Higher Microhardness Values Research Articles

Efficacy of Different Finishing and Polishing Systems on Surface Roughness and Microhardness of Highly Aesthetic Composites

ABSTRACT
 Objectives: The aim of this study is to examine the effect of three different types of highly esthetic composite resin, which will be used for aesthetic purposes in the anterior region, on the surface roughness and microhardness by the application of three different finishing and polishing systems, with three-dimensional Optical Profilometer, Vickers microhardness device and SEM analysis.
 Materials and methods: Three different composite resins were used in the study; supra-nanofil(Tokuyama Estelite Asteria), supra-nano spherical(Tokuyama Omnichroma), nanohybrid(Kuraray Clearfil Majesty Esthetic) were used. 40 samples of each composite resin were prepared, 120 in total. After the polymerization and correction processes, ten samples from each group that did not undergo any polishing process were separated as the control group. Then, they were randomly divided into three groups for the polishing process: 4-stage aluminum oxide coated disc(3M Sof-lex disc), beige and pink 2-step spiral rubber consisting of aluminum oxide-containing diamond particles(3M Sof-lex spiral), polyurethane, diamond granules. containing light blue rubber and spiral rubber(Ivoclar Vivadent OptraGloss). Surface roughness(Ra) was measured on all samples with a conventional profilometer device. Then, one sample surface from each group was examined with the Optical Profilometer device and the Scanning Electron Microscope, and all samples were subjected to microhardness testing with the Vickers Microhardness Tester.
 Results: As a result of our study, the lowest roughness values were observed in the control group, while the highest roughness values were observed in the Ivoclar Optragloss group. The groups studied with Kuraray Clearfil Majesty Esthetic composite showed higher roughness values compared to other composite groups, but no statistically significant difference was found with other composite groups(p>0.05). In our study, the lowest microhardness values were observed in the control group, while the highest microhardness values were observed in the Sof-Lex Disk group. The difference between the groups treated with Kuraray Clearfil Majesty Esthetic composite and the other composite groups was found to be statistically significant(p

Comparative Evaluation of The Microhardness of Artificial Teeth of Various Composition

Statement of the problem: To help physicians choose the right materials for treatment planning, it is necessary to investigate to the mechanical and physical characteristics of denture teeth made with new technology. Objective: This study aims to investigate the comparative microhardness of artificial teeth with different composition. Materials & Methods: A total of 96 specimens (n=32) were prepared using three different types of artificial teeth (conventional polymethylmethacrylate, , and nanohybrid composite) (Group CA - Conventional PMMA, Group IS - Isosite Group DCL - double cross-linked acrylic). Surface hardness values were determined using a microhardness tester (Shimadzu HMV Corporation, Tokyo, Japan) with a load of 500 g and a dwell time of 15 seconds. Three indentations were obtained for each sample and the Vickers Hardness Number (VHN) was calculated and averaged. One-way analysis of variance (ANOVA) and post-hoc Tukey HSD tests were used for statistical analysis. The statistical significance level of the data was taken as α=0.05. Results: The highest microhardness values were observed in Group IS (53.96 ± 8.5 VHN) and the lowest in Group CA (53.55±9.9 VHN). However, no statistically significant difference was found between the groups (P>0.05). Conclusions: For the durability and function of prosthetic rehabilitations performed by clinicians, the choice of artificial teeth should not be ignored, based on cost and accessibility criteria.

The effect of different curing distances on the microhardness of flowable bulk-fill composite materials

Background: The microhardness of a composite resin is a vital parameter that is used to determine its clinical behavior. Measuring the microhardness of a composite resin has been used as an indirect method to assess its degree of conversion and extent of polymerization. The purpose of this in vitro study was to evaluate the effect of three curing distances (0, 2, and 4 mm) on the microhardness of the top and bottom surfaces of three types of flowable bulk-fill composite resins (smart dentin replacement, Opus bulk fill flow, and Tetric N). Material and method: Sixty-three specimens from the three types of composite resins (n=21) were fabricated using Teflon mold with a 4mm depth and a 5 mm internal diameter and cured for 20 seconds. For each material, three subgroups were fabricated according to the position of the light curing tip from the top surface; at 0, 2, and 4 mm distances. Microhardness was measured using the Vickers test with a 50-g load for 15 seconds for the top and bottom surfaces of all the samples. Results: The microhardness values were decreased in the following order; 0mm > 2mm > 4mm curing tip distance, for both sides and Tetric N had the highest microhardness values. Significant differences in microhardness were recorded between the top and bottom surfaces for all the specimens (p<0.05). Conclusion: Increasing the distances between the tip of the light cure and the surface of flowable bulk-fill resins can significantly decrease the microhardness of the bottom surfaces compared to the top surfaces.

