THERMAL-SHOCK TESTS OF BETA-SIC PELLETS PREPARED FROM LASER SYNTHESIZED NANOSCALE SIC POWDERS

Nanoscale SiC powders, produced by laser synthesis from gaseous precur sors, have been successfully used to prepare sintered pellets. All the sintered samples showed the low temperature beta-SIC structures and p resented an enhanced thermal conductivity (> 20%) with respect to mate rials prepared from commercial powders. Samples hardness and toughness , comparable with commercial products, confirmed the good samples qual ity, The thermal shock tests have been performed by irradiating the pe llets with a Nd-YAG pulsed laser (pulse duration and energy: 0.25 mu s and 0.18 J or 0.4 ms and 0.65 J). The laser fluence (power density) w as increased by reducing the spot size, up to the appearance of a visi ble surface damage, The threshold values for the structural damage wer e quantified using a heat flux parameter phi(abs)root t(p). The measur ed threshold value rose from ca. 20 MW/m(2) root s for the best materi als prepared from commercial SiC powders to ca. 24 MW/m(2) root s for the newly developed beta-SiC.