Engineering Commons^™

Effect Of The Filler Morphology On The Crystallization Behavior And Dielectric Properties Of The Polyvinylidene Fluoride-Based Composite, Suzana Filipović, Nina Obradović, Cole Corlett, William G. Fahrenholtz, Martin Rosenschon, Ekkehard Füglein, Radovan Dojčilović, Dragana Tošić, Jovana Petrović, Antonije Đorđević, Branislav Vlahović, Vladimir B. Pavlović

Materials Science and Engineering Faculty Research & Creative Works

Ceramic/polymer composites can be chemically stable, mechanically strong, and flexible, which make them candidates for electric devices, such as pressure or temperature sensors, energy storage or harvesting devices, actuators, and so forth. Depending on the application, various electrical properties are of importance. Polymers usually have low dielectric permittivity, but increased dielectric permittivity can be achieved by the addition of the ceramic fillers with high dielectric constant. With the aim to enhance dielectric properties of the composite without loss of flexibility, 5 wt.% of BaTiO₃-Fe₂O₃ powder was added into a polyvinylidene fluoride matrix. The powder was …

A Priori Procedure To Establish Spinodal Decomposition In Alloys, Simon Divilov, Hagen Eckert, Cormac Toher, Rico Friedrich, Adam C. Zettel, Donald W. Brenner, William G. Fahrenholtz, Douglas E. Wolfe, Eva Zurek, Jon Paul Maria, Nico Hotz, Xiomara Campilongo, Stefano Curtarolo

Materials Science and Engineering Faculty Research & Creative Works

Spinodal decomposition can improve a number of essential properties in materials, especially hardness. Yet, the theoretical prediction of the onset of this phenomenon (e.g., temperature) and its microstructure (e.g., wavelength) often requires input parameters coming from costly and time-consuming experimental efforts, hindering rational materials optimization. Here, we present a procedure where such parameters are not derived from experiments. First, we calculate the spinodal temperature by modeling nucleation in the solid solution while approaching the spinode boundary. Then, we compute the spinodal wavelength self-consistently using a few reasonable approximations. Our results show remarkable agreement with experiments and, for NiRh, the calculated …

Ultra-Fast Annealing Improves Snr And Long-Term Stability Of A Highly Multiplexed Line-By-Line Fbg Array Inscribed By Femtosecond Laser In A Coreless Fiber For Extreme-Temperature Applications, Farhan Mumtaz, Bohong Zhang, Jeffrey D. Smith, Ronald J. O'Malley, Rex E. Gerald, Jie Huang

Electrical and Computer Engineering Faculty Research & Creative Works

This study reports the fabrication of an 4th-order line-by-line Fiber Bragg Gratings (FBG) array using femtosecond laser inscription within a highly multimode coreless optical fiber, with a particular focus on achieving substantial multiplexing capabilities. An ultra-fast annealing procedure is employed, resulting in an impressive enhancement of the FBG sensor's fringe visibility by approximately 13 dB, signifying a notable improvement of approximately ~4 dB. This substantial enhancement contributes to the long-term stability and performance of the multiplexed FBG array in extreme temperature conditions. The systematic fabrication approach employed for the multiplexed FBG array guarantees a high signal-to-noise ratio (SNR) for each …

A Super-Hard High Entropy Boride Containing Hf, Mo, Ti, V, And W, Suzana Filipovic, Nina Obradovic, Greg E. Hilmas, William G. Fahrenholtz, Donald W. Brenner, Jon Paul Maria, Douglas E. Wolfe, Eva Zurek, Xiomara Campilongo, Stefano Curtarolo

Materials Science and Engineering Faculty Research & Creative Works

Super-Hard (Hf,Mo,Ti,V,W)B2 Was Synthesized by Boro-Carbothermal Reduction and Densified by Spark Plasma Sintering. This Composition Was Produced for the First Time as a Single-Phase Ceramic in the Present Research. the Optimized Ceramic Had a Single Hexagonal AlB2-Type Crystalline Phase with a Grain Size of 3.8 µm and Homogeneous Distribution of the Constituent Metals. the Vickers Hardness Exhibited the Indentation Size Effect, Increasing from 27 GPa at a Load of 9.8 N to as High as 66 GPa at a Load of 0.49 N. This is the Highest Hardness Reported to Date for High Entropy Boride Ceramics.