Hardening Mechanism of Thick (Ti,Cr,V)N Composite Coatings with Multi-layer Nano-columnar Dendrites Microstructure

The 300 μm thick (Ti,Cr,V)N nanocomposite coatings were prepared by plasma spraying technique combined with combustion synthesis reaction of N and Ti-Cr-V reconstituted composite powders, and their microstructure and hardening mechanism were explored. The phases and microstructures were analysed by X-ray diffractometer, X-ray photoelectron spectroscopy and scanning electron microscopy, transmission electron microscopy, respectively, and a microhardness tester was employed to measure the microhardness. The main phase of the composite coating is (Ti,Cr,V)N solid solution, which has a multilayered structure of elongated columnar dendrites arranged in parallel, with different solidification positions resulting in crystal bundles possibly having different orientations. The composite coating has nanoscale fine crystals, as well as two typical strengthening models, "dislocation-TB" and "lattice distortion", which together contribute to the high hardness of the (Ti,Cr,V)N composite coating. The (Ti,Cr,V)N composite coating containing 10wt.% Cr has better surface morphology and the highest microhardness value (1844.80 HV0.5).

Characterisation of weld bead and microhardness of SS316L weld overlays on S355J2+N steel using GTAW under E-type magnet

In this study, a three-pole (E-type) electromagnet with magnetic configurations north-south-north (NSN) and south-north-south (SNS) was installed in the GTAW process to generate a combination of two symmetrically transverse external magnetic fields around the weld arc and the molten pool. The effects of magnetic fields obtained by these two types of magnetic configurations (NSN and SNS) on the weld bead characteristics and microhardness in GTAW were analysed. In these experiments, high-strength low alloy (HSLA) S355J2+N grade with a thickness of 10 mm was selected as the substrate material and S316L as the filler wire. Using magnetic fields during the welding process successfully enhanced the weld bead appearance and shape and improved the mechanical characteristics of weld overlays. It was also observed that for different values of excitation current, magnetic fields generated with both configurations ( i.e., NSN and SNS) provide greater bead width, a higher penetration shape factor, and higher microhardness values in comparison to specimens welded with conventional GTAW. The NSN and SNS configurations of the E-type magnet improve the penetration shape factor by 58% and 46%, respectively. These configurations were more suitable for weld overlays (cladding) and hardfacing. However, the observations indicated an enhancement in microhardness for all excitation current values by employing the NSN and SNS magnetic configurations.

Development of technology for obtaining functional coatings from Kh15Yu5 steel powders

The paper presents the results of research on the development of technology for the application of functional coatings with high values of adhesion strength, microhardness and wear resistance using the method of supersonic cold gas dynamic spraying. Oxidized powder from X15Yu5 steel was used as a starting material for obtaining such coatings.

The green synthesis of carbon quantum dots (CQDs) and characterization of polycaprolactone (PCL/CQDs) films

The synthesis of photoluminescent carbon quantum dots (CQD) from natural products is one of the most remarkable types of carbon-based nanomaterials due to their small size, high water solubility, nontoxicity, high stability, and excellent biocompatibility. New RC-CQDs have been prepared from natural material (rosehip fruit) via a hydrothermal method. CA-CQDs samples were synthesized from a synthetic carbon source (citric acid) by the same method for comparison with RC-CQDs. The maximum quantum yields of the as-prepared RC-CQDs and CA-CQDs samples were 23.8% and 9.6%, respectively. High-resolution transmission electron microscopy (RTEM) of RC-CQDs revealed a sphere shape with an approximate size of 5 nm, CA-CQDs were greater than 5 nm. Biodegradable polycaprolactone (PCL), which is used in bioengineering applications thanks to its mechanical and biodegradable properties, was used as a polymer matrix in this study. The PCL/RC-CQDs and PCL/CA-CQDs nanocomposite films were produced via liquid phase ultrasonic mixing at different amounts of RC-CQDs and CA-CQDs in PCL matrix (0.3-; 0.5-; 1.2-; 2.0% and 4.0% by weight), while unfilled PCL was also produced for comparison. The structural, mechanical, and biodegradable behaviors of PCL/RC-CQDs nanocomposite films have been investigated to improve the mechanical properties of PCL and increase its potential usability in load-bearing applications. PCL/RC-CQDs-2.0 film gave the maximum tensile strength value (17.65 MPa) with an increment of 27.7% and the highest value of the yield strength 9.02 MPa (an increase of 40.9%) and the highest value of microhardness 4.80 HV0,025 (an increase of 14.8%) were obtained using PCL/RC-CQDs-4.0 film compared with the PCL. The tensile strength and % elongation at break values of the PCL/CA-CQDs-0.3 film decreased by 14.8% and 133.1% compared with the PCL, respectively. The microhardness of the PCL/CA-CQDs-0.3 film was 5.48 HV0,025, increasing by 31.1% in comparison with 4.18 HV0,025, for the PCL. Biodegradability test results showed that films containing RC-CQDs exhibited lower weight loss than the PCL and films containing CA-CQDs. This result was attributed to the amorphous structure, low surface roughness and high contact angle of the RC-CQDs containing films. And also, CA-CQDs made PCL films more hydrophilic according to low contact angle results.

