Alumina Single-Crystal Fibre Reinforced Alumina Matrix for Combustor Tiles

Processing and Properties of a Porous Oxide Matrix Composite Reinforced with Continuous Oxide Fibers

“…Embrittlement is most severe with cyclic loading beyond the proportional limit because oxygen that penetrates via the matrix cracks will react with the interphase and the fibers. This can be achieved by adding an interphase which either forms a crackdeflecting interface with the fibers, 13-15 has itself a low fracture toughness (e.g., "cleavable" oxides 16 or a porous layer [17][18][19] ), or forms a gap between fiber and matrix (fugitive coating). However, in wet environments the problem persists since the boron oxidation products volatilize as boron hydroxides.…”

“…3,10 This effect is most pronounced for carbon coatings, but the introduction of BN coatings and boron additives has improved the situation in oxidizing environments, where BN oxidation products (liquid boron oxide) help in healing matrix cracks. 18,20 The use of a porous matrix to isolate fibers from matrix cracks is a second, more recent approach for developing damage-tolerant composites. 3,11 To avoid degradation in oxidizing (especially wet) environments, structural design strategies therefore usually require that the stresses remain below the matrix cracking stress.…”

Influence of Zirconia Interfacial Coating on Alumina Fiber‐reinforced Alumina Matrix Composites

“…13,14 Thus, the real challenge lies in processing of a dense matrix around the fibers, without subjecting it to temperatures that degrade them. 15,16 Previous studies in this area used sapphire-reinforced alumina-matrix microcomposites (sintered at 1450°C, 2 h) to test effect of monazite and hibonite (CaAl 12 O 19 ) 17 coatings showed evidences of crack deflection; however, it was concluded that matrix densities of 85% (the maximum achieved in the study) were insufficient to completely confirm the effectiveness and contribution of the coatings. This was based on the observation that the control composites had the same mean ultimate strengths as the composites using coated fibers; however, the control composites did have a significantly lower Weibull modulus.…”

“…However, there have been reports on the fiber strength degradation using monazite coatings at high temperature, which is mainly attributed to the formation of by‐products of the precursor system with monazite that cause fiber strength degradation via stress‐corrosion cracking, which again is identified as the bottle neck with these coatings . Thus, the real challenge lies in processing of a dense matrix around the fibers, without subjecting it to temperatures that degrade them . Previous studies in this area used sapphire‐reinforced alumina–matrix microcomposites (sintered at 1450°C, 2 h) to test effect of monazite and hibonite (CaAl 12 O 19 ) coatings showed evidences of crack deflection; however, it was concluded that matrix densities of 85% (the maximum achieved in the study) were insufficient to completely confirm the effectiveness and contribution of the coatings.…”

Fugitive Interfacial Carbon Coatings for Oxide/Oxide Composites

“…[1][2][3][4] The primary approach toward this control has been through the application of fiber coatings, which provide weakly bonded interfaces that ultimately increase the strain-to-failure of the composites through crack deflection and fiber pullout. A variety of coatings have been developed for use in ceramic-matrix composites (CMCs) [5][6][7][8][9][10][11][12][13][14][15][16][17] with varying degrees of success; however, BN 18 -21 and carbon [22][23][24] remain the most widely used interface materials.…”