Cf/Sic Ceramic Matrix Composites With Extraordinary Thermomechanical Properties Up To 2000 °C, Min Sung Park, Jian Gu, Heesoo Lee, Sea Hoon Lee, Lun Feng, William Fahrenholtz

Materials Science and Engineering Faculty Research & Creative Works

The thermomechanical properties of carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC CMCs) were studied up to 2000 °C using high temperature in situ flexural testing in argon. The CMC specimens were fabricated using an ultrahigh concentration (66 vol%) aqueous slurry containing nano-sized silicon carbide powder. The SiC powder compacts were obtained by drying the slurry and were densified using the precursor impregnation and pyrolysis (PIP) method with field assisted sintering technology/spark plasma sintering (FAST/SPS). The high relative density of the SiC green body (77.6%) enabled densification within 2.5 days using four PIP cycles. In contrast, conventional PIP processes …

Thermodynamic Analysis Of Metal Segregation In Dual Phase High Entropy Ceramics, Steven M. Smith, William G. Fahrenholtz, Gregory E. Hilmas, Stefano Curtarolo

Materials Science and Engineering Faculty Research & Creative Works

Equilibrium Gibbs' free energy calculations were used to determine metal segregation trends between boride and carbide solid solutions containing two metals that are relevant to dual phase high entropy ceramics. The model predicted that Ti had the strongest tendency to segregate to the boride phase followed by Zr, Nb, Mo, V, Hf, and Ta, which matches experimental results of measured compositions. The ratio of a metal in the carbide phase to the content of the same metal in the corresponding metal boride had a linear trend with the change in standard Gibbs' free energy of reaction for a metal carbide …

Dielectric Properties Of Polycrystalline And Single Crystal (100) Strontium Titanate From 4 To 295 K, Hung Trinh, Alan Devoe, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

The dielectric properties of single crystal and polycrystalline SrTiO₃ (ST) were investigated from 295 to 4 K. Relative permittivity (εr) and loss tangent (tan(δ)) were measured systematically as a function of direct current (DC) voltage (0 V/cm to 800 V/cm), frequency (100 Hz to 1 MHz), and temperature (295 K to 4 K) for type (100) single crystal SrTiO₃ (SC-ST) and for polycrystalline SrTiO₃ (PC-ST). Calculated equivalent series resistance (ESR) data are also reported. Overall, the permittivity of ST showed a dependence on temperature, DC voltage, and frequency. Dependences on voltage and frequency were only observed at …

Dielectric Properties Of Polycrystalline And Single-Crystal Magnesium Oxide At High Temperatures, Alan Devoe, Hung Trinh, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

The electrical properties of high-purity magnesium oxide (MgO) samples sintered between 1500 and 1650°C were investigated up to 800°C. Dielectric constant, loss tangent and electrical conductivity were measured between 25 and 800°C. Optimum electrical properties were obtained for the sample sintered at 1600°C. The impurities in polycrystalline and single crystal MgO were discussed to understand their effect on electrical properties and the role of grain boundaries. Higher dielectric losses of polycrystalline samples as compared to the single crystal MgO were attributed to the presence of grain boundaries. MgO could be a useful dielectric material for capacitor applications up to 600°C.

