Cedillos, O.

Grasso, S.

Jayaseelan, D.D

Konings, R.

Lee, W.E.

Manara, D.

English

Engineering Conferences International

Engineering Conferences InternationalECI Digital ArchivesUltra-High Temperature Ceramics: Materials forExtreme Environment Applications III ProceedingsSpring 4-13-2015Processing and Characterisation of (Ta,Hf )CUltra-High Temperature Ceramics.O. CedillosImperial College LondonS. GrassoQueen Mary UniversityD. ManaraInstitute for Transuranium ElementsD.D JayaseelanImperial College LondonR. KoningsInstitute for Transuranium ElementsSee next page for additional authorsFollow this and additional works at: http://dc.engconfintl.org/uhtc-iiiPart of the Materials Science and Engineering CommonsThis Conference Proceeding is brought to you for free and open access by the Proceedings at ECI Digital Archives. It has been accepted for inclusion inUltra-High Temperature Ceramics: Materials for Extreme Environment Applications III by an authorized administrator of ECI Digital Archives. Formore information, please contact franco@bepress.com.Recommended CitationO. Cedillos, S. Grasso, D. Manara, D.D Jayaseelan, R. Konings, and W.E. Lee, "Processing and Characterisation of (Ta,Hf)C Ultra-High Temperature Ceramics." in "Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications III", G. Franksand C. Tallon, University of Melbourne Eds, ECI Symposium Series, (2015). http://dc.engconfintl.org/uhtc-iii/5AuthorsO. Cedillos, S. Grasso, D. Manara, D.D Jayaseelan, R. Konings, and W.E. LeeThis conference proceeding is available at ECI Digital Archives: http://dc.engconfintl.org/uhtc-iii/5Processing and Characterisation of (Ta,Hf)C Ultra-High Temperature Ceramics. O.Cedillos1, S. Grasso2, D. Manara3, D.D. Jayaseelan1, R. Konings3, M. Reece2 and W.E. Lee1  1Centre for Advanced Structural Ceramics, Imperial College London, UK 2School of Engineering & Materials Science, Queen Mary University of London 3Institute for Transuranium Elements, Karlsruhe, Germany  Ultra-high Temperature Ceramics: Materials for Extreme Environment Applications III, Gold Coast Australia, April 13th 2015. TaC-HfC system • TaC-HfC compounds extremely high melting (~4000°C).  • Some disagreement about Tm  in literature.   • Information on properties is scarce.  • Difficult to process due to high temperatures needed.  [1] P. DiMare, Smithsonian Air & Space Magazine, September 2007. Conceptual Hypersonic Vehicle [1] Phase Crystal System Structure Type Space Group Lattice parameter  a (Å) TaC B1 Cubic NaCl Fm3m 4.456 HfC B1 Cubic NaCl Fm3m 4.641 Processing Routes  Sintering (SPS) Ground and Sieved Reactants (Ta,Hf,C) Reactive SPS (RSPS) Synthesis (SHS) Sintered Product Dry ball mill Sintering (SPS, HP) Rotary evaporator Commercial TaC and HfC Sintered Product Reactive routes Solid state diffusion routes Sieved Wet ball mill (ethanol) Processing Routes Sintering (SPS) Ground and Sieved Reactants (Ta,Hf,C) Reactive SPS (RSPS) Synthesis (SHS) Sintered Product Dry ball mill Sintering (SPS, HP) Rotary evaporator Commercial TaC and HfC Sintered Product Reactive routes Solid state diffusion routes Sieved Wet ball mill (ethanol) Route #1 Synthesis and Sintering of 4TaC-1HfC by RSPS • Strongly exothermic, self-propagating high-temperature synthesis (SHS) using Ta, Hf powders and carbon black.  • SHS rapidly densifies UHTCs at high T in short t.  • Combination of methods used to synthesize and sinter TaC-HfC ceramics in one step.  • A minimum of 20 MPa applied. Higher loads (60 MPa) applied after SHS reaction (1400°C). Heating rate of 210°C/min used for all samples.   