Top Surface Hardness Research Articles

Comparison of the microhardness of lowviscosity bulk-fill composite resins

The aim of this study is to compare the microhardness of five different low-viscosity bulk-fill composites. The bulk-fill composites used in the study; Estelite Bulk-fill flow (EBF), Filtek Bulk-fill (FBF), SureFil SDR flow (SDR), Tetric EvoFlow Bulk fill (TEFBF), X-tra Base (XBF). Cylindrical molds with a diameter of 5 mm and a height of 4 mm were used for the Vicker's Micro Hardness (VMH) test. Bulk-fill composite resins were placed in these molds at once. The polymerization of the composites was achieved for 20 seconds with the LED light curing. A total of 50 composite discs were prepared (n=10). Then the microhardness of the top and bottom surfaces was measured using MVK-H1 Microhardness Tester (Akashi Co, Tokyo, Japan. Depth of polymerization of each sample was recorded. Data were analyzed by using the Kruskal Wallis H and Mann Whitney-U tests. The bottom and top surface hardness values of the XBF composite samples (43.82±0.95 MPa, 47.87±0.59 MPa) were statistically significantly higher than the other bulk-fill composite samples (p<0.001). The bottom and top surface hardness values of the FBF composite (27.85±0.56 MPa, 22.05±1.40 MPa) were found to be statistically lower than other bulk-fill composite samples (p<0.001). Among the low-viscosity bulk-fill composites used in the study, except for FBF, the VMH values of the others were found to be above 0.80, and it was observed that they reached sufficient microhardness.

Surface microstructure of an IN718 3D coating manufactured by Laser Metal Deposition

Laser Metal Deposition (LMD) is a well-known additive manufacturing (AM) process that offers the ability to repair metal parts, among other benefits. We have focused on IN718 parts that evolve in environments that strongly favor wear. Therefore, a good knowledge of the contact surface microstructure and its properties is necessary to better understand the tribological behavior of these parts. However, the microstructure of the top surface (which is most susceptible to wear) of IN718 coatings deposited by LMD is not particularly well documented in the literature. Most of the studies devoted to this alloy have focused on the study of the cross-sectional microstructure, and the few articles dealing with the top surface microstructure have been devoted to the Laser Powder Bed Fusion (LPBF) process. In this article, four IN718 coatings were successfully fabricated with high density using different scanning strategies. When viewing the microstructure from the top surface, the EBSD map showed a very heterogeneous microstructure with an alternation of fine and coarse grains. It also showed a weak overall texture, but a strong local texture within the fine and coarse grain region. EBSD analysis of the cross-sectional area of the coated section also revealed a microstructure variation along the build direction (BD) with the appearance of small grains between layers after some layers have been deposited. Analysis of both sides of the coated part allowed us to get a better understanding of the final microstructure. We were able to show that this heterogeneous microstructure leads to a spatial variation of the top surface hardness, the pattern of which is directly related to the scanning strategy. Finally, we found that the surface hardness of IN718 LMD samples is higher than that of conventionally produced IN718, which is a promising result in terms of repairing metal parts with good tribological properties.

Mechanical Properties of Experimental Composites with Different Photoinitiator.

Objective The effect of different photoinitiators on mechanical properties of experimental composites was evaluated. Materials and Methods Resin composites were formulated by using a blend of bisphenol A-glycidyl and triethylene glycol (50/50 wt%) dimethacrylate monomers, and 65 wt% of barium aluminium silicate and silica filler particles. Photoinitiators used were 0.2% camphorquinone (CQ) and 0.8% co-initiator (DMAEMA); 0.2% phenyl-propanedione and 0.8% DMAEMA; 0.1% CQ + 0.1% phenyl propanedione and 0.8% DMAEMA; 0.42% mono(acyl)phosphine oxide (MAPO); and 0.5% bis(acyl)phosphine oxide (BAPO). Specimens ( n = 10) were light cured by using a multiple-emission peak light-emitting diode for 20 seconds at 1,200 mW/cm 2 of irradiance and Knoop hardness and plasticization, depth of cure, flexural strength, and elastic modulus were evaluated. Data were statiscally analyzed at significance level of α = 5%. Results Experimental composites containing MAPO and BAPO photoinitiators showed the highest values of flexural strength, elastic modulus, top surface hardness, and lower hardness reduction caused by alcohol compared with CQ. Composites containing CQ and PPD showed similar results, except for depth of cure and hardness of bottom surface. Conclusion BAPO and MAPO showed higher flexural strength, elastic modulus, hardness on top surface, and lower polymer plasticization to CQ.

