Interface Engineering of the Tungsten-Fiber-Reinforced Tungsten Composites J. Du*, T. Höschen, J-H. You, Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstr.2, 85748 Garching, Germany * corresponding author: [email protected] (address since 1st Mai 2011 : Forschungszentrum Jülich GmbH, EURATOM Association, 52425 Jülich, Germany) A toughening method for tungsten is proposed based on the reinforcement of tungsten fibers (W f /W m composites) and engineered interfaces. The interfacial parameter determination results show that selected interfaces satisfy to the interfacial debonding criterion. The interfacial debonding and fiber sliding were demonstrated by micro-mechanical 3-point bending test. The predicted stress-strain curve of the W f /W m composites with multiple fibers agree with the theoretical one, supporting the primary motivation of the thesis. Motivation: Tungsten/Tungsten composite A novel toughening method for tungsten (W), was proposed and developed based on the reinforcement of tungsten fibers (W f /W m composite) and engineered interfaces. The underlying toughening mechanism is analogous to that of a fiber-reinforced ceramic matrix composite (CMC). This work opened a new pathway to improve the toughness of tungsten as a structural material. composite stress composite strain pseudo-toughness CMC composite toughening mechanism • crack deflection • Interface debonding • fiber sliding • energy dissipation W f /W m composite concept W matrix W wire Analysis system: Single filament (fiber) composite 2 f r l f m z i s 2 f r l f m z i s =150m :2~3mm H:~0.3mm W f with interface magnetron sputtering chemical vapor deposition W f W f /W m cut & polished Fiber push-out test Experiment Specimen preparation Carbon 600 nm Cu 170 nm Cu 480 nm Cu/W m ZrO x /Zr m ZrO x /W m ErO x /W m Er/W m ErO x 600 nm 1000 nm ZrO x 150 nm 260 nm 450 nm 950 nm Lubricating coating Ductile coating Multiple-layer coating Oxide coating Designed interfaces 20.7 23 20.5 17.3 15.6 16.7 18.3 21.9 16 16.8 13.1 15.8 17.2 9.8 0 5 10 15 20 25 ZrOx 150 ZrOx 450 ZrOx 950 ZrOx&W 260 ErOx 600 ErOx 1000 ZrOx/Zr m ZrOx/W m ErOx/W m Er/W m Cu/W m Cu 170 Cu 480 carbon Average enrgy absorption (kJ/m^2 fiber fiber Result-Push-out test curve The area below the curve corresponds to the total amount of work done by the applied load—average energy absorption Δ, kJ/m 2 Result-Interfacial fracture energy ( i ) calibration and debonding criterion verification P H R R L 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0 10 20 30 40 50 Load (N) Displacement (mm) A, P d B C, P fr Interface: ZrOx 450 Specimen thickness: 0.226 mm 0.05 0.10 0.15 0.20 0.25 0 500 1000 1500 2000 2500 3000 3500 Stress p (MPa) Specimen thickness H(mm) 2 3 0.6 J/m i Interface: ZrOx 450 1 1 2 2 2 1 2 ( 1) f f BH BH R R i f R f E p e e BR B H : Specimen thickness 2 d f P p R (Liang,1993) i Mode 2 fracture energy for the debonding event 9.61 5.86 2.89 3 2.99 2.03 1.23 3.5 3.46 2.01 7.66 12.34 7.41 0 2 4 6 8 10 12 14 16 ZrOx 150 ZrOx 450 ZrOx 950 ZrOx&W 260 ErOx 600 ErOx 1000 ZrOx/Zr m ZrOx/W m Er/W m ErOx/W m Cu/W m Cu170 Carbon Fracture energy (J/m^2) Fiber fracture Interfacial debonding Elastic mismatch i f 0 5 . 0 1 5 . 0 1 0 5 . 1 5 . 0 1 Fracture mechanism He,1989 Debonding criterion ≤ ≤0.25 0.25 Interface fracture energy i Fiber fracture energy f (≈320 J/m 2 ) f f f f c f i f c f 1 3 2 2 / S f f f f c f l f c f t s f s f f t The stress-strain curves is typical for a toughened composite, supporting the motivation of this work. 0 200 400 600 800 1000 1200 1400 1600 1800 0 0.5 1 1.5 2 2.5 3 3.5 Strain (%) Stress (MPa) mc sat y u Fiber pull out Interface: ZrOx450 Fiber volume: cf=0.6 Budiansky 1995 3 2 2 2 3 ( 2 ) (2 3 ) 3 f mc D D S D D S m m mc A r c mc f f m mc m cE cE 2 f c D f m mf i E E c cEr 2 f A m m R c f cE E cE 1 3 2 2 (1 ) / S f f f m f R c m f l r c EE c Er ( / ) (1 ) f c S f t R s f a m cE l r c E / sat s f a f t cE Evans 1994 A toughening method for tungsten is proposed based on the reinforcement of tungsten fibers (W f /W m composites) and engineered interfaces. The interfacial parameter determination results show that selected interfaces satisfy to the interfacial debonding criterion. The interfacial debonding and fiber sliding were demonstrated by micro-mechanical 3-point bending test. The predicted stress-strain curve of the W f /W m composites with multiple fibers agree with the theoretical one, supporting the primary motivation of the work. Interfacial fracture energy i of investigated interfaces The main focus of this work lies in the investigation of the interfacial fracture behavior of W f /W m composites with various engineered interfaces to demonstrate the feasibility of synthesizing a toughened W f /W m composite using the CMC toughening mechanism. Goal and focus of this work W matrix W wire W matrix W wire • W fiber, u > 2.5 GPa, u > 2% • Interface thickness m The fracture properties of the engineered interface are the key factors controlling the overall composite toughness. Micro-mechanical 3-point bending test (ZrO x 260) 2 m W fiber top W C Interface delamination c a) oxide interface: ZrO x 450 b) ductile interface: Cu 480 c) lubricating interface: C 600 Interface deformation and delamination can cause higher interfacial fracture energy. 1 m matrix typical W wire surface structure fiber ZrO x 450 a Conclusion Result-Crack deflection demonstration Result-Behavior prediction of W f /W m composite with multiple fibers The calculated ratios lie between 0.003 and 0.034. satisfying the 0.25 criterion. The debonding criterion is satisfied ! specimen thickness: 0.226mm y f f yield R c / y f yield f E u f f u c 2.1% u