TEM Study of the High‐Temperature Oxidation Behavior of Hot‐Pressed ZrB ₂ – SiC Composites

Abstract

The oxidation behaviors of ZrB 2 ‐ 30 vol% SiC composites were investigated at 1500°C in air and under reducing conditions with oxygen partial pressures of 10 4 and 10 − 8 Pa, respectively. The oxidation of ZrB 2 and SiC were analyzed using transmission electron microscopy ( TEM ). Due to kinetic difference of oxidation behavior, the three layers (surface silica‐rich layer, oxide layer, and unreacted layer) were observed over a wide area of specimen in air, while the two layers (oxide layer, and unreacted layer) were observed over a narrow area in specimen under reducing condition. In oxide layer, the ZrB 2 was oxidized to ZrO 2 accompanied by division into small grains and the shape was also changed from faceted to round. This layer also consisted of amorphous SiO 2 with residual SiC and found dispersed in TEM . Based on TEM analysis of ZrB 2 – SiC composites tested under air and low oxygen partial pressure, the ZrB 2 begins to oxidize preferentially and the SiC remained without any changes at the interface between oxidized layer and unreacted layer.