Hardness Hv Research Articles

The physical characteristics of tetragonal FeAl2 under pressure

Using the quasi-harmonic Debye model combine with density functional theory, the lattice structure, elastic constants, polycrystalline moduli, hardness, the Debye temperature θD and heat capacity at constant volume Cv of t-FeAl2 are investigated. The lattice parameters obtained through theoretical simulations are in excellent agreement with the X-ray powder diffraction measurement results. The elastic constants Cij reveal that t-FeAl2 is mechanically stable, with all Cij increasing monotonically as pressure rises. The phonon dispersion curve confirms the dynamical stability of t-FeAl2. Furthermore, the polycrystalline moduli were estimate by the Hill approximation. The ratio of bulk modulus and shear modulus, Poisson's ratio σ and the Vickers hardness Hv under pressure are also calculated. Our results reveal that t-FeAl2 is a hard material with a high Hv that behaves brittlely. Finally, the temperature and pressure-dependence of Cv and θD in the range of 0–1600 K and 0–60 GPa have been obtained and discussed. The results show that the effect of temperature on Cv is more significant than that of pressure, while the pressure has a greater influence on the θD than that of temperature.

Significantly toughened PZT-based piezoelectric ceramics simultaneously keeping excellent electrical properties via incorporating trace amount of yttria-partially-stabilized zirconia

Piezoelectric ceramics are prone to cracking during functioning due to the repetitively applied high stress. Hence, toughened ceramics with robust microstructures are highly desired for resisting the potential cracks. Toughening of Lead Zirconium Titanate (PZT) based piezoelectric ceramics with high d33·g33 for ignition applications is investigated in this work. Yttria-partially-stabilized zirconia (YPSZ) particles were incorporated into the PZT-based piezoelectric ceramics via conventional solid state reaction. Measurements of mechanical properties of as-sintered ceramics indicate that incorporation of an appropriate amount of YPSZ significantly improves the fracture toughness of PZT-based ceramics by 38.7%, meanwhile the piezoelectric coefficient still remains at a high level with a decrease of less than 7%. When doping 0.5 wt% YPSZ, the optimal comprehensive properties can be obtained as follows: fracture toughness KIC = 1.41 MPa·m1/2, Vickers hardness HV = 4.60 GPa, piezoelectric coefficient d33 = 462 pC/N, planar electromechanical coupling factor kp = 60.1%, and dielectric constant ε33T/ε0 = 1750. This successful toughening mechanism paves a way in developing functional ceramics simultaneously possessing superior fracture toughness and electrical properties via doping an appropriate content of YPSZ submicron particles.

Enhancing thermoelectric and mechanical properties of p-type Cu3SbSe4-based materials via embedding nanoscale Sb2Se3

Cu3SbSe4, a promising p-type thermoelectric (TE) material consisting of earth-abundant, nontoxic, cost-efficient and eco-friendly constituent elements. However, its low TE performance is relatively poor because of the low carrier concentration and mobility. Herein, we synergistically optimize the electrical and thermal transport properties of Cu3SbSe4 via embedding nanoscale Sb2Se3. The Sb2Se3 nanophase markedly increases the carrier concentration and carrier effective mass simultaneously, resulting in a higher power factor of ∼1100 μW m−1 K−2. Surprisingly, Sb2Se3 nanophase induces high-density phase boundaries and dislocations, which significantly depress the lattice thermal conductivity. The multiple effects of incorporation of Sb2Se3 boost Cu3SbSe4 to an outstanding ZT value of ∼0.86 at 673 K for Cu3SbSe4 +1.5 mol% Sb2Se3 composite, which is ∼1.70 times as high as that of pristine Cu3SbSe4. It is highly remarkable that Cu3SbSe4 with nanoscale Sb2Se3 is mechanically robust, showing the Vickers hardness (Hv) and fracture toughness (KIC) of ∼2.54 GPa and ∼0.73 ± 0.02 MPa m½, which are ∼20% and ∼12% higher than those of pristine Cu3SbSe4, respectively. This work provides guidance for enhancing the comprehensive TE and mechanical properties of the copper-based chalcogenides by embedding nanophases.

