Increase In Microhardness Values Research Articles

A comparative study of laser fluence effect on surface modification and hardness profile of austempered ductile iron

The impact of laser transformation hardening (LSH) and Laser surface melting (LSM) on an austempered ductile iron (ADI) alloy was investigated. Various laser fluences (J mm−2) were irradiated on the ADI specimens, obtained by different beam powers and scanning speeds to reach the optimum parameters to attain a surface with a good combination of high hardness and deep hardened depth, together with obtaining minimal distortion and crack-free surface. ADI surfaces were treated by means of high-power Nd:YAG laser in continuous wave mode. A detailed investigation of the obtained microstructure was characterized via optical and scanning electron microscopy attached to an EDX analyzer as well as X-ray diffraction analysis. Such a wide laser fluence range has a considerable effect on the achieved microstructure. A process parameter map was established which indicated that three different laser treatments were induced under such values of laser fluences: a laser transformation hardening, a partial laser melting, and a complete laser melting. The results revealed that to produce a hardened microstructure, specimens have to be operated within a very small range of laser fluence from 9.6 up to 29 J mm−2, achieving surface hardness values around 900 HV0.1 and depths of approximately 184–700 μm, respectively. Meanwhile, partial melting of the treated layer took place at a medium energy density range from 37 to 112 J mm−2, by a further increase in laser fluence (120–360 J mm−2), complete melting occurred which resulted in a deeper treated layer that reached 3.5 mm with an increase in microhardness value to almost 1100 HV0.1 at 360 J mm−2. The obtained microstructure in case of low laser fluence consisted of an austenite dendritic structure with undissolved graphite nodules, however, at medium and high laser fluence, the microstructure contains large cementite plates, iron-silicon carbides, a small area of ledeburite structure, and some retained austenite. The quantitative amounts of such phases directly depend on the applied laser fluence. Such phases were identified by means of EDX analysis.

Effect of Combined Laser Thermal and Shock Wave Effects on the Mechanical and Tribological Properties of Steels.

Herein, we present the results of an experimental study on the mechanical properties of Fe-C alloys with different carbon contents (0.2, 0.45, and 0.8%) in a wide range of deformation rates (10-3-103 s-1) and abrasive wear resistance, which underwent combined laser thermal (laser surface hardening-LSH) and laser shock wave (Laser Shock Peening-LSP) processing. The combined treatment modes included a different sequence of exposure to laser thermal and laser-induced shock pulses on the material. The amplitude and duration of laser-induced shock waves were measured using a laser Michelson interferometer. The mechanical properties of steel samples were studied under conditions of uniaxial tension under static loads on a standard universal testing machine, the LR5KPlus, and under dynamic loading, tests were carried out on a specialized experimental complex according to the H. Kolsky method using a split Hopkinson rod. The abrasive wear resistance of hardened surfaces was studied using the Brinell-Haworth method. Studies have shown that the use of a combination of LSH and LSP treatments leads to an increase in both the mechanical properties of steels and abrasive wear resistance compared to traditional laser hardening. It has been established that in the combinations considered, the most effective is laser treatment, in which LSP treatment is applied twice: before and after LSH. Thus, after processing steels using this mode, an increase in the depth of the hardened layer was recorded-by 1.53 times for steel 20, by 1.41 times for steel 45, and by 1.29 times for steel U8-as well as a maximum increase in microhardness values by 22% for steel 20, by 27% for steel 45, and by 13% for U8 steel. The use of this mode made it possible to obtain the maximum strength properties of the studied materials under static and dynamic loading, which is associated with an increase in the volume fraction of the strengthened metal and high microhardness values of the strengthened layer of traditional LSH. The dependences of abrasive wear of the studied steels after various combinations of LSP and LSH impacts were established. It is shown that the greatest wear resistance of the studied steels is observed in the case when the LSH pulse is located between two LSP pulses. In this case, abrasive wear resistance increases by 1.5-2 times compared to traditional LSH.

