Values Of HV Research Articles

Effect of polymer composition on mechanical and tribotechnical properties in a friction pair with steel

The article presents the results of kinetic indentation and wear tests of polymer samples from ultrahigh molecular weight polyethylene (UHMWPE), high molecular weight polyethylene (HMWPE), polyethylene terephthalate (PET), polyoxymethylene (POM). The determination of the micromechanical properties of polymers was carried out on the Nanoscan-4D device. diamond triangular Berkovich pyramid with a maximum loading force of 10 mN. The values of microhardness HV, modulus of elasticity E, work on elastic deformation We, work on plastic deformation Wp were obtained. Wear tests were performed on a friction machine with a vertical axis of rotation according to the scheme: “three steel balls rigidly fixed in a mandrel (steel ShКh15) - the wide side of a rectangular polymer sample” without the use of lubricant at normal temperature. Patterns of changes in the depth of wear holes were established depending on the composition of the polymer. PET samples had minimal wear and had maximum wear resistance, followed by POM, UHMWPE and HMWPE samples in descending order of wear resistance. The microhardness values of the samples were determined, and its minimum values were obtained for UHMWPE, and the microhardness of PET, HMWPE and POM samples was 4.47, 1.45 and 1.18 times higher than that of UHMWPE, respectively. The work of elastic–plastic deformation had maximum values on UHMWPE samples, and minimum values on PET samples.

Effect of Nystatin Coated Copper Oxide (CuO) Particles on Mechanical, Thermal, and Antifungal Properties of Polymethyl Methacrylate (PMMA)–Based Denture Materials

Polymethyl methacrylate (PMMA) has garnered significant attention in the field of dentistry due to its wide applications. This paper proposes the incorporation of the nystatin coated copper oxide (CuO) particles having desirable conductivity and antifungal properties, as a filler in the PMMA denture to address their low thermal conductivity, low impact strength, low fatigue resistance, and microbial adhesion. The prepared nystatin coated CuO particles were characterized with several analytical techniques. The nystatin coated CuO particles were mixed in different ratios (0%, 1%, 2%, and 4%) in PMMA corresponding to groups C, E1, E2, and E3, respectively. The prepared samples of composite PMMA with nystatin coated CuO were evaluated to determine their transverse strength, impact strength, Vickers hardness (HV), and thermal conductivity. Furthermore, antifungal properties of CuO particles, nystatin coated CuO particles, and their acrylic composites were evaluated against Candida albicans. Scanning electron microscopy (SEM) analysis confirmed the particles’ spherical and irregular shapes. The particle sizes range from nano to micron level. Fourier‐transform infrared spectroscopy (FTIR) and energy dispersive X‐ray spectroscopy (EDX) analysis confirmed the coating of nystatin on CuO. X‐ray diffraction (XRD) analysis showed the diffraction patterns and planes of CuO monoclinic shape structure. The composite prepared to have higher values of HV (19.53 ± 0.65, 20.16 ± 0.37, and 21.11 ± 0.75, respectively) as compared to the control. The impact strength values were measured high at 14.12 ± 5.55 kJ/m2 for 2% containing nystatin coated CuO acrylic resins compared to control and other groups. The conductivity increased linearly with the addition of CuO particles. The addition of CuO particles causes a reduction in flexural strength as compared to the control group. As the concentration of nystatin coated CuO (1%, 2%, and 4%) in acrylic samples increased, the antifungal properties were improved. Thus, the incorporation of optimized concentrations of nystatin coated CuO particles in acrylic resin resulted in the improved mechanical, thermal, and antifungal properties.

A Study on Electromagnetic Riveting Behavior of High-Strength Rivets Depending on Hardness

Recently, the application of aluminum based on ultra-high strength steel is expanding around high-end models of electric vehicles, so it is necessary to develop strategic welding/joining technologies for these materials. In the case of overseas advanced automobile companies, such development is being carried out at the level of introducing mass production facilities through the development of joining technology, but in Korea, the localization rate of original core technology and related equipment in the field of welding and joining is still very insufficient. Therefore, in this study, in order to develop a high-strength rivet suitable for the rivet process during the multi-material bonding process, cold forging steel was used to attain an appropriate level of hardness through changes in the microstructure through heat treatment. Rivets with different hardness were fabricated through heat treatment, and flaring and tensile test were conducted. As a result of flaring test of rivets, buckling occurred with hardness values of Hv 447 and 486, while cracks occurred without buckling in rivets with hardness values of Hv 506. But as a result of tensile shear test using GA980 and Al5052 materials, there was no significant difference in tensile shear load values according to hardness values of the rivets.

