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A large number of structural applications of ceramic materials involve gradients and temporal variations of high temperatures and strains. Therefore the elastic characterization of ceramics at high temperature is fundamental to evaluate the expected behavior in use.
The RFDA method provides an in-situ material characterization procedure that plots out Young’s modulus, Shear modulus and Poisson’s ratio at room temperature or as function of temperature up to 1700°C.
This characterization method is based on analysis of the Impulse Response Function (IRF).

An IRF is built up by various mode shapes associated with the resonance frequencies and damping ratios.
The resonance frequencies and damping ratios (Q-1) can be found from the measured IRF and can be computed with the RFDA algorithm.
To calculate the elastic properties the following input is required: Sample dimensions & mass, fundamental resonant frequency.

In contrast to the elastic constants, the internal friction is a measure of energy dissipation during vibration or impact and can provide important additional information on material performance, especially in damage-related processes where defects such as cracks may lead to unusually high damping factors.
The RFDA instruments are even suitable to measure porous ceramic materials where only very small strains are involved.

This test method is described in many standards such as: ASTM E1876, C1259, ISO 12680-1:2005, ISO 20343:2017, ISO 17561, DIN EN 843, DIN EN820 and many more.

Publications

Measurement of the High Temperature Elastic Modulus of Alumina Ceramics by Different Testing Methods.
Authors:

Nie, G. L., Bao, Y. W., Wan, D. T., & Tian, Y. (2018). Key Engineering Materials (Vol. 768, pp. 24-30).

Abstract:

Alumina ceramics are widely used in the demanding high temperature applications in which the high temperature elastic moduli (EHT) is a key property for their reliability and safety. In this paper, the elastic modulus of alumina was determined by dynamic method (impulse excitation technique) and static tests (three-point bending test and four-point bending test). For the static tests, the relative method was applied to determine the accurate deflection measurement in the heating furnace. The measured results revealed that the modulus of alumina slowly decreased from RT to 1000 °C and rapidly decreased with the increasing temperatures from 1000 °C to 1300°C. The EHT evaluated by dynamic method were higher than that tested by static tests with the reason of that impulse excitation technique only applied small forces onto a sample such that defects activity is negligible. Also the resonant frequencies couldn’t be measured easily at high temperature, because the vibration signal emitted by the sample was weak. The static approaches combined with relative method were beyond the limit to high temperatures, and they can be also used to evaluate the ultra-high temperature modulus.

Fabrication of calcium hexaluminate‐based porous ceramic with microsilica addition
Authors:

Li, Y., Xiang, R., Xu, N., Wang, Q., Li, S., Wu, M., & Yang, C. (2018). International Journal of Applied Ceramic Technology 15(4), 1054-1059.

Abstract:

Calcium hexaluminate (CA6) based porous ceramic was prepared with α-alumina powders and nanometer-sized calcium carbonate by using a direct foaming technique with the addition of calcium aluminate cement and microsilica. The microsilica lead to the acceleration of CA6 formation. Moreover, the shrinkage, densification, and elastic modulus at room temperature were enhanced with increasing microsilica content. But the hot elastic modulus showed obvious reduction between 1100 °C and 1200 °C if the microsilica content was over 0.5 wt%. Further, α-Al2O3 appeared in the specimens with and without microsilica after treatment at 1550 °C, and the proportion of CA6 grains having a high aspect ratio rised after microsilica addition.

Young’s modulus evolution during heating, re-sintering and cooling of partially sintered alumina ceramics.
Authors:

Gregorová, E., Pabst, W., Nečina, V., Uhlířová, T., & Diblíková, P. (2019). Journal of the European Ceramic Society

Abstract:

The Young modulus of partially and fully sintered alumina ceramics, obtained by firing to different temperatures (range 1200–1600°C), has been determined via impulse excitation, and the evolution of Young’s modulus of partially sintered alumina with temperature has been monitored from room temperature to 1600°C. As expected, the room-temperature Young modulus of the partially sintered materials is lower than all theoretical predictions. With increasing temperature Young’s modulus decreases, until the original firing temperature is exceeded and sintering (densification) continues, resulting in a steep Young’s modulus increase. During heating and cooling the temperature dependence obeys a master curve for alumina, unless the temperature of the original firing is excessively low.

Influence of the measurement method and sample dimensions on the Young's modulus of open porous alumina foam structures.
Authors:

Grabenhorst, J., Luchini, B., Fruhstorfer, J., Voigt, C., Hubálková, J., Chen, J., … & Aneziris, C. G. (2018). Ceramics International

Abstract:

Within this study the influence of the sample shape, the cell size and the measurement method on the Young’s modulus E of open cell foam alumina was investigated. The measurement methods used for the determination of E were the impulse excitation technique, the longitudinal ultrasonic measurement, the quasi-longitudinal ultrasonic measurement and the three point bending technique (3PB). The samples comprising the smallest height, yielded the highest E values for all measurement methods due to its processing, causing higher densities and homogeneity and hence leading to increased E values. Furthermore, its smaller area moment of inertia results in a higher beam deflection for a fixed force applied in 3PB. Thus, in the case of this shape, the forces involved during the 3PB tests were much lower and a smoother test could be performed and resulted in higher E values. Problems were found for the determination of E by the impulse excitation technique at large cell sizes (10 and 20 ppi). This was attributed to a reduction of the vibrating surface beneath the microphone capturing the audio signal. Ultrasonic methods performed robustly, however have to be conducted with care (e.g. Poisson’s ratio assumption).

Microstructure, thermal conductivity and simulation of elastic modulus of MAX-phase (Ti2AlC) gel-cast foams.
Authors:

Fey, T., Stumpf, M., Chmielarz, A., Colombo, P., Greil, P., & Potoczek, M. (2018). Journal of the European Ceramic Society 38(10), 3424-3432.

