Developments in Oxide Fiber Composites

Abstract

Prospects for revolutionary design of future power generation systems are contingent on the development of durable high-performance ceramic composites. With recent discoveries in materials and manufacturing concepts, composites with all-oxide constituents have emerged as leading candidates, especially for components requiring a long service life in oxidizing environments. Their insertion into engineering systems is imminent. The intent of this article is to present a synopsis of the current understanding of oxide composites as well as to identify outstanding issues that require resolution for successful implementation. Emphasis is directed toward material systems and microstructural concepts that lead to high toughness and longterm durability. These include: the emergence of La monazite and related compounds as fiber-coating materials, the introduction of the porous-matrix concept as an alternative to fiber coatings, and novel strategies for enabling damage tolerance while retaining long-term morphological stability. Additionally, materials and mechanics models that provide insights into material design, morphology evolution, and composite properties are reviewed.

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

“…load transfer and crack deflection) and also to shield the fiber from the oxidizing environment. It has been well documented in literature that non-oxide fiber-reinforced CMCs experience significant degradation in their desired properties at operating temperatures due to oxidation [29,32,35,[38][39][40]. This dual use of the fiber coating makes the superior strength and creep resistance of non-oxide fiberreinforced CMCs available for advanced engineering applications.…”

“…There are three approaches to achieve damage tolerant CMCs. These microstructural design philosophies enable uncorrelated fiber failure within the CMC, which dissipates more energy as the fibers fail, debond, and are pulled out of the matrix separately from one another [12,16,29]. Figure 7 shows an example of fiber pullout in SiC/BN/SiC CMC after a tensile fatigue test.…”

“…The porous matrix also enables cracks to deflect around the fiber and has been successfully demonstrated [34][35][36][37][38]. See Zok and Levi [16] and Zok [29] for an extensive review of the mechanisms and mechanical properties of porous-matrix CMCs. Figure 8d depicts a more recent design philosophy using fugitive coatings.…”

“…These non-oxide CMCs have excellent high-temperature mechanical properties and retain these properties well, for the most part. SiC/SiC CMCs have been evaluated and tested in hot-section components of turbine engines [29,72] and are also being considered for other high temperature aerospace applications such as leading edges on hypersonic vehicles due to their superior creep performance and the high strength of SiC fibers. These high-temperature oxidizing environments demand materials that are thermodynamically stable and oxidation resistant.…”

“…Oxidation embrittlement is a particular problem [18,29,41,42] in which oxygen reacts with the fibers and matrix of a CMC, causing them to form strong bonds and defeating the crack-deflecting properties intended. Oxidation embrittlement tends to occur at intermediate temperatures (600-900…”