Creep and microstructure of Nextel™ 720 fiber at elevated temperature in air and in steam

Tensile and creep performance of a novel mullite fiber at high temperatures

“…8 (left), a stress exponent of 2.8 and 3.9 was measured for CeraFib 75 and Nextel 720, respectively. The findings for Nextel were similar to the results measured by Armani [15]. On his studies, Armani presented values of n for Nextel 720 of about 3 when the fibers were tested under stresses lower than 300 MPa, and values of 5 when tested with loads higher than 300 MPa.…”

“…Another fact of relevance seen on the tests was the measured stress exponent and its relation to the dominant creep mechanisms. Previous works relate interface-reaction controlled creep, n % 3, for Nextel 720 tested with stresses lower than 300 MPa and dislocation creep or void growth, n % 5, for higher loads [15]. The results here reported are in the middle of the aforementioned for the commercial fiber.…”

“…Deléglise [14] reported that Nextel 720 fibers tested at 1200°C retained only 20% of its room temperature strength while Wilson [13] stated a strength retention of 80% at the same temperature. It is also possible to find creep studies in the literature showing that these fibers are also susceptible to creep at those temperatures [14][15][16]. Additionally, Schmücker [17,18] noticed in his works that the sub-micrometer fiber grains are prone to coarsening at high temperatures, and the phenomenon can be aggravated when the fibers are embedded in a matrix [19].…”

Creep of Hi-Nicalon S Ceramic Fiber Tows at 800 deg C in Air and in Silicic Acid-Saturated Steam

“…applies to Hi-Nicalon T M S fiber tows and is consistent with results found in literature for ceramics [4,94,193,194]. DiCarlo et al noted that for ceramic materials, the Monkman-Grant log-log plots "typically fall on one straight-line master curve" [94] and this is the case for Hi-Nicalon The evidence that the Monkman-Grant relationship for Hi-Nicalon T M S fiber tows is independent of environment is further supported by a review of the data for air and steam (unsaturated) from Steffens and Shillig.…”

Creep and Oxidation of Hafnium Diboride Based Ultra High Temperature Ceramics at 1500C

“…the effects of compressive stress and SiC content) in light of the observed effects of grain size. To accomplish this, the minimum creep rates were normalized to a grain size of 1 μm using Equation 31, which was also employed by Armani [118] and Winder [13]. Based on the grain size analysis conducted in this section, the gain size exponent, m, was set at 2.…”