Microstructure changes of diamond and amorphous carbon under shear conditions

Diamond is an important tool material in ultra-precision machining. Many researches are conducted about the amorphous carbon (a-C) generated during diamond grinding. However, most of them are not able to clarify the transition mechanism of diamond crystal, which just focus on the amorphization results. This paper divides the amorphization process into three parts: peel, disorder and steady state based on the simulation results of molecular dynamics (MD) to obtain a deep understanding of the transitions under different shear conditions. The change laws of a-C composition in each part are obtained by mathematical deductions and the critical strains for transitions are calculated, finding that critical strain can unify the relationships between physical state, material properties, and amorphization in diamond. In addition, the similarities of microstructures between different a-C are analyzed to accelerate the MD modeling of fluidic a-C (fa-C) obtained by the grinding process. The results prove that different solid a-C (sa-C) convert into the same structure under the specific shear condition, but the conversion rate depends on sa-C density.