A pulse technique was proposed for the investigation of the dynamics and micro-mechanisms of plastic deformation of material beneath the indenter during micro-indentation. It was shown that the process of indenter penetration, under pulse loading conditions, involved several distinct stages (sometimes as many as 4) which differed with regard to kinetics and activation parameters. In each material, the first stage was characterized by a high strain rate (≥ 103/s) and by contact stresses which exceeded the static hardness by a factor of 5 to 10. The typical values of the activation volumes during the first stage were of the order of 10-30m3. This was close to the volume which was occupied by an ion in the lattice. During the remaining stages, the activation volume in ionic crystals increased up to about 10-28m3. This was equal to 10b3, where b was the Burger’s vector of glide dislocations. The dynamics of the initial stages of indenter penetration were therefore governed by elastic, and then plastic, deformation which involved non-equilibrium point defects (probably interstitials or crowdions). The role played by point defects in mass transfer beneath the indenter, and its contribution to microhardness, was estimated. In soft materials (NaCl, LiF), during long indentation times (≥1s), the contribution of point defects was estimated to be more than 10%. In the case of hard materials, it was closer to 100%. The dynamics of the final stages of indenter penetration in soft crystals were governed by dislocation creep. In all of the investigated materials, the plastic deformation beneath the indenter - for short indentation times - occurred mainly via the generation and motion of interstitials and interstitial clusters which contained a few atoms.

Investigation of Time-Dependent Characteristics of Materials and Micromechanisms of Plastic Deformation on a Sub-Micron Scale by a New Pulse Indentation Technique. Y.I.Golovin, A.I.Tyurin, B.Y.Farber: Journal of Materials Science, 2002, 37[4], 895-904