Elasto-plastic deformation of glass-like carbons heat-treated at different temperatures

Abstract

Nano-indentation of glass-like carbons (GCs) heat-treated at different temperatures was carried out with a 3 μm radius spherical tipped indenter. The effect of crystal structure and micro-texture on elastic and elasto-plastic deformation resulting from the indentation was observed. The elastic modulus and yield stress of GCs was found to reduce with elevation of heat treatment temperature (HTT). The power law fitting constant k for the elasto-plastic deformation of the loading stress–strain curves by the indentation and the indentation elasticity index k/ E* reduced with development of the graphitic structure of GC, so that ‘elasticity’ of GC decreased with the elevation of HTT of GCs. Hysteresis loops were observed on the indentation force–displacement curve during the loading–unloading cycle. Hysteresis energy loss, which corresponds to the area of the hysteresis loops, increased with the elevation of HTT for the same terminal load. The indentation ductility index D, the ratio of hysteresis energy loss to total indentation energy, was linearly dependent on indentation elasto-plastic deformation strain ε ep. The indentation elasto-plastic modulus m, which is obtained from the slope of the plots of D versus ε ep, reduced with the elevation of HTT of GCs. From the reduction of m, it was concluded that ‘plasticity’ (or ‘ductility’) of GC increased with the elevation of HTT of GCs.