金剛石是自然界中最硬的晶體材料，近幾十年來(lái)，人們一直在為進(jìn)一步提高金剛石材料的硬度而不斷努力。研究表明，晶粒尺寸為10-30 nm的納米金剛石努氏硬度高達(dá)110-140 GPa，明顯高于單晶金剛石。平均孿晶厚度為5-8 nm的納米孿晶金剛石的維氏硬度可達(dá)175-200 GPa，是單晶金剛石硬度的兩倍，打破了已知超硬材料的硬度極限。能否進(jìn)一步提高金剛石材料的硬度就成為新型超硬材料設(shè)計(jì)和制備的一個(gè)重要科學(xué)問(wèn)題。

來(lái)自燕山大學(xué)田永君院士團(tuán)隊(duì)的溫斌教授等，與美國(guó)芝加哥大學(xué)的王雁賓教授合作，提出了一種新型的交織納米孿晶金剛石結(jié)構(gòu)。通過(guò)分析交織納米孿晶界對(duì)位錯(cuò)滑移臨界分切應(yīng)力的影響，利用Sachs模型，計(jì)算了交織納米孿晶金剛石的硬度。結(jié)果表明，交織納米孿晶界比一般納米孿晶更能提高金剛石的硬度。其硬化機(jī)理是由于交織孿晶界阻礙了更多滑移面上的位錯(cuò)移動(dòng)，進(jìn)而增加了位錯(cuò)滑移的臨界分切應(yīng)力。直接的分子動(dòng)力學(xué)模擬進(jìn)一步驗(yàn)證了這一結(jié)果。這項(xiàng)研究工作將為新型超硬材料的實(shí)驗(yàn)合成提供一條新思路。

該文近期發(fā)表于npj Computational Materials 6: 119 （2020），英文標(biāo)題與摘要如下。

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 individual 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-diamond; this result is further verified by MD simulations. This work provides a new strategy for designing new super-hard materials in experiments.