Microhardness Data Research Articles

Effect of welding parameters on microstructure and mechanical properties of GMAW welded S275 steel welded zone

This study investigates the effect of welding parameters on the microstructural evolution and mechanical properties, such as tensile strength and hardness, in mild steel plates welded using gas metal arc welding (GMAW). The welding parameters examined include welding current, arc voltage, and gas flow rate, with ER K-71 T filler wire as the consumable material. Results indicate that a higher welding current and reduced gas flow rate result in a maximum tensile strength of approximately 533 MPa. However, discrepancies were noted in the microhardness data across different zones, with the heat-affected zone (HAZ) exhibiting a hardness of 115.8 HV, while the weld zone and base metal showed values of 76.7 HV and 112.9 HV, respectively. Microstructural analysis revealed the presence of bainite and ferrite with a tempered martensitic structure in the welded area, demonstrating that the combination of welding parameters plays a critical role in controlling phase transformations and mechanical behavior. It is essential to reconcile the observed hardness values with the conclusions drawn to ensure accurate interpretation of the data.

Effect of the use of remineralization agents before resin infiltration on the treatment of initial enamel lesions: an in-vitro study

AimThis study aimed to evaluate the effect of the use of remineralization agents before the application of resin infiltration on the treatment of initial enamel lesions.Materials and methodsEighty buccal enamel samples were prepared from human molars, and artificial initial lesions were formed after 96 h of incubation with a demineralizing solution. The samples were randomly divided into 8 groups (n = 10) including a remineralizing agent (Tooth Mousse, Medical Mineral Gel, Remin Pro), resin infiltration (ICON), and a combined treatment of both. Remineralizing agents were applied in pH cycle for 7 days. Baseline, demineralization, and after-treatment fluorescence (FluoreCam and DIAGNOdent Pen), surface microhardness (HMV-2T), surface roughness (M300C), OCT (Maestro-2) and ultrasonic system (Novascope 4500) data were obtained for all groups. The sample surfaces were examined under SEM/EDX (SU3500) at x1000. Data were statistically analyzed using the Two-Way Robust ANOVA and Bonferroni tests (p < 0.05).ResultsThere was no statistically significant difference between the groups for microhardness, roughness, OCT, DIAGNOdent Pen, ultrasound, and FluoreCam size/intensity values (p = 0.582; p = 0.963; p = 0.884; p = 0.923; p = 0.051; p = 0.268; p = 0.793 respectively). The effect of the treatment procedure showed a significant difference (p < 0.001), except for the roughness values (p = 0.984). The lowest Calcium (Ca) ratio (%atomic) was observed in the RI group in the EDX analysis.ConclusionRemineralizing agents and resin infiltration methods may be used in combination or alone in the treatment of initial enamel lesions. Combining remineralizing agents with resin infiltration does not alter the efficacy of the treatment.

The transient thermal ageing of Eurofer 97 by mitigated plasma disruptions

Plasma disruptions in a commercial-scale tokamak will impose high magnitude, short-duration thermal loads on its plasma-facing first wall. Despite a plethora of mitigation measures, these severe, off-normal events are likely to briefly expose the structural materials of the first wall to significant temperature excursions. Eurofer 97, the reference structural material for the plasma-facing first wall of the EU DEMO tokamak, is a reduced activation 9Cr steel with a normalised and tempered ferritic/martensitic microstructure. Repeated exposure to the thermal effects of disruptions over the operating lifetime of a reactor may promote a cumulative evolution of Eurofer 97′s microstructure, affecting key material properties crucial to first wall performance. This novel transient thermal degradation mechanism has been explored via a laser-based transient heating experiment, supported by time-dependent finite element thermal analysis studies of DEMO’s water-cooled lithium–lead first wall during a mitigated plasma disruption. Transient-affected samples of Eurofer 97 were characterised via scanning and transmission electron microscopy techniques (SEM/TEM), including electron backscatter diffraction (EBSD), energy-dispersive X-ray spectroscopy (EDX), and selective area electron diffraction (SAED). Microhardness and magnetisation testing data are also presented. A single 700 °C thermal transient was found sufficient to coarsen and partially recrystallise Eurofer 97′s tempered martensite sub-grains at the tungsten-Eurofer 97 interface. Further transient exposure at 700 °C resulted in the significant growth of equiaxed grains, the nucleation of intergranular Cr-rich M7C3 and M23C6 carbides, and the coarsening of V-rich and intra-granular Ta-rich MX precipitates. The microstructural effects of 850 °C transients are also reported. Notably, after 1,000 transients at 850 °C the hardness of Eurofer 97 was found to have decreased by 32 %.

