Effects of Steam Environment on Creep Behavior of Nextel™610/Monazite/Alumina Composite at 1,100°C

Abstract

The tensile creep behavior of a N610™/LaPO 4 /Al 2 O 3 composite was investigated at 1,100°C in laboratory air and in steam. The composite consists of a porous alumina matrix reinforced with Nextel 610 fibers woven in an eight-harness satin weave fabric and coated with monazite. The tensile stress-strain behavior was investigated and the tensile properties measured at 1,100°C. The addition of monazite coating resulted in~33% improvement in ultimate tensile strength (UTS) at 1,100°C. Tensile creep behavior was examined for creep stresses in the 32-72 MPa range. Primary and secondary creep regimes were observed in all tests. Minimum creep rate was reached in all tests. In air, creep strains remained below 0.8% and creep strain rates approached 2×10 −8 s −1 . Creep run-out defined as 100 h at creep stress was achieved in all tests conducted in air. The presence of steam accelerated creep rates and significantly reduced creep lifetimes. In steam, creep strain reached 2.25%, and creep strain rate approached 2.6×10 −6 s −1 . In steam, creep run-out was not achieved. The retained strength and modulus of all specimens that achieved run-out were characterized. Comparison with results obtained for N610™/Al 2 O 3 (control) specimens revealed that the use of the monazite coating resulted in considerable improvement in creep resistance at 1,100°C both in air and in steam. Composite microstructure, as well as damage and failure mechanisms were investigated.

Creep of Nextel™ 610 Fiber at 1100°C in Air and in Steam

“…Results of this study are in good agreement with those reported for Nextel ™ 610 fiber tows and single filaments at 1100°C and 1090°C . Results for oxide–oxide CMCs with Nextel ™ 610 fibers also have similar MG parameters. The rupture time of the Nextel ™ 610/alumina CMCs at 1100°C can be predicted from the MG relationship determined for Nextel ™ 610 fibers, as previously demonstrated for prediction of the creep lifetimes of a woven Nextel ™ 610/aluminosilicate CMC .…”

“…The MG plot of the creep‐rupture data obtained in this work is shown in Fig. , where published results for Nextel ™ 610 fibers and for Nextel ™ 610/alumina CMCs are included for comparison. The MG plot in Fig.…”

“…Data for Nextel ™ 610 single fibers from DiCarlo et al . Data for CMC at 1100°C in air and in steam from Ruggles‐Wrenn et al …”

“…Oxide–oxide CMCs exhibit damage tolerance combined with inherent oxidation resistance, and have good high‐temperature mechanical properties in air . However, recent studies show dramatic degradation of mechanical performance of oxide–oxide CMCs at elevated temperature in steam . When a CMC is subjected to mechanical loading at elevated temperature in steam, multiple degradation and failure mechanisms may operate simultaneously.…”

Degradation of Nextel™ 610‐based oxide‐oxide ceramic composites by aluminum oxychloride decomposition products

“…Current oxide‐oxide CMCs are stable up to 1100 or 1200°C in air, but the wide variety of environments and temperatures they may be exposed to during processing and use, particularly in combustion environments, is still of great concern. For example, CMCs that contain Nextel™ 610 fibers (alumina) have higher creep rates and shorter creep rupture times in steam . CMCs that contain Nextel™ 720 fibers (alumina‐mullite) have higher creep rates and shorter creep rupture times in steam and in argon .…”