Impact of light-curing distance on the effectiveness of cure of bulk-fill resin-based composites

ObjectiveTo investigate the effect of light-curing distance on the effectiveness of cure (EC) of bulk-fill resin-based composites (RBCs). Materials and methodsTwo bulk-fill RBCs (a Tetric N-Ceram Bulk Fill (TN) and a Filtek Bulk Fill (FK)) are evaluated. Specimens (4 mm high) are cured for 20 s at different distances (0 mm (D0), 2 mm (D2), 4 mm (D4), 6 mm (D6) and 8 mm (D8)) and stored for 24 h in 100% relative humidity at 37 °C. The top and bottom surface hardness (SH) (n = 12) are assessed using a Knoop microhardness tester and the EC is calculated. The EC is characterized by the hardness ratio (HR) (mean bottom: top SH). An HR of 0.8 is used as the benchmark for an effective/adequate cure. Data are analyzed using one-way analysis of variance and Tukey’s post hoc test (α = 0.05). Correlations between the top and bottom surfaces are examined using the Pearson correlation (α = 0.05). ResultsFor the TN, the HR at D8 is significantly lower than all other light-curing distances, while for the FK, it is significantly lower than D0 only. ConclusionThe effect of light-curing distance on the EC of bulk-fill RBCs is material dependent. Notwithstanding the light-curing distance, the EC of the FK and TN is below the threshold HR value of 0.8 when photopolymerized for 20 s in 4 mm increments in black opaque molds.

Effect of fiber reinforcement on color stability and degree of polymerization of different composite resins

Aim: The aim of this in vitro study was to determine the effect of fiber-reinforcement on the color changes and degree of polymerization of two different composite resins. Materials and Methods: A bulk-fill composite resin and a methacrylate-based composite resin with A2 shade were used in this study. Three groups of specimens (control group with no reinforcements, polyethylene fiber-reinforced composite and glass fiber-reinforced composite groups) were prepared from each composite. The color change of the specimens with polymerization was measured. Then, to determine the degree of polymerization, the hardness ratios were calculated by measuring the bottom and top surface hardness of all specimens. The data were analyzed by analysis of variance, Duncan's multiple range tests, and Independent sample t-test. Results: Statistical analysis of variance presented the significance difference between composite and fiber for color change (P < 0.05). The highest color change by polymerization was seen in the polyethylene fiber-reinforced bulk-fill composite group. It was found that the addition of fiber to composite resins significantly reduced the degree of polymerization (P < 0.05). Conclusion: The addition of fiber may lead to color change and reduce the degree of polymerization of composite resins. The amount of change may differ depending on the structural properties of the composite resins and fiber.

Better Surface Integrity and Tribological Properties of Steel Sintered by Powder Metallurgy.