Effects of polishing or glazing on surface roughness and microhardness after milling CAD-CAM ceramic materials

Objective: This study aimed to evaluate the surface roughness and microhardness of CAD-CAM ceramic blocks after different surface finishing protocols. Materials and methods: Three ceramics were evaluated: lithium disilicate, leucite-reinforced feldspathic and zirconia-reinforced lithium silicate. Ninety specimens were obtained and distributed into 3 groups (n=10): polishing (specimens were polished with an abrasive rubber kit); conventional glaze (according to the manufacturer's recommendations); and, extended glaze (the specimens were kept for 15 minutes at maximum firing temperature and the furnace was kept closed until reaching 200ºC). In all specimens, a drill was used to simulate the milling machine and thus obtain the initial roughness. Surface roughness was evaluated before and after the finishing protocols, while Vickers microhardness was performed only after the finishing protocols. Roughness data were analyzed to repeated measures two-way ANOVA and Bonferroni post-hoc test and ANOVA with Welch correction and Games-Howell test were used to analyze microhardness data (α = 0.05). Results: Both conventional and extended glazes showed greater smoothness for lithium disilicate and zirconia-reinforced lithium silicate ceramics, while for Empress, extended firing of the glaze provided greater surface smoothness. Regarding microhardness, there was no statistically significant difference among the protocols for the same material. The conventional glaze group made from lithium disilicate did not show a significant difference in microhardness values in relation to the other groups. Conclusion: The application of glaze improves the surface smoothness of the ceramics after milling procedure. There is no change in microhardness with different surface finishing protocols.

Fatigue life evaluation of laser welded lap joints of dissimilar aluminum alloys

Abstract Constant amplitude fatigue tests were conducted on 6061/7075 dissimilar aluminum alloy laser welded lap specimens, as well as weld line cross-section hardness measurements. The fatigue test results show that the specimens exhibit multiple fracture modes that exit near the weld seam. The microhardness data on weld line cross-section from 7075 side to 6061 side display a sharp change and the softening phenomenon is serious. The hardness variation in heat affected zone of laser welding is very shallow, and its hardness is close to that of the base material. It was found that there are slag inclusions and pores in the weld seam when observing the fatigue fracture surface using SEM, and a small amount of secondary cracks were generated. However, stress concentration plays a dominant role in causing specimen fracture under fatigue loading, rather than welding defects. Defective specimens are found to have higher fatigue strength. The fatigue life prediction results obtained by the notch stress method and the hot spot stress method are both conservative and fall within two factor lines. The hot spot stress method has relatively higher accuracy for life prediction. The accuracy of both methods in predicting life is influenced by the location of the fracture.

Effect of radiotherapy on the surface roughness and microhardness of contemporary bioactive restorative materials.

The aim of this in vitro study was to evaluate the effect of radiotherapy on the surface microhardness and roughness of different bioactive restorative materials. A total of 60-disc specimens (5mm × 2mm) were performed in four groups (n = 15 each) from Equia Forte HT, Cention N, Activa Bioactive Restorative, and Beautifil II. Following the polishing procedure (600, 1000, 1200 grit silicon carbide papers), all specimens were irradiated at 2Gy per fraction, five times a week for a total dose of 70Gy in 30 fractions over 7weeks. Before and after the irradiation, the specimens were analyzed regarding the surface roughness and microhardness. Surface morphology was also analyzed by scanning electron microscopy. Kruskal-Wallis test, Wilcoxon test, and paired sample t-test were used for statistical analysis. Significant differences were found after radiation with increased mean roughness of both Cention N (p = 0.001) and Beautifil II (p < 0.001) groups. In terms of microhardness, only the Beautifil II group showed significant differences with decreased values after radiation. There were statistically significant differences among the groups' roughness and microhardness data before and after radiotherapy (p < 0.05). The effect of radiotherapy might differ according to the type of the restorative material. Although results may differ for other tested materials, giomer tends to exhibit worse behaviour in terms of both surface roughness and microhardness. In patients undergoing head and neck radiotherapy, it should be taken into consideration that the treatment process may also have negative effects on the surface properties of anti-caries restorative materials.

