The sp2-sp3 transition and shear slipping dominating the compressive deformation of diamond-like carbon

The uniaxial compression tests of diamond-like carbon (DLC) films are conducted via molecular dynamics to investigate their mechanical properties and deformation mechanisms by considering different factors including strain rates, temperatures, void defects and compliance. It is found that during the compression, large sp³C clusters expand themselves by annexing neighboring sp²C atoms which experience sp²-sp³ transition. Moreover, the sp³C-sp³C bonds along the direction perpendicular to the compressive direction are elongated and the rupture of such bonds leads to the compressive failure of DLC films. Furthermore, the stress relief of DLC films is the result of competition between internal relative slip and diffusion relaxation. The relative slip is dominant with low temperature and high compression strain rate, which makes the DLC films own high strength and exhibit brittleness. However, with high temperature and low strain rate, these films become ductile and their strength are degraded due to the activation of diffusion relaxation.