Short-term flexural creep deformation in synroc-C

• Published in: Journal of materials science 2003-08, Vol.38 (15), p.3223-3231
• Main Authors: LATELLA, B. A, LIU, T, SNOWDEN, K. U, MEHRTENS, E. G, LUMPKIN, G. R, GAN, B. K
• Format: Article
• Language: English
• Subjects: Activation energy; Applied sciences; Building materials. Ceramics. Glasses; Cavitation; Ceramic industries; Chemical industry and chemicals; Condensed matter: structure, mechanical and thermal properties; Creep; Creep rate; Creep strength; Creep tests; Deformation mechanisms; Exact sciences and technology; High temperature; Inert atmospheres; Materials science; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Miscellaneous; Oxidation; Phase transitions; Physics; Stresses; Technical ceramics; Temperature; Theta projections
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1023/A:1025121601596

The flexural creep behaviour of synroc-C in an inert atmosphere was studied at temperatures of 860°C, 900°C and 940°C under constant-load conditions in four-point bending. Applied stresses ranged from 100 to 160 MPa. Individual creep curves show primary and secondary creep but little or no tertiary creep stage. The log of the creep rate was found to increase linearly with log of the applied stress at each temperature over the entire stress range. Analysis of the creep data using the Norton power-law function revealed that the stress exponent decreased from 3.3 ± 0.6 for the 860°C and 900°C data to 2.0 ± 0.2 for the 940°C data, and an activation energy of 440 ± 40 kJ/mol was obtained over the entire temperature and stress range. Comparative analysis with the theta-projection equation was found to adequately represent the data yielding an activation energy of 464 kJ/mol while also showing a trend for the stress exponent to decrease with increasing temperature. Microstructural examination revealed extensive cavitation on the tensile surface of the creep specimens subjected to higher stresses at 900°C and 940°C. Dynamic high temperature X-ray diffraction analysis indicated little change in the phase assemblage apart from a slight reduction in the amount of the hollandite phase at higher temperatures which was attributed to a minor amount of oxidation. The possible creep damage mechanism was explored with reference to creep test results and microstructural modifications and the implications of the observations are discussed.