Effect of a BN interlayer on the tensile strength of NiAl coated sapphire fibers

Hajas, D.; Kyrsta, Stepan; Schneider, Jochen M.

doi:10.1016/j.scriptamat.2006.04.011

Cited by 8 publications

(4 citation statements)

References 17 publications

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“…No large facets, steps, or preferential crack direction can be discerned. Earlier results have shown that no significant change in σ 0 is detected after annealing and/or etching of the as‐received fibers 17 . These results are displayed for comparison.…”

Section: Resultsmentioning

confidence: 65%

“…During annealing, IP75‐coated fibers without a BN interlayer fractured and tensile testing was therefore not possible. This has also been observed on fibers coated with NiAl and may be due to thermally induced stress causing fracture of the sapphire 17 . It is likely that the same mechanism is at least in part responsible for the strength degradation of these annealed fibers as for the “as deposited fibers” discussed in the section “Al 2 O 3 /IP75 before annealing.” This is supported by the fracture surface analysis, where large smooth fracture surfaces i.e., mirrors were identified, similar to the one displayed in Fig.…”

Section: Resultsmentioning

confidence: 72%

“…Single crystal α‐Al 2 O 3 fibers were used as reinforcing fibers, due to their chemical stability and high strength at room and high temperature (2.1–3.4 GPa at room temperature and 1.0–1.7 GPa at 1100°C 12 ). According to Hu et al , 13 BN forms no reaction products with α‐Al 2 O 3 at the composite fabricating temperature of 1300°–1400°C, which is important in order to maintain high fiber strength 14–20 …”

Section: Introductionmentioning

confidence: 99%

“…It has been reported that the fiber strength is degraded during composite fabrication. The main reasons for this behavior are thought to be: (a) chemical reactions between fiber and matrix and/or impurities originating from the matrix and/or binders causing morphological changes on the fiber surface, 14–20 (b) Coefficient of thermal expansion (CTE) mismatch between fiber and matrix causing thermal stresses during cooling from the fabrication temperature, 17 (c) hot pressing induced fiber fracture, 15,16 and (d) surface diffusion of Al 2 O 3 causing morphological changes on the fiber surface 14,15,17,21 …”

Section: Introductionmentioning

confidence: 99%

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Tensile Strength of Ni₄₅Al₄₅Cr_7.5Ta_2.5‐Coated Sapphire Fibers

Hajas

Gebhardt

Chen

et al. 2008

Journal of the American Ceramic Society

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Continuous single-crystal a-Al 2 O 3 fibers were coated with Ni 45 Al 45 Cr 7.5 Ta 2.5 (IP75) alloy by physical vapor deposition (PVD). The strength of the coated fibers was evaluated by tensile testing and compared with the strength of uncoated fibers. The effect of temperature during diffusion bonding as well as the presence of a BN interlayer deposited by chemical vapor deposition (CVD) on the fiber strength was studied. Fibers coated with IP75, but without a BN interlayer, retained 23% of their initial strength after the PVD process and fractured during heat treatment. Evidence for thermal stress induced twin formation is presented. Fibers coated with a BN interlayer retained their initial strength during the coating processes. However, only 13% of their initial strength could be retained after the heat treatment. Here, chemical reactions cause morphological changes of the fiber surface. These may act as stress concentration sites, resulting in the extensive strength reduction reported here. These data are important for formulating future strategies avoiding or minimizing strength degradation during production of intermetallic matrix composites.

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Section: Resultsmentioning

confidence: 65%

Section: Resultsmentioning

confidence: 72%