High strength, high conductivity and good softening resistance Cu-Fe-Ti alloy

Cu alloys with high strength, high electrical conductivity (EC) and good softening resistance (SR) are urgently needed in many fields. A Cu-1.06 wt% Fe-0.44 wt% Ti alloy was designed concerning the calculation of phase diagrams. It was expected that the Fe2Ti phases could precipitate to obtain high performance. The designed alloy was prepared and it obtained the most excellent properties of 211 HV hardness, 542 MPa tensile strength, 9.8% uniform elongation, 79% IACS EC and 575 °C softening temperature after solid solution, cold rolling (90% reduction of thickness) and aging at 450 °C for 24 h. The Fe2Ti phases indeed precipitated in the Cu matrix, which proved the alloy design idea. The precipitation kinetics, interaction between recrystallization and precipitation, and the effects of precipitation on strength, EC and SR were discussed. It was concluded that the precipitation driving force of the Fe2Ti phase itself in Cu was weak, and the cold rolling could significantly promote the precipitation. The precipitation of Fe2Ti slowed down the recrystallization to a certain extent. The high strength and high EC were mainly due to the precipitation strengthening and purification effects of the Fe2Ti precipitation on the Cu matrix. Besides, the good SR was mainly due to the low diffusion rate of Fe in Cu and the weak precipitation driving force of Fe2Ti.

Composition optimization of Zr55Cu30Al10Ni5 bulk metallic glass using cluster formula approach

Compositions of typical binary and ternary bulk metallic glasses have previously been interpreted via a cluster formula approach, i.e., a good glass former is formulated by a nearest-neighbor cluster matched with one or three glue atoms, with a free electron number per unit formula approaching 24. In this study, a classical quaternary glass composition Zr55Cu30Al10Ni5, representative of bulk metallic glasses of complex chemistry and dual-glassy structure, is interpreted and optimized using a dual-cluster formula approach, i.e., a chemical formula representing two single-cluster formulas. First, the number of atoms in the dual-cluster formula is estimated from combinations of all possible single-cluster formulas of the major devitrification phase CuZr2, which ranges from 28 to 34. Second, the free electron number of each element is estimated using the Cu-Zr single-cluster formulas. Third, the reference composition Zr55Cu30Al10Ni5 is approximated into integer forms of 27 to 36 atoms and their free electron numbers are calculated using the assigned free electron numbers of the elements. The so-formulated compositions are examined for glass forming abilities via copper-mold arc melting. The atomic densities, the critical temperatures, the HV hardness, the volume fractions of the glassy phase in the ingots, and the activation energies of crystallization all point to a 32-atom chemical formula Zr17Cu10Al3Ni2 (Zr53.13Cu31.25Al9.38Ni6.25) as the optimal glass former, with its electron number per unit formula falling slightly below 48. This work confirms the 24-electron rule for single-cluster formulas and provides an easy route towards understanding the complex chemistries of bulk metallic glasses via multiple single-cluster formulas.

The Precipitation Behavior of a Cu-Ni-Si Alloy with Cr Addition Prepared by Heating-Cooling Combined Mold (HCCM) Continuous Casting.

A Cu-Ni-Si alloy containing (Ni + Si) ≥ 5 wt.%, with the addition of Cr, is fabricated by HCCM continuous casting and two steps of aging treatment. The evolution of the microstructures and precipitations, as well as the effect of Cr atoms, is studied in this paper. An excellent combination of mechanical property (hardness HV 250–270) and electrical conductivity (46–47 %IACS) is obtained by the first step aging at 500 °C for 0.25 h and the second step aging at 450 °C for 1 h. The cold rolling and aging process are directly conducted on the solution treated specimens fabricated by HCCM continuous casting process without hot deformation, since the excellent homogeneity of matrix is obtained by solution treatment with δ-Ni2Si precipitates dissolved. It is found that the formation of discontinuous precipitation is suppressed by the formation of Cr3Si cores of 5–10 nm before the formation δ-Ni2Si. Then, the nucleation and growth of δ-Ni2Si precipitates occurs around the boundaries of these Cr3Si cores, leading to an enhanced nucleation rate. This study provides a promising direction for the design and optimization of Cu-Ni-Si alloys based on the further understanding of the effect of the addition of Cr.