Abstract:

MAX-phase (Ti2AlC) gel-cast foams manufactured using agarose as gelling agent were investigated in terms of their microstructural, mechanical and thermal properties. The microstructural analysis of Ti2AlC foams made using SEM were compared with those using X-ray micro tomography. The Young’s Modulus of Ti2AlC foams was determined using the impulse excitation technique. This experimental data was correlated with the Gibson-Ashby, Spriggs and Cross-property relation models. The thermal conductivity measurements were carried out by Laser-Flash analysis correlating to the pore network in the Ti2AlC foam structure derived from μCT measurement. FEM-simulations of the mechanical behaviour were carried out on real structure models to determine a strut wise stress distribution under load.

Direct laser sintering of reaction bonded silicon carbide with low residual silicon content.
Authors:

Meyers, S., De Leersnijder, L., Vleugels, J., & Kruth, J. P. (2018). Journal of the European Ceramic Society

Abstract:

Additive manufacturing (AM) techniques are promising manufacturing methods for the production of complex parts in small series. In this work, laser sintering (LS) was used to fabricate reaction bonded silicon carbide (RBSC) parts. First, silicon carbide (SiC) and silicon (Si) powders were mixed in order to obtain a homogeneous powder. This powder mixture was subsequently laser sintered, where the Si melts and re-solidifies to bind the primary SiC particles. Afterwards, these SiSiC preforms were impregnated with a phenolic resin. This phenolic resin was pyrolysed yielding porous carbon, which was transformed into secondary reaction formed SiC when the preforms were infiltrated with molten silicon in the final step. This resulted in fully dense RBSC parts with up to 84 vol% SiC. The optimized SiSiC combined a Vickers hardness of 2045 HV, an electrical conductivity of 5.3 × 10³ S/m, a Young’s modulus of 285 GPa and a 4-point bending strength of 162 MPa.

Porosity effect on microstructure, mechanical, and fluid dynamic properties of Ti2AlC by direct foaming and gel‐casting.
Authors:

Potoczek, M., Chmielarz, A., Innocentini, M. D. D. M., da Silva, I. C., Colombo, P., & Winiarska, B. (2018). Journal of the American Ceramic Society 101(12), 5346-5357.

Abstract:

Ti2AlC foams possessing an almost completely open porosity ranging from 87 to 93 vol% were manufactured by gel-casting using agarose. By laying the samples on a Ti3AlC2 powder bed while sintering at 1400 °C, it was possible to retain a large amount of the Ti2AlC phase in the final ceramic foams. Increasing the agarose content in the slurry decreased the amount of total porosity as well as the cell and cell window size. The average cell size ranged from 335 to 615 μm and the average cell window size ranged from 72 to 162 μm for foams with a porosity of 87 and 93 vol%, respectively. A reduction in total porosity and in average cell and cell window size led to a decrease in permeability of the cellular structures. The strength of the foams ranged from 1.60 to 2.79 MPa, depending on the amount of porosity.

Enhanced mechanical properties of SiC reticulated porous ceramics via adjustment of residual stress within the strut.
Authors:
Liang, X., Li, Y., Sang, S., Xu, Y., Chen, Y., Li, B., & Aneziris, C. (2018). International Journal of Applied Ceramic Technology 15(1), 28-35.
Abstract:

Silicon carbide reticulated porous ceramics (SiC RPCs) with multi-layered struts were fabricated by polymer replica technique with SiC slurry, followed by infiltrating alumina slurries containing andalusite under vacuum condition. The effects of andalusite addition on the microstructure and mechanical properties of SiC RPCs were investigated, also the residual stress within the multi-layered strut was predicted. Theoretical calculations showed that the residual tensile stress generated in the outer layer of SiC RPCs because of its larger thermal expansion coefficient of infiltration slurry than that of SiC slurry at elevated temperature. Furthermore, the addition of andalusite reduced the thermal expansion coefficient and Young’s modulus of infiltration slurries, thereby significantly reducing the residual stress of the outer layer in multi-layered struts. The reduced residual tensile stress within the outer layer was beneficial to eliminate surface cracks on the struts, thus improving the mechanical properties and thermal shock resistance of SiC RPCs.

Temperature dependence of indentation size effect, dislocation pile‐ups, and lattice friction in (001) strontium titanate.
Authors:
Javaid, F., Johanns, K. E., Patterson, E. A., & Durst, K. (2018). Journal of the American Ceramic Society , 101(1), 356-364.
Abstract:

Nanoindentations with a Berkovich type indenter were performed on (001) strontium titanate (STO) single crystal at 25 degrees C and 350 degrees C, analyzing the influence of temperature on the indentation size effect (ISE) and dislocation structure around the residual impression. It is found that the STO exhibits an ISE, which is strongly reduced at 350 degrees C compared to 25 degrees C. The dislocation structure around the residual impression has been resolved using an etch-pit technique. At 25 degrees C, the extension of the dislocation pile-ups were found to be shorter as compared to 350 degrees C. This also correlates with the smaller size effects at 350 degrees C. Peach-Koehler forces and the elastic-plastic indentation stress field were used to model the influence of the lattice frictional stress on the dislocation pile-ups. Based on an equilibrium position of the outermost dislocations, the average lattice frictional stresses were calculated to be 89 MPa and 46 MPa at 25 degrees C and 350 degrees C, respectively.

Defect-mediated multiple-enhancement of phonon scattering and decrement of thermal conductivity in (YxYb1-x) 2SiO5 solid solution.
Authors:
Tian, Z., Lin, C., Zheng, L., Sun, L., Li, J., & Wang, J. (2018). Acta Materialia , 144, 292-304.
Abstract:

Rare earth (RE) silicates are promising candidates for environmental and thermal barrier coating (ETBC) materials. Low thermal conductivity is one of the main concerned thermal properties in ETBC design. We herein adopted multiple phonon scattering mechanisms to lower thermal conductivity of (YxYb1-x)2SiO5 solid solutions. Bulk samples were prepared by hot pressing method and RE atomic occupations, Raman spectra, thermal conductivities were measured as well as Debye temperature was obtained from temperature dependent Young’s modulus. It is interesting to note that huge mass and size misfits between Yb and Y ions dominate the decrement of thermal conductivity. Furthermore, Yb2+ increases the concentration of oxygen vacancy, and it further decreases heat conduction. This work highlights the possible defect engineering in RE silicates for their advances in ETBC applications.