FARKLI CAM İYONOMER SİMANLARIN RENK STABİLİTELERİ VE MİKROSERTLİKLERİ

Objective
 Glass ionomers are preferred in many different
 treatment procedures in dentistry due to their positive
 features. The aim of this study is to evaluate the
 color difference and microhardness values of various
 glass ionomer cement after storing them in different
 solutions.
 Material and Method
 A total of 120 samples were prepared, including 40 of
 each of the Equia Forte, AHfil Silver, and Ionofil glass
 ionomers. Each glass ionomer sample was stored in
 distilled water, cola, tea, and coffee solutions. Color
 and microhardness measurements of the specimens
 were performed before and after a week before it was
 immersed in solutions. The color measurements of the
 samples were evaluated with a spectrophotometer and
 microhardness values were evaluated with Vickers
 microhardness device. For color analysis, color
 changes (ΔE) were calculated by obtaining the values
 of L*, a*, and b* of the samples before and after a week
 after being immersed in solutions. The data obtained
 were evaluated by variance analysis (ANOVA) and
 Tukey’s test.
 Results
 Except for specimens stored in cola for AHfil Silver,
 microhardness values were increased for all materials
 immersed in test solutions. The highest color change
 was obtained in coffee for Equia Forte, in the samples
 immersed in cola for AHfil Silver and Ionophil (p

Microstructural and Mechanical Behavior Investigations of Nb-Reinforced Mg–Sn–Al–Zn–Mn Matrix Magnesium Composites

This research focuses on the fabrication and characterization of TAZ532-xNb composites, employing high-purity, micron-sized powders of Mg, Sn, Al, Zn, Mn, and Nb as the raw materials. These powders were subjected to a paraffin coating process aimed at mitigating oxidation. The formation of composites was achieved via hot pressing and was followed by surface preparation and analysis using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). An X-ray diffraction (XRD) study was conducted to identify the microstructural phases. Quantitative assessments including the theoretical density, actual density, and relative density were computed, and their fluctuations in relation to the increasing Nb reinforcement ratio were scrutinized. Furthermore, the mechanical attributes of the composites, such as hardness and tensile strength, were assessed via experimental procedures. The absence of oxygen-related peaks in the XRD patterns endorsed the successful execution of the paraffin coating technique and protective gas atmosphere during sintering. The detection of α-Mg, Mg2Sn, MgZn, Mg17Al12, and Nb phases within the Nb-reinforced composite patterns authenticated the formation of the intended phases. Notably, the relative density values of the composites surpassed 95%, indicating efficient sintering. SEM results disclosed a densely packed microstructure, with Nb reinforcement particles evenly distributed along the grain boundaries, devoid of particle clustering or significant grain growth. These composites manifested exceptional wetting characteristics, which can be attributed to the employment of Mg alloy as the matrix material. EDS data confirmed the proportions of Nb within the composites, aligning with the quantities incorporated during fabrication. The composites showcased an increase in microhardness values with the escalating Nb reinforcement ratio, credited to the harder constitution of Nb particles in comparison to the matrix alloy. Concurrently, tensile strength showed a significant improvement with the increment in Nb reinforcement, while elongation values peaked at a specific Nb reinforcement level. The positive evolution of tensile strength properties was ascribed to the escalated Nb reinforcement ratio, grain size, and consequent higher sample densities.

Evaluation of the remineralizing efficacy of GC Tooth Mousse Plus and Enafix using surface microhardness and surface roughness analysis in deciduous molars: an in vitro study

Aim: To compare and evaluate using surface microhardness measurement, and surface roughness analysis in deciduous molars using GC Tooth Mousse Plus and Enafix. Material and methodology: A four-equal window acid resistant varnish was placed around the exposed enamel surface of forty removed deciduous molars before they were submerged in a demineralizing solution and remineralized for weeks using Tooth Mousse Plus and Enafix. Statistical Analysis Used: One Way ANOVA and Post Hoc Turkey test (P<0.05) were used Results: Following 4 weeks of remineralization, all specimens underwent SEM analysis and revealed indications of thickening of their inter-rod material. Tooth Mousse Plus also revealed pronounced remineralization evidence. Enafix demonstrated greater resistance to breakdown during the last acid exposure. Surface micro hardness (SMH) and surface roughness (Ra) both showed comparable results, with a noticeable decrease in roughness values and an increase in microhardness values, while Enafix showed a greater source of remineralization and Tooth Mousse Plus showed a greater resistance to the final acid challenge. Conclusion: Enafix has demonstrated superior resistance to the final acid trial, whereas superior remineralization property was seen in GC Tooth Mousse Plus.