Measurement of aluminum alloys plasticity under their dynamic and static loading by the Vickers pyramid

The paper considers the possibility of assessing the plasticity of aluminum alloys and aluminum matrix composites by the method of quasi‑static and micro‑impact indentation at pre‑impact velocities in the range of 1–3 m/s. It is proposed to use a pyramidal Vickers indenter for testing, which allows creating a constant amount of deformation. The characteristic plasticity values for industrial aluminum alloys and aluminum matrix composites of the Al‑Fe‑Cr system δ=0.83–0.98 are established. The influence of the deformation rate on the dynamicity coefficient Kd, which is the ratio of dynamic and static hardness, is shown. It was found that the increase in Kd for aluminum matrix composites is more significant than for other materials. At the same time, the well‑known expression linking plasticity with other mechanical characteristics: hardness HV and modulus of elasticity E, is not fulfilled for the studied aluminum matrix composites. The difference in the values of δ, calculated based on the parameters of the print and as a function of E/HV, can serve as an additional sign of the atypical behavior of materials during deformation.

Role of active slip systems induced with holmium impurity in Bi-2212 ceramics on mechanical design performance and morphological properties

Effect of Ho/Bi partial replacement in Bi2.1-xHoxSr2.0Ca1.1Cu2.0Oy (Bi-2212) superconductors on the fundamental structural, morphological and mechanical performance properties are investigated by Scanning Electron Microscopy (SEM) and Vickers hardness (Hv) measurement techniques. Crystallinity quality and surface morphology including the microcrystal coalescence orientations, grain alignment distributions, microscopic structural problems, microvoids, internal defects, uniform surface view, porosity and particle growth distribution are visually examined with the aid of SEM. Basic mechanical performance and characteristic features of Bi/Ho substituted Bi-2212 superconducting ceramics (0.00 ≤ x ≤ 0.10) are also determined with Vickers tests conducted at various loads intervals 0.245–2.940 N. Experimental findings show that the characteristic features enhance seriously in case of x = 0.01 due to refinement of crystallinity quality and slip systems. Thus, the optimum Ho concentration presents the highest mechanical fracture strength to the load applied as a result of better uniform surface appearance and grain orientations, well-connected flaky layers, larger particle size distribution and denser structure, confirmed by the SEM investigations. Namely, much more load is required to accelerate the dislocation movement and crack propagation to the terminal velocity for critical size growth. The fracture predominantly takes place in the transcrystalline regions and hence the propagations are easily controlled with the optimum Ho dopant ions. On the other hand, the increase in the Ho ions in Bi-2212 structure induces the crack-initiating defects for new stress concentration sites. In conclusion, the permanent and non-recoverable deformations appear at even lower indentation test loads. All samples present indentation size effect feature depending on the dominant character of elastic recovery mechanism. Further, original hardness parameters are semi-empirically analyzed in the plateau limit regions using mechanical modelling approaches for the first time. Based on the analyses, Hays–Kendall model exhibits the closest results to the experimental findings.

Study of mechanical properties and wear resistance of nanostructured Al 1100/TiO2 nanocomposite processed by accumulative roll bonding

Aluminum (Al) composites have been extensively developed for automotive applications due to their high specific strength. Therefore, in this study, an Al-titanium dioxide (TiO2) nanocomposite was processed using the accumulative roll bonding (ARB) process. The mechanical characteristics of monolithic and nanocomposites specimens made with 0, 1, 2, and 3 wt% TiO2 nanoparticles as reinforcement were studied at several ARB passes. According to the microstructure of the composites, rolling after five passes achieves a homogenous distribution of reinforcement particles, ultrafine and elongated grains of the matrix. After five ARB passes, the TiO2 particles were uniformly dispersed. Finally, scanning electron microscopy and energy dispersive spectroscopy revealed that the Al-TiO2 nanocomposite had an appropriate dispersion of TiO2 nanoparticles. Vickers microhardness improves as the number of accumulative roll bonding passes increases. Furthermore, after five passes, Vickers microhardness testing revealed that the sample with 3%TiO2 has the greatest hardness value of 112 HV, which is significantly greater than the 44 HV hardness value of the ARB-processed aluminum. The mechanical properties of the specimens, yield and ultimate strengths, improved with the addition of TiO2 nanoparticles. Due to good bonding among the components, mechanical parameters such as microhardness and tensile strength were more than three times better than the Al matrix.

