In:
Journal of the American Ceramic Society, Wiley, Vol. 101, No. 9 ( 2018-09), p. 4203-4223
Kurzfassung:
Nextel™ 610 alumina fibers and alumina‐ YAG (yttrium‐aluminum garnet) matrices were used to make oxide‐oxide ceramic matrix composites ( CMC s) with and without monazite (La PO 4 ) fiber‐matrix interfaces. Twelve sequential aluminum oxychloride (Al OC l) infiltrations with 1 hour heat treatments at 1100°C and a final 1 hour heat treatment at 1200°C were used for matrix densification. This matrix processing sequence severely degraded CMC mechanical properties. CMC tensile strengths and interlaminar tensile ( ILT ) strengths were less than 10 MP a and 1 MP a, respectively. Axial fracture of Nextel™ 610 fibers was observed after ILT testing, highlighting the extreme degradation of fiber strength. Extensive characterization was done to attempt to determine the responsible degradation mechanisms. Changes in Nextel™ 610 fiber microstructure after CMC processing were characterized by optical microscopy, SEM , and extensively by TEM . In Al OC l degraded fibers, grain boundaries near the fiber surface were wetted with a glass that contained Y 2 O 3 /SiO 2 or Y 2 O 3 /La 2 O 3 /P 2 O 5 /SiO 2 , and near‐surface pores were partially filled with Al 2 O 3 . This glass must also contain some Al 2 O 3 and initially some chlorine. Al OC l decomposition products were predicted using the FactSage ® Thermochemical code, and were characterized by mass spectrometry. Effects of Al OC l precursors on monazite coated and uncoated Nextel™ 610 fibers tow and filament strength were evaluated. A mechanism for the severe degradation of the oxide‐oxide CMC s and Nextel™ 610 fibers that involves subcritical crack growth promoted by release of chlorine containing species during breakdown of intergranular glasses in an anhydrous environment is proposed.
Materialart:
Online-Ressource
ISSN:
0002-7820
,
1551-2916
DOI:
10.1111/jace.2018.101.issue-9
Sprache:
Englisch
Verlag:
Wiley
Publikationsdatum:
2018
ZDB Id:
2008170-4
ZDB Id:
219232-9