Enamel Remineralization Efficacy of Coconut Milk and Lyophilized Coconut Extract in Different Concentrations on Demineralized Enamel Surfaces: An In-Vitro Study.

Aim The current study's objective is to determine the remineralizing efficacy of freeze-dried lyophilized coconut extract and coconut milk made from freshly grated coconut on artificial carious lesions produced by pH cycling. Materials and methods Freshly extracted coconut pulp was split into two parts. The first half was blended to obtain coconut milk, and the second part was freeze-dried and lyophilized. Tooth slabs were prepared from extracted third molar teeth. After being demineralized for 72 hours, the tooth samples were remineralized by submerging them in the appropriate remineralizing solution, which is as follows: Group 1 received 25 mL of the Remineralization solution (the control); Group 2 received 2.5 g of coconut milk and 25 mL of the solution (1:1); and Group 3 received 5 g of coconut milk and 25 mL of the solution (2:1). 2.5 g of freeze-dried, lyophilized coconut extract was given to Group 4 along with 25 mL of remineralization solution (1:1), and 5 g of freeze-dried, lyophilized coconut extract was given to Group 5 along with 25 mL of remineralization solution (2:1). Microhardness and contact angle measurements were made. An Excel spreadsheet was filled up with values from after demineralization, and after remineralization. A statistical analysis was performed using SPSS 26.0 (IBM Corp., Armonk, NY). Using descriptive statistics, the pretreatment mean values for the microhardness and contact angle of the various groups were evaluated. Post-hoc Tukey tests were utilized to compare the analytic results of the various groups. Results Among the various concentrations of freshly extracted coconut milk, the contact angle inconcentrations of 1:1 was 81.22 ± 1.62 deg, and that in concentrations of 2:1 was 88.01 ± 1.85 deg. Between the two concentrations of the lyophilized coconut extract group, the contact angle in 1:1 was 75.05 ± 2.29 deg, and in 2:1 was 71.37 ± 0.85 deg. In the coconut milk group, the value of microhardness was 261 ± 6.4 kg/cm2 at a lower concentration and 322 ±3.9 kg/cm2 at a higher concentration. In the lyophilized coconut group, the lower concentration exhibited a microhardness of 211 ±7.2 kg/cm2, whereas in the higher concentration, it was 324 ±4.04 kg/cm2. Conclusion Of the various concentrations of coconut milk and lyophilized coconut used, coconut milk at a higher concentration exhibits the highest contact angle, and the latter at a higher concentration exhibits the lowest contact angle. In both groups, high concentrations of the material exhibited high microhardness values compared to lower concentrations of the same.

Effect of aging and fiber-reinforcement on color stability, translucency, and microhardness of single-shade resin composites versus multi-shade resin composite.