Production of transverse magnetic field annealed brass band and how the production process influences the mechanical properties, as well as their correlation and compliance

This paper examines the effect of the thickness h, the deformation reached during the last cold rolling operation ε and the final normalized annealing mode v on the mechanical properties of brass band. The paper looks at the correlation between the ultimate strength σв, elongation and hardness HV in terms of their meeting the specification. The production of L68 brass band involved semi-continuous casting, hot rolling to the thickness of 6 mm and cold rolling to h = ~0.56–0.96 mm with intermediate annealing at H = 1.5–2.7 mm ensuring the deformation ε within 62 to 72%. The intermediate and final continuous annealing lines are equipped with three-phase TFIH (Transverse Flux Induction Heating) units. An intermediate annealing mode has been established that ensures the grain size of 40–80 μm. The strip travel speed was varied as follows during final annealing: ν = 30–46 m/min. The authors determined the stochastic dependences of the properties on ν , h and ε, as well as the annealing modes that are necessary to achieve each property. Actual correlations HV(σв), δ(σв) within the specified ranges were considered versus the properties of the band produced by deformation. It was established that the cold rolling process, together with the heat treatment mode, has an effect on the properties of annealed band and, vice versa, on the heat treatment mode that is necessary to achieve the required properties. With hardness being the same, the induction heat annealed brass band has a higher ultimate strength в than the band produced by normalized final deformation. As a result, the linear relationship σв = f(HV) of the rolled band produced by normalized final annealing is shifted in relation to the optimum position of such relationship within the specified limits adopted in the period when the rolled band was exclusively produced by final deformation. Consequently, the final annealing mode ranges that are necessary for achieving certain properties within the specified ranges, do not match, thus making the task of having the resulting properties hit the above ranges more challenging. Thus, it is proposed to use online control and annealing control to eliminate rejects, and to use the annealing mode-required property relationships obtained from the given data for setting up the initial process mode.

Anodizing parameters optimization of Ti–6Al–4V titanium alloy using response surface methodology

The present paper depicts application of response surface methodology (RSM) for optimizing the anodizing parameters of Ti–6Al–4V (TA6V) titanium alloy. Three operating parameters, i.e., voltage (V), temperature (T) and time (t), are designed as factors by using RSM design. Reliable regression models were established between the input parameters and the given responses, namely oxide thickness (e), Vickers hardness (Hv) and polarization resistance (Rp) with regression coefficients multiples of 0.940, 0.925, 0.865, respectively, indicating good agreement between the experimental values and those predicted using the quadratic model.The predicted values of V (42.67 V), t (45.9 min) and T (29.5 °C) are the optimal anodization combination leading to a TiO2 layer with the best compromise between the oxide thickness (28.7 μm), Vickers hardness (321.90) and bias resistance (6.37 MΩ cm2). It was observed that the hardness characteristic is more affected by anodizing time and temperature, and less sensitive to voltage and parameter interactions. Polarization resistance is strongly influenced by voltage, modestly influenced by anodizing time and temperature, and less sensitive to parameter interactions. Moreover, higher anodizing parameters lead to higher thickness. Therefore, RMS could be a suitable method to optimize anodizing parameters of titanium alloys.

Influential Parameters and Multi Objective Optimization of Bagasse and Palm Kernel Natural Fibre Plates Using Taguchi Assisted Topsis

Composites that have a good to lower weight ratio can be used to replace conventionally used Engineering Materials. The properties of natural fibers are almost equal to that of artificial fibres. Natural fibers can be used in many applications and is also a cost-effective material. Bagasse fibre reinforced with dry palm kernel fibre powder is used to improve mechanical properties and fabricated in plate form. In this research work, the input constraints that have been used to fabricate the plate are 10, 20, 30 wt% of bagasse fibre, 10, 20, 30 wt% of palm kernel fibre, at 10, 15, 20 MPa compression pressure and 2, 4, 6 mm of speciemn thickness respectively. The optimization has been performed by Taguchi L27 orthogonal array and influence of output parameters viz. Tensile Strength (MPa), Flexural Strength (MPa) and Hardness (Hv) have been measured by using statistical analysis of variance. The multi-criteria decision making of the output parameters has been performed by Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). This research offers new insight into decision-making, particularly in the optimization part, to increase the strength and mechanical property of natural fiber composites.