Low-temperature and single-step synthesis of fully-dense MgAl2O4 by reaction spark plasma sintering Al2O3 and MgO nano-oxides

The availability of commercial nano-powders and the rapidly maturing powder metallurgy technology have enabled researchers to develop advanced ceramics, with tailored microstructure and improved properties. However, a major challenge in the production of MgAl2O4, from Al2O3 and MgO, is the relatively high-volume expansion (5–8%) accompanying spinellization. This study demonstrates the possibility to prepare fully-dense and single-phase magnesium aluminate spinel, at low temperature and in short time, without the use of a sintering aid. This is achieved by sonication of magnesia and alumina followed by reaction spark plasma sintering. X-ray powder diffraction and scanning electron microscopy methods were used to characterize the starting nano-powders, sonicated powder mixture, spinel formation, and fractured specimens. The values of HV, K1c, and GIC were obtained from indentation measurements. The chemical composition, the SEM images, and the X-ray maps of magnesium and aluminum, confirmed the stoichiometry and homogeneity, at nano scale, of the densified specimens. The fully dense spinel, obtained at 1300 °C and 30 min, had average grain size of 40.92 nm, HV of 17.29 ± 0.185 GPa, K1c of 2.129 ± 0.106 MPa mm1/2, and GIC of 15.488 J/m2.

First Demonstration of Space-Borne Polarization Coherence Tomography for Characterizing Hyrcanian Forest Structural Diversity

Structural diversity is recognized as a complementary aspect of biological diversity and plays a fundamental role in forest management, conservation, and restoration. Hence, the assessment of structural diversity has become a major effort in the primary international processes, dealing with biodiversity and sustainable forest management. Because of prohibitive costs associated with the ground measurements of forest structure, despite their high accuracy, space-borne polarization coherence tomography (PCT) can introduce an alternative approach given its ability to provide a vertical reflectivity profile and spatiotemporal resolutions related to detecting forest structural changes. In this study, for the first time ever, the potential of space-borne PCT was evaluated in a broad-leaved Hyrcanian forest of Iran over 308 circular sample plots with an area of 0.1 ha. Two aspects of horizontal structure diversity, including standard deviation of diameter at breast height (σdbh) and the number of trees (N), were predicted as important characteristics in wood production and biomass estimation. In addition, the performance of prediction algorithms, including multiple linear regression (MLR), k-nearest neighbors (k-NN), random forest (RF), and support vector regression (SVR) were compared. We addressed the issue of temporal decorrelation in space-borne PCT utilizing the single-pass TanDEM-X interferometer. The data were acquired in standard DEM mode with single polarization of HH. Consequently, airborne laser scanning (ALS) was used to estimate initial values of height hv and ground phase φ0. The Fourier–Legendre series was used to approximate the relative reflectivity profile of each pixel. To link the relative reflectivity profile averaged within each plot with corresponding ground measurements of σdbh and N, thirteen geometrical and physical parameters were defined (P1−P13). Leave-one-out cross validation (LOOCV) showed a better performance of k-NN than the other algorithms in predicting σdbh and N. It resulted in a relative root mean square error (rRMSE) of 32.80%, mean absolute error (MAE) of 4.69 cm, and R2* of 0.25 for σdbh, whereas only 22% of the variation in N was explained using the PCT algorithm with an rRMSE of 41.56%. This study revealed promising results utilizing TanDEM-X data even though the accuracy is still limited. Hence, an entire assessment of the used framework in characterizing the reflectivity profile and the possible effect of the scale is necessary for future studies.