Elastic properties of porous porcelain stoneware tiles.
Authors:
Rambaldi, E., Pabst, W., Gregorová, E., Prete, F., & Bignozzi, M. C. (2017). Ceramics International , 43(9), 6919-6924.
Abstract:

Porcelain stoneware tiles are industrially processed by using high sintering temperatures and fast firing cycles that result in products characterized by an almost impervious surface layer surrounding a rather porous bulk material. Since mechanical properties are affected by porosity, the knowledge of the material stiffness is an important parameter to define the service behavior of tiles. In the present investigation, porcelain stoneware samples having different closed porosity were investigated in order to understand the influence of the porosity on the elastic constants of the materials. Based on the quantitative XRD phase composition, elastic constants have been calculated via Voigt-Reuss-Hill averaging, and the influence of porosity has been taken into account via power-law and exponential relations. It is shown that the effective elastic constants predicted by exponential and power-law relations are in agreement with experimental values. It may be concluded that for this class of materials, in the porosity range below 14–16%, both exponential and power-law relations are helpful tools to design tiles with controlled microstructure and tailored mechanical properties.

Improvement of the mechanical properties of SiC reticulated porous ceramics with optimized three-layered struts for porous media combustion.
Authors:
Liang, X., Li, Y., Liu, J., Sang, S., Chen, Y., Li, B., & Aneziris, C. G. (2017). Ceramics International , 43(4), 3741-3747.
Abstract:

Silicon carbide reticulated porous ceramics (SiC RPCs) with three-layered struts were fabricated by polymer replica method, followed by infiltrating alumina slurries containing silicon (slurry-Si) and andalusite (slurry-An), respectively. The effects of composition of infiltration slurries on the strut structure, mechanical properties and thermal shock resistance of SiC RPCs were investigated. The results showed that the SiC RPCs infiltrated with slurry-Si and slurry-An exhibited better mechanical properties and thermal shock resistance in comparison with those of alumina slurry infiltration, even obtained the considerable strength at 1300 °C. In slurry-Si, silicon was oxidized into SiO2 in the temperature range from 1300 °C to 1400 °C and it reacted with Al2O3 into mullite phase at 1450 °C. Meantime, the addition of silicon in slurry-Si could reduce SiC oxidation of SiC RPCs during firing process in contrast with alumina slurry. With regard to slurry-An, andalusite started to transform into mullite phase at 1300 °C and the secondary mullitization occurred at 1450 °C. The enhanced mechanical properties and thermal shock resistance of SiC RPCs infiltrated alumina slurries containing silicon and andalusite were attributed to the optimized microstructure and the triangular zone (inner layer of strut) with mullite bonded corundum via reaction sintering. In addition, the generation of residual compressive stress together with better interlocked needle-like mullite led to the crack-deflection in SiC skeleton, thus improving the thermal shock resistance of obtained SiC RPCs.

Controlled nanoscale precipitation to enhance the mechanical and biological performances of a metastable β Ti-Nb-Sn alloy for orthopedic applications.
Authors:
Bahl, S., Krishnamurthy, A. S., Suwas, S., & Chatterjee, K. (2017). Materials & Design , 126, 226-237.
Abstract:
Toward engineering a new generation of low modulus titanium alloys for orthopedics, we present new insight into the control of nanoscale precipitation in a metastable β Ti-32Nb-2Sn alloy. Nanoscale α precipitates from β phase were obtained by one-step heat treatment at 500 °C. The nanoscale precipitates markedly improve the tensile strength (≈ 1070 MPa) while affording lower modulus (≈ 82 GPa) than conventional metallic biomaterials. Besides age-hardening at 500 °C, an unexpected phenomenon of age-softening is observed even in the presence of nanoscale α precipitates when aged at 600 °C. This effect is attributed to significant softening of the β phase due to compositional changes, as revealed by the elemental mapping in transmission electron microscopy (TEM). TEM elemental mapping reveals that Sn partitions preferentially in the β phase on aging at 500 °C and does not show any preferential partition on aging at 600 °C. The passive layer at the surface enriches in Sn content after aging at 500 °C and consequently affects the electrochemical behavior of the alloy. The alloy supports the proliferation, and osteogenesis of human mesenchymal stem cells. This study provides new understanding for processing Ti-Nb-Sn alloys in biomedical applications.
In situ crystallization and elastic properties of transparent MgO–Al2O3–SiO2 glass‐ceramic.
Authors:
Sant’Ana Gallo, L., Célarié, F., Audebrand, N., Martins Rodrigues, A. C., Dutra Zanotto, E., & Rouxel, T. (2017). Journal of the American Ceramic Society , 100(5), 2166-2175.
Abstract:
Glass-ceramics (GC) generally possess enhanced mechanical properties compared to their parent glasses. The knowledge of how crystallization evolves and affects the mechanical properties with increasing temperature is essential to optimize the design of the crystallization cycle. In this study, we crystallized a glass of the MgO–Al2O3–SiO2 system with nucleating agents TiO2 and ZrO2. The crystallization cycle comprised a 48 hour nucleation treatment at the glass-transition temperature followed by a 10 hour growth step at a higher temperature. During this cycle, the evolution of crystalline phases was followed by high-temperature X-ray diffraction (HTXRD), which revealed the presence of karooite (MgO·2TiO2), spinel (MgO·Al2O3), rutile (TiO2), sillimanite (Al2O3·SiO2), and sapphirine (4MgO·5Al2O3·2SiO2). The same heat treatment was applied for in situ measurement of elastic properties: elastic modulus, E, shear modulus, G, and Poisson’s ratio, ν. The evolution of these parameters during the heating path from room temperature to the final crystallization temperature and during the nucleation and the crystallization plateaus is discussed. E and G evolve significantly in the first two hours of the growth step. At the end of the crystallization process, the elastic and shear moduli of the GC were approximately 20% larger than those of the parent glass.
Temperature-dependent volume fraction of polar nanoregions in lead-free (1− x)(B i 0.5 N a 0.5) Ti O 3− x BaTi O 3 ceramics.
Authors:
Vögler, M., Novak, N., Schader, F. H., & Rödel, J. (2017). Physical Review B , 95(2), 024104.
Abstract:
The formation and temperature evolution of polar nanoregions (PNRs) in relaxor ferroelectrics is an intriguing issue that is still under debate. Therefore, we present an approach to estimate the volume fraction of PNRs by the example of the relaxor ferroelectric, (1−x)(Bi0.5Na0.5)TiO3−xBaTiO3 (BNT-xBT). A detailed analysis of the Young’s modulus, which is highly sensitive to small structural distortions, at temperatures 25∘C<T<800∘C for both poled and unpoled samples, is correlated to the temperature evolution of PNRs by utilizing a composite model. The extracted volume fraction of the PNRs and the increasing Young’s modulus above the formerly suggested Burns temperature indicate that the formation of the PNRs does not occur at a defined temperature but rather in a broad temperature range starting around ∼720∘C.
Processing, microstructure and elastic properties of mullite-based ceramic foams prepared by direct foaming with wheat flour.
Authors:
Gregorová, E., Pabst, W., Uhlířová, T., Nečina, V., Veselý, M., & Sedlářová, I. (2016). Journal of the European Ceramic Society, 36(1), 109-120.
Abstract:
Mullite-based ceramic foams with bulk densities as low as 0.4g/cm3, porosities between 49 and 88% and average foam cell sizes in the range 100-320μm are fabricated by direct foaming from suspensions containing wheat flour and partial sintering at 1600°C. Stereology-based image analysis is used to determine a complete set of global microstructural descriptors, i.e. the porosity from foam cells (8-88%), interface density, mean curvature integral density and the related pore size measures (mean chord length and Jeffries size). Elastic constants are determined via impulse excitation (Young’s moduli 2.3-21.4GPa, shear moduli 0.9-8.8GPa, bulk moduli 1.5-12.9GPa, Poisson ratios 0.193-0.234). Elastic moduli obey the power-law prediction (Gibson-Ashby relation for open-cell foams) for foams with porosities higher than 70%, but for lower porosities they are significantly lower, due to concave pores in the partially sintered matrix.
Influence of pore former on porosity and mechanical properties of Ce 0.9 Gd 0.1 O 1.95 electrolytes for flue gas purification.
Authors:
Charlas, B., Schmidt, C. G., Frandsen, H. L., Andersen, K. B., Boccaccini, D., Hansen, K. K., … & Kaiser, A. (2016). Ceramics International, 42(3), 4546-4555.
Abstract:

