Esposito, Laura

Honda, Kou

Melandri, Cesare

Nakashima, Kunihiko

Saito, Noritaka

English

Engineering Conferences International

Engineering Conferences InternationalECI Digital ArchivesUltra-High Temperature Ceramics: Materials forExtreme Environment Applications III ProceedingsSpring 4-16-2015Effect of Ni-Nb Interlayer Thickness on MechanicalProperty of Hf B2 Composite JointsKou HondaKyushu University, JapanNoritaka SaitoKyushu University, JapanKunihiko NakashimaKyushu University, JapanCesare MelandriCNR-ISTEC ItalyLaura EspositoCNR-ISTEC, ItalyFollow 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 CitationKou Honda, Noritaka Saito, Kunihiko Nakashima, Cesare Melandri, and Laura Esposito, "Effect of Ni-Nb Interlayer Thickness onMechanical Property of Hf B2 Composite Joints" in "Ultra-High Temperature Ceramics: Materials for Extreme EnvironmentApplications III", G. Franks and C. Tallon, University of Melbourne Eds, ECI Symposium Series, (2015). http://dc.engconfintl.org/uhtc-iii/10Effect of Ni-Nb Interlayer Thickness on Mechanical Property of HfB2 Composite JointsKou Honda, Noritaka Saito, and Kunihiko NakashimaKyushu University, JapanCesare Melandri, and Laura EspositoCNR-ISTEC, ItalyApril 16, 2015   UHTC: Material For Extreme Environment Applications Ⅲ15年5月7日木曜日Background - Ultra High Temperature CeramicsProspective applications・Poor sinterability and workability↳Several borides, carbides, and nitrides    of the group Ⅳ and Ⅴ metalsExcellent properties・High melting points（> 3000℃）・Good thermo-mechanical properties・Chemical stabilityProblemsIt is difficult to produce the large and complex shaped parts of UHTCs.For the practical use, an effective method of bonding will be required. UHTCs：Ultra High Temperature CeramicsTi, Zr, Hf, Ta -B2, -C, -NB atoms in a structural complex leads to increases in the B–Bbond strength and an increase in the stiffness of the crystal lat-tice along with increases in melting temperature (Tm), hardness(HV), strength (s), and chemical stability.TheM–B bond strength in diborides depends on the degree ofelectron localization around the M atoms. The valence electronconfiguration in isolated B atoms is 2s22p. In metal borides, theouter electron configurations are sp2 and sp3, which promotestrong covalent bonding. In diborides, B atoms are electron ac-ceptors, while the M atoms are electron donors. Each M atomdonates two electrons (one to each B), which converts M to adoubly charged cation, while B atoms become singly chargedanions. So, theMB2 formula can be expressedM21(B!)2.31,32,40–45The electron configurations vary depending on the donor prop-erties of M, which produces a diversity of crystal structure typesand properties. The M–B bonds have ionic characteristics as aresult of the donor–acceptor interactions, but they also havecovalent characteristics due to partial excitation of d electronsand the formation of spd hybrid configurations. The tendencyfor B atoms to form sp2 and sp3 hybrids also affects properties.However, hardness and brittleness are lower than the corre-sponding carbides because the B structural complexes combinesp3 hybridization with the lower-strength sp2 (and even lower-strength s2p and sp) configurations, whereas the carbon atoms incarbides exhibit only sp3 hybridization.As shown in Fig. 2, the crystal structure of Group IV–VItransition metal diborides is primitive hexagonal (AlB2-type,P6/mmm space group). The unit cell contains one MB2 formulaunit. The structure is composed of layers of B atoms in 2Dgraphite-like rings or nets, which alternate with hexagonallyclose-packed M layers. Each M atom is surrounded by six equi-distant M neighbors in its plane and 12 equidistant B neighbors(six above and six below the M layer). Each B is surrounded bythree B neighbors in its plane and by six M atoms (three aboveand three below the B layer).The unit-cell parameters and interatomic distances for dibor-ides are summarized in Table II. In general, B–B separationcontrols the a-axis length. However, the