Effects of the addition of multi-walled carbon nanotubes on the microstructure and properties of Ti(C,N)-based cermets prepared by spark plasma sintering

To improve the toughness of Ti(C,N)-based cermets, multi-walled carbon nanotubes (MWCNTs) and nano-WC were added, and spark plasma sintering (SPS) technology was applied. The effects of the addition of MWCNTs on the phase composition, microstructure, and the comprehensive properties of Ti(C,N)-based cermets were investigated. The results show that the cermet (0.4 wt% MWCNTs) prepared by SPS (1350 °C, 16 min, and 35 MPa) has uniform microstructure and excellent comprehensive properties. The hardness and fracture toughness of this sample reach maximum values of HV 3050.29 and 10.90 MPa·m1/2, respectively. Compared with the sample without MWCNTs, the values are increased by 82.57% and 105.66%, respectively. A small number of carbon atoms from the MWCNTs enter the lattice of Ti (C,N) solid solution, which is conducive to improving the bonding ability and high-temperature wettability between MWCNTs and the matrix, thus enhancing the strength and toughness of the matrix materials. The addition of MWCNTs plays a bridging and toughening role at different interfaces. Moreover, the addition of nano-WC is conducive to the plastic flow and particle rearrangement of hard particles at high temperature.

Classification of GaoFen-3 full-polarization data based on combining polarization characteristics

To explore potential applications of GaoFen-3 (GF-3) fully polarimetric synthetic aperture radar (SAR) data in ground-feature classification, we selected Jiangxiang Town, Nanchang County as the research area and used GF-3 quad-polarization strip I (QPSI) data for classification. Pauli decomposition, Krogager decomposition, and the H / A / α decomposition model were used to decompose the GF-3 full-polarization data; combined with the backscattering coefficient values of GF-3’s HH, HV, VH, and VV polarization data, feature optimization was performed, and the optimal ground-object features for feature classification were obtained. The random forest (RF) method was used to classify the optimal features, and the results were then compared and verified. The results demonstrate that the component after polarization decomposition of H / A / α is more important in classification than the original backscattering coefficient values of HH, HV, VH, and VV. GF-3 single-phase SAR data were used for ground-feature classification in a crop-intensive area of South China, and the optimal feature optimization results included H / A / α decomposition and synthesis components of the alpha, anisotropy, red, entropy, blue, green, and polarization backscattering coefficients of VV. The RF method’s classification accuracy was higher than that of the maximum-likelihood, support-vector-machine, and neural-network methods. Using this approach, GF-3 data classification’s overall accuracy was up to 78.17%, and the Kappa coefficient was 0.738. This study has clear practical significance and reference value for the selection of classification methods for ground features based on GF- 3 data in cloudy and rainy areas.

HIPIMS/UBM PVD Coating Equipment Designed to Coat Universal Sized Broaches

This paper describes a physical vapor deposition (PVD) coating equipment, as well as the according deposition parameters suitable to provide hard nitride coatings on broaches up to a length of 2.2 m. The octagonal-shaped vacuum chamber reached a height of 4.5 m and a diameter of 1.2 m. To explore a sufficient and reproducible film, an adhesion test sample and tools were subjected to a pretreatment in a Cr2+ Ar+ high-power impulse magnetron sputtering (HIPIMS) plasma prior to the actual film deposition. Two deposition methods were applied: reactive unbalanced magnetron (UBM) sputtering was introduced to deposit TiAlN-based coatings from Ti50Al50 2.5 m long targets. Alternatively, multilayer coatings were generated by reactive simultaneous UBM sputtering from Ti50Al50 and TiAl6V4 targets, respectively, and chromium targets utilizing high-power impulse magnetron sputtering (HIPIMS) technology. In the latter case, three cathodes were furnished with 0.9 m long targets lined up upon each other. A segmented UBM cathode design was described to meet economic deposition if varying tool sample lots in the deferring workpiece lengths have to be handled in industrial practice. The resulting (TiAl/Cr)N multilayer coatings attained typical hardness values of HV 2800 and an adhesion measured by critical load up to 50 N. The cutting performance of this coating was evaluated by simulated shaping tests over a test length of 210 m on C 45 steel. The (TiAlV/Cr)N showed an improved wear behavior by factor of 2 to 3 compared to TiN deposited by cathodic arc operated in an industrial PVD coater. A real comparison was undertaken, applied to a 1.3 m long model broach. (TiAl/Cr)N showed a prolongation in industrial lifetime by 150% compared to TiN.