INVESTIGATION OF THE STRUCTURE AND INFLUENCE OF ION EXCHANGE ON THE MICROHARDNESS OF LOW-ALKALI TRANSPARENT GANITE GLASS-CERAMICS

Transparent glass-ceramics are attracting more and more attention as a material for protecting the screens of electronic devices. The paper considers the possibility of carrying out ion-exchange of transparent gahnite glass-ceramics containing a small Na2O content. The structure and properties of glass-ceramics before and after ion-exchange were studied by x-ray diffraction analysis, transmission electron microscopy, Raman spectroscopy, laser-induced breakdown spectroscopy, and Vickers hardness determination. It is shown that, under certain conditions, ion-strengthening of glass ceramics with a low content of alkali ions can lead to an increase in microhardness values.

Effect of Sodium Fluoride Varnish and Potassium Iodide on Remineralization Efficacy of Silver Diamine Fluoride

The purpose of this study was to compare the effect of sodium fluoride(NaF) varnish and potassium iodide(KI) on remineralization efficacy of silver diamine fluoride(SDF) by measuring microhardness and evaluating surface morphology by scanning electron microscope(SEM). Artificial caries lesions were induced on extracted primary molars and vickers microhardness was measured. Specimens were randomly separated into 4 groups for treatment. The specimens in group I were treated with SDF, group II with NaF varnish after SDF, group III with KI after SDF and group IV with distilled water. After 8 days of pH cycling, vickers microhardness was measured and difference before and after treatment was calculated. For SEM, 2 samples were evaluated respectively after enamel polishing, lesion formation and after pH cycling. Group III showed highest increase in microhardness. Group I showed higher increase in microhardness than Group II but without statistical difference. Group IV showed lowest increase in microhardness value among 4 groups. On SEM image, group I, II and III showed smoother and less irregular surface compared to group IV. Amorphous crystal pellicles were observed in group III. In conclusion, SDF, SDF and NaF, SDF and KI groups showed smoother surface and increase in microhardness suggesting the possibility that remineralization effect might take place in oral conditions. In addition, in limited conditions of this study, applying NaF varnish after SDF did not increase the remineralization efficacy of SDF while KI significantly increased the remineralization efficacy of SDF. However, additional study considering various conditions that might affect demineralization and remineralization in clinical situations need to be conducted.

The Effect of Toothpastes Containing Natural Ingredients Such As Theobromine and Caffeine on Enamel Microhardness: An In Vitro Study.

The current study aimed to investigate the effect of biocompatible kinds of toothpastes containing natural ingredients such as theobromine and caffeine on the enamel microhardness after demineralization. 72 maxillary premolar teeth extracted for orthodontic purposes were used in this study. Primary enamel surface microhardness examinations were performed using a Digital Micro Vickers Hardness Tester following the Knoop technique (50 g load for 15 s with three indentations at various points). The specimens were immersed in lactic acid (pH = 5.4) for 7 days, washed with distilled water, dried, and then retested for microhardness. According to the type of toothpaste used for brushing, all specimens were categorized as follows: Group 1, Theodent classic® toothpaste (theobromine); Group 2, Power Energy toothpaste (caffeine); Group 3, Colgate toothpaste (fluoride); and Group 4, distilled water as the negative control. The specimens were retested for enamel microhardness after brushing 2 times a day for one month. After brushing with different types of toothpaste, for all experiment groups, the increase in microhardness values in the demineralized enamel surfaces was significant and there were significant differences between them (p value <0.05). The fluoride group had the highest microhardness and had a significant difference with the caffeine and distilled water groups, but there was no significant difference with the theobromine group (p value <0.05). In the theobromine group, the hardness was considerably higher than in the caffeine and distilled water groups. There was no significant difference between the caffeine and distilled water groups. Theobromine toothpaste had the same remineralization effect as that of fluoride toothpaste, while caffeine toothpaste had no positive effect on the remineralization process.