a-axis length is also af-fected by M–B contact. For ZrB2, which has the largest M atomof the diborides, the B–B distance is 1.83 Å (a/O3), which ex-ceeds the ‘‘normal’’ B–B distance (1.74 Å) by 0.09 Å due tostretching of the B–B bonds by Zr–Zr contact. Likewise, thesmallest M atoms (Cr, V) lead to reductions in the B–B distance.From crystal chemical considerations, the length of the a-axis isa balance between two forces: (1) repulsion between atoms in theM layers and (2) attraction between atoms in the B nets.26,29,30As a result, stable AlB2-type diborides do not form for M atomssmaller than Cr or larger than Zr. The B–B bond length forminimum strain in the boron nets has been estimated to beB1.75Å, which is the value for TiB2.29The M–B distance in diborides increases linearly with theM:B radius ratio, increasing from 2.30 Å for CrB2 to 2.54 Å forZrB2. The M–B separation is equal to ða2=3þ c2=4Þ1=2, which islarger than the sum of the M and B radii (Table II). Generally,the structural data indicate that bonding in the B nets controlsthe lattice parameters in the AlB2-type structure. Because the B–B bonds are strong relative to the other bonds, increases in the a-axis with increasing M size are minimal. In contrast, no sucheffect is observed for the c-axis. Hence, the c:a ratio increaseswith increasing M atom size. Owing to separation of the close-packed M planes by B nets, the c-axis is always substantiallylarger than 2RM. In summary, differences among diborides re-sult from different M radii, which lead to variations in the in-teratomic bond lengths. Larger changes are observed for the c-axis than for the a-axis due to the relative bond strengths.(2) Structure-Property RelationsHardness, bulk modulus, Debye temperature (YD), Tm, coeffi-cient of thermal expansion (CTE), thermal conductivity (k), andenthalpy of formation ðDHof Þ are some properties that are re-lated to bond strength (cohesive energy). Generally, the combi-nation of bonds (M–M, B–B, and M–B) influences the materialproperties. However, in some cases, a specific type of bond con-trols a property.31 For example, B–B and M–B bonds in dibor-ides control hardness and thermal stability. Hardness is,therefore, a qualitative indicator of bond strength.47The thermal and elastic properties of diborides are summar-ized in Table III.48–54 The data indicate that the Group IV di-borides have lower CTE and higher Young’s modulus andthermal conductivity than Group V diborides.26 The propertychanges suggest that B–B bonds are strongest for Group IV at-oms (Ti, Zr, and Hf) and the bonds weaken as atomic numberincreases across a period of the Periodic Table. Grimvall andGuillermet46 found it useful to correlate cohesive energy and Tmtrends to the average number of valence electrons per atom forisostructural diborides. For example, the series ScB2, TiB2, VB2,CrB2, MnB2, and FeB2 have 9, 10, 11, 12, 13, and 14 valenceelectrons, respectively. With its 10 valence electrons (3.3 elec-trons per atom), TiB2 possesses the highest melting temperatureof the group. Higher or lower numbers of valence electrons re-sult in lower melting temperatures.Fig. 1. A comparison of the melting temperatures of the most refrac-tory members of several classes of materials. Several borides, carbides,and nitrides have melting temperatures above 30001C and are consideredultra high-temperature ceramics. For comparison, the melting tempera-ture of Zr is B18501C and the melting temperature of Hf is B22271C.Table I. Summary of Some Structural, Physical, Transport,and Thermodynamic Properties of ZrB2 and HfB2Property ZrB2 HfB2Crystal system space groupprototype structureHexagonal5P6/mmm AlB2Hexagonal6P6/mmm AlB2a (Å) 3.17 3.139c (Å) 3.53 3.473Density (g/cm3) 6.1195 11.2126Melting temperature (1C) 32451 33801Young’s modulus (GPa) 4899 48011Bulk modulus (GPa) 215 212Hardness (GPa) 239 287Coefficient of thermalexpansion (K!1)5.9% 10!6 7 6.3% 10!6 7Heat capacity at 251C(J & (mol &K)!1)48.28 49.57Electrical conductivity (S/m) 