Impact of adhesive primer and light-curing on polymerization kinetics of self-adhesive resin cement in association with free radical reaction.

This study analyzed the impact of adhesive primer and light-curing on the polymerization kinetics of urethane dimethacrylate-based self-adhesive resin cement combined with free radical reaction. Specimens were prepared by mixing the cement paste with or without adhesive primer. Subsequently, specimens were light-cured or set without light-curing. The degree of conversion (DC), Vickers hardness (Hv), and free radical concentrations were repeatedly measured up to 168h after the curing initiation. Irrespective of the curing procedures, DC, Hv, and free radical concentration rapidly increased during the initial 30min of curing. The specimens cured with adhesive primer and/or light-curing generally showed higher values of DC, Hv, and radical concentration than those set by chemical curing alone, especially during the initial polymerization phase. Kinetic analysis using a linear mixed model revealed that the adhesive primer had a higher coefficient estimate than light-curing, indicating that the former had a higher impact on the polymerization. Additionally, the adhesive primer alleviated the Hv reduction caused by water and air during the initial polymerization phase, although light-curing hardly prevented the polymerization inhibition. Therefore, we suggest that application of adhesive primer is beneficial to achieve higher degree of conversion and better mechanical properties of self-adhesive resin cements by enhancing free radical reactions.

Effect of Fe doping on structural, elastic and electronic properties of B2–ZrCu phase under hydrostatic pressure: A first-principles study

The effects of Fe doping and applied hydrostatic pressure on structural, mechanical and electronic properties of Zr8Cu8-xFex (x = 0, 1, 2, 3) are investigated via the first-principles calculations. The equation of state (EOS) is established for B2–CuZr crystalline structure. The values are in good agreement with previous experimental results. The phase stability is improved simultaneously by the substitution of Fe for Cu and enhanced hydrostatic pressure for Zr8Cu8-xFex (x = 0, 1, 2, 3). Doping concentration plays an important role in tuning the values of bulk modulus B. However, the values of Vickers hardness HV follows the sequence as: Zr8Cu6Fe2 > Zr8Cu7Fe1 > Zr8Cu5Fe3 > Zr8Cu8 (0–30 GPa). The sequence of B/G, Poisson's ratio ʋ is just opposite to that of HV. It implies a strong correlation between ductility and charge density topology (closely related to bonding character and substitutional atomic sites). Substitution of Fe for Cu tailor the metallic characteristic of Zr–Cu bond into more directional covalent characteristic of Zr–Fe bond, thus make doped Zr8Cu8-xFex (x = 1, 2, 3) harder and more brittle than non-doped Zr8Cu8. The hydrostatic pressure generally enhances the predominant metallic character of Zr8Cu8-xFex (x = 0, 1, 2, 3), thus make all doped and non-doped compositions transit into a more ductile regime. The combined effects of directional bonding and pressurizing thus make Zr8Cu6Fe2 (0 GPa) the most hard and brittle material and Zr8Cu8 (30 GPa) the most ductile material among all compositions.

A study on tribological behaviour and analysis of ZnO reinforced AA6061 matrix composites fabricated by stir casting route