Synergistic integration of laser shock peening and heat treatment for refined microstructure and enhanced mechanical properties in additively manufactured 17–4PH stainless steel

This study explores the combined effects of laser shock peening (LSP) and heat treatment (HT) on the microstructure, residual stress, and mechanical behaviour of selective laser-melted 17–4 precipitation-hardened (PH) stainless steel. Subsequently, laser shock peening (LSP) was performed on both as-printed (AP) and heat-treated (HT) sample surfaces, and their microstructure, residual stress, and mechanical behaviour were evaluated. The severe plastic deformation (SPD) resulted in significant compressive residual stresses (CRS) in the surface layer of the AP+LSP (-879 MPa) and AP+HT+LSP (-850 MPa) samples. Laser peening caused dislocation accumulation and micro-level grain refinement in the sample's deformed layers, improving its mechanical properties. The AP+HT+LSP sample shows significant improvements over the as-printed (AP) sample. The fraction of high-angle grain boundaries (HAGBs) and high misorientation angles were higher in the AP+HT+LSP sample, and its effect is revealed in the microhardness data. The collective contribution of precipitation strengthening, Hall-Petch, CRS, dislocation strengthening, and increased fraction of HAGBs is observed in mechanical and microstructural aspects of laser shock peened specimens.

The Effect of the Environment on the Case Hardening Characteristics of AISI 1018 Steel during Cassava Leaf Pack Cyaniding

As part of a comprehensive study on eco-friendly processing techniques, the influence of the heat treatment environment on the case hardening of AISI 1018 steel using pulverized cassava leaf was studied. The process was carried out at two different temperatures (850 °C and 950 °C) and under three environmental conditions: Process 1, the control experiment, was carried out in air only; in Process 2, the medium comprised pulverized cassava leaves; and in Process 3 a combination of pulverized cassava leaves plus barium carbonate (BaCO3) was used as an energizer (CBC mixture). Vickers microhardness testing and scanning electron microscopy were used to evaluate the effect of the processing environment on the case hardening of the steel. As expected, regardless of the processing temperature, Process 1 resulted in little or no hardening of the steel surface. However, notable case hardening occurred when the steel specimens were subjected to either Process 2 or Process 3. Furthermore, the inclusion of barium carbonate in Process 3 significantly enhanced the case hardening effectiveness of the cassava leaf in terms of the rate of and maximum hardness achieved. A maximum enhancement was observed at 950 °C. After 1 h, the increase in hardness was 160% and 280% for Process 2 and Process 3, respectively. Upon increasing the processing time to 5 h, the increase in hardness due to Process 2 was raised to 254%, while that of Process 3 remained at approximately 280%. The diffusivity of AISI 1018 was calculated using the microhardness data. The diffusivity was highest in Process 2 samples with values of 1.568 × 10−9 m2/s at 850 °C and 1.893 × 10−9 m2/s at 950 °C. Effective case hardening of AISI 1018 steel was carried out using the medium of cassava leaf, without the addition of barium carbonate (BaCO3) as an energizer.

Preparation and Characterization of Nano Glass–ceramics from CeO2-doped Li2O-SiO2 System for Dental Applications

Glasses based on the basic composition of lithium disilicate (Li2O.2SiO2) together with derived samples containing increasing CeO2 replacing Li2O (0.1, 0.2, 0.5, 1 Mol %) were prepared by melting – annealing method, samples from the prepared parent glasses were thermally heat treated through two-step regime (450° C /10 h – followed by 650° C / 6 h) to convert them to their glass – ceramics derivatives. The main purpose of this study is to find out the main properties of the prepared glass – ceramics to be applied as dental candidates. The optical, FTIR, and thermal expansion properties of the parent glasses were examined to identify the main structural groups which are defined as tetrahedral stronger SiO2 building groups. The detailed separated crystalline phases within the prepared glass–ceramics were identified together with their textural features. The Vickers microhardness data for both the parent glasses and their glass -ceramics derivatives were evaluated. SEM and EDAX measurements indicate the ability of the prepared samples to form hydroxyapatite upon immersion in SBF solution.

