界分切应力。直接的分子动力学模拟进一步验证了这一结果。这项研究工作将为新型超硬材料的实验合成提供一条新思路。

该文近期发表于 npj Computational Materials 6 : 119 (2020)，英文标题与摘要如下，点击https://www.nature.com/articles/s41524-020-00387-3可以自由获取论文PDF。

Intersectional nanotwinneddiamond-the hardest polycrystalline diamond by design

Jianwei Xiao, Bin Wen, Bo Xu, Xiangyi Zhang, Yanbin Wang &Yongjun Tian

The hardness of nanotwinned diamond (nt-diamond) is reported to be more than twice that of the natural diamond, thanks to the fine spaces between twin boundaries (TBs), which block dislocation propagation during deformation. In this work, we explore the effects of additional TBs in nt-diamond using molecular dynamics (MD) calculations and introduce a novel intersectional nanotwinned diamond (int-diamond) template for future laboratory synthesis. The hardness of this int-diamond is predicted by first analyzing inpidual dislocation slip modes in twinned grains and then calculating the bulk properties based on the Sachs model. Here we show that the hardness of the int-diamond is much higher than that of nt-diamond. The hardening mechanism of int-diamond is attributed to the increased critical resolved shear stress due to the presence of intersectional TBs in nt-diamondthis result is further verified by MD simulations. This work provides a new strategy for designing new super-hard materials in experiments.

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