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High-entropy MAX phase (Ti 0.5 Nb 0.15 Zr 0.1 Mo 0.1 Ta 0.1 W 0.05) 2 AlC was synthesized via current-assisted sintering using Ti/Al/NbC/ZrC/MoC/TaC/WC as the raw material. The phase composition, microstructure, and elemental distribution are analyzed by X-ray diffraction, scanning electron microscope and transmission electron microscope with energy-dispersive spectrometer elemental analysis. The results obtained indicate that the as-synthesized bulk exhibits high purity with minimal elemental segregation at the grain boundary. The doped atoms caused numerous dislocations and severe lattice distortions in the crystal structure. By means of mechanical properties tests, the hardness, flexural strength, and fracture toughness of (Ti 0.5 Nb 0.15 Zr 0.1 Mo 0.1 Ta 0.1 W 0.05) 2 AlC are determined to be 9.3 ± 0.2 GPa, 433 ± 27 GPa, and 8.9 ± 0.3 MPa m1/2, respectively. These findings demonstrate notable enhancements in terms of hardening, strengthening, and toughening effects compared to the Ti 2 AlC phase. [ABSTRACT FROM AUTHOR]

In this study, the primary factors affecting the performance of PcBN (Polycrystalline cubic boron nitride) tool materials were investigated by high temperature/high pressure sintering through the variation of TiB 2 -Sialon volume ratio, the strength of TiB 2 -Sialon binder itself, as well as the matching of the average coefficient of thermal expansion (CTE) with cBN (Cubic boron nitride). The effects of TiB 2 -Sialon on the phase composition, microstructure, and mechanical properties of PcBN composites were studied by X-ray diffraction (XRD), universal testing machine, scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the properties of TiB 2 -Sialon binder are analogous to those of the corresponding composites. The phase composition of PcBN composite is not affected by the change of volume ratio. It was found that prepared composite, have TiB 2 rod crystals growing along the (100) plane and Sialon rod crystals growing on the (001) plane. The influence of the volume ratio of TiB 2 -Sialon on the mechanical properties of the composites is principally concerned with the density, mechanical properties, and thermal expansion coefficient of the used binder. The extent to which the binder matches the coefficient of thermal expansion is favorable to the strength of the composite. When the volume ratio of TiB 2 to Sialon was 1:3, the hardness (25.21 GPa, 37.44 GPa) and toughness (7.09 Pa m1/2 and 7.48 Pa m1/2) of TiB 2 -Sialon binder/TiB 2 -Sialon-cBN composites reached the maximum value, and the optimal impact resistance was also achieved. The density of the binder and the composite material was maximized when the volume ratio is 1:4. The average thermal expansion coefficient of the binder hoc tempore matches comparatively with cBN, and the interface bonding is better, displaying the best flexural strength (805.30 MPa and 1059.60 MPa) and wear ratio (2005). Therefore, adjusting the volume ratio of TiB 2 -Sialon within a certain range is beneficial to further enhance the binder's strength and mechanical properties. [ABSTRACT FROM AUTHOR]

The ceramic composites were designed through the regulation of the composition and temperature in the in-situ oxidized SiC/Al–Mg–Si composites process. The evolutions of the phase and microstructure were studied by X-ray Diffraction(XRD), Scanning Electron Microscope (SEM), and Transmission Electron Microscope(TEM) in different alloy addition and heating temperature. The products of in-situ oxidized SiC/Al–Mg–Si composites showed similar compositions due to high oxidation resistance on SiC since the heated temperature was below 1500 °C. Alloy addition dislodges the oxide shell on SiC. It promoted the oxidation of SiC, providing the sustained-release Si source to form the cordierite, mullite, and forsterite. Moissanite/spinel, mullite/spinel, and cordierite/spinel were obtained by controlling temperature or adding alloy. The mullite rods formed in 20% alloy addition samples at 1350 °C was detected. The step-like microstructure revealed that grains abide by a layer growth mechanism. The bending strength was enhanced from 13.83 ± 3.6 MPa to 22.32 ± 4.3 MPa by eutectic melting, which increased with the alloy addition and elevated temperature. [ABSTRACT FROM AUTHOR]

