Influence of interface impurities on the fracture energy of UHV bonded niobium-sapphire bicrystals

Korn, D.; Elssner, G.; Fischmeister, H. F.; ̈hle, M. Ru

doi:10.1016/0956-7151(92)90294-o

Cited by 68 publications

(47 citation statements)

References 18 publications

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“…This level, however, is well below the range of 70 -2400 J/m 2 that has been exhibited by ultra-high vacuum (UHV) diffusion-bonded bicrystals of sapphire/niobium processed with various orientation relations. [15][16][17][18][19] Such differences can be understood by considering the interfacial chemistry and specific mechanisms of toughening in the present PTLP bonded case. While interfacial porosity and brittle fracture/pullout of Nb 5 Si 3 particles are considered to have minor contributions to the measured crack resistance, ductile tearing of copper particles and frictional grain bridging in the alumina are expected to contribute significantly to the measured fracture resistance, and will be the focus of further discussion.…”

Section: Discussionmentioning

confidence: 99%

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Fracture and Fatigue Behavior at Ambient and Elevated Temperatures of Alumina Bonded with Copper/Niobium/Copper Interlayers

Kruzic

Marks

Yoshiya

et al. 2002

Journal of the American Ceramic Society

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Interfacial fracture toughness and cyclic fatigue-crack growth properties of joints made from 99.5% pure alumina partial transient-liquid phase bonded using copper/niobium/copper interlayers have been investigated at both room and elevated temperatures, and assessed in terms of interfacial chemistry and microstructure. The mean interfacial fracture toughness, G c , was found to decrease from 39 to 21 J/m 2 as temperature was raised from 25° to 1000°C, with failure primarily at the alumina/niobium interfaces. At room temperature, cyclic fatigue-crack propagation occurred at both the niobium/alumina interface and in the alumina adjacent to the interface, with the fatigue threshold, ∆G TH , ranging from 20 -30 J/m 2 ; the higher threshold values in that range resulted from a predominantly near-interfacial (alumina) crack path. During both fracture and fatigue failure, residual copper at the interface deformed and remained adhered to both sides of the fracture surface, acting as a ductile second phase, while separation of the niobium/alumina interface appeared relatively brittle in both cases. The observed fracture and fatigue behavior is considered in terms of the respective roles of the presence of ductile copper regions at the interface which provide toughening, extrinsic toughening due to grain bridging during crack propagation in the alumina, and the relative crack propagation resistance of each crack path, including the effects of segregation at the interfaces found by Auger spectroscopy.

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Section: Discussionmentioning

confidence: 99%

“…Results can be compared to fracture toughness behavior that has been reported for a variety of niobium/alumina samples prepared by conventional diffusion bonding methods, for which the interfacial chemistry and other factors may differ. [12][13][14][15][16][17][18][19] …”

Section: Introductionmentioning

confidence: 99%

Fracture and Fatigue Behavior at Ambient and Elevated Temperatures of Alumina Bonded with Copper/Niobium/Copper Interlayers

Kruzic

Marks

Yoshiya

et al. 2002

Journal of the American Ceramic Society

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“…Gibbesch et al [34] have compared the fracture energy of uhv and hv diffusion bonded niobium/alumina joints, and results indicate that equivalent G c values can be obtained at ≈300°C lower bonding temperature when the uhv environment and sputter cleaning are used. Korn et al cite an ≈200°C reduction in processing temperature when equal bonding pressures are used [35]. 4 aluminum to the ambient.…”

Section: Dissolution Of Alumina; Oxygen and Aluminum Diffusionmentioning

confidence: 99%

“…Thus, impurities that segregate to this interface can affect the resulting fracture strength directly through their effect on interfacial adhesion, and indirectly through the effect of adhesion on plastic dissipation accompanying fracture. Korn et al [35] and Elssner et al [48] examined the influence of interface impurities (Ag, S, Ti) on the fracture energy of uhv bonded niobium/sapphire bicrystals prepared at 1400°C.…”

Section: Role Of Interfacial Impuritiesmentioning

confidence: 99%

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Joining of alumina via copper/niobium/copper interlayers

et al. 2000

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Alumina has been joined at 1150°C and 1400°C using multilayer copper/niobium/copper interlayers. Four-point bend strengths are sensitive to processing temperature, bonding pressure, and furnace environment (ambient oxygen partial pressure). Under optimum conditions, joints with reproducibly high room temperature strengths (≈240 ± 20 MPa) can be produced; most failures occur within the ceramic. Joints made with sapphire show that during bonding an initially continuous copper film undergoes a morphological instability, resulting in the formation of isolated copper-rich droplets/particles at the sapphire/interlayer interface, and extensive regions of direct bonding between sapphire and niobium. For optimized alumina bonds, bend tests at 800°C-1100°C indicate significant strength is retained; even at the highest test temperature, ceramic failure is observed. Postbonding anneals at 1000°C in vacuum or in gettered argon were used to assess joint stability and to probe the effect of ambient oxygen partial pressure on joint characteristics. Annealing in vacuum for up to 200 h causes no significant decrease in room temperature bend strength or change in fracture path. With increasing anneal time in a lower oxygen partial pressure environment, the fracture strength decreases only slightly, but the fracture path shifts from the ceramic to the interface. Cu/Nb/Cu Interlayers R. A. Marks et al. Joining of Alumina via

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Plasticity at Multiple Length Scales in Metal–Ceramic Interface Fracture

Bonnell

Kiely

1998

phys. stat. sol. (a)

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Measurements of local plasticity in fracture of Ni–sapphire interfaces exhibit deformation on several length scales. The deformation processes are manifest as morphology on the surface of the Ni side of the fracture surface that can be quantified with scanning probe microscopies. Four scales of deformation are observed: ligamentary bridging, crack tip blunting, slip step formation and nanometer scale roughness. The relative amount of energy dissipated in each mechanism varies with interface strength and density of precipitates. Since the most energy intensive processes, i.e. ligamentary bridging and crack tip blunting, are associated with nano precipitates, large variations in interface toughness will be related to extrinsic factors.

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Influence of interface impurities on the fracture energy of UHV bonded niobium-sapphire bicrystals

Cited by 68 publications

References 18 publications

Fracture and Fatigue Behavior at Ambient and Elevated Temperatures of Alumina Bonded with Copper/Niobium/Copper Interlayers

Fracture and Fatigue Behavior at Ambient and Elevated Temperatures of Alumina Bonded with Copper/Niobium/Copper Interlayers

Joining of alumina via copper/niobium/copper interlayers

Plasticity at Multiple Length Scales in Metal–Ceramic Interface Fracture

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