The purpose of this study was to evaluate the effect of aging and fiber-reinforcement on the color stability, translucency, and microhardness of single-shade resin composites versus multi-shade resin composite. Four resin composites (Filtek Z250, Omnichroma, Vittra APS Unique, Zenchroma) were tested. Three subgroups of specimens were prepared for each of the composites: control, polyethylene fiber-reinforcement, and glass fiber-reinforcement- groups (n = 10/per group). The samples were subjected to aging for 10,000 thermal cycles. Color differences (ΔE00 ) were calculated after aging. Relative translucency parameter (RTP00 ) and microhardness values were calculated before and after aging. A two-way analysis of variance and the generalized linear model was used (p < 0.05). The lowest and highest ΔE00 values were found for Filtek Z250 (0.6 ± 0.2) and Omnichroma resin composites (1.6 ± 0.4), respectively. The ΔE00 value of the polyethylene fiber-reinforcement group (1.2 ± 0.6) was significantly higher than the ΔE00 value of the glass fiber-reinforcement group (1.0 ± 0.4, p < 0.001). The RTP00 value of the glass fiber-reinforcement group (1.92 ± 0.78) was significantly higher than the RTP00 value of the polyethylene fiber-reinforcement group (1.72 ± 0.77, p < 0.001). The highest microhardness values were found in glass fiber-reinforcement group (76.48 ± 17.07, p < 0.001). Single-shade resin composites were more translucent, had higher color change, and lower hardness than multi-shade resin composite. For relative translucency and microhardness, statistical significance was found in the material and fiber type interaction. The glass fiber-reinforcement provided higher translucency, lower color change and higher microhardness values than polyethylene fiber-reinforcement group after aging. Thermocycling had a significant impact on the color stability, translucency parameter, and microhardness of the tested resin composite materials. Single-shade resin composite materials have greater color-changing potential. The glass fiber-reinforcement optimize resin material mechanical properties and color stability more than polyethylene fiber-reinforcement.

Effect of inorganic fillers on the light transmission through traditional or flowable resin-matrix composites for restorative dentistry

ObjectivesThe aim of this in vitro study was to evaluate the light transmission through five different resin-matrix composites regarding the inorganic filler content.MethodsResin-matrix composite disc-shaped specimens were prepared on glass molds. Three traditional resin-matrix composites contained inorganic fillers at 74, 80, and 89 wt. % while two flowable composites revealed 60 and 62.5 wt. % inorganic fillers. Light transmission through the resin-matrix composites was assessed using a spectrophotometer with an integrated monochromator before and after light curing for 10, 20, or 40s. Elastic modulus and nanohardness were evaluated through nanoindentation’s tests, while Vicker’s hardness was measured by micro-hardness assessment. Chemical analyses were performed by FTIR and EDS, while microstructural analysis was conducted by optical microscopy and scanning electron microscopy. Data were evaluated using two-way ANOVA and Tukey’s test (p < 0.05).ResultsAfter polymerization, optical transmittance increased for all specimens above 650-nm wavelength irradiation since higher light exposure time leads to increased light transmittance. At 20- or 40-s irradiation, similar light transmittance was recorded for resin composites with 60, 62, 74, or 78–80 wt. % inorganic fillers. The lowest light transmittance was recorded for a resin-matrix composite reinforced with 89 wt. % inorganic fillers. Thus, the size of inorganic fillers ranged from nano- up to micro-scale dimensions and the high content of micro-scale inorganic particles can change the light pathway and decrease the light transmittance through the materials. At 850-nm wavelength, the average ratio between polymerized and non-polymerized specimens increased by 1.6 times for the resin composite with 89 wt. % fillers, while the composites with 60 wt. % fillers revealed an increased ratio by 3.5 times higher than that recorded at 600-nm wavelength. High mean values of elastic modulus, nano-hardness, and micro-hardness were recorded for the resin-matrix composites with the highest inorganic content.ConclusionsA high content of inorganic fillers at 89 wt.% decreased the light transmission through resin-matrix composites. However, certain types of fillers do not interfere on the light transmission, maintaining an optimal polymerization and the physical properties of the resin-matrix composites.Clinical significanceThe type and content of inorganic fillers in the chemical composition of resin-matrix composites do affect their polymerization mode. As a consequence, the clinical performance of resin-matrix composites can be compromised, leading to variable physical properties and degradation.Graphical

Composition, Structure and Properties of Antifriction Alloys Based on the Charge Obtained by Electrodispersion of Bronze Waste BrO5C25 in Kerosene