(HfMoTiWZr)C high entropy carbides (HEC) were prepared from the commercial carbide powders of IVB (Hf, Ti, Zr) and VIB (Mo, W) group metals of the periodic table via high energy ball milling (HEBM) and spark plasma sintering (SPS). Metal carbide powders (HfC, TiC, ZrC, Mo 2 C and WC) were HEBM'd for 3 h in a vibratory ball mill, and then SPS'd at different temperatures (1800, 1900, 2000 and 2100 °C). The HEBM'd powders and SPS'd ceramics were characterized in composition, density and microstructure using an X-ray diffractometer (XRD), a scanning electron microscope/energy dispersive spectrometer (SEM/EDS), a particle size analyzer and a pycnometer. Also, microhardness and sliding wear tests were conducted on the SPS'd ceramics. Based on the performed characterization, a single-phase FCC structure was observed at all sintering temperatures indicating a high entropy carbide ceramic, and they all have high hardness and wear resistance values. [ABSTRACT FROM AUTHOR]

During the selection of materials for anti-lithium ion corrosion, magnesium aluminate spinel has been found to have good corrosion resistance and low cost. During the preparation of light-weight spinel ceramics, it is considered to be kiln body material. In this work, spinel bubbles were prepared using electrofusion injection process. Bulk density, volume density and pressure resistance of spinel bubbles in different particle sizes were counted. Light-weight spinel bubble ceramics with different densities were prepared by using electrofused spinel bubbles as light aggregates and using ρ-Al 2 O 3 and caustic burnt magnesia powder as matrix powders. The microstructure of spinel bubbles with different particle sizes and light spinel ceramics was analyzed using scanning electron microscope. Results show that the spinel bubble has complete structure, good sphericity, perfect grain crystallization, and clear edges and corners. Although there are some fine cracks and cavities, grains are tightly bound. Compressive strength and bending strength of light-weight spinel ceramics, whose density were found to lie within the range of 0.99–1.63 g cm−3, were found to be 5.19–36.33 MPa and 3.48–12.84 MPa, respectively. [ABSTRACT FROM AUTHOR]

In this work, the properties of yttria-stabilized zirconia-based ceramics, Y-TZP containing Fe 2 O 3 as coloring agent were evaluated. Nanoparticled powder of 3Y-TZP (ZrO 2 - 3 mol.% Y 2 O 3) doped with different amounts of Fe 2 O 3 (0.002–0.136 wt%) were compacted into monolithical or multilayered samples and sintered at 1475 °C - 2 h. The samples were characterized by X-ray diffraction analysis (XRD), relative density, scanning electron microscope (SEM). Hardness and fracture toughness in the color interface were investigated using the Vickers indentation method and the biaxial flexural strength was determined by the piston on 3 balls method (P–3B). Furthermore, optical parameters were measured using spectrophotometry in regard to sample thickness and Fe 2 O 3 content. The results indicated a good adhesion between layers, proven by indentation cracks randomly growing between different regions, because the powders used produced very similar morphological characteristics. The different amounts of Fe 2 O 3 studied in this work did not interfere in densification, phase composition, or microstructure of the sintered ceramics. The fracture toughness and flexural strength did not significantly change due to the addition of Fe 2 O 3 , presenting values close to 7 MPa m1/2 and 1120–1150 MPa, respectively, in all studied compositions. On the other hand, increasing Fe 2 O 3 contents lead to an increase in the hardness of the material (1280–1330 H V), and higher contrast ratios (CR) with a consequent loss of translucency. Color variation (ΔE) depended also on the thickness of the material. [ABSTRACT FROM AUTHOR]

In this study, briquettes of Ti–TiB–TiB 2 composite were produced by mixing Ti and B powders, performing self-propagating high-temperature synthesis process and by applying hydrostatic pressure on the reaction products with a high-capacity press. Ti–TiB–TiB 2 was then coated to Ti 6 Al 4 V substrate by Electro-Spark Deposition (ESD) technique under two atmospheres of air and argon, single and double-layer coatings and in two energy levels of 40 W and 110 W as input powers. Coatings microstructure were examined by Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS) analyzer. Comparison of the coatings microstructure with the electrode microstructure shows that the coatings have a much finer microstructure than that of the electrode due mainly to the high solidification rate in the ESD process. Microstructural observations also revealed that the main phases in the coatings are needle-shaped TiB and particle-shaped TiB 2 in the Ti matrix. The coating microstructure was much finer due to an increase in solidification rate by reducing the input power from 110 to 40 W. In such a situation, two phases of TiB 2 and TiB with nanometer sizes were scattered in the Ti matrix. Also, due to the trapping of the gases in low input power of 40 W, a limited number of very small gas pores was created in the microstructure. Interface examination of the coating and the substrate by the Line Scan and X-ray Image show a good coherence of the coating with the substrate. Adhesion results showed that the bond strength between the coating and the substrate was higher than 50 MPa in all coatings. No crack was observed in the coatings after bending tests which were performed, in accordance with the intended standard, on the samples around a mandrel. The hardness of all coatings was increased with decreasing the input energy from 110 to 40 W. [ABSTRACT FROM AUTHOR]