PurposeThe most promising replacements for the industrial applications are particle reinforced metal matrix composites because of their good and combined mechanical properties. Currently, the need of matrix materials for industrial applications is widely satisfied by aluminium alloys. The purpose of this paper is to evaluate the tribological behaviour of the zinc oxide (ZnO) particles reinforced AA6061 composites prepared by stir casting route.Design/methodology/approachIn this study, AA6061 aluminium alloy matrix reinforced with varying weight percentages (3%, 4.5% and 6%) of ZnO particles, including monolithic AA6061 alloy samples, is cast by the most economical fabrication method, called stir casting. The prepared sample was subjected to X-ray photoelectron spectroscopy (XPS) analysis, experimental density measurement by Archimedian principle and theoretical density by rule of mixture and hardness test to investigate mechanical property. The dry sliding wear behaviour of the composites was investigated using pin-on-disc tribometer with various applied loads of 15 and 20 N, with constant sliding velocity and distance. The wear rate, coefficient of friction (COF) and worn surfaces of the composite specimens and their effects were also investigated in this work.FindingsXPS results confirm the homogeneous distribution of ZnO microparticles in the Al matrix. The Vickers hardness result reveals that higher ZnO reinforced (6%) sample have 34.4% higher values of HV than the monolithic aluminium sample. The sliding wear tests similarly show that increasing the weight percentage of ZnO particles leads to a reduced wear rate and COF of 30.01% and 26.32% lower than unreinforced alloy for 15 N and 36.35% and 25% for 20 N applied load. From the worn surface morphological studies, it was evidently noticed that ZnO particles dispersed throughout the matrix and it had strong bonding between the reinforcement and the matrix, which significantly reduced the plastic deformation of the surfaces.Originality/valueThe uniqueness of this work is to use the reinforcement of ZnO particles with AA6061 matrix and preparing by stir casting route and to study and analyse the physical, hardness and tribological behaviour of the composite materials.

Effect of ultrasonic vibration on microshear bond strength of flowable composite to enamel

Objective: The present study aimed to assess the influence of vibration effect on microshear bond strength (µSBS) of flowable composite to enamel. Material and Methods: Sixty non-carious extracted human premolar teeth were collected and randomly divided into six groups (n = 10) after being trimmed to produce a smooth flat surface: Flowable composites [Wave (SDI), Wave HV (SDI) and Grandioflow (Voco)] were used as bonding agents without or with vibration using an ultrasonic scaler (Mini Piezon, EMS, Switzerland). Composite resin, with an internal diameter of 0.7mm and height of 1mm, was cured on the substrate. The specimens’ µSBS was tested by a microtensile tester (Bisco, USA) at a crosshead speed of 0.5 mm/min. The bond strength values were analyzed using one-way ANOVA and post hoc Tukey test (p < 0.05). Results: Vibration did not lead to any significant difference in the µSBS values of Wave, Wave HV, and Grandio Flow µSBS values (P=0.690, P=1.000 and P=0.947, respectively). No significant difference was found between flowable composites in terms of micro shear bond strength to enamel (p > 0.05). Conclusions: The application of ultrasonic vibration might not be advantageous in terms of improving the shear bond strength of flowable composites to enamel. KEYWORDS Bond strength; Enamel; Flowable composite; Ultrasonic; Vibration.

Two-Lane Highways Crest Curve Design. The Case Study of Italian Guidelines

The main purpose of the research is to evaluate the crest vertical curves radii Rv, not considering a conventional value of the opposing vehicle height h2, but the average vehicle heights h2(m) and the value of the 15th percentile of the height distribution h2(15) of the passenger car population. The study only considered car models with more than 20,000 registered vehicles in Italy. One hundred and fifteen car models belonging to different brands were taken into consideration, for a total of over 9 million vehicles. For the statistical sample analyzed, the following vehicle heights were estimated: h2(m) = 1.48 m and h2(15) = 1.39 m. The deviations between the crest radii calculated with the Italian standard (h2 = 1.10 m), and those obtained for h2(m) = 1.48 m and h2(15) = 1.39 m are up to 12%. The differences ΔHv between the values of the visible vehicle body height Hv = Hv(t) calculated using, respectively, h2(15) = 1.39 m and h2(m) = 1.48 m are modest. The value h2(m) = 1.48 m could be adopted in order to reduce the highways construction costs. In fact, the research shows that the value h2 = 1.10 m is too conservative and leads to oversizing of the crest vertical curves. Therefore, it would be necessary to make an appropriate choice of h2 value in order to take into account the current heights of passenger cars.