The current research reports the improvement in surface integrity and tribological characteristics of steel prepared using a powder metallurgy (PM) by ultrasonic nanocrystal surface modification (UNSM) at 25 and 300 °C. The surface integrity and tribological properties of three samples, namely, as-PM, UNSM-25 and UNSM-300 were investigated. The average surface roughness (Ra) of the as-PM, UNSM-25 and UNSM-300 samples was measured using a non-contact 3D scanner, where it was found to be 3.21, 1.14 and 0.74 µm, respectively. The top surface hardness was also measured in order to investigate the influence of UNSM treatment temperature on the hardness. The results revealed that the as-PM sample with a hardness of 109 HV was increased up to 165 and 237 HV, corresponding to a 32.1% and 57.2% after both the UNSM treatment at 25 and 300 °C, respectively. XRD analysis was also performed to confirm if any changes in chemistry and crystal size were took place after the UNSM treatment at 25 and 300 °C. In addition, dry tribological properties of the samples were investigated. The friction coefficient of the as-PM sample was 0.284, which was reduced up to 0.225 and 0.068 after UNSM treatment at 25 and 300 °C, respectively. The wear resistance was also enhanced by 33.2 and 52.9% after UNSM treatment at both 25 and 300 °C. Improvements in surface roughness, hardness and tribological properties was attributed to the elimination of big and deep porosities after UNSM treatment. Wear track of the samples and wear scar of the counter surface balls were investigated by SEM to reach a comprehensive discussion on wear mechanisms. Overall, it was confirmed that UNSM treatment at 25 and 300 °C had a beneficial effect on the surface integrity and tribological characteristics of sintered steel by the PM that is used in a shock absorber for a car engine.

A Study of Composite Surface Hardness When Cured Using Special Accessories with a Curing Light

The study was carried out to compare the Vickers Micro-Hardness (VHN) of composite resin of different diameters (6 mm and 10 mm) prepared in a split mold. The 6 mm and 10 mm diameter composite resin samples were cured with the tip of a fiber optic light. Additional sample for same size were cured with the same tip after a mirror or a lens accessory was mounted to it. All the specimens were cured for 40 seconds. The hardness was calculated for both top and bottom at the center and the periphery. The results showed that the hardness of top surface was higher than that at the periphery. The mean hardness value for specimens cured with the light tip was higher than the hardness of specimens cured with their accessory. Conclusion mirror or lens didn’t potentiate light but distribute the energy to a larger area, resulting in less energy applied to the same small surface area, which reduced the hardness.

Influence of continuous laser treatment on microstructural evolution and mechanical properties of forged Ti-Zr alloy

The influence of different continuous laser injection parameters on microstructure, phase evolution and mechanical properties of Ti-30Zr-5Al-3V (30Zr, wt%) is systematically investigated. The as-prepared 30Zr alloy consists of α and β phase, whereas the surface of 30Zr alloy is composed of α′, α and β phases after laser surface re-melting (LSR). The surface microstructure of laser-treated 30Zr alloys is significantly refined and nanocrystalline is observed in the outermost layer after LSR. The top surface hardness of laser-treated 30Zr alloys is mainly affected by the form of α′ phase and microstructural refinement. Herein, the higher laser power density and longer laser dwelling time resulted in a higher surface hardness of 30Zr alloy. The cross-sectional microhardness of laser-treated 30Zr alloys decreased with increasing distance from the alloy surface.

Laser processing of Ti composite coatings reinforced with hydroxyapatite and bioglass

Composite coatings of titanium reinforced separately with hydroxyapatite (HAp) and bioglass (BG) were deposited on titanium substrate using Laser Engineered Net Shaping (LENS™). The microstructure, phase constituents, in vitro electrochemical, tribological and biological properties of these composite coatings deposited using different laser powers was studied. The composite coatings showed several reaction products such as Ca2P2O7, CaTiO3, Na2Ca2Si3O9 due to high temperature interaction of HAp and BG with Ti. The average top surface hardness of the Ti substrate was 148 ± 5 HV and that of the composite coatings was between 720 and 740 HV. As a result, the composite coatings exhibited significant increase in the in vitro wear resistance. The incorporation of HAp and BG in Ti increased the corrosion current, possibly due to the presence of residual stresses, but shifted the corrosion potential towards noble direction due bioactive reinforcements. In vitro proliferation of mouse embryonic fibroblast cells (NIH3T3) was found to be more on composite coatings than on titanium substrate demonstrating their superior cell-materials interactions.