The impact of the microstructural properties of alumina on its mechanical properties is examined in this study. Furthermore, a comparison of the mechanical behaviours of alumina samples obtained by two-step and existing sintering techniques is presented. The results are rationalised by evaluating the changes in the densities and grain sizes of alumina samples. Different two-step treatments were used on commercial alumina (99.7 mass%-Al 2 O 3 content, 0.73 μm average particle size) and compared with the existing sintering technique. Alumina powder was formed by uniaxial pressing, and the samples were treated using heat. Microstructural analyses of the samples were performed with a scanning electron microscope. The mean grain size was determined via the intercept method. Porosity was determined by the relationship between the apparent and theoretical densities of the sintered alumina. The bending strength test was performed based on ASTM 1161–13. Fracture toughness was measured based on the notch method. The microhardness test was performed using the Knoop technique. The results showed that mechanical properties of the samples prepared using two-step sintering were improved—the bending strength, fracture toughness, and Knoop microhardness increased from 286 to 303 MPa, 4.09–4.35 MPa m0.5, and 17.5–17.6 GPa, respectively—compared with those fabricated using the existing sintering technique, even with a higher porosity of 2.36% in samples obtained by two-step sintering and 1.80% in the existing sintering technique. Factorial analysis demonstrated that the temperature and holding time of the second step individually affect the relative density; however, the impact of temperature is more significant. Despite this, the interaction between temperature and holding time of the second step has the most significant impact on the average grain size. [ABSTRACT FROM AUTHOR]

To promote the densification and therefore the mechanical properties of boride-based ceramics, MgO was added as sintering aid into Os 0.9 Re 0.1 B 2 powders for densification by using spark plasma sintering (SPS). The Os 0.9 Re 0.1 B 2 powders were synthesized by mechanochemical method from powder mixture of Os, Re and amorphous B. The role of MgO on densification, phase composition, microstructure and mechanical properties (hardness, fracture toughness and wear behavior) were studied by using X-ray diffraction (XRD), scanning electron microscope (SEM) with energy-dispersive spectroscopy (EDS), micro indentation and ball-on-disk tribometer. The results show that, with the introduction of MgO as sintering aid, the relative density of the Os 0.9 Re 0.1 B 2 ceramic samples increased. When the MgO content reached 9 wt%, the as-sintered sample is almost fully dense. No obvious regularity was found from the samples with the addition of different content of MgO. Vickers hardness values of the samples with 0, 3 wt% and 9 wt% MgO are found to be very close with each other within the experimental error (~30 GPa), while the sample with the addition of 6 wt% MgO exhibits the highest hardness of ~35 GPa. The fracture toughness of the samples is decreased slightly with the addition of MgO. The friction coefficient and wear rate of the sample with the addition of 6 wt% MgO was also found to be the lowest among all samples, which indicate best wear resistance. As a whole, with the addition content of 6 wt% MgO, the Os 0.9 Re 0.1 B 2 ceramic sample performs relatively excellent mechanical properties among four groups of samples. [ABSTRACT FROM AUTHOR]

To enhance the fracture toughness and thermal shock resistance of the thermal barrier coatings (TBCs), detonation spraying has been used to prepare modified neodymium (Ⅲ) oxide (Nd 2 O 3)-doped yttria-stabilized zirconia (YSZ) TBCs containing 20 vol% (D1 coating) and 30 vol% (D2 coating) of boron nitride whiskers (BNws). Analyses were performed using a scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and a microhardness tester to examine the manner in which the doping content of different rare earth oxides affected the coating morphology, composition, and mechanical properties. The results denoted that the porosity of the D2 coating was 47.9% higher than that of the D1 coating; the whisker content was 30 vol% in the former and 20 vol% in the latter. The increased porosity reduced the microhardness and bond strength of the coating. However, the fracture toughness (KIC) of the D2 coating was increased to 2.67 MPa·m1/2 because the whisker content was 8.5% higher than that in the D1 coating. The thermal cycling life of the D2 coating was 245 cycles, and its thermal shock resistance was 9.9% higher when compared with that of the D1 coating. A TBC with better overall performance was obtained when BNw reached 30 vol%. [ABSTRACT FROM AUTHOR]

