Silicon creep-resistant grades

The creep resistance of silicon nitride-containing Lu-doped additives was shown to be three to five orders of magnitude greater than that of earlier grades containing Y- and / or Yb-additives [74, 75]. This material has the potential for prolonged operation at... 

During recent decades, extensive efforts have been made to control the grain boundary phase and to improve the heat resistance of silicon nitride, and this has led to significant improvements in high-temperature mechanical reliability. For example, some grades of commercial silicon nitrides have shown excellent creep resistance, even at temperatures above 1400 °C (45, 46]. Subsequent XRD analyses of these materials have revealed Lu2Si207 and Lu4Si2N207 as secondary phases. 

As shown in Figure 13.2 [21], the creep resistance of NT 154 at 150 MPa is much greater than that of earlier commercial grades of silicon nitride. Assuming a... 

The slopes of the lines in Figure 13.13, at > 0.75, are also typical for reaction-bonded silicon carbide [24, 28]. These data also indicate that over 75% of the measured axial tensile strain results from cavitation. The volumes generated by cavities are transferred primarily into axial tensile strain [25], which suggests that cavitation is the main creep mechanism of deformation in these ceramics. As the contribution of cavities to strain in SN 281 is dose to zero, creep in this material is fundamentally different from that of other grades of silicon nitride [15, 40, 41, 44]. The suppression of cavitation in SN281 is most likely the reason for its increased creep resistance. 

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