1.0% 107 7 9.1% 106 7Thermal conductivity(W & (m &K)!1)607 1049Enthalpy of formation at251C (kJ)!322.68 !358.17Free energy of formation at251C (kJ)!318.28 !332.271348 Journal of the American Ceramic Society—Fahrenholtz et al. Vol. 90, No. 5William G. Fah enholtz e  al. : J. Am. Ceram. Soc., 90 [5] 1347–1364 (2007)15年5月7日木曜日Background - Typical methods of ceramics bondingTransient Liquid Phase (TLP) bondingTypical examples of ceramics bondingMetalCeramicsCeramicsMetal brazing bondingLow melting metalOxide solder bondingCeramicsCeramicsBZrSolid state bondingHigh temperature and high pressure↓Cost ✕OxideBad wettability↓ Heat resistance ✕ ↓Adhesion ✕ CeramicsCeramics15年5月7日木曜日Background - TLP (Transient liquid phase) bonding➀ The cladding metals will melt and fill the gap between the ceramics and the core metal. ➁ The liquid cladding metals will diffuse through the core metal.➂ The interlayer will have higher re-melting temperature than the bonding temperature. A low cost and well-trusted bonding method at high temperature useCeramicsCeramicsRefractory core metalCladding low melting point metals Insert metalsTLP bonding     Cladding low melting metal       ➀➁ ➂15年5月7日木曜日ObjectiveThe TLP bonding using Ni-Nb interlayer was successfully applied to bond HfB2 composite in our previous work.(1)The adequate thickness of the interlayers of the joints is needed to explore.The present work aimed at investigating the effect of Ni-Nb interlayerthickness on the mechanical properties of HfB2 composite joints.(1)Noritaka Saito:J.Mater.Sci, 47, 8454-8463(2012)InterlayerNi-NbHfB2 composite jointsObjective15年5月7日木曜日Experimental procedure- Fabrication of HfB2 compositesRaw powdersPolishingSinteringMilling and MixingUniaxial pressing+300 MPa CIPing 1950℃ for 1 hUnder 0.1 MPa Ar with diamond slurryZrO2 milling media for 24 h in ethanolMoldingRelative density97.6% 2 μmMicrostructure of HfB2 compositeicrostru tur  of HfB2 compositeBondingHfB2 MoSi2HfB2 (2 μm, 99.5%) + 10 vol% MoSi2 (-2 μm, 99.9%)15年5月7日木曜日Experimental procedure- Fabrication of HfB2 composite jointsAtmosphere: 20 Pa VacuumTemperature: 1500°CHolding time: 30 minApplied pressure: 8.5 MPaQuenching• The interfacial region of joints were observed by using FE-SEM.• The mechanical properties of joints were evaluated by 4-points bending test.Hot pressingInterlayerCladding metal: NiCore metal: NbSample AHfB2compositeHfB2compositeNbNiNiNi2 μmNi2 μmNi127 μmNi : 0.40 μmNb 25.4 μmSample B15年5月7日木曜日Observation results of interfacial reaction15年5月7日木曜日(Nb,Hf)3B2NbNiSi(Nb,Hf)2NiSiNb5Si3Reactionlayer10 μmHfB2Sample A NbNb20:27 at%5μm36:24 at%Interfacial microimage of sample A (Nb : 127 μm, Ni : 2 μm)・The interdiffusion of Ni and Nb was not completed. ・The reaction layer mainly contained Si from MoSi2 sintering aid. ・The HfB2 composites hardly reacted to the interlayers.Nb-Ni-SiNbHfB2 compositeNb-Si130 μm15年5月7日木曜日HfB2Nb ssReactionlayer20 μmSample B(Hf,Nb)2Ni(Nb,Hf)5Si2(Nb,Hf)3B2 Nb5Si2 (Nb,Hf,Mo)45:16 at% 76:16:8 at%62:9 at% 51:17 at%Interfacial microimage of sample B (Nb : 25.4 μm, Ni : 0.40 μm) Nb solid solution5μmNb-Hf-Ni・The interdiffusion of Ni and Nb was not completed similar to Sample A.  ・The reaction layer contained Si and Hf from HfB2 composite.50 μmHfB2 compositeNb-Hf-SiNb-Hf-B15年5月7日木曜日Discussion on the interfacial reaction of sample AHfB2 compositeNbNiNb-SiNbNb-Ni-SiNb-Hf-BBefore bonding After bondingDuring heatingHfB2 composite➀ Enough amount of Ni-Nb melt was formed, and filled the gap between Nb and HfB2 composite. ➁ Nb and Si diffused into the other side respectively.