MICROSTRUCTURE, MECHANICAL PROPERTIES AND GEOMETRY OF A MODEL BATCH OF SEMI-SPHERICAL STEEL LINERS INTENDED FOR USE IN THE EXTRACTIVE INDUSTRY

The article presents the results of investigation of the microstructure and mechanical properties of Fe-based materials intended for the production of semi-spherical liners for experimental shaped charges. The tests were carried out on samples taken in three directions in relation to the rolling direction: 0°, 45° and 90°, of the following materials: cold-rolled sheets made of DC04 steel, hot-rolled sheets made of 04J steel, and cold-rolled strips made of 004G steel developed at Łukasiewicz – IMŻ and annealed at 650°C. Semi-spherical drawpieces with a diameter of 106.4 mm, intended for liners, were made of the sheets with the use of cold stamping. Tests of the microstructure and HV hardness of samples taken from the test batch were carried out on cross-sections along the pressing direction and the model batch – on sections transverse to the stamping direction The geometry of the model batch drawpieces was also measured. The ferrite grain size evaluation was performed according to the ASTM E112 standard using μgrain software with a grain size evaluation module using counting the number of intersections of grain boundaries with a circle.

(INVITED)Effects of LiF sintering additive on the microstructure and mechanical properties of hot-pressed CaF2 transparent ceramics

CaF2 raw powders were synthesized by the chemical precipitation technique, and CaF2 ceramics with LiF sintering additives were fabricated by the hot-pressing (HP) sintering technique. The effects of LiF sintering additives on the optical transparency, microstructure and microhardness of CaF2 ceramics were investigated. The CaF2 ceramic with 0.05 wt% LiF exhibiting the best transparency, and the transmittance at 500 nm and 1800 nm are 71.5% and 87.8%, respectively. The average grain size of CaF2 ceramics increases with rising the amount of LiF from 0 to 1 wt%, while, the Vickers hardness (Hv) decreases. The average grain size, Hv, and fracture toughness (KIC) for the CaF2 ceramic with 0.05 wt% LiF are 85.6 ± 6.2 μm, 2.24 ± 0.06 GPa, and 0.11 ± 0.02 MPa m1/2, respectively.

Synthesis, microstructure and indentation Vickers hardness for (Y3Fe5O12)x/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ composites

High-performance and low-cost composites are engineers’ dream for technological applications. To fulfill the material for an engineering application, it is important to understand the mechanical properties of the material. The primary goal of this research is to investigate the impact of nano-sized Yttrium iron garnet (Y3Fe5O12) addition on the microstructure and mechanical properties of the polycrystalline Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223) superconductor. Co-precipitation and solid-state reaction methods were utilized to prepare Y3Fe5O12 nanoparticles and Cu0.5Tl0.5Ba2Ca2Cu3O10-δ superconductor, respectively. (Y3Fe5O12)x/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ nanoparticle/superconductor composites were formed by adding small contents of Y3Fe5O12 (x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10 wt%) to the CuTl-1223 matrix. The volume fraction percentage of the main phase, CuTl-1223, was increased from 87.9 to 91.4% as x was adjusted from 0.00 to 0.04 wt%. The unit cell parameters (a and c) remained unchanged following the addition of Y3Fe5O12 nanoparticles to the host CuTl-1223. The porosity percentage (P %) was decreased from 39.1 to 29.4% as x was increased from 0.00 to 0.10 wt%. Thus, the addition of Y3Fe5O12 nanoparticles has the ability to reduce weak links and voids among the CuTl-1223 superconducting grains. The grain morphology for the prepared composites was identified through scanning electron microscopy. The different elemental compositions were detected by energy-dispersive X-ray measurements. Vickers microindentation hardness test was employed to study the mechanical strength of the prepared composites. Analysis and modelling of Vickers hardness (Hv) versus test load (F) were done through various models. Meyer’s empirical law showed that all the prepared composites follow normal indentation size effect behaviour. Hays and Kendall model clarified that the applied test load was sufficient to produce both elastic and plastic deformation for the investigated samples. The elastic/plastic deformation model indicated that the prepared samples contain an elastic relaxation portion that recovers after withdrawing the test load. The proportional sample resistance and modified proportional sample resistance models confirmed the HK model findings. Moreover, the HK model was found to be the most suitable model for describing the microhardness results of the prepared samples. Furthermore, the elastic modulus (E), yield strength (Y), fracture toughness (K) and brittleness index (B) for the prepared composites were calculated as function of Y3Fe5O12 addition.