Solute Enrichment in the Fusion Zone during Resistance Spot Welding of a Third Generation Advanced High Strength Steel

Resistance spot welding is a critical joining technique in automobile assembly. The load carrying properties of spot welds are generally accepted to correlate with weld diameter, which increases with increasing weld current or duration. The formation of a softened layer, or weld halo, surrounding the fusion zone in a spot-welded third generation (Gen3) advanced high strength steel (AHSS) was recently reported in the literature. To optimize weld performance by schedule design, it is necessary to understand the halo formation characteristics and potential impacts. Accordingly, welding of a Gen3 AHSS was performed using weld times between 130 – 1300 ms. Microhardness mapping characterized weld microhardness and the evolution of the halo during welding. Electron probe microanalysis and timeof-flight secondary ion mass spectrometry enabled measurement of solute distributions through the weld halo, while scanning electron microscopy was used for microstructural characterization. The solidified structure was examined using light-optical microscopy, and with the microhardness and compositional data, used to infer the mechanism by which the halo forms during welding. It was found that the halo develops due to solute rejection from a cellular solidification front that advances towards the center of the fusion zone while weld current is applied. Extended weld times increase the size of the weld halo and the solute content of the inner fusion zone. The decrease in weld halo microhardness and the increase in inner fusion zone microhardness is largely explained by the changes in local carbon content associated with halo formation.

Surface roughness, optical properties, and microhardness of additively and subtractively manufactured CAD-CAM materials after brushing and coffee thermal cycling.

To evaluate the surface roughness, optical properties, and microhardness of additively or subtractively manufactured CAD-CAM materials after simulated brushing and coffee thermal cycling. Two additively manufactured resins (Crowntec, CT and VarseoSmile Crown Plus, VS) and 3 subtractively manufactured materials (a reinforced composite (Brilliant Crios, BC), a polymer-infiltrated ceramic network (Enamic, VE), and a feldspathic ceramic (Mark II, VM)) were used to fabricate disk-shaped specimens (Ø10×1-mm) (n = 10). Surface roughness, Vickers microhardness, and color coordinates were measured after polishing, while surface roughness was also measured before polishing. Specimens were then subjected to 25000 cycles of brushing and 10000 cycles of coffee thermal cycling, and measurements were repeated after each time interval. Color difference (ΔE00 ) and relative translucency parameter (RTP) were calculated. Robust analysis of variance test was used to evaluate surface roughness, ΔE00 , and RTP data, while generalized linear model analysis was used for microhardness data (α = 0.05). Material type and time interval interaction affected tested parameters (p ≤ 0.002). In addition, material type affected all parameters (p < 0.001) other than surface roughness (p = 0.051), and time interval affected surface roughness and microhardness values (p < 0.001). Tested materials mostly had their highest surface roughness before polishing (p ≤ 0.026); however, there was no clear trend regarding the roughness of materials within different time intervals along with ΔE00 and RTP values within materials or time intervals. VS and CT had the lowest microhardness regardless of the time interval, while the remaining materials were listed as VM, VE, and BC in decreasing order (p < 0.001). Coffee thermal cycling only reduced the microhardness of VM (p < 0.001). Tested additively manufactured resins can be considered more susceptible to simulated brushing and coffee thermal cycling than the other materials, given the fact that their surface roughness and ΔE00 values were higher than previously reported acceptability thresholds and because they had the lowest microhardness after all procedures were complete.