A gradient nanostructure generated in pure copper by platen friction sliding deformation

A modified friction sliding process with a large applied normal load has been used to develop a gradient nanostructure in Cu using only a short processing time. A quantitative characterization of the variation in microstructure and strength has been carried out by combined use of electron backscatter diffraction and hardness measurements, and the data used to estimate the effective strain profile resulting from the processing treatment. The affected deformation volume extends to a large depth of more than 1mm, with a top surface hardness of 2.28GPa, corresponding to a four-fold increase compared to the initial undeformed material.

In situ synthesized TiB–TiN reinforced Ti6Al4V alloy composite coatings: Microstructure, tribological and in-vitro biocompatibility

Wear resistant TiB–TiN reinforced Ti6Al4V alloy composite coatings were deposited on Ti substrate using laser based additive manufacturing technology. Ti6Al4V alloy powder premixed with 5wt% and 15wt% of boron nitride (BN) powder was used to synthesize TiB–TiN reinforcements in situ during laser deposition. Influences of laser power, scanning speed and concentration of BN on the microstructure, mechanical, in vitro tribological and biological properties of the coatings were investigated. Microstructural analysis of the composite coatings showed that the high temperature generated due to laser interaction with Ti6Al4V alloy and BN results in situ formation of TiB and TiN phases. With increasing BN concentration, from 5wt% to 15wt%, the Young's modulus of the composite coatings, measured by nanoindentation, increased from 170±5GPa to 204±14GPa. In vitro tribological tests showed significant increase in the wear resistance with increasing BN concentration. Under identical test conditions TiB–TiN composite coatings with 15wt% BN exhibited an order of magnitude less wear rate than CoCrMo alloy—a common material for articulating surfaces of orthopedic implants. Average top surface hardness of the composite coatings increased from 543±21HV to 877±75HV with increase in the BN concentration. In vitro biocompatibility and flow cytometry study showed that these composite coatings were non-toxic, exhibit similar cell–materials interactions and biocompatibility as that of commercially pure titanium (CP-Ti) samples. In summary, excellent in vitro wear resistance, high stiffness and suitable biocompatibility make these composite coatings as a potential material for load-bearing articulating surfaces towards orthopaedic implants.

Laser processing of in situ synthesized TiB–TiN-reinforced Ti6Al4V alloy coatings

In situ synthesized TiB–TiN-reinforced Ti6Al4V alloy composite coatings were laser deposited on commercially pure Ti using premixed Ti6Al4V and BN powder. The amount of TiB/TiN was found to increase with increasing BN concentration and laser energy input. Due to the increase in the BN content from 5 to 15 wt.%, the top surface hardness and Young’s modulus increased from 543 to 877 HV and from 170 to 204 GPa, respectively, while the thickness of the coating varied from 467 to 1236 μm.

Laser processed TiN reinforced Ti6Al4V composite coatings

The purpose of this first generation investigation is to evaluate fabrication, in vitro cytotoxicity, cell–material interactions and tribological performance of TiN particle reinforced Ti6Al4V composite coatings for potential wear resistant load bearing implant applications. The microstructural analysis of the composites was performed using scanning electron microscope and phase analysis was done with X-ray diffraction. In vitro cell–material interactions, using human fetal osteoblast cell line, have been assessed on these composite coatings and compared with Ti6Al4V alloy control samples. The tribological performance of the coatings were evaluated, in simulated body fluids, up to 1000 m sliding distance under 10 N normal load. The results show that the composite coatings contain distinct TiN particles embedded in α+β phase matrix. The average top surface hardness of Ti6Al4V alloy increased from 394±8HV to 1138±61HV with 40 wt% TiN reinforcement. Among the composite coatings, the coatings reinforced with 40 wt% TiN exhibited the highest wear resistance of 3.74×10−6mm3/Nm, which is lower than the wear rate, 1.04×10−5mm3/Nm, of laser processed CoCrMo alloy tested under identical experimental conditions. In vitro biocompatibility study showed that these composite coatings were non-toxic and provides superior cell–material interactions compared to Ti6Al4V control, as a result of their high surface energy. In summary, excellent in vitro wear resistance and biocompatibility of present laser processed TiN reinforced Ti6Al4V alloy composite coatings clearly show their potential as wear resistant contact surfaces for load bearing implant applications.