This study compared the physical properties of conventional and monolithic yttria-zirconia (Yz) materials after low-temperature degradation (LTD). Bar-shaped specimens (2.0 mm thick × 4.0 mm wide × 16.0 mm in length) were produced. Autoclave aging was executed at 134°C under 2 bar pressure for 5 h. The surface characteristics were assessed using a confocal laser microscope, microstructural phase alterations via an X-ray diffractometer (XRD), 3-point flexural strength using a universal testing machine, Vickers microhardness via a digital microhardness tester, and toughness using a durometer. Fractured specimens and indented surfaces was observed via a scanning electron microscope for fractography characterization. All of the data underwent specific statistical tests considering their distribution and homogeneity. Regarding topography, different Yz materials were very similar after LTD. Conventional Yz materials were smoother. The XRD data support that both materials were mainly composed of tetragonal crystals, whereas slight monoclinic peaks were detected. Monolithic Yz showed higher flexural strength than conventional Yz. All of the fractures started on surface defects at the side where tensile stress was concentrated (opposite to load application) and propagated to the opposite side. Vickers microhardness and toughness analysis found that conventional Yz had higher performance than monolithic Yz. This study has found that there are slight differences in strength, hardness, and toughness between conventional and monolithic yttria-stabilized zirconia ceramics, although both materials demonstrate adequate performance for clinical use. [ABSTRACT FROM AUTHOR]

In this study, the preparation and consolidation of nanocrystalline LaB 6 powders originating from powder blends of La 2 O 3 , B 2 O 3 and Mg were reported. A consecutive route of mechanochemical synthesis (MCS) and purification was utilized for the achievement of nano-sized LaB 6 powders. As-synthesized powders were leached out from intermediate reaction products or impurities. Then, a sequential step of cold pressing (uniaxial pressure at 800 MPa) and pressureless sintering (at 1700 °C for 5 h under Ar gas flow) were utilized for the consolidation of the purified LaB 6 powders. The type of mill (vibratory and planetary high-energy ball mills) was employed as a MCS parameter to reveal its effect on the physical, microstructural and mechanical properties of the LaB 6 powders, and their bulk structures. Compositional, physical and microstructural properties of the products after powder processing were determined via X-ray diffractometer (XRD), particle size analyzer (PSA), differential scanning calorimeter (DSC), stereomicroscope (SM), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive spectrometer (EDS) coupled with both SEM and TEM, and vibrating sample magnetometer (VSM). The bulk properties of the LaB 6 consolidated from nanocrystalline powders with a minimum 99.99% purity, and ∼62 nm (for vibratory ball mill) or ∼74 nm (for planetary ball mill) average particle size were compared according to various properties. LaB 6 powders were synthesized in planetary mill at an approximately six times longer duration than that of in vibratory mill. According to the results, density, surface area and mean particle size values of the vibratory ball-milled samples (containing paramagnetic powders) are better than those of planetary ball-milled (containing diamagnetic powders) ones. However, mechanical properties such as hardness, surface roughness, wear rate, friction coefficient, and also electrical conductivity were improved in the planetary ball-milled LaB 6 bulks. [ABSTRACT FROM AUTHOR]

Abstract Tungsten and boron compounds belong to the group of superhard materials since their hardness could exceed 40 GPa. In this study, the properties of the tungsten boride WB x coatings deposited by radio frequency magnetron sputtering were investigated. The sputtering was performed from specially prepared targets that were composed of boron and tungsten mixed in a molar ratio of 2.5 and sintered in Spark Plasma Sintering (SPS) process. WB films were deposited on silicon (100) and stainless steel 304 substrates at temperatures of 23 ÷ 770 °C. Microstructure, chemical and phase composition were investigated by using Scanning Electron Microscope (SEM), X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD), respectively. The mechanical properties like Vickers hardness and Young's modulus were obtained by using nanoindentation test at a load of 5 ÷ 100 mN. The friction coefficient and wear resistance of αWB coatings were investigated in scratch test and reciprocal sliding wear instrumentation. Moreover, in order to investigate thermal properties, the αWB films were annealed at 1000 °C in argon/air for 1 h and at 250 °C for 2 h in air atmosphere. Results of our research confirm that αWB coatings can be considered as an alternative to superhard materials in the production of wear resistant, long-lasting tools. [ABSTRACT FROM AUTHOR]

