Deformation and Hardness of UHTCs as a Function of Temperature

Wang, J.; Vandeperre, Luc

doi:10.1002/9781118700853.ch10

Cited by 15 publications

(11 citation statements)

References 76 publications

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“…This rapid decrease in modulus at elevated temperature has been primarily attributed to the onset of grain‐boundary sliding and diffusional creep. Further, the transitions in modulus trends correspond to the transitions in deformation mechanisms shown by Wang and Vandeperre, showing power law creep for ZrB 2 between 1000°C and 2000°C, low temperature power law creep for ZrC from 1000°C to 1600°C with high‐temperature power law creep above 1600°C, and diffusional creep for ZrB 2 above 2000°C. Additionally, some of the decrease in modulus at 2200°C and 2300°C may be a result of the proximity of the ZrB 2 –ZrC–C eutectic at 2360°C…”

Section: Resultssupporting

confidence: 66%

Ultra‐High Temperature Mechanical Properties of a Zirconium Diboride–Zirconium Carbide Ceramic

2015

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The mechanical properties of a ZrB2‐10 vol% ZrC ceramic were measured up to 2300°C in an argon atmosphere. Dense billets of ZrB2‐9.5 vol% ZrC‐0.1 vol% C were produced by hot‐pressing at 1900°C. The ZrB2 grain size was 4.9 μm and ZrC cluster size was 1.8 μm. Flexure strength was 695 MPa at ambient, decreasing to 300 MPa at 1600°C, increasing to 345 MPa at 1800°C and 2000°C, and then decreasing to 290 MPa at 2200°C and 2300°C. Fracture toughness was 4.8 MPa·m½ at room temperature, decreasing to 3.4 MPa·m½ at 1400°C, increasing to 4.5 MPa·m½ at 1800°C, and decreasing to 3.6 MPa·m½ at 2300°C. Elastic modulus calculated from the crosshead displacement was estimated to be 505 GPa at ambient, relatively unchanging to 1200°C, then decreasing linearly to 385 GPa at 1600°C, more slowly to 345 GPa at 2000°C, and then more rapidly to 260 GPa at 2300°C. Surface flaws resulting from machining damage were the critical flaw up to 1400°C. Above 1400°C, plasticity reduced the stress at the crack tip and the surface flaws experienced subcritical crack growth. Above 2000°C, microvoid coalescence ahead of the crack tip caused failure.

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Section: Resultssupporting

confidence: 66%

Ultra‐High Temperature Mechanical Properties of a Zirconium Diboride–Zirconium Carbide Ceramic

2015

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“…Unlike the data collected in this study, both toughness and strength should decrease moderately with the increase in temperature, following temperature dependence of Young's modulus, which decreases by roughly 1% every 100°K . The real potency of these mechanisms should be analyzed in further studies in conjunction with the potential onset of other high‐temperature strength degradation mechanisms.…”

Section: Resultsmentioning

confidence: 72%

Fracture and property relationships in the double diboride ceramic composites by spark plasma sintering of TiB₂ and NbB₂

et al. 2019

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Bulk titanium diboride-niobium diboride ceramic composites were consolidated by spark plasma sintering (SPS) at 1950°C. SPS resulted in dense specimens with a density exceeding 98% of the theoretical density and a multimodal grain size ranging from 1 to 10 μm. During the SPS consolidation, the pressure was applied and released at 1950 and 1250°C, respectively. This allowed obtaining a twophase composite consisting of TiB 2 and NbB 2 . For these ceramics composites, we evaluated the flexural strength and fracture toughness and room and elevated temperatures. Room-temperature strength of thus produced bulks was between 300 and 330 MPa, at 1200°C or 1600°C an increase in strength up to 400 MPa was observed. Microstructure after flexure at elevated temperatures revealed the appearance of the needle-shape subgrains of NbB 2 , an evidence for ongoing plastic deformation. TiB 2 -NbB 2 composites had elastic loading stress curves at 1600°C, and at 1800°C fractured in the plastic manner, and strength was ranged from 300 to 450 MPa. These data were compared with a specimen where a (Ti, Nb)B 2 solid solution was formed during SPS to explain the behavior of TiB 2 -NbB 2 ceramic composites at elevated temperatures. K E Y W O R D Scomposite, elevated temperature strength, flexural strength, niobium diboride, titanium diboride

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“…The porous UHTC samples used for this paper are made of zirconium diboride (ZrB 2 ), which has a density of =100% = 6080 kg/m 3 in a 100% densified state. The melting point and thermal conductivity of ZrB 2 are 3505 K [20] and 56 W/mK [22], respectively. The different porosities and porous structures in these samples are achieved by partial sintering (see Fig.…”

Section: Uhtc Samplesmentioning

confidence: 99%

“…Further, Dittert et al [11] showed that the outflow of porous CMC exhibits significant local non-uniformities, which could potentially lead to film separation or early transition of the boundary-layer. UHTCs have an exceptionally high melting point, generally above 3000 K [20]. This property enables them to have higher surface temperatures that result in a higher amount of cooling by radiation (heat radiated back to space) compared to conventional materials as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

Flow Characterization of Porous Ultra-High-Temperature Ceramics for Transpiration Cooling

Ifti¹,

Hermann²,

McGilvray³

et al. 2022

AIAA Journal

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Porous Ultra-High-Temperature-Ceramics (UHTC) are a candidate group of materials for transpiration cooling of hypersonic vehicles due to their exceptionally high melting point, typically above 3000 K. Their high operating temperature permits a higher amount of radiative cooling than that achievable with conventional materials, which reduces the required coolant mass flow rate to cool the surface. This work experimentally examines the internal and external flow behaviour of porous UHTC made of zirconium diboride (ZrB 2 ) for the purpose of transpiration cooling. A dedicated ISO standard permeability test rig was built. The outflow velocity distribution was acquired employing miniature hot-wire anemometry. The data obtained for the pressure loss across the porous samples agree with the Darcy-Forchheimer model for flow in porous media; respective Darcy and Forchheimer permeability coefficients are calculated and reported. Cleaning the surface of the samples using sandpaper or an ultrasonic bath raised the permeability coefficient by up to 19%. The outflow velocity maps exhibit a good flow uniformity with an average standard deviation of 25.1% with respect to the mean value.Individual jets are absent, and the velocity varies within the same order of magnitude.

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Deformation and Hardness of UHTCs as a Function of Temperature

Cited by 15 publications

References 76 publications

Ultra‐High Temperature Mechanical Properties of a Zirconium Diboride–Zirconium Carbide Ceramic

Ultra‐High Temperature Mechanical Properties of a Zirconium Diboride–Zirconium Carbide Ceramic

Fracture and property relationships in the double diboride ceramic composites by spark plasma sintering of TiB₂ and NbB₂

Flow Characterization of Porous Ultra-High-Temperature Ceramics for Transpiration Cooling

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Deformation and Hardness of UHTCs as a Function of Temperature

Cited by 15 publications

References 76 publications

Ultra‐High Temperature Mechanical Properties of a Zirconium Diboride–Zirconium Carbide Ceramic

Ultra‐High Temperature Mechanical Properties of a Zirconium Diboride–Zirconium Carbide Ceramic

Fracture and property relationships in the double diboride ceramic composites by spark plasma sintering of TiB2 and NbB2

Flow Characterization of Porous Ultra-High-Temperature Ceramics for Transpiration Cooling

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Fracture and property relationships in the double diboride ceramic composites by spark plasma sintering of TiB₂ and NbB₂