Development of Ni + TiB2 metal matrix composite coating on AA6061 aluminium alloy substrate by gas tungsten arc cladding process

In the present research work Ni + TiB2 metal matrix composite coating was deposited on AA6061 aluminium alloy substrate using nickel and titanium diboride as precursor by gas tungsten arc cladding process. The TIG torch was used as heat source to melt the preplaced powder mixture. The mixture of TiB2 and Ni powders were taken as 10 wt% and 90 wt% respectively. The three level of currents were used as variable parameters to melt the pre-placed powder layer viz. 120Amp, 140Amp and 150Amp. The microstructure of coated layer was investigated by field emission scanning electron microscope (FESEM) and the chemical composition of the coated layer was detected by energy dispersive spectroscopy (EDS). From the microstructural study it was found that the coating exhibits good metallurgical bond between coated layer and substrate. For analyzing the micro-hardness of coated layer Vickers micro hardness testing was performed along the cross-section of the coated samples. The maximum microhardness value of coated layer was 1233 HV, for sample cladded at current of 150 Amp. It was observed that increase in micro hardness value of coated sample was about 11 times higher than that of the aluminium alloy substrate (110HV). It was found that with increase in applied current, amount of microhardness of coated sample increased.

The effects of combining erbium, chromium: Yttrium-scandium-gallium-garnet laser irradiation with fluoride application in controlling the progression of enamel erosion

ObjectiveIncreasing enamel resistance to acid may be useful for preventing cavitation and could reduce changes in the enamel’s microhardness. Topical fluoride application and laser irradiation promote acid resistance of dental substrates. The aim of the study was to assess the efficacy of erbium, chromium: yttrium-scandium-gallium-garnet laser irradiation in combination with fluoride application to control enamel erosion. DesignSixty human premolar specimens were prepared (N = 60) and were randomly assigned to 5 groups, twelve specimens in each group (n = 12/group) according to surface treatment. The groups were as follows: group 1 (C): control with no treatment; group 2 (F): application of 1.23% acidulated phosphate fluoride gel alone; group 3 (L): laser irradiation alone; group 4 (F+L): acidulated phosphate fluoride gel followed by laser irradiation; group 5 (L+F): laser irradiation followed by acidulated phosphate fluoride gel. All the specimens were eroded 10 min in citric acid. Baseline measurements were performed using a Vickers microhardness tester before surface treatment. Subsequently, all specimens were subjected to a 60 min erosion-remineralization cycle for five days followed by measurements of the final surface microhardness. Statistical comparisons were performed by a one-way analysis of variance and Tukey’s post hoc analysis. ResultsThe control, laser, and fluoride + laser groups showed a statistically significant decrease in microhardness values between baseline and post-erosion measurements (P < 0.05), indicating that these treatments could not prevent erosion progression. However, the fluoride and laser + fluoride groups showed a significant increase in microhardness values compared to baseline. ConclusionsOur results suggest that compared to that of the control group, acidulated phosphate fluoride application as well as laser irradiation prior to fluoride application increased enamel surface microhardness and prevented the progression of enamel erosion.

Erosion wear behavior of spark plasma-sintered Ti-6Al-4V reinforced with TiN nanoparticles

The extensive application of titanium alloys is delimited as their erosion wear properties deteriorate when exposed to erosive and harsh environments. The present research investigates the effects of TiN additions (2, 4, and 6 vol.%) on the Ti-6Al-4V alloy prepared by spark plasma sintering technique. Erosion wear behaviour of the composites was investigated by high-velocity solid particle erosion test and tribometer pin-on-disc friction module method. The duration of the test was 10 min, while the mass loss of the sample was recorded after 2-min interval. The surface analysis and phase identifications of the sintered composites were examined by optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. Microstructural analysis revealed a transformation from lamellar with β grain boundaries in Ti-6Al-4V alloy to bimodal structures upon addition of TiN nanoparticles. XRD patterns of the alloy indicated an increase in diffraction peaks from lower intensity to high intensity with an increase in TiN nanoparticle content. Erosion is visible in Ti-6Al-4V alloy, 4 and 6 vol.% TiN, but less severe with 2 vol.% TiN addition for all the test times. However, this is due to grain detachment of the hard phase regions between the matrix and the reinforcing phase of the composites. The results showed the presence of micro-voids on the eroded surfaces. It was found that Ti-6Al-4V alloy with TiN nanoparticle addition was resistant to erosion wear, while the recorded steady-state friction coefficients for all the samples range from 0.2 to 0.4. However, an increase in microhardness values ranges from 342 to 513 HV0.1.