Investigation of the microstructure and physical properties of directionally solidified ternary Al–8.8La–1.2Ni alloy

This paper systematically studies the microstructure evolution, microhardness and tensile property of Al–8.8La–1.2Ni ternary alloy with directionally solidified under a wide range of solidification rates by Bridgman-type growth apparatus. The directionally solidified microstructure of studied alloy consists aligned dendrites, and eutectics in the region between them. Primary dendrite arm spacing (λ1), secondary dendrite arm spacing (λ2) and microhardness (HV) were measured from both transverse and longitudinal sections of many samples. Also, ultimate tensile strength (σuts), tensile yield strength (σtys), ultimate compressive strength (σucs) and compressive yield strength (σcys) of the solidified many samples at room temperature the dependence of solidification rate (V) were carried out. The present results show that the solidification rate can change both microstructure and mechanical properties effectively. According to these results, it has been found that, for increasing values of V, the values of λ1 and λ2 decrease, the values of HV, σuts, σtys and σcys increase. Relationships between microstructural parameters (λ1, λ2) and mechanical properties (HV, σuts, σtys and σcys) expressed as function of solidification rate using a linear regression analysis method.

Structural and elastic properties, Vickers hardness and Debye temperature of (B1) BP: DFT study

A theoretical study of the structural parameters and elastic constants of boron phosphide (BP) compound with cubic rocksalt structure has been carried out using ab-initio density functional theory (DFT) and density functional perturbation theory (DFPT) calculations based on the plane-wave and pseudopotential (PW-PP) approach. Elastic anisotropy factors, Cauchy pressure, inverted Pugh’s ratio, aggregate mechanical moduli (shear modulus, Young's modulus and Poisson's ratio), Vickers hardness HV, elastic wave velocity as well as the Debye temperature θD and the melting point have been also calculated. Our obtained results are in general in good agreement with other data of the literature. The deviation between our obtained value (4.225 Ã…) of the lattice constant and the theoretical value (4.282 Ã…) of the literature is around 1.33%, while that between our obtained value (169.7 GPa) of the bulk modulus and the theoretical one (171 GPa) is only around 0.77%. The calculated values of HV and θD were found at around 30.5 GPa and 1254 K (1314.4 K), respectively. Â

Microstructural Characterization and Mechanical Properties of Rapidly Solidified Al-Si Systems by Chill Block Melt-Spinning Technique.

AlـSi alloys with compositions (0, 0.1, 0.5, 0.9 and 1.3 wt.% Si) were manufactured by chill block melt spinning method. The resulting ribbons samples have been characterized by xـray diffraction (XRD) and scanning electron microscope (SEM). Detailed analysis of (XRD) shows that presence of f.c.c Al solid solution and Si particles embedded within the aluminum grains. Microstructural examination resulted that microstructure of the melt spun ribbons are more fine and uniformly distributed. Rapid solidification technology led to increase the solubility of Si in αـAl as confirmed by XRD. Micro hardness measurements were also carried out by Vickers microـhardness tester at applied load 25gm forced and different dwell time. It is concluded that the Vickers hardness values are sensitive to applied load and indentation time. It is also found that the highest values of Hv is sensitive to presence of Si as columnar shape with fine grained of Al by high cooling rate.

Application of the concept of multifractal to control the quality of low-alloy steel

Relevance of the work. The quality control of manufactured metal products is carried out using both direct tests and non-destructive testing methods. It is proposedto use a multifractal approach in the analysis of the structure to predict the quality criteria for low-alloyed steel. Material and methods. Low-alloy steel with a ferritic-pearlitic structure was chosen as a material for research. Steel was subjected to heat treatment: heating to 920 °C and holding time for 300 sec. The samples were cooled to a temperature of 500 °C with different times. Results and discussion. The following parameters were used: the dimension of Hausdorff-Bezikovich D0, the homogeneity of fcalculated with the exponent q = –100 and 100, the coefficients of variation of the dimension of the elements of the structure with the most dense packing D-100and the most rarefied D100. The dependences of the multifractal characteristics of perlite and ferrite on the hardness and cooling time of the samples are established. There is a decrease in the hardness values of HV with an increase in the dimensional estimates of the structure of ferrite and pearlite, which is due to the increase in the cooling time of the metal to 500 °C from 29 to 93 000 sec. Conclusions.Based on the multifractal analysis of the ferritic-pearlitic structure of low-alloy steel, its hardness indicators were evaluated as a function of cooling time.

