Elastoplastic Indentation on Heat‐Treated Carbons

Abstract

A Vickers indenter, as an efficient mechanical microprobe, was applied to carbon materials heat‐treated at temperatures in the range 880°–2600°C. The plasticity of the carbon materials, which was enhanced by increasing the heat‐treatment temperature (HTT), was assessed from the relation between the indentation load, P, and the penetration depth, h. Using the concept of the true hardness, H, as a measure of plasticity and the experimental estimate of the H‐value, the plasticity of the carbon materials was examined as a function of their crystallographic parameters. The residual impression of the carbons at HTT > 1800°C was hardly visible on the indented surface after unloading, because of the nearly complete elastic recovery of the indented surface, yielding a very unique indentation P–h hysteresis in the loading/unloading cycle. The microscopic processes associated with this unique elastic recovery during unloading are discussed here in relation to the reversible slip of the dislocation‐network structures on the graphitic basal planes.