The effects of in-situ formed phases on the microstructure,mechanical properties and electrical conductivity of spark plasma sintered B4C containing Y2O3

B₄Cs without additive and 5, 10 and 15 wt % Y₂O₃ containing B₄Cs were produced by using spark plasma sintering (SPS) technique at different temperatures such as 1820, 1930 and 2030 °C and the effects of in-situ formed phases on the mechanical properties and electrical conductivity of B₄C were investigated. Microstructural investigations showed that the YB₄ phase was formed at 1820 °C and the YB₆ phase at 1930 °C. The hardness values of B₄C-YB₄ composites were higher than the value of B₄C sintered at 1820 °C while lower than that of sintered at 2030 °C. The fracture toughness steadily increased with increasing Y₂O₃ content. The electrical conductivity of B₄C sintered at 2030 °C increased by ～ 40 % with the contribution of in-situ formed YB₄ phase. Compared to B₄C-YB₄, B₄C-YB₆’s hardness was higher, while its fracture toughness and electrical conductivity were lower.     

Improvements in microstructural and mechanical properties of ZrO2 ceramics after addition of BaO

The effects of the addition of BaO on the sinterability, phase balance, microstructure, and mechanical properties of 8 mol% yttria-stabilized cubic zirconia (8YSZ) were investigated using scanning electron microscopy, X-ray diffraction (XRD) analyses, and micro-hardness testing. The 8YSZ powder was doped with 0–15 wt% BaO using a colloidal process. The undoped and BaO-doped 8YSZ specimens were sintered at 1550 °C for 1 h. The XRD analyses results showed that the specimens doped with up to 1 wt% BaO did not exhibit BaO-related peaks, indicating that BaO was completely solubilized in the 8YSZ matrix. However, when more than 1 wt% BaO was added, BaZrO₃-related peaks appeared, suggesting that the overdoped BaO did not dissolve in the 8YSZ matrix but formed a secondary phase of BaZrO₃ at high temperatures. Grain size measurements showed that the grain size of 8YSZ decreased with an increase in the amount of BaO added. The decrease in the grain size was owing to the fact that the grains of BaZrO₃, which precipitated at the grain boundaries and grain junctions of 8YSZ, increased the grain boundary cohesive resistance because of the pinning effect. This resulted in a decrease in the grain boundary mobility, and an increase in the grain boundary energy. Furthermore, while the addition of BaO to 8YSZ caused a slight decrease in the hardness of 8YSZ, the fracture toughness of 8YSZ increased from 1.64 MPa m^1/2 to 2.08 MPa m^1/2, owing to the resulting decrease in the grain size.     

Effect of particle size,heating rate and CNT addition on densification,microstructure and mechanical properties of B4C ceramics

Monolithic B₄C ceramics and B₄C–CNT composites were prepared by spark plasma sintering (SPS). The influence of particle size, heating rate, and CNT addition on sintering behavior, microstructure and mechanical properties were studied. Two different B₄C powders were used to examine the effect of particle size. The effect of heating rate on monolithic B₄C was investigated by applying three different heating rates (75, 150 and 225 °C/min). Moreover, in order to evaluate the effect of CNT addition, B₄C–CNT (0.5–3 mass%) composites were also produced. Fully dense monolithic B₄C ceramics were obtained by using heating rate of 75 °C/min. Vickers hardness value increased with increasing CNT content, and B₄C–CNT composite with 3 mass% CNTs had the highest hardness value of 32.8 GPa. Addition of CNTs and increase in heating rate had a positive effect on the fracture toughness and the highest fracture toughness value, 5.9 MPa m^1/2, was achieved in composite with 3 mass% CNTs.     