Plastic Zr-Al-Ni-Cu-Ag bulk glassy alloys containing quasicrystalline or β-Zr plus ω-Zr phases

Zr70–76Al7–7.5Ni13–15Cu2Ag2–5 glassy alloys were prepared by melt-spinning with Zr contents up to 76 at.%, greatly exceeding the highest Zr content of 70 at.% previously reported for Zr-based glassy alloys exhibiting a calorimetric glass transition. The 70–72Zr and 74Zr alloys were also cast as bulk rods up to 1.5 mm in diameter with glass and [glass + β-Zr + ω-Zr] phases, respectively, by ejection copper-mold casting. The crystallization temperature and Vickers hardness Hv for the glassy ribbons decrease with increasing Zr content from 70 to 76 at.%. The glassy rods show high yield strength (σy) of 1225–1346 MPa, high fracture strength (σf) of 1497–1499 MPa, and large compressive plastic strain (εp) of 9.7–3.2% for the 70–72Zr alloys. Similarly, the 74Zr rod with [glass + β-Zr + ω-Zr] phases shows σy of 1325 MPa, σf of 1472 MPa, εp of 2.4%. The 76Zr thick ribbon with [glass + β-Zr + ω-Zr] phases shows, in tension, high σy of 890 MPa, σf of 988 MPa, and plastic elongation of 0.3%. The Zr-rich glassy ribbons crystallize, showing three exothermic peaks upon heating. The first-stage peak is due to the precipitation of icosahedral quasicrystal (IQ) for the 70–72Zr ribbons, and β-Zr + ω-Zr for the 74–76Zr ribbons. These annealing-induced mixed-phase ribbons with Zr content above 72 at.% exhibit good bending plasticity, even though their HV is about 41% higher than for the as-spun glassy ribbons. Similarly, the 70Zr bulk rod, with [glass + IQ] phases obtained by annealing, shows a distinct increase in σy and σf to 1485 and 1575 MPa, respectively, as well as εp of 0.6%. Thus, the plastic Zr-rich bulk rods with glass, [glass + IQ], and [glass + β-Zr + ω-Zr] phase mixtures are encouraging for the future development of a new type of high-strength structural material.

DFT calculations of elastic, electronic and thermal properties of TiB2Mo

Abstract Ceramics are materials with good mechanical properties; however, low fracture toughness, intrinsic brittleness and poor resistance against oxidation at high temperatures are challenges limiting their applications. TiB2Mo is a ceramic material whose all elastic properties have not been calculated. In this study, we investigated the elastic, electronic and thermal properties of TiB2Mo structure using first principles calculations. All first principles calculations were based on the density functional theory as implemented in Quantum ESPRESSO code with the help of Thermo−pw as a post-processing code. Obtained lattice parameters of TiB2Mo structure were in good agreement with other previous theoretical studies. TiB2Mo structure was found to be mechanically and dynamically stable at ground state conditions. The results also show that TiB2Mo is brittle, anisotropic and metallic in nature. Based on the calculated Vicker’s hardness Hv, we noted that TiB2Mo is classified as a hard material with fracture toughness of above 7 MPam0.5; therefore, it is a promising ultra-high temperature ceramic.

