Surface Hardness Of Composites Research Articles

Influence of filler types on wear and surface hardness of composite resin restorations.

Wear and surface hardness of resin composites are of relevance from the clinical standpoint. With the incorporation of novel filler system, more studies need to be performed to investigate newly marketed resin composites. The objective of this study was to investigate the abrasive wear and surface hardness of dental restorative with different filler types. Nanohybrid filled Harmonize (HM) and Tetric N-Ceram (TNC), microhybrid filled Filtek Z250 (Z250), nanofilled Filtek Z350 (Z350) were included in the study. Twelve cylindrical resin composites specimens with 10 mm in diameter and 6 mm in thickness were prepared for abrasive wear test. Eight hundred cycles under 17 kg load were conducted for final wear by CW3-1 wear machine. The specimen was cleaned with an ultrasonic unit for 3 min followed with drying procedure. After measurement of weight loss and the density of specimens, the specimens were kept for measurement of surface hardness. Surface hardness was measured using a micro-hardness tester with a Vickers diamond indenter after polishing. Three specimens of each material were observed by scanning electron microscopy (SEM) after the abrasion to evaluate the morphology of the surface. Data were analyzed using one-way analysis of variance (ANOVA), followed by Tukey HSD test (α = .05). Z250 performed the least volume wear loss (41.1 ± 2.1 mm3), as well as the hardest value (102.7 ± 2.9 HV). There was no significant difference with the volume wear loss (p = 1.000) and surface hardness (p = 0.874) of HM and TNC. SEM images of nanohybrid filled HM and TNC represented smoother surface compared with other types of resin composites. Microhybrid Z250 showed the highest wear resistance and surface hardness, nanofilled and nanohybrid resin composites may still face the insufficient of wear and surface hardness quality.

Structure, phase composition and mechanical characteristics of layered composite materials based on TiB/xTi-Al/α-Ti (x = 1, 1.5, 3) obtained by combustion and high-temperature shear deformation

The effect of the ratio of titanium and aluminum in the Ti–Al intermetallic layer on the microstructure, phase composition, and mechanical characteristics of layered composite materials based on TiB/xTi-Al/α-Ti (x = 1, 1.5, 3) is studied systematically. The layered composite materials are obtained by combustion and high-temperature shear deformation. The green sample is a compressed sandwich blank consisting of two Ti–B and Ti–Al powder layers and an α-Ti titanium sheet. The mechanisms of phase and structure formation that occur during synthesis and subsequent high-temperature shear deformation in ceramic and intermetallic layers are described. It is shown that the synthesis between the initial components proceeds according to the reaction-diffusion mechanism. It has been found that the structure, grain size (from 200 nm to 15 μm), phase composition, and mechanical characteristics of the composite can be tuned by changing the initial composition and the delay time before applying external pressure. It is shown that the mechanical characteristics of the resulting composites depend on the location of macrolayers relative to the applied load during high-temperature shear deformation and have the following values: composite surface hardness up to 1800 HV, elastic modulus up to 300 GPa, elastic recovery up to 43, stress intensity factor up to 25.3 MPa m1/2, bending strength up to 650 MPa. The mechanical characteristics of the obtained composites are compared with known analogs, and the advantages are revealed.

New Materials Based on Polyvinylpyrrolidone-Containing Copolymers with Ferromagnetic Fillers.