Effect of nano-silica on the chemical durability and mechanical performance of fly ash based geopolymer concrete

In this study, the effect of nano silica on the short term severe durability performance of fly ash based geopolymer concrete (GPC) specimens was investigated. Four types of GPC were produced with two types of low calcium fly ashes (FAI and FAII) with and without nano silica, and ordinary Portland cement concrete (OPC) concrete was also cast for reference. For the geopolymerization process, the alkaline activator has selected a mixture of sodium silicate solution (Na₂SiO₃) and sodium hydroxide solution (NaOH) with a ratio (Na₂SiO₃/ NaOH) of 2.5. Main objectives of the study were to investigate the effect of usability or replaceability of nano silica-based low calcium fly ash based geopolymer concretes instead of OPC concrete in structural applications and make a contribution to standardization process of the fly ash based geopolymer concrete. To achieve the goals, four types of geopolymer and OPC concretes were subjected to sulfuric acid (H₂SO₄), magnesium sulfate (MgSO₄) and seawater (NaCl) solutions with concentrations of 5%, 5%, and 3.5%, respectively. Visual appearances and weight changes of the concretes under chemical environments were utilized for durability aspects. Compressive, splitting tensile and flexural strength tests were also performed on specimens to evaluate the mechanical performance under chemical environments. Results indicated that FAGPC concretes showed superior performance than OPC concrete under chemical attacks due to low calcium content. Amongst the chemical environments, sulfuric acid (H₂SO₄) was found to be the most dangerous environment for all concrete types. In addition, nano silica (NS) addition to FAGPC specimens improved both durability and residual mechanical strength due to the lower porosity and more dense structure. The FAIIGPC specimens including nano silica showed the superior mechanical performance under chemical environment.     

Chemical and mechanical properties of vinyl-ester/ABS blends

Various experimental techniques and finite element modelling (FEM) were employed to assess mechanical and chemical properties of vinyl-ester (VE)/poly(acrylonitrile-butadiene-styrene) (ABS) blends with different ABS particle content. The blends were to be used as a toughening agent for interlayer toughened VE/glass composite material. Firstly, the materials' fracture toughness and tensile properties were examined, the results showing excellent toughening potential of the blends as well as a non-linear trend for fracture toughness as a function of ABS weight content. The tensile testing of the blends served to define the yield point of the materials and to obtain their stress-strain curves, which were then used as input into finite element analysis models. The mechanical testing results suggested that a chemical reaction may have occurred between the constituents of the blends. Based on the Raman spectroscopy results and mechanical testing data, 7% of ABS was believed to be the critical ABS content where significant changes in the materials' chemical composition and consequently in mechanical properties occurred. Finally, FEM was undertaken to further verify the existence of this sudden variation in material's properties.     

Effect of Dy2O3 content on microstructure and mechanical properties of zirconia-toughened alumina

In this study, the effect of adding Dy₂O₃ on the microstructure and mechanical properties of zirconia-toughened alumina (ZTA) stabilised by yttrium oxide was investigated. ZTA-Dy₂O₃ composites with different Dy₂O₃ contents (0 wt%, 1 wt%, 2 wt%, 3 wt%, and 4 wt%) were prepared by sintering at 1600 °C for 4 h. The phases and structures of the samples were characterised through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Dy₂O₃ formed a solid solution c-DYZ with YSZ, and an appropriate amount of Dy₂O₃ could refine the grains and contribute to densification. The densities, hardness, flexural strength and toughness all increased and then decreased with increasing Dy₂O₃ content, reaching maximum values of 99.2%, 1741 ± 19 HV, 449 ± 10 MPa and 5.87 ± 0.42 MPa?m^1/2, respectively, at 3 wt% Dy₂O₃ content.     

Optimized structural and mechanical properties of borophosphate glass

A series of phosphate glasses composed of (65-x)P₂O₅–15BaO–5Al₂O₃–5ZnO–10Na₂O-xB₂O₃ (x = 0, 2, 4, 6, and 8 mol%) were successfully prepared using the melt-quenching method. The effects of the addition of boron trioxide (B₂O₃) on the physical, structural, and mechanical properties of the glasses were investigated. As the added content of B₂O₃ increased from 0 to 6 mol%, the glass exhibited increased density and transition temperature, and decreased molar volume, indicating optimization of the glass stability. Raman spectroscopy revealed that the introduction of B₂O₃ transformed the glass from a chain structure to a three-dimensional network structure, which enhanced the chemical stability of the glass by the cross-linking of long phosphate chains with boron ions. Regarding the mechanical properties, when the boron content was 6 mol%, the flexural strength of the glass was 41% higher than that of the undoped boron, while the Vickers hardness and Knoop hardness values increased by 20.58% and 7.05%, respectively, and the fracture toughness was slightly decreased. In general, improving the mechanical properties of phosphate glass is of great significance for increasing the applications of this glass.     