Lithium disilicate and zirconia reinforced lithium silicate glass-ceramics for CAD/CAM dental restorations: biocompatibility, mechanical and microstructural properties after crystallization

ObjectivesThe objective of this study was to define the impact of heating rate on the crystal growth, the mechanical properties, and the biocompatibility of three different kinds of CAD/CAM glass-ceramics treated with a conventional furnace. MethodsLithium disilicate (IPS EMax-CAD, Ivoclar Vivadent) (LS2) and two zirconia reinforced lithium silicate (ZLS) ceramics (Vita Suprinity PC, VITA Zahnfabrik; Celtra Duo, Dentsply Sirona) (ZLSS; ZLSC) were used. The mechanical properties and the crystal growth were evaluated on 42 specimens (n = 14 per group). The thermal treatments recommended by the manufacturers were carried out. All groups were tested for fracture toughness (Ft) and Vickers hardness (Hv). Scanning electron microscope (SEM) images were taken after a slight surface etching with hydrofluoric acid solution (1% for 20 s). Differential Thermal Analysis (DTA) was performed and cellular adhesion with human periodontal ligament stem cells (hPDLSCs) culture was qualitatively assayed. Data were analyzed with Repeated Measurements ANOVA and ANOVA followed by Tukey post hoc test. ResultsThe crystals’ mean size (±SD) after heat treatment was 1650.0 (±340.0) nm for LS2, 854.5 (±155.0) nm for ZLSS and 759.9 (±118.4) nm for ZLSC (p < 0.05 among the groups). As consequence of crystallization, the Hv was 6.1 ± 0.3 GPa for LS2, 7.6 ± 0.7 GPa for ZLSS and 7.1 ± 0.5 GPa for ZLSC (p < 0.05 for LS2 vs ZLSS and ZLSC), while the Ft was 2.2 ± 0.1 MPa m1/2 for LS2, 4.7 ± 0.8 MPa m1/2 for ZLSS and 3.8 ± 0.6 MPa m1/2 for ZLSC (p < 0.05 among the groups). The DTA curves showed a crystallization process for LS2, ZLSS and ZLSC at a temperature range 810–840 °C. The amount of adherent hPDLSCs was superior on LS2 than on ZLS. ConclusionsAll the CAD/CAM materials can be properly crystallized if heat treated following the manufacturers’ instructions. The crystallization process highly depends on temperature. ZLS glass ceramics show significantly inferior crystals dimensions and higher fracture toughness and Vickers hardness than LS2 ceramic. hPDLSCs cultured on LS2 have a superior adhesion than those cultured on ZLS. Clinical significanceThe value of this study relies on the demonstration that a proper heat-treatment of CAD/CAM lithium disilicate and ZLS glass ceramics generates products that are suitable for clinical use . The differences highlightable in mechanical properties and biocompatibility behavior do not affect their successful clinical application.

Effects of an external electric field applied during the solution heat treatment of the Al-Mg-Si-Cu alloy AA6111

Abstract The application of an external dc electric field during the solution heat treatment (SHT) of AA6111 Al alloy increased the as-quenched resistivity ρ and hardness H v. The increases represented reductions in SHT of 10–20 K required for a constant ρ or H v. Analysis of the results gave that the field reduced both the enthalpy and entropy of solution. The resulting reduction in Gibbs free energy gave increases of 0.03–0.04 at.% in solubility of Mg2Si (or Al –Mg– Si – (Cu)-vacancy complexes) at 400 –600 °C, amounting to a factor of 33% increase in solubility at 400 °C and 6% at 600 °C.

Results of metallographic observations of cultivator shares after spot electromechanical processing

Presented are the results of metallographic studies of the structure and properties of a cultivator share, hardened by spot electromechanical processing in its various high-wear areas. In the process of research, the manufacturer was offered recommendations on the technology of forming parts in the process of their manufacture. It has been established that spot electromechanical processing allows to obtain hemispherical hardened areas with a hardness of HV 7000 ... 7600 MPa, which will provide the effect of self-sharpening of their cutting parts during the operation of the cultivator shares. Spot electromechanical processing with two tools allows to provide through hardening of the cultivator share along the ends of the share wings. The proposed technology for hardening cultivator shares during their manufacture and repair will increase the durability of these parts during their operation.