Schematic of an SPS furnace [2] [2] M. Stuer, Z. Zhao, U. Aschauer, and P. Bowen: J. Eur. Ceram. Soc., 2010,  vol. 30, pp. 1335–43. Sintering conditions, density and XRD analysis Sintering conditions (tD, P) Density ρ (g/cm3) Relative density % 20 min, 20 MPa 8.7 ± 0.39 62.6 ± 0.30 10 min, 60 MPa 11.7 ± 0.18 83.3 ± 0.13 20 min, 60 MPa 12.5 ± 0.38 89.6 ± 0.36 SEM analysis of RSPS’d 4TaC-1HfC (BSEI) 20 min, 20 MPa 20 min, 60 MPa • TaC and HfC but little solid solution plus HfO2 contamination.  • Core/rim structure of HfO2/HfC, separate from TaC.  Processing Routes Sintering (SPS) Ground and Sieved Reactants (Ta,Hf,C) Reactive SPS (RSPS) Synthesis (SHS) Sintered Product Dry ball mill Sintering (SPS, HP) Rotary evaporator Commercial TaC and HfC Sintered Product Reactive routes Solid state diffusion routes Sieved Wet ball mill (ethanol) Route #2 Sintering conditions, density, MGS and XRD analysis Sintering conditions    (TD, tD, P) Density (g/cm3) Relative density (%) Mean Grain Size (µm) Grain size range (µm) 2100°C,  20 min,  60 MPa 13.8 ± 0.19 98.22 ± 0.13 6.4 1.4-20.5 4TaC-HfC after SHS+SPS • After SHS have TaC, HfC plus Ta2C, HfO2 and Ta2O5 contamination present.  • After high temp. SPS all Ta2C disappears.  SEM and EDS of 4TaC-1HfC after SHS+SPS 2100°C, 20 min, 60 MPa C O Hf Ta BSE images  SE image EDS map Note region of Hf-rich solid solution close to HfO2 and more remote region of Ta- rich solid solution.  Proximity to HfO2 leads to Hf-rich solid solution.  Processing Routes Sintering (SPS) Ground and Sieved Reactants (Ta,Hf,C) Reactive SPS (RSPS) Synthesis (SHS) Sintered Product Dry ball mill Sintering (SPS, HP) Rotary evaporator Commercial TaC and HfC Sintered Product Reactive routes Solid state diffusion routes Sieved Wet ball mill (ethanol) Route #3 Characterisation of 4TaC-1HfC fabricated by SPS • Commercial powders of TaC0.94 (-325 mesh, ABCR) and HfC0.94  (-325 mesh, ABCR) used.  • 4TaC-1HfC composition sintered at different temperatures (2050-2450°C) for 20 min and 30 MPa  • Solid solution formation evaluated by XRD, SEM, EDS and TEM.   Density and MGS of 4TaC-1HfC after SPS for 20 min and 30 MPa Sintering temperature (°C) Bulk density (g/cm3) Relative density (%) Mean grain size MGS (μm) Pore size (µm) 2050 10.94 ± 0.02 77.7 ± 0.18 - 0.48 ± 0.37 2150 12.01 ± 0.02 85.2 ± 0.17 - 0.56 ± 0.32 2250 13.10 ± 0.02 93.0 ± 0.16 3.2 1.17 ± 0.47 2350 13.28 ± 0.05 94.5 ± 0.38 5.1 1.61 ± 0.88 2450 13.35 ± 0.02 94.8 ± 0.17 6.2 1.79 ± 0.77 Maximum density after SPS ≥ 2350°C.   XRD & lattice parameter measurements 4TaC-1HfC Sample Lattice parameter (Å) Starting TaC (powder) 4.459 2050°C 4.461 2150°C 4.468 2250°C 4.473 2350°C 4.483 2450°C 4.484 Single phase solid solution after sintering ≥ 2350°C.   4TaC-1HfC Microstructural evolution of SPS’d 4TaC-1HfC HRTEM of 4TaC-1HfC after SPS 4TaC-1HfC after SPS at 2450°C, 20 min and 30 MPa Clean grain boundary with no glass suggesting solid state sintering and SAED index as cubic crystals. Characterisation of TaC, HfC and TaC-HfC solid solutions • Commercial powders of TaC0.94 (-325 mesh, ABCR) and HfC0.94 (-325 mesh, ABCR) used.  • TaC, HfC and TaC-HfC solid solutions (4TaC-1HfC, 1TaC-1HfC and 1TaC-HfC) sintered using a two-step sintering schedule:                i) 2100°C for 30 min and 55 MPa for high density               ii) 2350°C for 20 min and 30 MPa for solid solution.  • A high-density single-phase solid solution material was desired.  • Characterisation by XRD, SEM, EDS and TEM.  • Mechanical and thermal properties measured and Tm via laser melting.   