In-situ fabrication of Al(Zn)−Al2O3 graded composite using the aluminothermic reaction during hot pressing

In this study, the fabrication of multilayer Al(Zn)–Al2O3 with different volume fractions of Al2O3 was investigated. Al and ZnO powders were milled by a planetary ball mill, after which five-layer functionally graded samples were produced through hot pressing at 580°C and 90 MPa pressure for 30 min. Formation of reinforcing Al2O3 particles occurred in the aluminum matrix via the aluminothermic reaction. Determination of the ignition temperature of the aluminothermic reaction was accomplished using differential thermal and thermogravimetric analyses. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometery analyses were utilized to characterize the specimens. The thermal analysis results showed that the ignition temperatures for the aluminothermic reaction of layers with the highest and lowest ZnO contents were 667 and 670°C, respectively. Microstructural observation and chemical analysis confirmed the fabrication of Al(Zn)–Al2O3 functionally graded materials composites with precipitation of additional Zn in the matrix. Moreover, nearly dense functionally graded samples demonstrated minimum and maximum hardness values of HV 75 and HV 130, respectively.

ИЗУЧЕНИЕ ФАЗОВОГО СОСТАВА И ЭЛЕКТРОПРОВОДНОСТИ СПЛАВОВ СИСТЕМЫ Cu–Cr–Si–Ce–La

The phase composition and electrical conductivity of 12 as-cast samples of the Cu–Cr–Si–Ce–La system alloys were investigated. The concentration of chromium in the samples ranged from 0.5 to 1.0 wt. %; the concentration of silicon in samples was from 0.1 to 1.3 wt. %; the concentrations of rare-earth metals (cerium and lanthanum) ranged from 0.1 to 0.5 wt. %. The samples were studied by scanning electron microscopy and micro-X-ray spectral analysis, as well as by X-ray phase analysis. It is established that in the experimental samples in equilibrium with a solid solution based on copper, depending on the concentration of the alloying elements, intermetallides Cu6Ce and Cu6La, inclusions of metallic chromium, chromium silicides Cr3Si and Cr5Si3, and also silicide of lanthanum and cerium (La,Ce)Si2 were formed. In the course of the work, the Vickers microhardness was measured on the thin sections of the samples under study. The dependence of the values of the microhardness HV on the composition of the experimental samples was established. With increasing silicon concentration for fixed values of chromium, cerium and lanthanum, the microhardness values were increased. Also in the course of this study, the electric conductivity of the experimental samples was determined by a non-contact method in a rotating magnetic field at a temperature of 20 °C. The dependence of the electrical conductivity of the samples on the concentrations of alloying elements was determined. The data obtained in the course of this work may be of interest to engineers in the analysis of the use of rare earth metal additives in bronzes.

Elemental, microstructural, and mechanical characterization of high gold orthodontic brackets after intraoral aging.

The purpose of the present study was to investigate the elemental composition, the microstructure, and the selected mechanical properties of high gold orthodontic brackets after intraoral aging. Thirty Incognito™ (3M Unitek, Bad Essen, Germany) lingual brackets were studied, 15 brackets as received (control group) and 15 brackets retrieved from different patients after orthodontic treatment. The surface of the wing area was examined by scanning electron microscopy (SEM). Backscattered electron imaging (BEI) was performed, and the elemental composition was determined by X-ray EDS analysis (EDX). After appropriate metallographic preparation, the mechanical properties tested were Martens hardness (HM), indentation modulus (EIT), elastic index (ηIT), and Vickers hardness (HV). These properties were determined employing instrumented indentation testing (IIT) with a Vickers indenter. The results were statistically analyzed by unpaired t-test (α=0.05). There were no statistically significant differences evidenced in surface morphology and elemental content between the control and the experimental group. These two groups of brackets showed no statistically significant difference in surface morphology. Moreover, the mean values of HM, EIT, ηIT, and HV did not reach statistical significance between the groups (p>0.05). Under the limitations of this study, it may be concluded that the surface elemental content and microstructure as well as the evaluated mechanical properties of the Incognito™ lingual brackets remain unaffected by intraoral aging.