Spark Plasma Sintering Of Magnesium Titanate Ceramics, Suzana Filipović, Nina Obradović, William G. Fahrenholtz, Steven Smith, Miljana Mirković, Adriana Peleš Tadić, Jovana Petrović, Antonije Đorđević

Materials Science and Engineering Faculty Research & Creative Works

Magnesium titanate ceramics were prepared by reactive spark plasma sintering (SPS) at 1200 °C for 5 min. Prior to sintering, MgO and TiO₂ powders were mixed by high energy ball milling (HEBM) for 15, 30, or 60 min. The effect of milling time on phase composition was analyzed by X-ray diffraction (XRD) for milled powders and sintered specimens. The morphology of the sintered ceramics was investigated by scanning electron microscopy (SEM), while elemental distribution was determined by energy dispersive spectroscopy (EDS). The presence of the MgTi2O5 phase was detected in XRD and was confirmed by EDS analysis. Microcracking was …

Oxidation Of Additively Manufactured Zrb2–Sic In Air And In Co2 At 700–1000 °C, Marharyta Lakusta, Nicholas M. Timme, Abid H. Rafi, Jeremy Lee Watts, M. (Ming) C. (Chuan) Leu, Gregory E. Hilmas, William G. Fahrenholtz, David W. Lipke

Materials Science and Engineering Faculty Research & Creative Works

Oxidation behavior of additively manufactured zrb2–sic in air and in co2 is reported in the temperature range of 700–1000 °c. Observed scale morphologies in air and in co2 were similar, featuring an outer borosilicate layer and an inner porous zirconia layer containing partially oxidized silicon carbide particles and remnant borosilicate products. Oxide scale thicknesses and parabolic scaling constants in air were approximately twice those observed in co2 across all studied temperatures. Activation energies for oxidation of 140 ± 20 kj/mol in air and 110 ± 20 kj/mol in co2 were determined, indicating similar diffusion processes that appear to be rate-limiting. …

Vacancy Ordering In Zirconium Carbide With Different Carbon Contents, Yue Zhou, Jeremy Lee Watts, Cheng Li, William Fahrenholtz, Gregory E. Hilmas

Materials Science and Engineering Faculty Research & Creative Works

Zirconium carbide (ZrCx) ceramics with different carbon contents were prepared by reactive hot-pressing. The rock-salt structure of ZrCx was the only phase detected by x-ray diffraction of the hot pressed ceramics. The relative densities of ZrCx decreased as carbon content increased, in general. The actual carbon contents were measured by completely oxidizing the ZrCx ceramics to ZrO₂. For most compositions, the actual carbon contents were higher than nominal batched compositions, presumably due to carbon uptake from the graphite furnace and hot press dies. Selected area electron diffraction and neutron powder diffraction revealed the presence of carbon vacancy ordering …

Lunar In-Situ Aluminum Production Through Molten Salt Electrolysis (Lisap-Mse), Jacob Ortega, Jeffrey D. Smith, Fateme Rezaei, David Bayless, William P. Schonberg, Daniel S. Stutts, Daoru Frank Han

NASA-Missouri Space Grant Consortium

The goal of Artemis is to establish a sustained presence on the Moon. To achieve so, numerous resources are necessary. The Moon contains several essential elements needed to sustain human presence. Most of those elements are trapped in the form of minerals. To refine those minerals into useful materials, reduction methods are needed. Most reduction methods on Earth require large amounts of mass and power which is unrealistic for early stages of building a lunar base. To solve this problem, we are developing a concept of Lunar In-Situ Aluminum Production through Molten Salt Electrolysis (LISAP-MSE).

The LISAP-MSE project, if successful, …

Anisotropic Thermal Expansion In High-Entropy Multicomponent Alb2-Type Diboride Solid Solutions, Frédéric Monteverde, Mattia Gaboardi, Federico Saraga, Lun Feng, William Fahrenholtz, Gregory Hilmas

Materials Science and Engineering Faculty Research & Creative Works

High-entropy (HE) ultra-high temperature ceramics have the chance to pave the way for future applications propelling technology advantages in the fields of energy conversion and extreme environmental shielding. Among others, HE diborides stand out owing to their intrinsic anisotropic layered structure and ability to withstand ultra-high temperatures. Herein, we employed in-situ high-resolution synchrotron diffraction over a plethora of multicomponent compositions, with four to seven transition metals, with the intent of understanding the thermal lattice expansion following different composition or synthesis process. As a result, we were able to control the average thermal expansion (TE) from 1.3 x 10⁻⁶ to …

