AMORPHIZATION OF SIC UNDER ION AND NEUTRON-IRRADIATION

This paper presents results on the microstructure and physical propert ies of SiC amorphized by both ion and neutron irradiation. Specificall y, 0.56 MeV Si ions have been implanted in single crystal 6H-SiC from ambient through >200 degrees C and the critical threshold for amorphiz ation was measured as a function of the irradiation temperature. From a high resolution transmission electron microscopy (HRTEM) study of th e crystalline to amorphous transition region in these materials, elong ated pockets of amorphous material oriented parallel to the free surfa ce are observed. Single crystal 6H-SiC and hot pressed and sintered 6H and 3C SIC were neutron irradiated at approximately 70 degrees C to a dose of similar to 2.56 dpa causing complete amorphization. Property changes resulting from the crystal to amorphous transition in SiC incl ude a density decrease of 10.8%, a hardness decrease from 38.7 to 21.0 GPa, and a decrease in elastic modulus from 528 to 292 GPa. Recrystal lization of the amorphized, single crystal 6H-SiC appears to occur in two stages. In the temperature range of similar to 800-1000 degrees C, crystallites nucleate and slowly grow. In the temperature range of 11 25-1150 degrees C spontaneous nucleation and rapid growth of crystalli tes occur. It is further noted that amorphized 6H (alpha) SIC recrysta llizes to highly faulted fee (beta) SiC. (C) 1998 Published by Elsevie r Science B.V. All rights reserved.