Effect of Sn Addition on the Microstructure and Age-Hardening Response of a Zn-4Cu Alloy

The aim of this research is to assess the influence of Sn inclusion on the microstructure evolution and age-hardening response of a Zn-4Cu alloy. This is the first study to correlate the age-hardening response to the microstructure of Zn-4Cu alloy reinforced with different Sn contents. A series of Zn-4Cu-Sn alloys were successfully fabricated with different Sn concentrations in the range of 0.0–4.0 wt.% using permanent mold casting. The microstructure of Zn-4Cu-Sn alloys was investigated by means of a scanning electron microscope (SEM) attached with an energy dispersive spectroscope (EDS) and X-ray diffraction (XRD) line profile analysis. At room temperature, the Vickers microhardness measurements were used to assess the age-hardening response of alloys. The results show that the microhardness of the Zn-4Cu (ZC) binary alloy increases a little bit from 76 to 80 HV as the aging time increases from 2 to 128 h, respectively. For aging times up to 16 h, the microhardness of all Sn-containing alloys decreases but then increases again. The lowest hardness belongs to the ZC-1.5Sn alloy, and the Sn-Zn-3.0Sn alloy has the highest; the other alloys fall somewhere in between. At high aging times (64 and 128 h), the microhardness of all Sn-containing samples increased continuously with an increasing Sn content from 0.0 to 3.0 wt.%. When the Sn-containing alloys (3.5 and 4.0 wt.% Sn) were aged for 64 and 128 h, the hardness declined by 7.94% and 8.90% compared to their peak aging hardness values, respectively. By considering the structural changes that occur in the Zn-4Cu-Sn alloys, the reasons for the observed variations in microhardness data with increasing Sn content and aging time were elucidated. X-ray diffraction (XRD) data was analyzed to determine the zinc matrix’s lattice parameters, c/a ratio, and unit cell volume variations.

Study of Microhardness and Plasticity Parameter of Lead in External Magnetic Fields with Induction up to 0.5 T

Microhardness tests of samples of technically pure lead are carried out without and with exposure to external magnetic fields with inductions of 0.3 T, 0.4 T, and 0.5 T. The dependences of the C2-grade lead surface microhardnesses on the exposure times in a magnetic field are obtained, thus reflecting the influence of the magnetic field on the plastic characteristics of lead. The exposure time at which the maximum effect on microhardness occurs is revealed. Additional microhardness tests are carried out for cases with magnetic fields with inductions of up to 0.3, 0.4, and 0.5 T and exposure times of 0.25, 0.5, and 1 hour. Following the obtained microhardness data, the plasticity parameters of lead samples in their initial state and after exposure are calculated. The dependences of the plasticity parameters on the exposure times are shown. The behavior of the plasticity parameter of lead samples during their exposure to external magnetic field with induction up to 0.5 T is revealed. The percent changes in the values of microhardness depending on the magnetic field induction are shown.

In vitro bleaching efficacy of violet LED associated with 10% hydrogen peroxide and 10% carbamide peroxide

BackgroundThis in vitro study evaluated the efficacy and the effect over the dental enamel surface of violet LED dental bleaching associated to different concentrations of carbamide and hydrogen peroxide. MethodsHuman dental blocks (n = 100) were randomly distributed into 5 groups: 10% hydrogen peroxide (HP10), 10% carbamide peroxide (CP10), 10% hydrogen peroxide with violet LED (VHP10), 10% carbamide peroxide with violet LED (VCP10) and 35% hydrogen peroxide (HP35). The specimens were analyzed by Vickers microhardness test (n = 50) initially, immediately after and seven days after ending the bleaching protocol. For color analysis (n = 50), the specimens were evaluated for bleaching effectiveness (ΔE2000, ΔE1976) and whiteness index (ΔWID) with EasyShade spectrophotometer, before bleaching protocol and seven days after ending the bleaching protocol. The microhardness and color data were analyzed using one-way ANOVA with post-hoc Tukey test (α = 0.05). ResultsThe microhardness values showed difference among the investigated groups only immediately after the end of the dental bleaching (p < 0.05), with reduction for the groups HP35 (p < 0.01) and HP10 (p < 0.05), however the microhardness values were reestablished after seven days. Regarding the color changes, a difference between VHP10 and the others groups evaluated for ΔE2000 and ΔE1976 index was observed (p < 0.05). For ΔWID, there was no difference between the studied groups. ConclusionsViolet LED associated with low concentration bleaching agents did not show a negative effect on dental enamel regarding the surface microhardness. All bleaching protocols were effective, therefore, perceptible to human eyes.