Anisotropic Thermal Expansion In High-Entropy Multicomponent Alb2-Type Diboride Solid Solutions, Frédéric Monteverde, Mattia Gaboardi, Federico Saraga, Lun Feng, William Fahrenholtz, Gregory Hilmas

Materials Science and Engineering Faculty Research & Creative Works

High-entropy (HE) ultra-high temperature ceramics have the chance to pave the way for future applications propelling technology advantages in the fields of energy conversion and extreme environmental shielding. Among others, HE diborides stand out owing to their intrinsic anisotropic layered structure and ability to withstand ultra-high temperatures. Herein, we employed in-situ high-resolution synchrotron diffraction over a plethora of multicomponent compositions, with four to seven transition metals, with the intent of understanding the thermal lattice expansion following different composition or synthesis process. As a result, we were able to control the average thermal expansion (TE) from 1.3 x 10−6 to 6.9 …

Particle Migration In Large Cross-Section Ceramic On-Demand Extrusion Components, Austin J. Martin, Wenbin Li, Jeremy Lee Watts, Gregory E. Hilmas, Ming-Chuan Leu, Tieshu Huang

Materials Science and Engineering Faculty Research & Creative Works

Ceramic On-Demand Extrusion (CODE) is a direct ink writing process which allows for the creation of near theoretically dense ceramic components with large cross-sections due to oil-assisted drying. Yttria-stabilized zirconia (YSZ) colloidal pastes (∼d50 ≲ 1 µm) were used in CODE to produce dense (multi-road infill and ≳ 98% relative density), large continuous volume (> 1 cm3), and high fidelity (nozzle diameters ≲ 1 mm) structural ceramic components. However, many of these printed components underwent significant particle migration after forming. The reason for this particle migration defect was investigated using the coffee-ring effect for dilute solutions and rheological methods for …

Particle Migration In Large Cross-Section Ceramic On-Demand Extrusion Components, Austin J. Martin, Wenbin Li, Jeremy Lee Watts, Gregory E. Hilmas, Ming-Chuan Leu, Tieshu Huang

Mathematics and Statistics Faculty Research & Creative Works

Ceramic On-Demand Extrusion (CODE) is a direct ink writing process which allows for the creation of near theoretically dense ceramic components with large cross-sections due to oil-assisted drying. Yttria-stabilized zirconia (YSZ) colloidal pastes (∼d50 ≲ 1 µm) were used in CODE to produce dense (multi-road infill and ≳ 98% relative density), large continuous volume (> 1 cm3), and high fidelity (nozzle diameters ≲ 1 mm) structural ceramic components. However, many of these printed components underwent significant particle migration after forming. The reason for this particle migration defect was investigated using the coffee-ring effect for dilute solutions and rheological methods for …

Anisotropic Thermal Expansion In High-Entropy Multicomponent Alb2-Type Diboride Solid Solutions, Frédéric Monteverde, Mattia Gaboardi, Federico Saraga, Lun Feng, William Fahrenholtz, Gregory Hilmas

Mathematics and Statistics Faculty Research & Creative Works

High-entropy (HE) ultra-high temperature ceramics have the chance to pave the way for future applications propelling technology advantages in the fields of energy conversion and extreme environmental shielding. Among others, HE diborides stand out owing to their intrinsic anisotropic layered structure and ability to withstand ultra-high temperatures. Herein, we employed in-situ high-resolution synchrotron diffraction over a plethora of multicomponent compositions, with four to seven transition metals, with the intent of understanding the thermal lattice expansion following different composition or synthesis process. As a result, we were able to control the average thermal expansion (TE) from 1.3 x 10−6 to 6.9 …