Purpose. Study of the composition, structure and properties of antifriction alloys based on the electroerosion charge of bronze BrO5C25 obtained in a carbon–containing medium lighting kerosene.Methods. Dispersion of the waste of the BrO5S25 alloy was carried out at an installation for electrodispersing electrically conductive materials. The waste of the BrO5C25 alloy was used as metal waste. Lighting kerosene was used as the working fluid.As a result of exposure to short-term electrical discharges between the electrodes and the waste, their destruction occurred with the formation of fine particles. To obtain compacted materials, a Herzog TP 20 manual table press was used. Modern equipment and complementary methods of physical materials science were used to study the composition, structure and properties of the sintered products obtained.Results. Surface analysis showed that the alloys have a fine-grained structure, uniform phase distribution and a small number of pores. The analysis of the elemental composition found that carbon is contained on the surface of the new alloys, and all other elements Sn, Cu and Pb are distributed relatively evenly. The analysis of the studied alloys showed the presence of phases in them: Cu, CuSn, SnO, CuO, PbO, Pb. There are no carbide-forming elements in the alloy. It has been experimentally established that the composition, structure and properties of the charge dispersed by electroerosion of bronze BrO5C25 affect the tribological properties of the alloy blanks. In particular, the presence of free carbon in the alloy from the electroerosion charge obtained in kerosene, which acts as a solid lubricant, leads to a decrease in the coefficient of friction.Conclusion. It is shown that alloys obtained from an electroerosive charge have higher microhardness values in comparison with an alloy obtained from an industrially used charge. A significant increase in the microhardness of alloys is explained by the presence of highly hard particles formed during the quenching of metal vapors in the working fluid during dispersion. The presence of small fractions in electroerosive materials contributes to an increase in the density of compressions and a decrease in the porosity of workpieces.

Effect of an In-Office Bleaching Agent with Surface Pre-Reacted Glass-Ionomer Filler on the Enamel Surface: A In-Vitro Study.

In-office bleaching with high concentrations of hydrogen peroxide (H2O2) agents causes undesirable alterations in the enamel. Surface pre-reacted glass-ionomer (S-PRG) filler is a functional material known for its acid-neutralizing and demineralization-inhibition properties. This study evaluates the effect of S-PRG filler incorporation in H2O2-based bleaching on the enamel surface. Bovine enamel surfaces were bleached using a bleaching paste formulated with a liquid (35% H2O2) and a powder containing 5% or 10% S-PRG filler. The surface roughness and the Vickers microhardness of the treated enamel surfaces were evaluated. The enamel surfaces were observed under a scanning electron microscope (SEM) and analyzed using energy dispersive X-ray (EDX) technology. The surfaces were challenged by citric acid and observed by SEM. The specimens bleached with the paste containing the S-PRG filler showed lower enamel surface roughness and higher microhardness values than did those bleached with the plain paste (0% S-PRG filler); meanwhile, there were no significant differences between the 5% or 10% S-PRG filler groups. The S-PRG filler groups showed enamel surface morphologies similar to those of the non-bleached enamel, according to SEM observation, and EDX analysis detected the presence of fluoride and strontium ions. The S-PRG filler groups showed a higher resistance to erosion. The S-PRG filler mitigated the detrimental effects of bleaching agents on the enamel surface and provided resistance to erosion.

Effects of Acidic Beverages on Surface Microhardness of a New Ion-Releasing Restorative Material with Surface Sealant

Objective: Many factors in the mouth affect the clinical lifetime of materials. Acids, enzymes, acidic properties of food and beverages formed in the plaque could change the physicochemical properties of restorative materials. The aim of the study is to examine the effect of acidic beverages on the microhardness of alkasites, and conventional glass ionomers, with changes in surface coating applications. Materials and Methods: Forty specimens in eight mm diameter and two mm thick discs were made with each Cention N and Ionofil U. Half of the specimens were covered with surface sealant. In each of the four subgroups: cola, orange juice, sparkling mineral water and distilled water, 10 discs were stored for 5 minutes, three times a day for a week. Microhardness measurements were made after they were kept in an acidic environment. Results: Acidic beverages significantly reduce the microhardness of restorative materials. The highest microhardness value was observed in the Cention N group with surface sealant. The lowest microhardness value was observed in the Ionofil restorative material group without sealant. Conclusion: The acidic agents tested (cola, orange juice, and sparkling mineral water) have an effect on the reduction of surface microhardness of restorative materials. For clinical decision-making, Cention N is the most suitable material for restorations in patients who are at high risk for erosive conditions.

