Study and modelling of the thermo-mechanical behaviour of melt-textured YBaCuO-composites containing Ag and/or 211 particles

摘要

YBa_2Cu_3O_x high-T_c ceramic superconductors have been elaborated by the melt-textured-growth method with additions of Ag particles and/or Y_2BaCuO_5 (211 green phase) in order to study the fracture properties and the thermal shock resistance. The Vickers indenttion technique, initially devoted to the sole determination of the toughness has been used in conjunctionwith a new thermal shock resistance parameter. It makes use of the initial stage of stable propagation of Vickers indentation cracks when submitted to a thermal stress, and results in a generalisation of the fourth parameter of Hasselman. Whereas the toughness increases with increasing 211 content, does the thermal shock resistance decrease. This is explained with respect of the strongly microcracked (along the 011 planes) microstructure which is seen as a stacking of dense laminates bound by the 211 particles and subjected to a linear temperature gradient. The higher the number of bounding particles, the stiffer the quenched material, and the higher the induced thermal stress. This micro-mechanical model is implemented into a finite element software. The first results of the calculations confirm the above approach.