Influence of sintering temperature on conductivity and mechanical behavior of the solid electrolyte LATP

To warrant long-term reliability for application of electrolytes in solid state batteries also mechanical properties have to be considered. Current work concentrates on Li_1+xAl_xTi_2-x(PO₄)₃ (LATP), which based on its conductivity is a very promising material. Effect of sintering temperature (950, 1000, 1050, 1100 °C) on mechanical properties and conductivity was tested. Impedance tests were carried out and as main focus of the work the mechanical behavior of LATP samples was determined. The impedance tests results revealed that LATP sintered at 1100 °C had the highest ion conductivity. The LATP sintered at 1100 °C revealed also the highest elastic modulus and hardness, which appeared to be related mainly to a smaller lattice parameter with additional effects of lower porosity especially when tested at higher loads. The results indicate that enhancement of both mechanical behavior and conductivity requires lowering secondary phase content and densifying the microstructure of the material.     

The effect of stresses during crystallization on the crystallite size distributions

In some glasses during thermal annealing, nano crystals are formed, which scarcely grow with time and exhibit a very narrow crystal size distribution. In this paper, considerations on the crystallite size distributions are given. A variant of the nucleation theory including the role of an induction period is included in the model. Since non-isochemical systems are considered, the oversaturation is decreasing with time and therefore a model is chosen according to which the nucleation rate decreases. For the crystal growth velocity, a model recently derived was used which takes into account the stresses formed during the course of the crystallization process. It is found, that a model taking into account decreasing oversaturation, an induction period as well as the occurrence of stresses fully explains the crystallite size distributions experimentally observed which might even be narrower than those according to the theory of Lifshitz, Slyozov and Wagner.     

The obtaining of high-density specimens and analysis of mechanical strength characteristics of a composite based on ZrO2-WC nanopowders

The structures, processes of shrinkage, and phase composition of the compact system ZrO₂-WC, obtained by hot pressing with the transmission of high current, are considered in the article. We found that as a result of compaction, the ZrO₂-WC-ceramics have uniform density distribution, with the following optimal mode consolidation values T = 1,350°C, P = 30 MPa and t = 2 min. These conditions allow us to achieve the best combination of ceramic properties by criteria density and strength.     

Effect of polymer modification of the paste–aggregate interface on the mechanical properties of concretes

We investigated the effect of thin viscoelastic polymer coatings around aggregate particles on the mechanical properties of “micro-concretes” with a maximum aggregate diameter of 10 mm. Aggregate particles > 5 mm were pre-treated with a latex at dosages of up to 2% by mass and dried prior to using the treated aggregate in the micro-concrete mix. Cured prisms were tested in flexion. The results show that thin polymer coatings on aggregates have a significant effect on micro-concrete cracking behaviour at much lower polymer dosages than are commonly used in polymer-modified mortars. We observed a significant improvement in post-peak energy absorption relative to the use of the same amount of polymer dispersed in the bulk paste. But, under the conditions tested here, reductions in the strengths and moduli of the composites due to the polymer additions appear to have more than outweighed the observed positive effects of increases in fracture energy and characteristic length.     

The effect of the shape and size of the pores on the mechanical properties of porous HAP-based bioceramics

In this study, the influence of the shape and size of the pores on the mechanical properties of the obtained porous HAP-based bioceramics was investigated. The porous HAP-based bioceramics were obtained starting from spherical calcium hydroxyapatite powder, obtained by hydrothermal syntheses. The number of shapeless inter-agglomerate pores decreased and amount of spherical intra-agglomerate pores increased on increasing the sintering temperature from 1100 °C to 1250 °C. The shape of pores also changed with thermal treatment of specimens; the small pores remained spherical while the larger pores became more spherical in shape, as was proved by image analysis. A three-dimensional, finite element unit cell model was applied to evaluate the influence of pore shape on the mechanical strength of HAP ceramics. By analyzing the effect of the shape of pores to the fracture toughness of sintered porous HAP bioceramics, it was observed that the more spherical the pores were, the tougher became the bioceramics. After sintering at 1250 °C for 2 h, measured toughness was 1.31 MPa m^1/2, which is a relatively high value for this type of bioceramics.     