Production of Al–Mn/WC Composite Coatings with Electrodeposition in AlCl3–NaCl–KCl–MnCl2 Molten Salts

The hardness and wear resistance of amorphous Al–Mn alloy coatings can be improved by incorporating ceramic particles into them to extend their application. In this paper, Al–Mn/WC composite coatings have been prepared with electrodeposition in stirred AlCl3–NaCl–KCl–MnCl2 molten salts at 180 °C with the addition of WC particles. The effects of stirring speed (400–700 rpm) and cathode current density (15–75 mA/cm2) on the produced Al–Mn/WC composite coatings have been studied. At 600 rpm and 700 rpm, the Al–Mn/WC composite coatings exhibited the best uniform distribution of the embedded WC particles, with the tested microhardness value up to 650 HV0.1, compared with 530 HV0.1 of the Al–Mn alloy. Moreover, under various cathode current densities, the best quality of the Al–Mn/WC composite coating was obtained at 55 mA/cm2, with a homogeneous distribution of WC particles and the highest microhardness value (670 HV0.1). It is expected that this method could be extended to be applied for the preparation of aluminum-based and magnesium-based ceramic composite coatings.

Analyses of Experimental Dental Adhesives Based on Zirconia/Silver Phosphate Nanoparticles.

This study aimed to evaluate the incorporation of zirconia/silver phosphate nanoparticles to develop experimental dental adhesives and to measure their physical and mechanical properties. The nanoparticles were synthesized by the sonication method, and the phase purity, morphological pattern, and antibacterial properties with Staphylococcus aureus and Pseudomonas aeruginosa were assessed. The silanized nanoparticles were incorporated (0, 0.15, 0.25, and 0.5 wt.%) into the photoactivated dimethacrylate resins. The degree of conversion (DC) was assessed, followed by the micro-hardness and flexural strength/modulus test. Long-term color stability was investigated. The bond strength with the dentin surface was conducted on days 1 and 30. The transmission electron microscopy and X-ray diffractogram confirmed the nano-structure and phase purity of the particles. The nanoparticles showed antibacterial activities against both strains and inhibited biofilm formation. The DC range of the experimental groups was 55-66%. The micro-hardness and flexural strength increased with the concentration of nanoparticles in the resin. The 0.5 wt.% group showed significantly high micro-hardness values, whereas a non-significant difference was observed between the experimental groups for flexural strength. The bond strength was higher on day 1 than on day 30, and a significant difference was observed between the two periods. At day 30, the 0.5 wt.% showed significantly higher values compared to other groups. Long-term color stability was observed for all the samples. The experimental adhesives showed promising results and potential to be used for clinical applications. However, further investigations such as antibacterial, penetration depth, and cytocompatibility are required.

Investigation of microstructural, hardness, and thermal properties of mechanically milled Al-Co-Cu-Mg alloys

In this study characterization of a novel Al66Co20Cu13Mg1 alloy produced by the mechanical alloying method was investigated. The effect of milling time on the produced alloy's microstructural evaluations, microhardness, and thermal behaviors was investigated. Scanning electron microscope and X-ray diffractometer results demonstrated that as the milling time was increased, the homogeneity was increased, the particle size was decreased, crystalline cubic Al(Co, Cu) solid solution, α-Co(Cu, Mg) solid solution phase and Al2Cu phase were formed with the mechanical alloying effect after milling of 50 h. When the powder alloy was milled for 100 h, most of the elemental peaks such as Al and Cu disappeared, and Al3.892Cu6.108 phase was formed. The crystallite size of the alloy powders after 100 h of milling was found as 17.42 ± 2 nm. Moreover, as the milling time was increased, both the lattice strain and dislocation density were increased because of fractures, the formation of new intermetallic phases, and excessive deformations. The microhardness of the pressed powder alloys was increased due to the cold welding and intermetallic phases formed in the powder alloy with increasing milling times. The lowest and highest microhardness values are found to be 275 ± 10 and 376 ± 10 HV for the unmilled alloy and the 100 h of milled alloy, respectively.

Effect of laser power on the microstructure and property of ZrB2/ZrC in-situ reinforced coatings on zirconium alloy by laser cladding

ZrB2/ZrC in-situ reinforced coating was fabricated by laser cladding Ni60A + WC powder on zirconium alloy. The effect of laser power on the formation of coating, microstructure, reinforcements and microhardness was investigated. The results show that the good appearance of the coating was obtained and no defects such as pores and cracks were found. As the laser power increased, the width and height of the coating increased significantly. Reinforcements in the coating were mainly composed of fine α-Zr dendrites, granular and block ZrC and Zr(B, C)2. ZrB2/ZrC eutectic was formed inside the unmolten WC. The similar values of Gibbs free energy for forming ZrB2 and ZrC at elevated temperature made it easy to form lamellar eutectic. With increasing laser power, the growth of the secondary arm of dendrites was suppressed and the granular reinforcements gradually transformed to block reinforcements. The microhardness of coating increased significantly as increasing laser power. The highest value of microhardness (about 720HV0.5) was obtained when the laser power is 2.8 kW.

