Compression Deformation Mechanism of Silicon Carbide: I, Fine‐Grained Boron‐ and Carbon‐Doped β‐Silicon Carbide Fabricated by Hot Isostatic Pressing

Abstract

The deformation behavior of boron‐ and carbon‐doped β‐silicon carbide (B,C‐SiC) with an average grain size of 260 ± 18 nm containing 1 wt% boron was investigated by compression testing at elevated temperatures. Extensive grain growth during deformation was observed. The stress–strain curves were compensated for grain growth by assuming power‐law type of dependence on grain size and strain rate. The stress exponent n was ∼1.3 and the grain size exponent p was ∼2.7 at temperatures ranging from 1593° to 1758°C. The apparent activation energy of deformation Qd was ∼760 kJ/mol, which was lower than the activation energy for lattice diffusion of silicon and carbon in SiC and higher than that for grain‐boundary diffusion of carbon in SiC. These results suggest that the deformation mechanism of the fine‐grained B,C‐SiC is grain‐boundary sliding accommodated by the grain‐boundary diffusion.

Creep and Microstructural Evolution at High Temperature of Liquid‐Phase‐Sintered Silicon Carbide

“…These values compare well with previous results in LPS SiC containing Y 2 O 3 and Al 2 O 3 as sintering aids 12,29 and also for some SSS SiC. 14,17 As will be clear below, it is also important to note the duration of the tests: this was about 120 h for SiC-5YAG and more than 150 h for SiC-15YAG.…”

“…3), in good agreement with previously reported values for SiC. 12,17,20,24 (3) Microstructure of the Deformed Materials side the creep machine during the tests but not loaded. It was also observed that cavitation was significantly more important in SiC-15YAG than in SiC-5YAG.…”

“…These strain rates are also in good agreement with previously reported results in similar systems. 12,24 In addition, the materials studied here are significantly more creep resistant than some SSS SiC 14,17 and superplastic LPS SiC. 30 Figure 3 compares the strain rate versus stress logarithmic plot at the creep temperature for the two materials.…”

“…7,9 One of the most widely studied additive systems is Y 2 O 3 -Al 2 O 3 , especially when these components are chosen in the ratio 3:5 to form yttrium-aluminum garnet (YAG, Y 3 Al 5 O 12 ) 10,11 : the presence of crystalline YAG has been demonstrated to improve the fracture toughness at room temperature of LPS SiC. 2 The high-temperature compressive creep of SiC has been the focus of several works before, [12][13][14][15][16][17][18][19][20][21][22][23][24] although it has yet to be systematically studied. In particular, to the best of the authors' knowledge, the correlation between creep behavior and microstructural evolution in LPS SiC containing crystalline YAG as the secondary phase has only been studied once before, showing the effect of sintering time.…”

Effect of Oxygen Segregation at Grain Boundaries on Deformation of B, C‐Doped Silicon Carbides at Elevated Temperatures

“…Since the equiaxed grains were maintained even after deformation, grain-boundary sliding is a major deformation mechanism of HIPed SiC. Shinoda et al 29 reported n 5 1.3 and p 5 2.7 in deformation of 1 wt% B, C-doped SiC, which was fabricated by HIPing at 980 MPa. These values were almost identical with our results on HIPed SiC.…”