High‐Temperature Compression Deformation Behavior of Fine‐Grained Carbon‐Bonded Alumina

Abstract

Carbon-bonded alumina with 33 wt% residual carbon was tested in compression at room temperature and at temperatures between 700°C and 1500°C in quasi-static tests, creep tests, and stress relaxation tests. Therefore, a new high-temperature test set up with inert gas chamber and inductive heating was used. The tests were accomplished by investigations of microstructure and Young's modulus. At room temperature, the results exhibit a pronounced hysteresis for the first loading cycle, which almost completely disappeared in subsequent cycles. The creep tests showed characteristic curves for compression whereas primary and secondary (stationary) creep occurred. Above 1000°C, a strong increase in creep rate was detected, whereas almost no creep was observed below this temperature. All creep curves were approximated with the models of logarithmic and Andrade creep. The activation energy for creep was found to be 263 kJ/mol above 1150°C. The resistance against stress relaxation showed an anomaly with a minimum between 1000°C to 1200°C and a maximum between 1300°C and 1400°C.M. Rigaud-contributing editor Manuscript No. 37046.

Prediction of High Temperature Behavior of Open‐Cell Ceramic Foams Using an Experimental‐Numerical Approach

“…The testing times for these tests are greater than those of Solarek et al [1] for a more detailed investigation of the material behavior. No changes of the specimen diameter are observed during the tests, which is why a steady stress state is assumed.…”

“…[1] The result of the relaxation test with an initial stress of s 0 re ¼ 10 MPa is depicted in Figure 3b. At the beginning, the stress relaxation rate is very high and after 30 min 80% of the initial stress are relaxed in accordance with previously reported.…”

“…To ensure a more homogeneous distribution of temperature in the specimen, the molybdenum susceptors (TZM) are aligned above and below. For these tests, the displacement measurement can be carried out closer to the specimen, compared to the system used in the work of Solarek et al [1] The tests are performed at normal pressure in inert argon atmosphere, in order to prevent the oxidation of carbon. Therefore, the chamber with the specimen to be tested, is evacuated to a pressure of 2 Â 10 À1 mbar and filled with argon to 1 000 mbar twice previous testing.…”

“…More information about material tests are given in a previous work. [1] After a holding time of 20 min for a homogeneous temperature field in the sample, the force is increased with a rate of 250 N s À1 . In all tests, the loading axis is parallel to the pressing direction of the samples.…”

“…Creep and relaxation compression tests at bulk specimens of carbon-bonded alumina were performed by Solarek et al [1] for stresses and temperatures up to 1 500 C. Based on these investigations, an obvious creep behavior was observed for temperatures above 1 000 C and a predominantly primary creep in the tested time range of 30 min. There are many different models in the literature to describe the creep deformation behavior.…”