Morphological Evolution and Weak Interface Development within Chemical‐Vapor‐Deposited Zirconia Coating Deposited on Hi‐Nicalon™ Fiber

Abstract

The phase contents and morphology of a ZrO 2 fiber coating deposited at 1050°C on Hi-Nicalon TM by chemical vapor deposition (CVD) were examined as a function of deposition time from 5-120 min. The morphological evolution in the ZrO 2 coating was correlated to the development of delamination within the ZrO 2 coating. The delamination appears to occur as a result of: (i) continuous formation of tetragonal ZrO 2 nuclei on the deposition surface; (ii) martensitic transformation of the tetragonal phase to a monoclinic phase on reaching a critical grain size; and (iii) development of significant compressive hoop stresses because of the volume dilation associated with the transformation. Our observations suggest that it will be of critical importance to further understand and eventually control the nucleation and grain growth behavior of CVD ZrO 2 and its phase transformation behavior for its potential applications for composites.

Raman study of yttria-stabilized zirconia interfacial coatings on Nicalon™ fiber

“…18(and refs therein) Besides named factors, the influence of supports on the mechanism of tetragonal ZrO 2 phase nucleation (for coatings and films) must be taken into consideration too 19 . For example, the stabilization of t-ZrO 2 phase was observed not only for monolithic ceramic specimens but also within the CVD ZrO 2 coating on SiC fiber by Li et al 2,3 The authors noted also that a free carbon presenting as an impurity in coating can also influence on the stabilization of the tetragonal modification. It could be proposed with discretion that the Zr O Si bonds the formation of which at the Nicalon TM fiber/ZrO 2 coating interface was confirmed using Xray photoelectron spectroscopy by Baklanova et al 8 appear to be considered as stabilizing factor.…”

“…Recently the feasibility of using a CVD ZrO 2 fiber coating as an oxidation-resistant and weak interphase for structural composite materials such as SiC/SiC (CMC's) was proposed and thoroughly studied by Lee et al [1][2][3][4] They found that the CVD ZrO 2 interfacial coating on Nicalon type fiber exhibited desired tensile failure behavior, extensive crack deflection within the interface region and fiber debonding (i.e. weak interface behav- * Corresponding author.…”

The yttria-stabilized zirconia and interfacial coating on Nicalon™ fiber

“…As was noted by Lee and coworkers, 8 not only the weak interface character but the integrity and uniformity of the fiber coating are important in terms of protecting the fiber surface from matrix infiltration by CVI or melt infiltration. From this point of view, a dense undelaminated but compressively stressed coating, e.g.…”

“…Besides, it was detected the relationships between the oxygen partial pressure and the nucleation and morphologic characteristics of the ZrO 2 coating that was formed by CVD or magnetron sputtering methods. [7][8][9]11 These relationships were attributed to the grain size and oxygen deficiency effects, which appear to cause the stabilization of t-ZrO 2 . Thus, one can see that the ZrO 2 coating composed of predominantly tetragonal or cubic transformable phases can be fabricated with different experimental approaches.…”

“…Among alternative interphases the refractory oxide-based systems are considered as the most promising ones. [4][5][6] The feasibility of using a CVD ZrO 2 fiber coating as an oxidation-resistant and weak interphase for SiC/SiC composites was thoroughly examined by Lee and coworkers [7][8][9] They found that the CVD ZrO 2 coating exhibited desired tensile failure behavior and extensive crack deflection within the interface region. They concluded that the delamination within ZrO 2 layer occurred as result of the martensitic transformation of t-ZrO 2 nuclei to m-ZrO 2 on reaching a critical grain size and the development of significant compressive hoop stresses due to volume dilation and shear associated with the martensitic transformation.…”