Particle Migration In Large Cross-Section Ceramic On-Demand Extrusion Components, Austin J. Martin, Wenbin Li, Jeremy Lee Watts, Gregory E. Hilmas, Ming-Chuan Leu, Tieshu Huang

Materials Science and Engineering Faculty Research & Creative Works

Ceramic On-Demand Extrusion (CODE) is a direct ink writing process which allows for the creation of near theoretically dense ceramic components with large cross-sections due to oil-assisted drying. Yttria-stabilized zirconia (YSZ) colloidal pastes (∼d50 ≲ 1 µm) were used in CODE to produce dense (multi-road infill and ≳ 98% relative density), large continuous volume (> 1 cm3), and high fidelity (nozzle diameters ≲ 1 mm) structural ceramic components. However, many of these printed components underwent significant particle migration after forming. The reason for this particle migration defect was investigated using the coffee-ring effect for dilute solutions and rheological methods for …

Boro/Carbothermal Reduction Co-Synthesis Of Dual-Phase High-Entropy Boride-Carbide Ceramics, Lun Feng, William Fahrenholtz, Gregory E. Hilmas, Stefano Curtarolo

Materials Science and Engineering Faculty Research & Creative Works

Dense, dual-phase (Cr,Hf,Nb,Ta,Ti,Zr)B₂-(Cr,Hf,Nb,Ta,Ti,Zr)C ceramics were synthesized by boro/carbothermal reduction of oxides and densified by spark plasma sintering. The high-entropy carbide content was about 14.5 wt%. Grain growth was suppressed by the pinning effect of the two-phase ceramic, which resulted in average grain sizes of 2.7 ± 1.3 µm for the high-entropy boride phase and 1.6 ± 0.7 µm for the high-entropy carbide phase. Vickers hardness values increased from 25.2 ± 1.1 GPa for an indentation load of 9.81 N to 38.9 ± 2.5 GPa for an indentation load of 0.49 N due to the indentation size effect. Boro/carbothermal …

Thermal And Electrical Properties Of Spark Plasma Sintered (Ti,Cr)B2 Ceramics, Steven M. Smith, Lun Feng, William Fahrenholtz, Gregory E. Hilmas, Laura Silvestroni

Materials Science and Engineering Faculty Research & Creative Works

Thermal and electrical properties were measured for TiB2 ceramics containing varying CrB2 contents up to 33 mol%. The room-temperature thermal diffusivity decreased with increasing Cr content from 0.330 ± 0.003 cm2/s for pure TiB2 to 0.060 ± 0.003 cm2/s for (Ti0.66Cr0.33)B2. The amount of anisotropy in the coefficients of thermal expansion increased with increasing Cr content and the c-axis had the greatest dependence on Cr addition, with an increase of more than 25% in the thermal expansion for 33 mol% CrB2 compared to TiB2, whereas the a-axis only increased by about 8%. The electrical conductivity was the lowest for (Ti0.66Cr0.33)B2 …

Mechanical Properties Of Zrb2 Ceramics Determined By Two Laboratories, Jeffrey J. Swab, Jecee Jarman, William Fahrenholtz, Jeremy Lee Watts

Materials Science and Engineering Faculty Research & Creative Works

The mechanical properties for zirconium diboride (ZrB2) were measured at two laboratories and compared. Two billets of ZrB2 were prepared by hot-pressing commercial powder. The relative densities of the billets were >99% and with an average grain size of 5.9 ± 4.5 µm. Both laboratories prepared American Society for Testing and Materials (ASTM) C1161 B-bars for strength and ASTM C1421 bars with notch configuration A for fracture toughness. Specimens were machined by diamond grinding at the Army Research Laboratory (ARL) and electrical discharge machining (EDM) at Missouri S&T. Strength bars tested at Missouri S&T were polished to a.25 μm finish …