Impact of geopolymers on hard sludge formation on the secondary side of PWR steam generators under transient conditions

In modern steam generators (SG), some tube degradation phenomena are promoted by the formation of hard sludge (HS) on top of tubesheet. These phenomena reduce the efficiency of nuclear power plants (NPP). In some cases, SG deposits are primarily constituted by HS. This HS usually presents high concentrations of aluminum and silicon (up to 6.0 ± 0.1 wt% of Al and 2.7 ± 0.1 wt% of Si), together with high microhardness values (above 800 HV) at specific locations. In fact, there is evidence that the presence of aluminum and silicon is at the origin of the problematic of HS in SG during normal operation.Geopolymers are inorganic polymer materials constituted by a 3D-network of interlinked silica and alumina tetrahedra. Geopolymers present cementitious properties similar to HS. Geopolymers are formed under highly alkaline conditions and low temperature, by the polymerization of aluminosilicate and/or silicate oligomers. During NPP transient periods, geopolymer formation could be favor by the physicochemical conditions in the gaps arisen due to the different thermal contraction of SG tubes, deposits and tubesheet. Thus, it could be though that part of the HS formed in the crevice between tube and tubesheet of SG could correspond to geopolymers. In order to demonstrate this hypothesis, the mayor constituents of HS (magnetite, aluminum and/or silicon sources) have been autoclaved in representative secondary circuit transient conditions (cooldown). The effect the Si to Al ratio, the aluminosilicate source, the presence of magnetite and the chemical conditions in the crevice is also studied. The chemical, structural and morphological characterization of the resulting solids shows the presence of aluminosilicate compounds in some of the tested experimental conditions. However, these aluminosilicate compounds do not act as cementing agents agglomerating magnetite particles and therefore, they do not contribute to HS formation.

High entropy coating from AlCoCrCuFeNi alloy, obtained by laser alloying

The structural-phase state of the Al-Co-Cr-Cu-Fe-Ni system high-entropy alloy obtained by laser alloying of technically pure aluminium surface layers was investigated by XRD, EDX and metallographic analyses. It is shown that in the process of laser alloying the formation of an an ordered multicomponent substitution solid solution based on BCC lattice took place, which is typical for high-entropy alloys. The process of heterogeneous crystallization of high-entropy alloys AlCoCrCuFeNi and Al3CoCrCuFeNi was modeled taking into account cooling rates of the melt. It is established that the formation of the obtained structure is a consequence of high cooling rates of the melt and high content of aluminum in the laser alloying zone. The microhardness of the alloyed surface was higher compared to high-entropy alloys of this system obtained under equilibrium conditions and was equal to 6.59 GPa. Additional reasons that may affect the high values of microhardness are analysed.

The Effect of a Bioactive Oral System and CO2 Laser on Enamel Susceptibility to Acid Challenge.

This study evaluated the structural changes of enamel treated by the Regenerate system and carbon dioxide (CO2) laser against acid challenge. Thirty human enamel slabs were prepared and assigned into three groups: Group I: untreated (control); Group II: treated with the Regenerate system; and Group III exposed to CO2 laser. All specimens were subjected to an acid challenge (pH 4.5-7.0) for 14 days. Specimens were evaluated and compared at 120 points using five Raman microspectroscopic peaks; the phosphate vibrations ν1, ν2, ν3, and ν4 at 960, 433, 1029, and 579 cm-1, respectively, and the carbonate at 1070 cm-1, followed by Vickers microhardness test. The ratio of carbonate to phosphate was correlated to the equivalent microhardness numbers. The intensities of phosphate peaks ν1, ν2, and ν4 were reduced in all groups post-acid challenge, while the carbonate and ν3 were significantly increased (p < 0.000). Surfaces treated by Regenerate exhibited higher peak intensity of phosphate and carbonate before and after pH-cycling (p < 0.05). The mineral content in enamel had a direct effect on tissue microhardness, and the CO2-lased surfaces showed a reduced carbonate content and higher microhardness values. Both approaches induced surface changes that can protect enamel against acid challenge resulting in a significant benefit for dental healthcare.