Composite and Graded Material Solutions for Tungsten and

Composite and Graded Material Solutions for Tungsten and Other Plasma. Interactive Component Materials Yutai Katoh (ORNL) with input from: Lance Snead, Lauren Garrison, (populate here)

Background – Bulk tungsten undergoes severe degradation during irradiation • Irradiation-induced toughness degradation for tungsten • Initial hardening-associated embrittlement • Ductile-to-brittle transition at temperatures of interest • Caused primarily by intrinsic defects • Followed by progressive degradation in fracture toughness • Severe decrease in fracture strength in brittle regime • Likely related with solid transmutations

Composites and graded components have been proposed as potential solutions • Laminate composites • Cu-W laminate composites in EU program • Steels-W graded composites – laminate (or 3 D) • Fiber composites • Wf/Wm • Ceramic fiber/Wm • 3 D composites • Ductile phase-matrix composites • Cu/W “ductile phase toughened” composite Henager et al.

Cu/W Laminate Composite • Appeared ductile even at RT as prepared • Loss of ductility after HFIR irradiation to low doses • Relying on extreme tungsten texture does not work (note implication to W fibers) Garrison et al. (submitted) Henager et al.

Analyzing laminate composites using criterion for minimum ductile phase volume fraction for pseudo-ductile failure • Cu/W(cold worked) laminate concept does not present adequate design space • As-fabricated composite exhibited ductility because W foil was ductile • Potential workaround options: • Choose stronger ductile phase material • Use low strength tungsten(? ) • Use non- or semi-continuous tungsten 1 Min. volume fraction of ductile phase • Minimum ductile phase volume fraction per simple composite theory: 0. 9 0. 8 0. 7 0. 6 f = 0. 5 0. 4 0. 3 0. 2 Pure Cu/W(0. 1 t) laminate Unirr 0. 1 0 0 100 200 300 Temperature (degree C) 400 500

Design space for ductile-brittle laminate composites with cold worked W as the brittle phase • “Choosing a stronger ductile phase material” may not be a viable option • Even 14 YWT requires a volume fraction of ~0. 8 to achieve ductile failure • Plot is for RT • Elevated temperature does not help because ductile phase softens • For graded laminate structures, stronger ductile phase gives enhanced ability to prevent catastrophic failure

Design space for ductile-brittle laminate composites with weaker W as the brittle phase • Single crystal tungsten strength data from ORNL is used (UTS = 430 MPa) • Plot is for RT • Effect of elevated temperatures is not very significant • Useful design spaces exist with Cu, RAF, and ODS steel as the ductile phase • Obviously consideration of irradiation hardening narrows the design spaces (not considered here)

Conclusions/implications so far • Cold worked W may not be an adequate brittle phase material to constitute brittle-ductile laminate composites regardless of selection for ductile phase material • Use of low strength W may achieve proper brittle-ductile laminate composite design. With this option, • Cu alloys and conventional RAF present usable design spaces • High strength ductile phase material (such as ODS steel) broadens design space • Time evolutions of W properties need to be considered • Irradiation hardening of W will narrow design spaces • Further irradiation embrittlement (strength degradation) of W will widen design spaces • Brittle-ductile laminate composite is not an ideal concept with W • Ductile phase-matrix composite (with discontinuous or semi-continuous W) should be a more viable concept • Continuous fiber composites are also worth investigating

Refractory metal/alloy fiber composites • Large body of previous works for gas turbine engine applications • Matrix materials: SS, Fe. Cr. Al, superalloys, refractories • Wire materials: W, W-Re-Hf. C, Mo alloys • Focus on high temperature strength • Little attention to toughness at low temperatures Ritzert and Dreshfield, 1992

W Composite (Source: ICFRM-17 CFP) Wf/Wm composites – feasibility considerations • Unirradiated properties assumed • W-Re fiber UTS = 2 GPa; E = 400 GPa • CVI W matrix UTS = 300 MPa; E = 400 GPa • Simple ROM-based theory presents adequate design space • Curtin model for CFCC presents adequate rupture margin beyond matrix cracking Typical UTS for W-Re fibers

Wf/Wm composites – effect of matrix strengthening • Early irradiation may cause • Strengthened CVI W matrix – UTS > 300 MPa; E = 400 GPa • Unchanged W-Re fiber UTS = 2 GPa; E = 400 GPa • Simple ROM-based theory predicts potential loss of pseudo-ductility with matrix strengthening • Curtin model for CFCC presents adequate rupture margin beyond matrix cracking after a doubled matrix strength Typical range for aligned Vf

Wf/Wm composites – effect of fiber weakening • Strength decrease is expected for W-based fibers upon irradiation • Strength degradation for W-Re fiber – UTS = 400 MPa; E = 400 GPa • No significant change in CVI W matrix – UTS = 300 MPa; E = 400 GPa • Simple ROM-based theory predicts likely loss of pseudo-ductility unless extreme matrix strength loss is assumed • Curtin model for CFCC predicts brittle failure at fiber volume fractions up to ~0. 3 Typical range for aligned Vf

Case for Si. Cf/Wm composites • Unirradiated properties assumed • Si. C fiber UTS = 2. 6 GPa; E = 400 GPa • CVI W matrix UTS = 300 MPa; E = 400 GPa • Simple ROM-based theory presents adequate design space • Curtin model presents adequate rupture margin beyond matrix cracking for practically all Vf Typical range for aligned Vf

Case for Si. Cf/Wm composites – effect of matrix strengthening • Early irradiation may cause • Strengthened CVI W matrix – UTS >> 300 MPa; E = 400 GPa • Unchanged W-Re fiber UTS = 2 GPa; E = 400 GPa • Simple ROM-based theory presents workable design space as the matrix strength doubles • Curtin model presents adequate rupture margin beyond matrix cracking after the matrix strength doubles Typical range for aligned Vf

Conclusions/implications – fiber composites • Continuous fiber W(-x)f/Wm composites • Composite theories indicate plenty of design space available in unirradiated condition • Reasonable composite mechanical properties will likely be maintained until significant fiber strength degradation takes place • Continuous fiber Si. Cf/Wm composites • Plenty of design space is available in both unirradiated and irradiated conditions • Significant irradiation-induced embrittlement is not anticipated for Si. Cf/Wm composites unless unknown interphase instability results in enhanced bonding, friction, or fiber damage.

Summary – open for discussion Ductile-brittle laminate composite Continuous fiber, brittlematrix composite Discontinuous or semicontinuous brittle phase composite - Limited design space - Tungsten fiber - Ductile metal matrix, composites will be tungsten dispersed - Weak tungsten needed severely limited by composites may serve - Why don’t go for fiber degradation certain purposes discontinuous or semi- Si. C fiber, tungsten - Semi-continuous options? matrix composites may tungsten – ductile - May still be used in be viable for high metal composite may graded PFC temperature PFC enhance high temperature properties W/RAF laminate (Garrison) FZJ WC in Fe matrix (Álvarez et al. , 2015)

ORNL Interest and Directions • Composite concepts and materials of interest • All kinds of W-based composites • Laminate FGM - ongoing • Continuous fiber (W and Si. C), W-matrix composites – preliminary research • W-alternative options for PFM and PFCM • Carbon materials are still of interest as PFCM • Some of emerging refractory ceramics and composites are potentially attractive • Application of advanced manufacturing • • Powder bed additive manufacturing Ultrasonic additive manufacturing Field-assisted sintering-based rapid processing Conventional manufacture routes for materials evaluation • Tungsten CVI • Hot press and HIP