Oxidation behavior of hot pressed ZrB2–SiC and HfB2–SiC composites

Effect of Si3N4 Addition on Oxidation Resistance of ZrB2-SiC Composites

“…In addition, cyclic oxidation studies were carried out on the composites at 1300 • C for a total duration of 24 h in air. The experimental set-up and the method of specimen preparation for isothermal and cyclic oxidation studies have been described in an earlier report [6].…”

“…The combined effect of both SiC and Si 3 N 4 as reinforcements on the oxidation behavior of ZrB 2 needs further study. For suitable comparison, it is necessary to use some data from our earlier work [6]. This report aims to fill this gap by examining the influence of Si 3 N 4 addition on the oxidation behavior of ZrB 2 -SiC composites.…”

Strength of hot pressed ZrB2–SiC composite after exposure to high temperatures (1000–1700 °C)

“…But the increased oxide scale thickness of Z30S compared to Z20S appears to be due to the formation of cracks on the top surface of oxide scale. Cracks formed in oxide layer in ZrB 2 -SiC composite may be due to residual stresses generated by ionic diffusion, growth of ZrO 2 , pressure exerted by CO (g) and volatile B 2 O 3 (g) formed in subsurface, volume changes during oxidation and CTE mismatch between oxide products, as reported by Mallik et al 18 Since the cracks were found only on B 2 O 3 oxide surface of Z30S, stresses generated due to ionic diffusion, growth of ZrO 2 can be ruled out. On the other hand, formation of CO (g) and content of SiO 2 in glassy phase due to partial oxidation of SiC by reaction (2) increases with increase in SiC contents.…”

“…From Table 1, it was found that grain size decreases with increases in SiC contents in ZrB 2 -SiC composites. The corresponding hardness and fracture toughness increased with SiC contents, as the hardness of SiC (25)(26)(27)(28)(29)(30) ) is more than ZrB 2 (15)(16)(17)(18) ). The trend of flexural strength dependence on volume fraction of SiC may be due to counter balancing the increment in strength due to grain size and residual tensile stress generates in ZrB 2 phase during cooling after hot pressing since the CTE of ZrB 2 (6.8 × 10 −6 / • C) is higher than SiC (4.5 × 10 −6 / • C).…”

“…But the presence of SiO 2 phase on SiC shows partial oxidation of SiC at 1000 • C for 5 h. It has been reported that the oxidation of SiC phase in ZrB 2 -SiC composites start at temperature >1100 • C due to perennial oxidation of ZrB 2 . 18 But the oxidation of micron size SiC single phase starts as early as at 843 • C. 19 So it is possible to partially oxidize SiC in ZrB 2 -SiC at 1000 • C for 5 h. Previous work by authors 13 has shown that part of B 2 O 3 remains in the oxide scale of ZrO 2 after oxidation of hot pressed ZrB 2 having 1 wt% B 4 C after exposure to 1000 • C for 5 h. So, the glassy phase in the oxide scale is B 2 O 3 rich silicate glass having some amount of SiO 2. The binary phase diagram for SiO 2 -B 2 O 3 shows that B 2 O 3 can dissolves up to ∼75% of SiO 2 at 1000 • C. 5 So, oxidation of ZrB 2 -SiC composite at 1000 • C can be represented by chemical reactions (1)-(3).…”