Cascaded Sapphire Fiber Bragg Gratings Inscribed By Femtosecond Laser For Molten Steel Studies, Dinesh Reddy Alla, Deva Prasad Neelakandan, Farhan Mumtaz, Rex E. Gerald, Laura Bartlett, Ronald J. O'Malley, Jeffrey D. Smith, Jie Huang

Electrical and Computer Engineering Faculty Research & Creative Works

This research reports a distributed fiber optic high-temperature sensing system tailored for applications in the steel industry and various other sectors. Recent advancements in optical sensor technology have led to the exploration of sapphire crystal fibers as a solution for sensing in harsh environments. Utilizing a femtosecond (fs) laser, cascaded fiber Bragg gratings (FBGs) were meticulously fabricated within a multimode sapphire optical fiber. These FBGs endowed the system with distributed sensing capabilities and underwent rigorous testing under extreme temperatures, reaching up to 1,800 °C. The study delves into the investigation of the FBG reflection spectrum, facilitated by the development of …

Final-Stage Densification Kinetics Of Direct Current–Sintered Zrb2, Austin D. Stanfield, Steven M. Smith, Suzana Filipović, Nina Obradović, Vladimir Buljak, Gregory E. Hilmas, William Fahrenholtz

Materials Science and Engineering Faculty Research & Creative Works

Final-stage sintering was analyzed for nominally phase pure zirconium diboride synthesized by borothermal reduction of high-purity ZrO₂. Analysis was conducted on ZrB₂ ceramics with relative densities greater than 90% using the Nabarro–Herring stress–directed vacancy diffusion model. Temperatures of 1900°C or above and an applied uniaxial pressure of 50 MPa were required to fully densify ZrB₂ ceramics by direct current sintering. Ram travel data were collected and used to determine the relative density of the specimens during sintering. Specimens sintered between 1900 and 2100°C achieved relative densities greater than 97%, whereas specimens sintered below 1900°C failed to …

Intragranular Tungsten-Titanium Carbide Composite Ceramics Via Gas-Solid Displacement Reactions, Ryan Daniel Dempsey

Doctoral Dissertations

"Research presented herein details the synthesis and characterization of nanocomposite ceramics featuring novel heterogeneous microstructures of potential interest in a variety of electrical and structural applications. Specifically, W-TiCy composite ceramics featuring tungsten nanoprecipitates located primarily within TiCy grains have been produced via sintering of intragranular nanocomposite powders produced via reaction processing-based techniques. This dissertation details the thermodynamic basis and applied kinetics of a processing scheme for fabricating nanocomposite ceramics whose morphological heterogeneity reflects that originally developed in the powder state. The first study in this series overviews the motivation for applying metallothermic displacement reactions, conducted through gaseous intermediates, to solid …

Effect Of Mechanical Activation On Carbothermal Synthesis And Densification Of Zrc, Nina Obradović, Lun Feng, Suzana Filipović, Miljana Mirković, Darko Kosanović, Jelena Rogan, William Fahrenholtz

Materials Science and Engineering Faculty Research & Creative Works

Zirconium carbide ceramics were prepared by carbothermal reduction of ZrO₂ and C that were mixed by high-energy ball milling. Powders were milled for times from 0 to 120 min in air. As milling time increased, the surface area of the powders increased, indicating significant particle size reduction. Milled powders were reacted at 1600 °C and then densified by spark plasma sintering at 2000 °C, which was sufficient to convert the starting powders to zirconium carbide. Unmilled powders did not reach full density. Milled powders reached full density, but ZrO₂ impurities were found for specimens prepared from powders milled …

High Temperature Confocal Scanning Laser Microscopy Analysis Of Dead-Burned Magnesia Aggregates, Tyler Richards, Viraj Athavale, Jeffrey D. Smith, Ronald J. O'Malley