Single layered porous Ce0.9Gd0.1O1.95 electrolytes were fabricated by tape casting using different types, shapes and sizes of pore formers and their respective strength and stiffness were compared. The sintered bodies were characterized by scanning electron microscopy, mercury porosimetry, impulse excitation technique (Young modulus) and flexural strength measurements, to investigate the role of the different pore formers on the properties of the compounds. The compared techniques used to evaluate porosity give consistent results. The ratio between open and total porosities, evaluated from mercury porosimetry, varies depending on the used pore formers. The stiffness and strength of the compounds show an exponential dependency to the total porosity. By considering the open porosity instead (functional porosity), we observe that samples with platelets shaped pore formers have higher in-plane strength than spherical pore formers. An optimum can be found in term of Weibull strength and strain of samples obtained with the various pore formers by considering the dependency on the functional open porosity instead of the total porosity.

Temperature‐Dependent Deformation and Dislocation Density in SrTiO3 (001) Single Crystals.
Authors:
Patterson, E. A., Major, M., Donner, W., Durst, K., Webber, K. G., & Rödel, J. (2016). Journal of the American Ceramic Society, 99(10), 3411-3420.
Abstract:

This study evaluates the change of flow stress as related to dislocation density in SrTiO3 single crystals in order to provide guidance for later electrical studies. The key parameters varied are temperature and loading rate during the deformation. It is found that in <100>-oriented SrTiO3 single crystals, the dislocation density is enhanced by plastic deformation, more so at higher temperature as compared to room temperature. The experimental approach of quantifying the dislocation density through a determination of ex situ X-ray diffraction rocking curves was successfully applied over the upper temperatures region of the lower temperature ductility zone for strontium titanate, i.e., in the so-called “A-regime”. For 1.0% deformed samples deformed at 300°C, a fourfold increase in dislocation density to 1.4 × 1013 m-1 was found as compared to the nondeformed state (3.7 × 1012 m-1). Cross-section techniques confirmed that the observed dislocation densities measured at the surfaces were identical to those seen in the core of the crystals. The use of rapid changes in loading rate provided an estimate for activation volume of the dislocation core for both 25°C and 300°C.

Oxidation-induced mechanical deterioration and hierarchical cracks in glassy carbon.
Authors:
Liu, W. D., Liu, M., & Zhang, L. C. (2016). Carbon, 100, 178-186.

Abstract:

Glassy carbon (GC) is a widely used non-graphitizing carbon material, and has excellent resistances to physical and chemical attacks. However, as other carbon materials, GC is subject to the oxidation-induced deterioration. Many researchers have been trying to study the underlying oxidation mechanisms, but a convenient in-situ technique is unavailable. This paper aims to provide a facile method to investigate the mechanical property change of GC subjected to oxidation. It was found that during cyclic heating/cooling from room temperature to 500 °C, the elastic modulus decreased permanently. After two cycles, notable hierarchical cracking started on the surface, forming regular surface patterns through cracking bifurcations and leading to delamination. The oxidation of GC was proved by energy dispersion spectrum elemental analysis and comparative test with protective argon gas. The study concluded that the formation of surface oxidation layer is the main cause of mechanical deterioration and hierarchical cracking.
Theoretical and experimental determination of the major thermo-mechanical properties of RE 2 SiO 5 (RE= Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) for environmental and thermal barrier coating applications.
Authors:
Tian, Z., Zheng, L., Wang, J., Wan, P., Li, J., & Wang, J. (2016). Journal of the European Ceramic Society, 36(1), 189-202.
Abstract:
X2-RE2SiO5 orthosilicates are promising candidate environmental/thermal barrier coating (ETBC) materials for silicon-based ceramics because of their excellent durability in high-temperature environments and potential low thermal conductivities. We herein present the mechanical and thermal properties of X2-RE2SiO5 orthosilicates based on theoretical explorations of their elastic stiffness and thermal conductivity, and experimental evaluations of the macroscopic performances of dense specimens from room to high temperatures. Mechanical and thermal properties may be grouped into two: those that are sensitive to the rare-earth (RE) species, including flexural strength, elastic modulus, and thermal shock resistance, and those that are less sensitive to the RE species, including thermal conductivity, thermal expansion coefficient, and brittle-to-ductile transition temperature (BDTT). The orthosilicates show excellent elastic stiffness at high temperatures, high BDTTs, very low experimental thermal conductivities, and compatible thermal expansion coefficients. The reported information provides important material selection and optimization guidelines for X2-RE2SiO5 as ETBC candidates.
Temperature-dependent R-curve behavior of the lead-free ferroelectric 0.615 Ba (Zr 0.2 Ti 0.8) O 3–0.385 (Ba 0.7 Ca 0.3) TiO 3 ceramic.
Authors:
Vögler, M., Acosta, M., Brandt, D. R., Molina-Luna, L., & Webber, K. G. (2015). Engineering Fracture Mechanics, 144, 68-77.
Abstract:
The temperature-dependent crack growth resistance behavior of the lead-free (1 − x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (x = 0.385) ceramic was characterized using compact-tension specimens from 25 °C to 60 °C. The observed plateau fracture toughness at 25 °C was found to be approximately 37% lower than commercial Pb(Zr,Ti)O3. At elevated temperature, the maximum fracture toughness displayed a decrease, which was found to be related to the temperature-dependent elastic and ferroelastic properties. Mechanical measurements are presented that demonstrate decreasing effective switching strain, coercive stress and Young’s modulus with increasing temperature.
Mechanical properties and damage tolerance of bulk Yb 3 Al 5 O 12 ceramic.
Authors:
Wang, X., Xiang, H., Sun, X., Liu, J., Hou, F., & Zhou, Y. (2015). Journal of Materials Science & Technology, 31(4), 369-374.
Abstract:
Yb3Al5O12 has potential applications as thermal barrier coatings (TBCs) because it shows low thermal conductivity and close thermal expansion coefficient to nickel-based superalloys. As a prospective TBC material, besides superior thermal properties, the mechanical properties are also important. In this paper, we present the mechanical properties of Yb3Al5O12 including elastic moduli, hardness, strength, and fracture toughness. The Young’s modulus of Yb3Al5O12 is 282GPa. The shear-modulus-to-bulk-modulus ratio of Yb3Al5O12 is 0.63, which indicates relatively low shear deformation resistance. In addition, Yb3Al5O12 exhibits high strength and fracture toughness but low hardness compared to yttria stabilized zirconia (YSZ), the most successful TBC material. SEM observation reveals that the fracture surface of Yb3Al5O12 displays “layered structure feature”, which is caused by crack deflection. Investigation based on Hertzian contact test demonstrates that Yb3Al5O12 is a damage-tolerant ceramic. Crack deflection and bridging can arouse shear faults, dissipate the local damage energy, and restrict the crack propagation within the material, which play an important role in enhancing the damage tolerance. The superior mechanical properties and good damage tolerance ensure Yb3Al5O12 a promising candidate for TBC applications.
Mechanically induced self-propagating reaction and consequent consolidation for the production of fully dense nanocrystalline Ti 55 C 45 bulk material.
Authors:
El-Eskandarany, M. S., & Al-Hazza, A. (2014). Materials Characterization, 97, 92-100.
Abstract:
We employed a high-energy ball mill for the synthesis of nanograined Ti 55 C 45 powders starting from elemental Ti and C powders. The mechanically induced self-propagating reaction that occurred between the reactant materials was monitored via a gas atmosphere gas-temperature-monitoring system. A single phase of NaCl-type TiC was obtained after 5 h of ball milling. To decrease the powder and grain sizes, the material was subjected to further ball milling time. The powders obtained after 200 h of milling possessed spherical-like morphology with average particle and grain sizes of 45 μm and 4.2 nm, respectively. The end-products obtained after 200 h of ball milling time, were then consolidated into full dense compacts, using hot pressing and spark plasma sintering at 1500 and 34.5 MPa, with heating rates of 20 °C/min and 500 °C/min, respectively. Whereas hot pressing of the powders led to severe grain growth (~436 nm in diameter), the as-spark plasma sintered powders maintained their nanograined characteristics (~28 nm in diameter). The as-synthesized and as-consolidated powders were characterized, using X-ray diffraction, high-resolution electron microscopy, and scanning electron micros-copy. The mechanical properties of the consolidated samples obtained via the hot pressing and spark plasma sintering techniques were characterized, using Vickers microhardness and non-destructive testing techniques. The Vickers hardness, Young’s modulus, shear modulus and fracture toughness of as-spark plasma sintered samples were 32 GPa, 358 GPa, 151 GPa and 6.4 MPa·m 1/2 , respectively. The effects of the consolidation approach on the grain size and mechanical properties were investigated and are discussed.