Density, relative density, MGS and pore size after SPS Sample Bulk density (g/cm3) Relative density (%) Mean grain size (μm) Pore size (µm) TaC 14.25 ± 0.02 98.3 ± 0.14 6.2 0.58 ± 0.13 4TaC-1HfC 13.77 ± 0.02 97.7 ± 0.09 8.5 1.83 ± 0.09 1TaC-1HfC 12.94 ± 0.03 95.7 ± 0.29 4.2 1.35 ± 0.63 1TaC-4HfC 11.31 ± 0.03 87.0 ± 0.26 4.4 1.26 ± 0.32  HfC 10.81 ± 0.01 85.3 ± 0.10 1.8 1.01 ± 0.72       HfC difficult to sinter, small grain size. SEM of TaC, HfC and TaC-HfC solid solutions after SPS • Grains plus trapped pores.  • Smaller grains with HfC.  • EDS shows even distribution of Hf and Ta in solid solutions.  XRD and lattice parameter measurements Sample Lattice parameter (Å) TaC 4.459 4TaC-1HfC 4.484 1TaC-1HfC 4.536 1TaC-4HfC 4.594 HfC 4.636 Lattice parameter follows Vegards law  TEM of 4TaC-1HfC after SPS 4TaC-1HfC SPS’d @ 2450°C, 20 min and 30 MPa Mechanical properties of TaC, HfC and TaC-HfC solid solutions after SPS Composition Vickers hardness (HV1) Nanohardness (GPa) Elastic modulus  E (GPa) KIC       (MPa*m1/2) TaC 13.9 ± 0.7 13.3 ± 0.73 458 ± 6.6 2.72 ± 0.30 4TaC-1HfC 17.1 ± 1.2 19.3 ± 1.33 459 ± 5.8 2.92 ± 0.91 1TaC-1HfC 20.4 ± 2.3 22.1 ± 1.87 549 ± 11.2 2.98 ± 0.77 1TaC-4HfC 15.0 ± 0.5 16.73 ± 3.00 438 ± 17.8 3.43 ± 0.63 HfC 10.2 ± 0.7 10.52 ± 1.04 283 ± 9.6 2.91 ± 0.51 Thermal diffusivity and conductivity • Thermal conductivity normalised to 100%TD using Maxwell-Eucken equation to remove effect of porosity.  Thermal expansion (CTE) Composition Coefficient of thermal expansion (CTE) (10-6/K) Temperature range (°C) TaC 7.08 25-2000 4TaC-1HfC 7.24 25-2000 1TaC-1HfC 7.41 25-2000 1TaC-4HfC 7.59 25-2000 HfC 7.66 25-2000 Laser melting of TaC, HfC and TaC-HfC solid solutions Laser melting experiments at ITU (Karlsruhe, Germany). Samples heated using a 4.5 kW Nd:YAG CW laser. Surface temperature and intensity of reflected light recorded.  Schematic of  laser-melting system Melting behaviour of HfC Tm = 3959oC Reported melting points and comparison with this work     Melting temperature Tm (°C) Authors Year TaC (C) 4TaC-1HfC 1TaC-1HfC 1TaC-4HfC HfC (C) Agde and Alterthum 1930 3877  3940 3900 3881 3887 Rudy 1965 3983 (0.88) 3965 3945 3934 3928 (0.94) Andrievskii et al. 1967 3840 (0.98) 3990 - - 3750 (0.97) Gusev et al.  1985 4002 3960 3917 3937 3948 Okamoto 1998 3969 (0.88)         Okamoto 2001 - - - - 3942 (0.94) This work - 3768 (0.94) 3905 3803 3847 3959 (0.94) • Highest melting temperatures ever measured with such high accuracy.  Microstructural characterisation of laser-melted HfC a) b) c) ` a) Molten pool of HfC,  b) Grain texture of melted HfC  c) Dendritic microstructure at laser spot centre. SEM analysis of laser melted TaC TEM of a FIB section of laser melted TaC TEM analysis shows only TaC1-x grains and SAED confirms only cubic crystals on TaC after laser melting. Conclusions • Examined a range of processing routes and demonstrated it is possible to make (Hf,Ta)C solid solutions from commercial powders via SPS. • Basic thermal and mechanical properties measured and shown largely to be suitable for UHTC applications. • Measured ultra high melting temperatures with high degree of accuracy.  Acknowledgements Consejo Nacional de Ciencia  y Tecnología (México) Centre for Advanced Structural Ceramics Imperial College London EPSRC Material Systems for Extreme Environments programme grant (EP/K008749/1, XMat) 

Processing and Characterisation of (Ta,Hf)C Ultra-High Temperature Ceramics.

https://dc.engconfintl.org/cgi/viewcontent.cgi?article=1001&amp;context=uhtc-iii

Processing and Characterisation of (Ta,Hf)C Ultra-High Temperature Ceramics.

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