Simulation and Optimization of Shot Peening Process for CoCrFeNiAlx High-Entropy Alloy

In this work, Ti-10V-2Fe-3Al alloy was selected as the test material, and the shot peening process of a CoCrFeNiAlx system high-entropy alloy was simulated based on effective test conditions, and the effects of dry shot peening and wet shot peening on the surface properties were determined. Preliminary simulation results the surface of the test sample display a clear plastic deformation state that gradually diminishes and shifts towards the outermost layer. The stress transfer of the test sample gradually decreases, showing a gradient change, and the twin density also shows a random sample change. Then, the high-entropy alloy shot peening process was optimized, and the best process parameters were determined by analyzing the microhardness data, depth of action layer, and surface state. It was found that after wet shot peening, a new characteristic peak is generated, and with the increase in the size of the shot, its overall kinetic energy becomes increasingly higher, the strain energy of the material surface becomes increasingly higher, and the grain refinement is relatively high. This work provides a new approach to investigating the issues that are present during the shot peening process of CoCrFeNiAlx system high-entropy alloys.

Moldflow Simulation and Characterization of Pure Copper Fabricated via Metal Injection Molding.

Metal injection molding (MIM) is a representative near-net-shape manufacturing process that fabricates advanced geometrical components for automobile and device industries. As the mechanical performance of an MIM product is affected by green-part characteristics, this work investigated the green part of pure copper processed with MIM using the injection temperature of ~180 °C and injection pressure of ~5 MPa. A computational analysis based on the Moldflow program was proposed to simulate the effectivity of the process by evaluating the confidence of fill, quality prediction, and pressure drop of three distinctive regions in the green part. The results showed that the ring and edge regions of the green parts showed localized behavior, which was related to processing parameters including the position of the gate. A microstructural observation using scanning electron microscopy and a 3D X-ray revealed that both the surface and body matrix consisted of pores with some agglomeration of micro-pores on the edges and ring part, while any critical defects, such as a crack, were not found. A microhardness analysis showed that the three regions exhibited a reasonable uniformity with a slight difference in one specific part mainly due to the localized pore agglomeration. The simulation results showed a good agreement with the microstructures and microhardness data. Thus, the present results are useful for providing guidelines for the sound condition of MIM-treated pure copper with a complex shape.

Flexural Strength and Vickers Microhardness of Graphene-Doped SnO2 Thin-Film-Coated Polymethylmethacrylate after Thermocycling

Removable dental prostheses are commonly fabricated using polymethylmethacrylate, a material that does not have favorable mechanical properties and needs reinforcement with particles such as graphene. The aim of this study was to evaluate the flexural strength (FS) and Vickers microhardness of a heat-polymerized polymethylmethacrylate coated with graphene-doped stannic oxide (SnO2) thin films using a thermionic vacuum arc method after thermocycling. Forty bar-shaped specimens (65 × 10 × 3 mm) were fabricated using a heat-polymerized denture base resin and divided into four groups according to the graphene-doped SnO2 thin film surface coating performed: No-coat (uncoated), Coat-15 s (coating duration of 15 s), Coat-20 s (coating duration of 20 s), and Coat-30 s (coating duration of 30 s) (n = 10). The thermionic vacuum arc method was used to coat both surfaces of the specimens of each test group with varying durations, and surface coating was verified using Fourier Transform Infrared Spectroscopy. Specimens were subjected to 10,000 cycles of thermocycling. Atomic force microscopy was used to evaluate the surfaces of all specimens before and after thermocycling. Microhardness values were measured five times and averaged. Then, each specimen was subjected to a three-point bending test, and FS values were calculated. Data were analyzed using one-way analysis of variance and Bonferroni tests (α = 0.05). Differences among test groups were nonsignificant when FS data were considered (p = 0.605). However, significant differences were observed among test groups when Vickers microhardness data were considered (p &lt; 0.001). Coat-30 s had the highest hardness (p ≤ 0.003), while the difference among remaining groups were nonsignificant (p ≥ 0.166). Graphene-doped SnO2 thin film surface coatings did not significantly affect the FS of tested heat-polymerized denture base resin but increased the Vickers microhardness when the coating duration was 30 s.