Amelioration of the tribological behaviour of carbon/Ti–6Al–4V and graphite/Ti–6Al–4V couples by plasma nitriding of the titanium alloy

This article reports on the influence of nitriding treatment of titanium alloy on the tribological behaviour of amorphous carbon or graphite/Ti–6Al–4V couples. This contact was investigated in pin-on-disc geometry in an ambient atmosphere. The pins were made of amorphous carbon or graphite and the discs were made of Ti–6Al–4V, nitrided or not. The treatment of nitriding for this study was an N2–H2 plasma nitriding at a low temperature (700 °C) for 12 h. In these conditions, the top surface hardness was improved by a factor of 3. In this study, the mechanism of transfer and wear of carbon against Ti–6Al–4V, nitrided or not, has been studied with a scanning electron microscope, an optical microscope, etc. The analyses show that the nitriding of Ti–6Al–4V improves the tribological behaviour of the couples investigated. In fact, with the disc made of Ti–6Al–4V, the wear of carbon is very high and the disc is worn down at the end of the test. In contrast, after nitriding of the disc, the wear of carbon decreases, and there is a carbon film transfer on the disc. Moreover, with the nitriding of Ti–6Al–4V, the friction coefficient is stabilized, whereas without the nitriding of Ti–6Al–4V, the curve of the friction coefficient is marked by a very important increase during a short time. With the pin in graphite, the nitriding decreases the friction and increases the adhesion on the disc. Furthermore, the tests have shown that the contact temperature increases with the nitriding of Ti–6Al–4V.

Influence of LED irradiance on flexural properties and Vickers hardness of resin-based composite materials

ObjectiveTo investigate the effect of irradiance through choice of LED light-curing unit (LCU) and fiber-optic tip on the mechanical properties of methacrylate resin-based composites (RBCs). MethodsRectangular bar-shaped specimens (25mm×2mm×2mm) of four RBCs, irradiated from one side for the manufacturer's recommended times with one of two LED LCUs, and with either 8 or 13mm tip diameter, were tested in three-point bend for flexural strength and modulus of elasticity; Vickers hardness was measured on top and bottom surfaces, on overlapped and non-overlapped irradiation sites. The effects and interactions of all factors were examined by analysis of variance. ResultsWhile the materials tested differed significantly for all properties (P<1×10−6), there was no significant effect for LCU, tip, or irradiance for flexural strength or modulus of elasticity. For hardness, the only significant effect overall was due to irradiance on the bottom surface. ConclusionsBoth LCUs and both tips could be used to give adequate top surface hardness, but the recommended maximum increment thickness is too great for adequate cure at the bottom with the tested LCUs at the recommended times. An extended experimental design would be valuable to test behavior at much elevated irradiances.

Effect of different light curing units on Knoop hardness and temperature of resin composite

To evaluate the influence of quartz tungsten halogen and plasma arc curing (PAC) lights on Knoop hardness and change in polymerization temperature of resin composite. Filtek Z250 and Esthet X composites were used in the shade A3. The temperature increase was registered with Type-k thermocouple connected to a digital thermometer (Iopetherm 46). A self-cured polymerized acrylic resin base was built in order to guide the thermocouple and to support the dentin disk of 1.0 mm thickness obtained from bovine tooth. On the acrylic resin base, elastomer mold of 2.0 mm was adapted. The temperature increase was measured after composite light curing. After 24 h, the specimens were submitted to Knoop hardness test (HMV-2000, Shimadzu, Tokyo, Japan). Data were submitted to ANOVA and Tukey's test (alpha = 0.05). For both composites, there were no significant differences (P > 0.05) in the top surface hardness; however, PAC promoted statistically lower (P < 0.05) Knoop hardness number values in the bottom. The mean temperature increase showed no significant statistical differences (P > 0.05). The standardized radiant exposure showed no influence on the temperature increase of the composite, however, showed significant effect on hardness values.