Characterization of Hybrid Bio-Ceramic Hydroxyapatites Reinforced by Expanded Perlite-TiO2-ZrO2-MgO-P2O5

Background: Hydroxyapatite, which is naturally and synthetically available, is often used as a biomaterial because of its similarity to bone. Aim: In this study, Natural hydroxyapatite powder, synthesized from sheep bone, and synthetic hydroxyapatite were used as matrix. Materials and Methods: Hybrid bio-ceramic composites were obtained by adding 5 wt. % expanded perlite-TiO2-ZrO2-MgO-P2O5 to both matrixes. The bio-ceramic materials which were mixed with mechanical mixer for 30 minutes were pressed with hydraulic press under 25 MPa pressure and sintered at 900°C for 1 hour. Density, micro-hardness, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis were performed to determine characteristics of the samples. Results: As a result, it was identified that the micro-hardness of natural hydroxyapatite was higher. In addition, the increase in micro-hardness values of ZrO2-reinforced samples was higher than the TiO2-reinforced samples. Conclusion: Hydroxyapatite, calcium silicate, calcium phosphate structures were observed in XRD analysis. Micro-pores were observed in TiO2-reinforced samples while more dense structures were observed in ZrO2-reinforced samples.

Effect of die parameters on the grain size, mechanical properties and fracture mechanism of extruded AZ31 magnesium alloys

The study was carried out to evaluate the effect of extrusion ratio and extrusion die angle on the mechanical properties and microstructure of AZ31 magnesium alloy at 300 °C extrusion temperature with three different extrusion ratio of 1.77, 2.68, 3.55 and die angles of 100, 150, 200. It was identified that microstructure was significantly refined for all extrusion ratios. The average size was decreased to the range of 4.1 μm–13.3 μm from 22.4 μm. By increasing extrusion ratio, it was observed that the tensile properties were considerably improved at room temperatures and tensile strength was reached to maximum 331 MPa after extrusion when initial measured value was 168.28 MPa. Significant grain refinement, enhanced mechanical strength and increase in microhardness values were observed with smaller die angles. It was observed that DRX mechanism is active and it supports the grain refinement. Dimples seen on the fractured surface were deeper that indicates the enhanced ductility of the material. Finally, among all the tests higher extrusion ratio with lower die angle gives better grain distribution in the microstructure and higher mechanical strength to the product.

Influence of carbon content on the martensitic transformation of titanium stabilized austenitic stainless steels

Austenitic stainless steels (ASS) are corrosion resistant alloys in which the desirable mechanical properties may be attained by cold working in the final stages of the fabrication process. This manufacturing process may induce martensitic transformation from the austenitic phase, where the chemical composition plays an important role as it influences the stacking fault energy (SFE). Therefore, this work evaluated the influence of carbon content on martensitic transformation of Ti stabilized ASS. Thus, the austenite transformed into martensite by cold rolling was observed by Light Optical Microscopy (LOM) and quantified by Vibrating Sample Magnetometer (VSM), and X-Ray Diffraction (XRD) for Ti stabilized ASS with different carbon contents. The experimental results about the martensitic transformation behavior for each alloy were compared with previous results on other ASS and Duplex Stainless Steel (DSS), tested in similar conditions, verifying a high correlation with a sigmoidal model previously applied in these alloys. Additionally, it was carried out a SFE analysis, estimated by thermodynamic model, corroborating that the alloy’s carbon content has a strong influence on the material’s stability. Finally, it was observed a sudden increase in microhardness value as a consequence of the high amount of austenite transformed into martensite at very low strains that might affect the steels performance in several applications.

Antibacterial efficacy and remineralization capacity of glycyrrhizic acid added casein phosphopeptide-amorphous calcium phosphate.

