THE STRAIN-RATE DEPENDENCE OF THE HARDNESS OF A1N DOPED SiC N^N. Ur-rehmanCentre for Advanced Structural Ceramics Department of Materials, Imperial College London, London SW7 2AZ, UK

摘要

Tailored nanoindentation experiments were used to determine the strain rate dependence of the hardness of A1N doped SiC. It is shown that in the nano-indentation regime, where cracking is limited, the hardness of SiC reduces by 0.8 GPa per decade reduction in strain rate at room temperature for both a coarse and fine grained material. The coarse grained material was tested at higher temperatures as well and the strain rate sensitivity increases strongly with temperature becoming 1.6 GPa and 2.9 GPa per decade of strain rate at 373 K and 473 K respectively. Estimates for the strain rate dependence of the lattice resistance (Peierls' stress) of SiC derived from these measurements agree quite well with high temperature data for SiC. These experiments therefore open up the possibility to determine real constitutive equations for plasticity in SiC and other armour ceramics.