Materials Science and Engineering Faculty Research & Creative Works

Dead-Burned Magnesia is a Commonly Used Material in the Manufacturing of Refractories for the Steelmaking Industry. Aggregates of Dead-Burned Magnesia Contain Secondary Phases Due to the Impurities within the Magnesite Rock Used in its Production. While These Phases Can Aid in Sintering Magnesia, They May Have Some Impact on the High-Temperature Performance of the Refractory Product. High-Temperature Confocal Scanning Laser Microscopy Was Utilized to Observe the Behavior of Dead-Burned Magnesia Aggregates at Elevated Temperatures (Up to 1550°C). Liquid Formation Was Detected Even at Temperatures Below 1350°C. in Some Cases, This Liquid Quickly Exuded from the Aggregate Surface. This Liquid Phase …

High Temperature Dielectric Properties Of Calcium Zirconate, Alan Devoe, Hung Trinh, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

The electrical properties of dense, high purity CaZrO3 discs, sintered at 1380°C with and without added ZrO2, were investigated up to 950°C. Dielectric constant, loss tangent, and electrical conductivity were measured from 25 to 725°C, and the real and imaginary impedances were measured between 800 and 950°C by impedance spectroscopy techniques. Dielectric constant increased by 8% above 300°C and loss tangent increased from.1% at 25°C to ∼2% above 300°C. Activation energy of electrical conductivity determined between 300°C and 950°C by alternative current (AC) and direct current (DC) measurements. These results indicate that CaZrO3 could be a useful dielectric material for …

The Effect Of Crystal Anisotropy On Fracture Toughness And Strength Of Zrb2 Microcantilevers, Tamás Csanádi, Ahmad Azizpour, Marek Vojtko, William Fahrenholtz

Materials Science and Engineering Faculty Research & Creative Works

The influence of crystal anisotropy on the micromechanical properties of ceramic grains plays an important role in the design of the macromechanical performance of bulk polycrystalline samples. To this end, the effect of crystal orientation on fracture toughness and strength was investigated by microcantilever bending experiments combined with finite element method (FEM) simulations in grains of a polycrystalline ZrB2 sample. The sample was prepared by hot pressing and the crystal orientations were determined by electron backscatter diffraction after careful surface preparation. The bending tests were carried out on notched and unnotched microcantilevers cut from specific grains along the prismatic (⊥ …

Thermal And Electrical Properties Of Spark Plasma Sintered (Ti,Cr)B2 Ceramics, Steven M. Smith, Lun Feng, William Fahrenholtz, Gregory E. Hilmas, Laura Silvestroni

Materials Science and Engineering Faculty Research & Creative Works

Thermal and electrical properties were measured for TiB₂ ceramics containing varying CrB₂ contents up to 33 mol%. The room-temperature thermal diffusivity decreased with increasing Cr content from 0.330 ± 0.003 cm²/s for pure TiB₂ to 0.060 ± 0.003 cm²/s for (Ti_0.66Cr_0.33)B2. The amount of anisotropy in the coefficients of thermal expansion increased with increasing Cr content and the c-axis had the greatest dependence on Cr addition, with an increase of more than 25% in the thermal expansion for 33 mol% CrB₂ compared to TiB₂, whereas the …

Strength Retention Of Single-Phase High-Entropy Diboride Ceramics Up To 2000°C, Lun Feng, William Fahrenholtz, Gregory E. Hilmas, Yue Zhou, Jincheng Bai

Materials Science and Engineering Faculty Research & Creative Works

The mechanical properties of single-phase (Hf_0.2,Nb_0.2,Ta_0.2,Ti_0.2,Zr_0.2)B₂ ceramics with high purity were investigated. The resulting ceramics had relative density greater than 99%, and an average grain size of 4.3 ± 1.6 μm. At room temperature (RT), the Vickers hardness was 25.2 ± 0.6 GPa at a load of 0.49 N, Young's modulus was 551 ± 7 GPa, fracture toughness was 4.5 ± 0.4 MPa m1/2, and flexural strength was 507 ± 10 MPa. Flexural strength increased by more than 50% from 507 ± 10 MPa at RT to 776 ± …