The aim was to evaluate remineralization capacity and antibacterial efficiency of Tooth Mousse and various amounts of glycyrrhizic acid added Tooth Mousse on primary tooth enamel. Three groups were formed; Group 1 (CPP-ACP), Group 2 (CPP-ACP + 5% glycyrrhizic acid), and Group 3 (CPP-ACP + 10% glycyrrhizic acid) in order to evaluate remineralization capacity. Enamel samples were immersed in demineralization solution and then remineralization agents were applied. Surface microhardness and SEM analyses were performed at the beginning, after demineralization and remineralization. For antibacterial tests, four groups were formed; Group 1, Group 2 and Group 3 and Group 4 (control). Biofilms were then exposed to 10% sucrose eight times per day for 7 days. After biofilm growth period, samples were treated with materials to evaluate antibacterial efficiency except control group. After application of materials, samples were incubated 2 more days at 37°C and at the end of this period, absorbance values of biofilms were determined and data were analyzed. An increase in microhardness values was Group 2 > Group 3 > Group 1, respectively, but there were no significant differences. After remineralization, microhardness values showed significant increases when compared to demineralized groups, but there was no significant difference. All groups showed decreased absorbance value of biofilm when compared with control group but they were insignificant. It was observed that both in Group 2 and Group 3, glycyrrhizic acid did not have a negative effect on remineralization and although they have an increase, it was insignificant. Although glycyrrhizic acid added CPP-ACP groups showed increased antibacterial activity, they were not statistically significant.

The comparative evaluation of the effects of antioxidants pretreatment on remineralization of demineralized dentin - In vitro study

Context: Mechanical performance of dentin is of significant significance for the overall function of the teeth. Remineralization of carious dentin is the ultimate goal in re-establishing the functionality of the affected tissue to regain and maintain the mechanical properties of dentin. Functional remineralization of the affected dentin involves stabilization of both inorganic and organic component, but remineralizing agents stabilize only inorganic content. Hence, to stabilize organic content and to bring in functional remineralization, the use of anti-collagenolytic and anti-elastastic agents was considered for this study. Aims: The aim is to assess and compare the effect of antioxidants pretreatment on remineralization of demineralized dentin-in vitro study. Settings and Design: Experimental randomized analytical- in vitro study. Subjects and Methods: Ninety specimens were subjected to artificial caries lesions and were randomly divided into six groups based on the pretreatment with white tea, and grape seed extract (GSE) followed by casein phosphopeptide amorphous calcium phosphate and casein phosphopeptide amorphous calcium phosphate with fluoride. All the specimens were subjected to pH cycling regimen. The specimens were subjected to Vickers micro-hardness test to obtain the micro-hardness values. Statistical Analysis Used: The values were statistically analyzed using one-way analysis of variance. Results: After pH cycling, GSE showed a significant increase in micro-hardness values (46.57 ± 3.51 VHN), followed by white tea (42.56 ± 5.20) with the level of significance

Influence of SiAlON Ceramic Reinforcement on Ti6Al4V Alloy Matrix via Spark Plasma Sintering Technique

The titanium-based composite was fabricated by strengthening Ti6Al4V alloy with addition of SiAlON ceramics utilizing spark plasma sintering technique. Ti6Al4V and SiAlON powders were mixed in a T2F Turbula mixer with different proportions (5, 10, 15 and 20 vol%) and the admixed powders were consolidated using spark plasma sintering to produce titanium matrix composites. The characterization of the sintered composites was performed using X-ray diffraction, optical microscopy and scanning electron microscopy. The influence of SiAlON additions on densification, microstructure, microhardness and fracture morphology were investigated on the sintered composites. The experimental results revealed that the densification of the sintered titanium matrix composites was in the range of 95%–98%, which decreased with an increase in SiAlON addition. However, an increase in microhardness values ranging from 363 to 574 HV0.1 was achieved. The microstructure shows that the SiAlON ceramic particle was uniformly distributed within the titanium matrix composites which comprises of a mixture of lamellar colonies with β grain boundaries. The fracture features of all composites exhibit mixed fracture of both intergranular and transgranular fracture mechanism.