Local structure change evidenced by temperature-dependent elastic measurements: Case study on Bi1/2Na1/2TiO3-based lead-free relaxor piezoceramics.
Authors:
Dittmer, R., Jo, W., Webber, K. G., Jones, J. L., & Rödel, J. (2014). Journal of Applied Physics, 115(8), 084108.
Abstract:
The temperature-dependent Young’s modulus Y(T) of the lead-free piezoceramics of 0.8Bi1/2Na1/2TiO3-0.2Bi1/2K1/2TiO3 (20BKT) and 0.96(0.8Bi1/2Na1/2TiO3-0.2Bi1/2K1/2TiO3)-0.04BiZn1/2Ti1/2O3 (4BZT) is measured with the impulse excitation technique and contrasted with corresponding dielectric and structural data. While the dielectric properties suggest a phase transition, the high resolution XRD patterns remain virtually unchanged from room temperature up to high temperatures, confirming no change in their long-range order. In contrast, the elastic properties indicate a broad and diffuse ferroelastic transition denoted by a minimum in Y(T). By analogy to the elastic and dielectric data of PbZrxTi1−xO3 and PLZT, it is concluded that 20BKT and 4BZT are relaxors with polar nanoregions embedded in a metrically cubic matrix. Interestingly, no indication for the freezing temperature was reflected in any of the employed measurement techniques. From the saturation of Y(T), it is suggested that the Burns temperature may be approximated as 700 °C. Moreover, it is found that the modification with the ternary end-member BiZn1/2Ti1/2O3 results in an increase in Young’s modulus. A comparison with the Bi1/2Na1/2TiO3-BaTiO3-K0.5Na0.5NbO3 yields the same results.
Reticulated Porous Foam Ceramics with Different Surface Chemistries.
Authors:
Voigt, C., Zienert, T., Schubert, P., Aneziris, C. G., & Hubálková, J. (2014). Journal of the American Ceramic Society, 97(7), 2046-2053.
Abstract:
The aim of this study was to discuss the influence of different filter surface chemistries on the properties of foam filters. For reliable results, it is essential to ensure comparable structural properties (cell size and strut thickness) for all different surface chemistries (Al2O3, MgAl2O4, 3Al2O3·2SiO2, SiO2, and TiO2) possess the same structural properties (cell size and strut thickness). Filters made of 100% of the investigated materials and alumina skeletons coated with the investigated materials were prepared. The coated alumina samples were sintered in one and two steps. The processing route with two sintering steps resulted in improved mechanical properties and comparable shrinkage and strut thickness. The 100% bulk foams possessed different pore sizes due to the differences of the material shrinkage. In this study, a comparison of the experimental investigated properties of the ceramic foam filters and the theoretically calculated values for foam materials derived from the bulk material properties is established.
Elastic anomalies in tridymite-and cristobalite-based silica materials.
Authors:
Pabst, W., Gregorová, E., & Kutzendörfer, J. (2014). Ceramics International, 40(3), 4207-4211.
Abstract:
Cristobalite and tridymite are the main SiO2 phases in silica bricks, a widespread refractory product. The elastic properties of cristobalite at room temperature have been extensively studied, because it is known for auxetic behavior, i.e. negative Poisson ratios, whereas the elastic properties of tridymite are essentially unknown. Here we show that silica brick materials, consisting almost entirely of tridymite and cristobalite, exhibit remarkable anomalies in the temperature dependence of the Young modulus: in the intermediate temperature range between approximately 50 and 250 °C these materials become very compliant, with stiffness minima of around 60% of the room temperature values, with a broad transition region at the low-temperature end, a sharp transition at the high-temperature end and a precisely reproducible hysteresis during heating and cooling. Furthermore, it is shown that Young’s moduli at around 800 °C can be more than three times as high as the room temperature values.
Microstructure characteristics related to the high temperature fracture resistance of the ESIS silicon nitride reference material. In ECF14, Cracow 2002.
Authors:
Roebben, G., Erauw, J. P., Lube, T., Duan, R. G., Cambier, F., & Van der Biest, O. (2013, February).
Abstract:
To better understand the high temperature properties of the ESIS SiliconNitride Reference Material, the secondary phases it contains are investigated using X-raydiffraction, Differential Scanning Calorimetry and optical microscopy image analysis. TheImpulse Excitation Technique was used to determine the elastic and damping properties,both at room and elevated temperature.Tests revealed the presence of a substantial amount of amorphous intergranular phase,which passes a glass transition around 950°C. This observation is used to interpret thehigh temperature fracture strength of the silicon nitride, as determined by other partners inthe Reference Material Testing Program. It is also shown that the amorphous intergranularphase has limited or no tendency to crystallise, which will facilitate interpretation of timeandloading-rate-dependent and long term behaviour at elevated temperature.Differences between surface and core of the sintered plates are observed. The content ofa crystalline iron phase and the lattice parameters of the â-Si3N4 are larger in the corethan in a surface region of about 1mm thickness. Concurrently the near surface samplesshow a higher Young’s modulus. These observations will be taken into account whenfurther assessing the structural integrity of the ESIS Silicon Nitride Reference Material.
Structure and performance of polymer-derived bulk ceramics determined by method of filler incorporation. In IOP Conference Series: Materials Science and Engineering (Vol. 47, No. 1, p. 012054). IOP Publishing.
Authors:
Konegger, T., Schneider, P., Bauer, V., & Liersch, A. (2013).
Abstract:
The effect of four distinct methods of incorporating fillers into a preceramic polymer matrix was investigated with respect to the structural and mechanical properties of the resulting materials. Investigations were conducted with a polysiloxane/Al2O3 /ZrO2 model system used as a precursor for mullite/ZrO2 composites. A quantitative evaluation of the uniformity of filler distribution was obtained by employing a novel image analysis. While solvent-free mixing led to a heterogeneous distribution of constituents resulting in limited mechanical property values, a strong improvement of material homogeneity and properties was obtained by using solvent-assisted methods. The results demonstrate the importance of the processing route on final characteristics of polymer-derived ceramics.
Theoretical Prediction and Experimental Investigation on the Thermal and Mechanical Properties of Bulk β‐Yb2Si2O7.
Authors:
Zhou, Y. C., Zhao, C., Wang, F., Sun, Y. J., Zheng, L. Y., & Wang, X. H. (2013). Journal of the American Ceramic Society, 96(12), 3891-3900.
Abstract:
The thermal and mechanical properties of β-Yb2Si2O7 were investigated using a combination of first-principles calculations and experimental investigations. Theoretically, anisotropic chemical bonding and elastic properties, weak interatomic (010) and (001) planes in the crystal structure, damage tolerance, and low thermal conductivity are predicted. Experimentally, preferred orientation, superior mechanical properties, and damage tolerant behavior for hot-pressed bulk β-Yb2Si2O7 are approved. Slipping along the weakly bonded {010}, {001}, or {100} planes, grain delamination, buckling, and kinking of nanolaminated grains are identified as main mechanisms for damage tolerance. The anisotropic linear thermal expansion coefficients (CTEs) are: αa = (3.57 ± 0.18) × 10−6 K−1, αb = (2.49 ± 0.14) × 106 K−1, and αc = (1.48 ± 0.22) × 10−6 K−1 (673–1273 K). A low thermal conductivity of ~2.1 W (m·K)−1 at 1273 K has been confirmed. The unique combination of these properties endow it a potential candidate for thermal barrier coating (TBC)/environmental barrier coating of silicon-based ceramics.
Isothermal and adiabatic Young's moduli of alumina and zirconia ceramics at elevated temperatures.
Authors:
Pabst, W., Gregorová, E., & Černý, M. (2013). Journal of the European Ceramic Society, 33(15), 3085-3093.
Abstract:
The elastic moduli (Young’s moduli) of alumina and zirconia ceramics with porosities ranging from almost dense (2-3%) to highly porous (46-52%), the latter prepared with starch as a pore-forming agent, have been measured via impulse excitation and four-point bending tests from room temperature up to more than 1200 °C. It is shown that, independent of the temperature and the material, the porosity dependence of the Young’s modulus is well predicted by our exponential relation and that, irrespective of porosity, the temperature dependence follows a master curve that is characteristic of the material (for alumina exhibiting a decrease with a gradually growing tangent slope and for zirconia exhibiting a steep decrease with an inflection point at moderately elevated temperatures below 400 °C). Differences between isothermal (static) and adiabatic (dynamic) values are negligible as long as the materials are purely elastic (i.e. at temperatures below approximately 1000 °C).
Temperature-dependent R-curve behavior of Pb (Zr 1− xTix) O 3.
Authors:
Seo, Y. H., Vögler, M., Isaia, D., Aulbach, E., Rödel, J., & Webber, K. G. (2013). Acta Materialia, 61(17), 6418-6427.
Abstract:
The compositional dependent fracture behavior of soft PZT (Pb0.99Ba0.01(Zr1−x Tix )0.98Nb0.02O3) ceramics in the vicinity of the morphotropic phase boundary was characterized using compact‐tension specimens. The compositions with 0.40 ≤ x ≤ 0.55 displayed an increasing fracture resistance with crack extension (R‐curve behavior). It was observed that the rhombohedral composition and the compositions near the morphotropic phase boundary showed the largest toughness enhancement. R‐curve behavior was found to be influenced by the ferroelastic coercive stress, saturated remanent strain, and elastic modulus, which were experimentally measured for each composition. X‐ray diffraction measurements were performed and compared to the fracture results to investigate the impact of phase and lattice distortion on ferroelastic toughening behavior.
Elastic behaviour of zirconium titanate bulk material at room and high temperature.
Authors:
López-López, E., Erauw, J. P., Moreno, R., Baudín, C., & Cambier, F. (2012). Journal of the European Ceramic Society, 32(16), 4083-4089.
Abstract:
Zirconium titanate (ZrTiO4) is a well known compound in the field of electroceramics, however, its potential for structural applications has never been analysed. Moreover, it is compatible with zirconia, thus, zirconium titanate–zirconia composites might have potential for structural applications in oxidizing atmospheres. Nevertheless, there are currently no data about elastic properties of zirconium titanate materials in the literature. In view of the importance of these properties for the structural integrity of components subjected to high temperature and mechanical strains, an attempt was done in this work to determine the elastic properties of ZrTiO4, both at room and high temperature. Young’s modulus (161 ± 4 GPa), shear modulus (61 ± 1 GPa) and Poisson’s ratio (0.32 ± 0.01) values at room temperature have been estimated for a fully dense single phase ZrTiO4 material from experimental data of sintered single phase ZrTiO4 materials with different porosities (6–19%). Values for room temperature Young’s modulus are in agreement with those obtained by nanoindentation. Young’s modulus up to 1400 °C shows an unusual dependence on temperature with no significant variation up to 500 °C an extremely low decrease from 500 to 1000 °C (≈0.02–0.03% every 100 °C) followed by a larger decrease that can be attributed to grain boundary sliding up to 1400 °C.
Modeling the mechanical properties of optimally processed cordierite–mullite–alumina ceramic foams by X-ray computed tomography and finite element analysis.
Authors:
Zhang, L., Ferreira, J. M., Olhero, S., Courtois, L., Zhang, T., Maire, E., & Rauhe, J. C. (2012). Acta Materialia, 60(10), 4235-4246.
Abstract:
Bulk and cellular cordierite ceramics were prepared from a non-stoichiometric powder consisting of corundum, talc (triclinic), α-quartz, K-feldspar, kaolinite, mullite and a small amount of a glass phase. The optimal sintering processing route was evaluated to obtain good mechanical properties. A high flexural strength of 120 MPa and a Young’s modulus of 99 GPa were achieved. The ceramic foams were fabricated by impregnation of polymer preforms with the optimized stock suspension. The mechanical properties of ceramic foams were studied by impulse excitation and compression tests. The Gibson–Ashby model predicted the ceramic foam’s effective modulus and its elastic limit strength well, as measured experimentally. In addition, the actual three-dimensional (3-D) structure obtained from X-ray computed tomography (CT) coupled with the finite element method (FEM) was used to calculate the Young’s modulus and the elasticity limit of the ceramic foam; however, this did not produce aby better agreement between the calculated values and the experimental results. The discrepancy between the Gibson–Ashby model and FEM could probably be attributed to the accuracy and small volume of representative reconstructed 3-D cellular structure. Taking account of the effect of the internal hollow structure on the stress localization in the ceramic struts, the CT–FE modeling provides a good measure of the adaptability and predictability of actual ceramic foam structures for realistic damage modeling.
Preparation, microstructure, and mechanical properties of TiB2 using Ti3AlC2 as a sintering aid.
Authors:
Zheng, L., Li, F., & Zhou, Y. (2012). Journal of the American Ceramic Society, 95(6), 2028-2034.
Abstract:
Titanium diboride (TiB2) was successfully hot‐pressed at 1500°C using titanium aluminum carbide (Ti3AlC2) as a sintering aid. The mechanisms for the improved sinterability of TiB2 by the addition of Ti3AlC2 involve, first, the Al coming from the decomposition of Ti3AlC2 can eliminate the oxide layer on the surface of TiB2; second, the TiCx (also from the decomposition of Ti3AlC2) has a positive influence on the densification of TiB2 due to its plasticity at high temperatures. TEM observations reveal that the interface between TiB2 and TiCx is coherent and strong, free of amorphous layers and oxide phases. An optimized composition of TiB2‐10 wt% Ti3AlC2 was obtained with the unique combination of mechanical properties, including the elastic modulus of 567 GPa, the fracture toughness of 4.8 MPa·m1/2, the flexural strength of 711 MPa, and the hardness of 25 GPa.
Optimization of the strength of SOFC anode supports.
Authors:
Frandsen, H. L., Ramos, T., Faes, A., Pihlatie, M., & Brodersen, K. (2012). Journal of the European Ceramic Society, 32(5), 1041-1052.
Abstract:
During operation solid oxide fuel cells are stressed by temperature gradients and various internal and external mechanical loads, which must be withstood. This work deals with the optimization of the strength of as-sintered anode supported half-cells by imposing changes to production parameters, such as powder milling and sintering temperature. The strength was measured with the ball-on-ring method, and analyzed with a large displacement finite element model. Weibull statistics were used to describe the distribution of strengths. The influence on the Weibull strength of the many different processing parameters was found to be quantifiable in terms of cell porosity to a large extent. The results were validated with an independent set of measurements of strength and stiffness by uniaxial tension and the impulse excitation technique, respectively. For application of the finding in relation to the SOFC technology a mathematical frame to determine the optimal porosity of a SOFC system is presented.
Preparation and characterization of porous alumina–zirconia composite ceramics.
Authors:
Pabst, W., Gregorová, E., Sedlářová, I., & Černý, M. (2011). Journal of the European Ceramic Society, 31(14), 2721-2731.
Abstract:
Four types of porous alumina–zirconia composites on the alumina-rich side, differing in the zirconia content (10–40wt.%), have been prepared by starch consolidation casting with different amounts of corn starch (10–50vol.%), and the resulting microstructures have been studied via the Archimedes method, microscopic image analysis and mercury porosimetry (bulk density, porosity, pore size and pore size distribution), with special regard to the evolution of the microstructure as a result of (partial) sintering in the temperature range 1100–1530°C. An influence of the composition on pore size and shape has been observed. Elastic properties (Young’s moduli) of the composites are measured via the impulse excitation method and the resonant frequency method and compared with micromechanical relations expressing the dependence of Young’s modulus on porosity. It is found that the exponential relation and the sigmoidal average provide the best descriptions for the Young’s moduli of materials with this type of microstructure.
Effect of Ti dopant on the mechanical properties and oxidation behavior of Zr2 Al (Si) 55 ceramics.
Authors:
Lu, X., Xiang, H., He, L. F., Sun, L., & Zhou, Y. (2011). Journal of the American Ceramic Society, 94(6), 1872-1877.
Abstract:
Ti-doped Zr2[Al(Si)]4C5 solid solutions were prepared by an in situ hot-pressing method and its effect on the mechanical properties and high-temperature oxidation behavior were investigated. The solid solutions show comparable hardness, strength, and fracture toughness with Zr2[Al(Si)]4C5 except modulus, which decreases with Ti dopant content. The stiffness is maintained up to 1600°C, which derives from the clean grain boundaries without glassy phases. The oxidation resistance of [Zr1−x(Ti)x]2[Al(Si)]4C5 solid solutions at 1000°–1300°C is improved remarkably. The improved oxidation resistance is mostly due to the formation of a more protective oxide scale consisting of (Zr,Ti)O2, Al2O3, and mullite.
The shaping and densification of silicon carbide while avoiding alumina as a sintering additive.
Authors:
Rade, K., Novak, S., & Kobe, S. (2011). Journal of Materials Science and Engineering. A, 1(3A), 301.
Abstract:
Silicon carbide is a very promising material for various applications because of its extraordinary properties that result from its covalent structure. For any potential use in the biomedical field, the alumina that is usually employed as a sintering additive, should be avoided because of the adverse effect that aluminium has on the human body. In our investigations we employed several different approaches to the densification of silicon carbide; however, most of the focus was on achieving the highest possible green density. This was eventually achieved with an optimised electrophoretic deposition, while the sintering was carried out without any sintering additives, using only the addition of boron and carbon or using Mg compounds. The sintering conditions, i.e., the temperature and the atmosphere, were adapted accordingly. We have shown that the green density is strongly dependent on the compaction technique and can reach 64.5 vol.%, for parts formed by electrophoretic deposition from well-dispersed aqueous suspensions that are subsequently isostatically pressed. In the absence of a sintering additive the samples with a green density above a threshold value of approximately 58-60 vol.%, revealed a neck formation when sintering in a vacuum, while the densification remained negligible up to 2,000 °C. The density of the boron-and-carbon-containing samples reached 9%, of the theoretical value and the mechanical properties were up to 250 GPa, 220 MPa and 3.9 MPa·m 1/2 for the elastic modulus, flexural strength and fracture toughness, respectively. For the air-sintered samples containing MgO the density reached 75%, while for the mechanical properties the achieved values were 79 GPa, 180 MPa and 3 MPa·m 1/2 for the elastic modulus, flexural strength and fracture toughness, respectively. We have also shown that the addition of MgO in combination with sintering in the open air significantly promotes densification due to an enhanced diffusion.
Pressureless Sintering and Properties of Ti3AlC2.
Authors:
Lu, X., & Zhou, Y. (2010). International journal of applied ceramic technology, 7(6), 744-751.
Abstract:
Pressureless sintering of titanium aluminum carbide (Ti3AlC2) is difficult due to its easy decomposability at high temperatures, thus decomposition must be avoided during sintering. In this work, pressureless sintering was performed in different embedded powders and Al4C3 was found to be effective to inhibit Ti3AlC2 from decomposition due to the offering of Al rich ambience. High-density Ti3AlC2 was obtained by pressureless sintering in Al4C3 powder bed without additives. The good sinterability is due to the special crystal structure of Ti3AlC2 and the easy diffusion of Al atoms. The mechanical properties of pressureless sintered Ti3AlC2 are comparable to those of the hot-pressed ones.

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