This study was aimed to assess the effects of reinforcement nanoparticles content, on the microstructural features, mechanical properties, and corrosion-related properties of Ni-Co-Cr 2 O 3 nanocomposite coatings. Scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD) analysis were employed in order to evaluate the microstructural features and chemical composition of the nanocomposites. Moreover, the microhardness tester and electrochemical impedance spectra (EIS) tests coupled with potentiodynamic polarization measurements were used to investigate the mechanical and corrosion-related properties, respectively. Results demonstrate that albeit the volume fraction of cobalt in coating, average particle size, Cr 2 O 3 nanoparticle content in coating, and microstructural features are of prime significance in determining the mentioned properties of the nanocomposite coatings, Co content is more important. Actually, Cr 2 O 3 nanoparticles serve as suitable nucleation sites for Co particles deposition throughout the microstructure. Thus, combined actions of Cr 2 O 3 nanoparticles incorporation and their optimal content ensures the nucleation of high population of Co particles, which significantly contributes to the improvement in the properties. The Ni-Co-8.9 wt%Cr 2 O 3 nanocomposite coating exhibits the superior mechanical and corrosion-related properties. [ABSTRACT FROM AUTHOR]

In this work green tapes comprised of TiC and SiC were further processed by lamination, pyrolysis and liquid silicon infiltration. The in-situ synthesis of MAX phase Ti 3 SiC 2 by silicon infiltration was investigated and discussed. The synthesis was supported by thermodynamic calculations. The mechanical and microstructural properties of the siliconized composites were studied. The processing route, in combination with Laminated Object Manufacturing (LOM) resulted in the successful fabrication of a three-dimensional gear. The gear showed a defect-free structure with a linear shrinkage of less than 3% relative to the green state. Thus, this approach can be considered as a near-net-shaping process of ceramic components with complex geometries. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) coating was fabricated on mullite fiber using polycarbosilane as SiC precursor. The concentration of the precursor solution and the dip-coating cycle were considered variables to determine optimum amounts. Results showed that the SiC coating prepared with 0.01 mol/L SiC precursor for one impregnation cycle was uniform and thin. It had a thickness of 62.2 nm, which completely covered the mullite fiber. This SiC coating inhibited the reaction between the fibers and the matrix. It also weakened interface bonding, thereby resulting in a toughened fracture behavior of the composite with SiC coating. [ABSTRACT FROM AUTHOR]

Abstract: In this study, hydroxyapatite and calcium apatite-based bio-ceramic composite coatings were produced on Ti6Al4V alloy by plasma electrolytic oxidation (PEO) in the electrolyte consisting of calcium acetate (CA) and β-calcium glycerophosphate (β-Ca-GP) for different treatment times. Coating thickness, phase structure, coating morphology of the cross section, elemental composition, adhesion strength, wear resistance and tribological property of the PEO coatings were analyzed by eddy current method, X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDX mapping), micro scratch tester and tribometer, respectively. The average thickness of the coatings varied from 28 to 52µm with increasing times. The XRD results indicated that anatase (TiO2), rutile (TiO2), TiP2, TCP (Ca3(PO4)2), perovskite – CaTiO3 and hydroxyapatite (Ca10(PO4)6(OH)2) phases were formed on the Ti6Al4V alloy after PEO. According to the EDS mapping results, uniform Ca and P elemental distributions were observed on the surface of PEO coatings. The adhesion strengths of the PEO coatings enhanced with increasing time. The wear resistances and tribological properties of the PEO coatings were greater than those of the uncoated Ti6Al4V alloys, and they were increased with increased time. [Copyright &y& Elsevier]

Abstract: Mode I fracture toughness of SiC particle-dispersed ZrB2 matrix composite has been measured using DCDC specimen. Compression test results of the DCDC specimen show that the fracture toughness of the composite is independent of crack length with an average toughness . Optical microscope and SEM observations reveal a flat crack path and fracture surface with no significant toughening mechanisms in the composite either through grain boundary deflection or SiC particle introduction. Comparison with previous ZrB2 matrix composites, in addition to other short crack test methods, there is an agreement with the results between what this study has come upon with respect to previous work. [Copyright &y& Elsevier]