Effects of irradiance, wavelength, and thermal emission of different light curing units on the Knoop and Vickers hardness of a composite resin

The aim of this study was to evaluate the effects of irradiance, light emission wavelength, and heating of different light curing units on the Knoop and Vickers hardness of a hybrid composite resin. The specimens were irradiated during 40 s with ten different light curing units, LEDs, and halogen lights. The spectral emission of each light curing unit was assessed by a spectrometer, the irradiance was measured by two commercial radiometers, and the heating measured with a thermocouple. After 48 h of storage in a dark recipient under a 100% humidity condition, the Knoop and Vickers hardness tests were carried out. The hardness results were analyzed by ANOVA, and Tukey HSD test (p < 0.05). The results showed that the surface hardness of the composite resin depends not only on the irradiance, but strongly on the emission wavelength and heating of the light curing units. It was observed, a linear correlation between the conversion degree and radiant exposure. In addition, it is suggested that the well known base to top surface hardness ratio convention of 80-90% is not appropriate to evaluate curing efficiency of composites, since the top surface is not always sufficiently polymerized.

Improved nitridation efficiency and mechanical property of stainless steel surface after N 2–H 2 plasma nitridation at low temperature

In the thermochemical process of stainless steel nitridation, the improvement of mechanical properties is governed by the way the nitrogen diffusion profiles extend into the material. The efficiency of conventional thermal or ionic nitridation is substantially reduced at temperatures lower than 550 °C because of low nitrogen diffusivity. The present study shows that improved nitrogen transport can be obtained after nitridation in N 2–H 2 plasma at floating potential, that is without cathodic bias on the samples. Such cold conditions allow for the iron matrix to be nitrided in a depth range of 10 μm at a temperature as low as 430 °C. Under these conditions, the top surface hardness was increased by a factor of three. Using the nanoindentation technique on cross-sections prepared on plasma nitrided samples, we could determine the profiles of hardness and Young modulus. Unexpectedly, the Young modulus was shown to be almost unaffected by the treatment. Furthermore, hardness profiles correlated very well with the nitrogen chemical profile and the results showed that the interface between the treated layer and the untreated part of the sample was very abrupt. The high level of surface strengthening and the increased nitridation efficiency at low temperature are thought to be a consequence of an activation of surface transport and diffusion using plasma (cold) conditions at floating potential.

Improved nitrogen transport in Fe–C alloys during NH 3 plasma nitridation

In the thermochemical process of Fe–C alloy nitridation, improvements of mechanical properties are governed by the way the nitrogen diffusion profiles extend into the material. Up to now, thermal or ionic nitridation cannot be achieved at temperature lower than 550°C because of the strong lowering of nitrogen diffusivity. The present study shows that improved nitrogen transport can be obtained after nitridation in NH 3 plasma without cathodic bias on the samples. Such cold conditions allow the iron matrix to be nitrided in a depth range of 100–400 μm at a temperature as low as 350°C. The top surface hardness was shown to be improved by a factor of 3. This surface strengthening, markedly superior to that obtained with the classical treatments, is a well-known consequence of the temperature lowering that avoids coarsening of nitride microprecipitates. In addition, using this particular process, no growth of compound layer was observed at the surface. This absence of diffusion barrier is clearly beneficial to the improvement of the nitrogen transport. The high nitridation efficiency obtained at low temperature may be explained by an enhanced grain boundary diffusion due to defects generated by hydrogenous radicals produced in the plasma.