Study on the microstructure evolution mechanism of copper single phase alloys under deep undercooling conditions

This article mainly used the deep undercooling technology to treat Cu60Ni40, Cu60Ni38Co2, and Cu60Ni35Co5 alloys to obtain different undercoolings. By using high speed cameras, the rapid solidification process was recorded to analyze the relationship between its evolution law and the magnitude of undercooling. When observing its microstructure, it was also found that there was a critical undercooling degree throughout its entire solidification process. The influence of Co element addition on solidification rate, recalescence effect, and critical undercooling of copper based single-phase alloys under undercooling conditions was explored. EBSD analysis was conducted on the refined microstructure of the alloy that achieved the maximum undercooling, and the significance of grain orientation and orientation difference distribution was found. TEM tests were conducted on a Cu60Ni38Co2 alloy with a maximum undercooling of 259 K, and it was found that there are high-density dislocation networks in some areas within them. Finally, the Vickers hardness of the above alloys was measured and recorded using a microhardness tester (HVS-1000Z), and the evolution between microhardness and undercooling, as well as the changes in microhardness under critical undercooling, were analyzed. Based on the analysis of EBSD, TEM, and microhardness data above, it is found that grain refinement at high undercooling is dominated by recrystallization.

Glasses and Glass–Ceramics from Li2O-KF-TiO2-SiO2 System Doped with SiC

Unfamiliar invert host silicate glass from the system SiO2-TiO2-KF-Li2O was prepared together with SiC doped samples by traditional melt-quenching technique. Collective characterization of the prepared glasses through FTIR, optical, thermal and microhardness properties were measured to justify the effect of silicon carbide (SiC) on the resultant data. Silicon carbide is selected because its known high mechanical and thermal properties and extended applications of SiC- containing candidates in several domains. Structural FTIR characterization of the prepared glasses reveals familiar silicate network in spite of their invert percent together with the suggested sharing of Si-Ti or Ti-Ti or fluoride units. Optical spectra show only distinct UV absorption with additional small peaks at 380–420 nm in high percent of SiC. Such UV spectra are assumed to originate from unavoidable traces of ferric ions contaminated within the raw materials used for the preparation of glasses. The known high thermal and mechanical properties of silicon carbide are identified to be reflected on the measured thermal expansion and Vickers microhardness data. Samples from the parent glasses were thermally heated to produce their corresponding glass-ceramic derivatives. X-ray diffraction analysis indicate the formation of the peculiar orlovite crystalline phase as a major one due to the presence of all the constituents within the chemical composition of the invert glass. Also, some minor crystalline phases of lithium silicate or lithium titanium silicate are identified. It is assumed that the presence of self-nucleation Li2O and high negatively charged fluoride anions beside the conditional oxide of TiO2 facilitate the ease of nucleation and crystallization of the formed crystalline phase. SEM results confirm the x-ray data showing different crystalline features with the addition of SiC.

Physical-mechanical properties of a flowable nanofiber-reinforced resin composite

This in vitro study aimed to evaluate the effect of toothbrushing simulated test on wear and roughness of different low-viscosity resin composite, as well as the polymerization shrinkage stress. Thirty rectangular specimens (5 × 10 × 3 mm) were prepared and assigned into three different low-viscosity resin composites (n=10): Filtek flow Z350 (Z350); NanovaPro fill (Nanova), and SureFil SDR Flow (SDR). The specimens were brushed for 100.000 cycles using a toothbrushing testing machine with soft bristle tips (Colgate Classic, Colgate-Palmolive Co., Osasco, Sao Paulo, Brazil) and dentifrice suspension (Colgate MFP, Colgate-Palmolive Co.) in deionized water under a 300 g load. The surface roughness (Ra) (n=10) (before and after brushing) and wear (mm) (n=10) were measured by roughness tester. Also, the microhardness (KHN) (n=5) and shrinkage stress (MPa) (n=5) were evaluated. Data were analyzed by one-way for wear, microhardness and shrinkage stress data and two-way for roughness ANOVA and Tukey test (α = 0.05). The Nanova group presented higher final roughness (1.79±0.36) (p &lt; 0.031), wear (13.87±3.26) (p &lt;0.001) and microhardness (52.56±1.7) than the other groups (p &lt; 0.006). For tensile test, all materials showed no difference in relation to shrinkage stress (p= 0.468). The Nanova group showed higher wear and roughness than the other groups. SDR and Z350 were statistically more resistant to wear.