Influence of ball milling duration of quarry dust on the properties of nickel-quarry dust composite coating

The main purpose of this research is to investigate the effect of various ball milling duration on the surface morphology, hardness and wear properties of nickel- quarry dust (Ni-QD) composite coating on aluminium alloy 6061 (AA6061) substrate. Ni-QD composite coatings were deposited on zincated AA6061 substrate by using electrodeposition technique. The quarry dust particles were prepared by ball milling process at 5, 10, 15 and 20 hours. Later, the quarry dust particles were added to nickel citrate bath at 50 g/l for electrodeposition of Ni-QD composite coating. The electrodeposition process was carried out for 1 hour at 40º C, under the current density of 3 A/dm2. X-ray Fluorescence (XRF), X-ray Diffraction (XRD) and scanning electron microscope (SEM) analyses were carried out in order to investigate the influence of ball milling duration on the prepared quarry dust as well as the produced composite coating. In addition, microhardness and wear testing of Ni-QD composite coatings were also performed in this study. The microhardness values of the nickel composite coatings using ball milled quarry dust are higher than using crushed quarry dust. The microhardness values for all nickel composite coatings produced from crushed and ball milled quarry dust increases from 190.6 to 282.2. The increase in microhardness values is due to the high density of quarry dust in the electrolyte. The damage of the wear scar was improved, as the ball milling duration increases from 0 to 20 hours.

Chemical exchange between dentin pre-tratment with CPP-ACP and GIC on demineralized dentin in deciduous molars

Aim: To assess the effect of the chemical exchange between restorations using high-viscosity glass ionomer cement (GIC) and the casein phosphopeptide amorphous calcium phosphate CPP-ACP treatment on primary demineralized dentin by analyzing the hardness changes caused by calcium, phosphate and fluoride uptake. Methods: 40 deciduous molars were selected and randomly assigned to four groups according to dentin pretreatment and dentin condition. Class I cavity preparations were performed in 40 sound primary molar samples, equally divided into groups G1 (sound dentin) and G2 (demineralized dentin). Sub-groups (n=10) were set in order to aid in investigating the isolated GIC action or its association with CPP-ACP. This study was conducted in vitro and assessed the chemical exchange under two conditions, namely: sound and demineralized dentin (pH cycling); This in vitro study examined the mechanical and chemical exchange under two conditions – sound and demineralized dentin (pH cycling) – to simulate the mineral loss that occurs for the caries lesion. The 40 teeth first received a topical application of ACP-CPP and a restoration of high viscosity GIC. The 20 teeth assigned to the groups (G1 and G2) were only restored with GIC. The specimens were sliced and prepared for Knoop hardness test (KHN), Micro Raman, and FEG microhardness analysis groups. The statistical analysis used ANOVA and Bonferroni post-test at a 5% significance level. EDS (Dispersive Energy Spectroscopy) and FEG (High-resolution scanning electron microscope) data were qualitatively described. Results: Increased hardness was observed in all sites that had direct contact with GIC in the sound and demineralized dentin samples in all groups (p&lt;0.001); microhardness showed no differences after CPP-ACP application (p&gt;0.05). The direct contact between GIC in sound and demineralized dentins resulted in an increased phosphate peak in the FEG and EDS evaluations. Conclusion: ACP-CPP associated with GIC showed no increase in microhardness values of the demineralized dentin substrate. The exchange between the GIC and the demineralized dentin may induce changes in the mechanical properties of the substrate and in the uptake of mineral ions.Uniterms: dentin; prevention; caries; remineralization; demineralization; biomechanics

Influence of spark plasma sintering on microstructure and corrosion behaviour of Ti-6Al-4V alloy reinforced with micron-sized Si3N4 powder

Abstract Ti-6Al-4V-Si3N4 composites were effectively fabricated by spark plasma sintering (SPS) technique. The addition of Si3N4 on Ti-6Al-4V was varied from 5% to 15% (wt fraction). The effect of Si3N4 addition on the densification, microstructure, and microhardness and corrosion behaviour of Ti-6Al-4V was investigated. An increase in microhardness value was recorded from 325.46 HV0.1 to 585.73 HV0.1. X-ray diffraction (XRD) analysis showed that the intensity of diffraction peaks of Si3N4 phase in the composites increased. The sintered Ti-6Al-4V reinforced with Si3N4 compacts revealed the non-existence of intermediate phases, such as TiSi2 (titanium silicide) which was expected. SEM analysis of the spark plasma sintered composites revealed α and β phase microstructures in Ti-6Al-4V with uniform distribution of Si3N4 particulates in the matrix. The corrosion resistance property of the material was improved by the addition of Si3N4 from 0.986629 mm/year to 0.030547 mm/year.