Effect of rare earth oxides addition on the mechanical properties and coloration of silicon nitride ceramics

The aim of this study was to evaluate the mechanical properties and coloration of silicon nitride ceramics in the presence of RE₂O₃ (RE = Nd, Eu or Dy). Dense Si₃N₄ ceramics were prepared by gas pressure sintering at 1800 °C for 2 h. XRD analysis confirmed the complete transformation of α-Si₃N4 to β-Si₃N₄. The fracture toughness and flexure strengths were 11.93 ± 0.56 MPa·m^1/2, 667 ± 40.98 MPa with the addition of Eu₂O₃ (SE). Base on the SEM image, the pull-out, bridging and deflection of large grains were observed and contributed to the increase in mechanical properties. The chromaticity of sintered bodies was measured using a spectrophotometer. The color difference of the ceramics is due to the formation of different color developing compounds according to the EDS. Results showed that high-toughness and colorful Si₃N₄ ceramics can be prepared using YAG:Ce³⁺ as sintering additive and RE₂O₃ as the colorant.     

The effect of an oxygen partial pressure gradient on the mechanical behavior of perovskite membrane materials

In application of perovskite as oxygen conducting materials the membrane is operated at elevated temperatures under an oxygen gradient. The effect of the partial pressure difference on the mechanical properties is reported in the current work. Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) and La_0.58Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) samples were annealed under an oxygen gradient. The mechanical properties of cross-sections were characterized using indentation testing. Chemical strains for BSCF and LSCF were too small to detect them after cooling to RT by XRD; however, the results suggest that the indentation crack length is affected by chemical strains for LSCF, but not for BSCF. An anisotropy of the indentation crack length and corresponding apparent fracture toughness is related with the interaction of domain switching and residual strain that is probably also associated with the observation that vacuum (10⁻⁵ mbar) annealed LSCF showed surface cracking on heating in air, whereas for BSCF such fracture features were not observed.     

Effect of mechanical properties on the ballistic resistance capability of Al2O3-ZrO2 functionally graded materials

Because Al₂O₃ exhibits high strength and hardness, it is prevalently used as a ceramic material. ZrO₂ is often added to increase the toughness of such a material. Therefore, this study mixed Al₂O₃ and ZrO₂ to formulate functionally graded materials (FGMs). four-layer and eleven-layer Al₂O₃-ZrO₂ FGM_S were produced from Al₂O₃ and ZrO₂ mixtures by sintering at 1500 °C. Moreover, testing sheets were created by mixing various ratios of Al₂O₃ and ZrO₂ to analyze their fracture toughness and hardness. The results revealed the 90% Al₂O₃-10% ZrO₂ sheet to exhibit a hardness of 15.12 GPa, and the 50% Al₂O₃-50% ZrO₂ sheet to attain a fracture toughness as high as 4.7 MPa m^0.5. The impact resistance test involved analyzing various types of testing sheets, including the four-layer Al₂O₃-(0%, 10%, 20%, 30%) ZrO₂ FGM, eleven-layer Al₂O₃-(0–100%) ZrO₂ FGM, 100% Al₂O₃ composite material, 90% Al₂O₃-10% ZrO₂ composite material, 70% Al₂O₃-30% ZrO₂ composite material, and 50% Al₂O₃-50% ZrO₂ composite material. The ballistic tests showed that FGMs of the same areal density (4.64 g/cm²) or thickness (11 mm) attained the highest energy absorption. The experimental results confirmed that FGMs can delay the formation and propagation of ceramic cones. Specifically, toughened alumina materials prevent the growth of radial and circumferential cracks, delay the formation of ceramic cones, decrease cones hitting against the back plane, and increase the penetrating resistant capability of the ceramic materials experiencing bullet impact, features important for applications in fields such as aerospace, aviation, automobile, the military industry, and biomedicine     