➂ The thick reaction layer was formed uniformly. Ni-Nb melt➀NbSi➁ ➂15年5月7日木曜日Discussion on the interfacial reaction of sample B➀ Smaller amount of Ni-Nb melt was formed. ➁ Nb directly touched and reacted with HfB2 composite. ➂ The reaction layer was formed complexly. Nb-Ni melt➀➁ ➂NbNiHfB2 compositeNb ssHf-Nb-NiNb-Hf-B Nb-Hf-SiHfB2 compositeBefore bonding After bondingDuring heating15年5月7日木曜日Ni-Nb meltNb-Ni meltSample A Sample BDifference in the interfacial reaction is due to the difference in the amount of Ni-based melt.Summary of interfacial reactionHfB2  compositeNbHfB2  compositeNb15年5月7日木曜日4-points bending test15年5月7日木曜日Electrical discharge machining2 mm ×2.5 mm ×25 mmCuttingBondingPolishingStrength measurement at R.T. and at H.T. (1000℃)4-points bending testElectrical discharge machiningφ10mm 2mm 2.5mm HB10M HB10M with diamond slurryFabrication process of bending beams for 4-points bending testBBBBBBBBBBBBB      HfB2  φ10 mmmmm  HfB2  15年5月7日木曜日l: 10 mmL: 20 mm25 mmw: 2.5 mmt: 2 mmPressure Pressure3P(L-l)2wt2σ=Bending stress (MPa)Maximum Load (N)Loading span (mm)Support span (mm)Width (mm)Thickness (mm)σPlLwt:::::: Crosshead speed ：1mm/minNumber of Trials ：3 timesConditions  ：1000°C in airCrosshead speed ：1mm/minNumber of Trials ：5 timesR.T. tests for JointsH.T. tests for JointsR.T. tests for HfB2 CompositeCrosshead speed ：1mm/minNumber of Trials ：12 timesExperimental procedure of 4-points bending test15年5月7日木曜日Result and discussion of 4-points bending test0"100"200"300"400"500"600"0" 0.5" 1" 1.5" 2" 2.5" 3" 3.5" 4"412 MPa337 MPa187 MPaBending Strength (MPa)Joint Sample398 MPaA(R.T.)A(H.T.)B(H.T.)B(R.T.)H.T.：1000°C6005004003002001000462 ± 45.7 MPaHfB2 Composite at R.T.15年5月7日木曜日0"100"200"300"400"500"600"0" 0.5" 1" 1.5" 2" 2.5" 3" 3.5" 4"412 MPa337 MPa187 MPaBending Strength (MPa)Joint Sample398 MPaA(R.T.)A(H.T.)B(H.T.)B(R.T.)H.T.：1000°C6005004003002001000comparable strengthResult and discussion of 4-points bending testSampleA and Sample B had similar strength, and had comparable strength with HfB2 composite strength at R.T.462 ± 45.7 MPaHfB2 Composite at R.T.15年5月7日木曜日・From SEM observation of the fracture surfaces, similar Nb-Si were found. ・Ductile metal Nb would decrease the influence of residual stress in the cooling period of the bonding process.Result and discussion of 4-points bending test5μm5μmSample A Sample BNb5Si3 Nb5Si2SampleA and Sample B had similar strength, and had comparable strength with HfB2 composite strength at R.T.15年5月7日木曜日0"100"200"300"400"500"600"0" 0.5" 1" 1.5" 2" 2.5" 3" 3.5" 4"412 MPa337 MPa187 MPaBending Strength (MPa)Joint Sample398 MPaA(R.T.)A(H.T.)B(H.T.)B(R.T.)H.T.：1000°C6005004003002001000Result and discussion of 4-points bending testIn Sample A,  the H.T. strength was slightly decreased compared with the R.T. strength.In Sample B,  the H.T. strength was significantly decreased. 462 ± 45.7 MPaHfB2 Composite at R.T.15年5月7日木曜日Nb7Ni6+Nb2Ni6Result and discussion of 4-points bending test・Some intermetallics phases of Ni-Nb were found.・These Ni-Nb intermetallics have relatively low melting temperature. ・The presence and softening of these intrmetallics would be a possible reason why the H.T. strength of Sample B was found to be small.In Sample A,  the H.T. strength was slightly decreased compared with the R.T. strength.In Sample B,  the H.T. strength was significantly decreased. 15年5月7日木曜日・HfB2 composite joints were well-bonded by TLP bonding using Ni-Nb interlayer.・Different thickness of Ni-Nb interlayer caused different reaction in the interfacial region.・The different reaction was due to the difference in the amount of Ni-based melt. ・Two kinds of the joints revealed the similar strength at room temperature because similar Nb-Si was formed on the interfacial region regardless of the different reaction.・Because Ni-Nb intermetallics have relatively low melting temperature, the intermetallics would significantly decrease the high temperature strength of the joints bonded with small amount of Ni.The present work aimed at investigating the effect of Ni-Nb interlayerthickness on the mechanical properties of HfB2 composite joints.Summary15年5月7日木曜日Thank you !15年5月7日木曜日

Effect of Ni-Nb Interlayer Thickness on Mechanical Property of HfB2 Composite Joints

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Effect of Ni-Nb Interlayer Thickness on Mechanical Property of HfB2 Composite Joints

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