Effect of printing parameters on mechanical properties of extrusion-based additively manufactured ceramic parts

The purpose of this study is to investigate the effect of printing parameters on the physical and mechanical properties of additively manufactured ceramics (alumina and zirconia). Sample parts were obtained by extrusion-based additive manufacturing of a ceramic-binder mixture and subsequent post-processing (debinding and sintering). Their mechanical properties (microhardness, flexural strength, toughness) were measured and correlated with the printing parameters. Part orientation is the most significant factor for microhardness and flexural strength in both ceramic materials. Parts with vertical orientation show higher hardness while horizontal samples show higher flexural strength compared to their respective counterparts. Extrusion velocity was found to be insignificant for hardness and flexural strength. However, a marginal increase in fracture toughness with the increase in the extrusion velocity was observed. The fracture toughness of additively manufactured ceramics shows an increasing trend with elastic modulus and flexural strength and a decreasing trend with hardness and sintered density.     

Effect of zirconia addition amount in glaze on mechanical properties of porcelain slabs

Applying toughened glaze layer on porcelain slabs can improve the fracture toughness of slabs and greatly reduce the production cost. In this study, porcelain slabs glaze with high toughness was fabricated by the processes of impregnation glazing and single firing method, using opaque frits, kaolin clay as the main raw materials, zirconia as an additive, and the effect of the addition amount of zirconia in glaze on fracture toughness of porcelain slabs was investigated. The results showed that the type and content of crystal phase of the glaze were greatly influenced by the addition amount of zirconia. Meanwhile, compared with the base glaze, the hardness and fracture toughness of the sample with zirconia glaze were significantly improved. Porcelain slabs with 10 wt% zirconia in glaze, sintering at 1200 °C, exhibited higher quality glaze and outstanding properties, including a water absorption of 1.95%, a Vickers hardness of 6.36 GPa, and a fracture toughness of 2.71 MPa m^1/2. The toughening mechanism of the glaze layer was as follows: a large number of zirconium silicate grains with high hardness were generated by the reaction of added zirconia with silica in the glass phase, which increased the content of crystal phase and then prevented the propagation of cracks; moreover during the martensitic transformation of the tetragonal zirconia grains, the volume and shear strain were generated to offset the stress field generated by the crack tip, thus toughening the material.     

The effect of elastomeric nano-particles on the mechanical properties and crystallization behavior of polypropylene

Generally, toughness of polypropylene (PP) is an issue which has been investigated for many years to search for improvements. A traditional approach is to blend with rubber particles to enhance the toughness of PP yet modulus of PP decreases accordingly. Recently, we have achieved a good balance of toughness and stiffness of PP via blending PP with a small amount of elastomeric nano-particles (ENP). Based on our measurements, mechanical properties of the blends studied both the toughness of PP at room temperature and at −20 °C show substantial increase. On the other hand, the stiffness of the PP blends retains or even possesses a slight enhancement. One of the reasons for this improvement is due to the fact that the ENP is not only a toughening modifier but also a nucleation agent for the PP. The nucleation density of the blends increases, while the crystallization kinetics of the blends becomes faster compared with the pure PP samples.     

Fracture mechanical behavior of concrete and the condition of its fracture surface

In this research project, a series of uniaxial, deformation controlled tensile tests were performed in order to study the fracture mechanical behavior of concrete. The parameters under investigation were the strength of concrete, curing conditions, concrete temperature and loading rate. The fracture surfaces of the tested specimens were investigated in detail and their condition was quantified using the fractal geometry. The evaluation of the experimental results and the results of the fractological investigation displayed correlations between the shape of the stress-crack opening relation of concrete and the values of the roughness as well as the fractal dimension of its fracture surface for all parameters under investigation. Relationships were drawn between the individual material as well as test parameters and the degree of concrete heterogeneity, which proved to be decisive for the formation and propagation of cracks in concrete. It was concluded that the roughness of the fracture surfaces might be considered as a representative replica of the crack system correlating directly with the concrete heterogeneity.