The article investigates the peculiarities of the effect of ferromagnetic fillers (FMFs) of various natures (Ni, Co, Fe, FeCo, SmCo5) on the formation of the structure and properties of 2-hydroxyethylmethacrylate (HEMA) with polyvinylpyrrolidone (PVP) copolymers. The composites were characterized using FTIR-spectroscopy, SEM, DMTA, magnetometry of vibrating samples, specific electrical resistivity studies, and mechanical and thermophysical studies. The formation of a grafted spatially crosslinked copolymer (pHEMA-gr-PVP) was confirmed and it was established that the FMF introduction of only 10 wt.% into the copolymer formulation increased the degree of crosslinking of the polymer network by three times. The surface hardness of composites increased by 20–25%. However, the water content decreased by 16–18% and lay within 42–43 wt.%, which is a relatively high number. The heat resistance of dry composites was characterized by Vicat softening temperature, which was 39–42 °C higher compared to the unfilled material. It was established that the obtained composites were characterized by a coercive force of 200 kA × m−1 and induction of a magnetic field at the poles of 4–5 mT and 10–15 mT, respectively. The introduction of FMF particles into pHEMA-gr-PVP copolymers, which, in the dry state, are dielectrics, provides them with electrical conductivity, which was evaluated by the specific volume resistance. Depending on the FMF nature and content, as well as their orientation in the magnetic field, the resistance of filled materials could be regulated within 102–106 Ohm·m. Therefore, the modification of HEMA with PVP copolymers by ferromagnetic fillers of various natures provides the possibility of obtaining materials with unique predicted properties and expands the fields of their use, for instance as magnetic sorbents for various applications, as well as the possibilities associated with their being electrically conductive materials that can respond by changing of electrical conductivity, depending on various factors.

A low-shrinkage, hydrophobic, degradation-resistant, antimicrobial dental composite using a fluorinated acrylate and an oxirane.

To develop a low shrinkage, hydrophobic, degradation-resistant, antimicrobial dental composite using a fluorinated acrylate, and a difunctional oxirane. The effects of a fluorinated acrylate (2-(perfluorooctyl)ethyl acrylate; PFOEA), a difunctional oxirane (EPALLOY™ 5001; EP5001), and a three-component initiator system (camphorquinone/ethyl 4-dimethylaminobenzoate/4-Isopropyl-4'-methyldiphenyl iodonium Tetrakis (pentafluorophenyl) borate; CQ/EDMAB/Borate) on bisphenol A glycidyl dimethacrylate: triethylene glycol dimethacrylate (BisGMA:TEGDMA) composite surface hardness, degree of monomer-to-polymer conversion, hydrophobicity, translucency, mechanical properties, polymerization shrinkage and shrinkage stress, degradation, water imbibition, and antimicrobial properties were determined. Overall the experimental composites had comparable mechanical properties and lower volumetric polymerization shrinkage and shrinkage stress as compared to BisGMA:TEGDMA controls. Addition of PFOEA increased composite hydrophobicity, but it decreased degree of cure, ultimate transverse strength, and translucency. It also decreased polymerization shrinkage and shrinkage stress. The use of the CQ/EDMAB/Borate initiator system was beneficial for the cure and mechanical properties of the 30% w/w PFOEA group. However, it decreased the hydrophobicity and translucency of those composites. The addition of EP5001, at the low concentration used in this work, did not contribute to reduced polymerization volumetric shrinkage or antimicrobial properties, but it did reduce shrinkage stress. A mechanically viable hydrophobic composite system with reduced polymerization shrinkage and shrinkage stress has been developed by adding PFOEA and EP5001. However, the addition of EP5001 did not render the composite antimicrobial due to the low concentration used. Further research is needed to determine the lowest concentration at which EP5001 provides antimicrobial activity. The composites developed here have the potential to improve longevity of traditional BisGMA:TEGDMA composite systems.

Tribological properties of organotin compound modified UHMWPE

Abstract A range of ultra-high molecular weight polyethylene (UHMWPE)/tetraphenyltin (Ph4Sn) nanocomposites were fabricated by hot-pressing. The surface hardness and crystallinity of composites were studied. It revealed that the surface hardness of the composites decreased slightly, and the changing trend of crystallinity was consistent with the hardness. The tribological properties of composites under seawater lubricating conditions were investigated. The experimental results showed that the friction coefficients of the composites almost keep the same but the wear reduced sharply. With the increases of Ph4Sn content, the wear of composites first decreases significantly and then increases, meanwhile the friction coefficient remains basically unchanged. The dominant wear mechanism has changed from adhesive wear to plastic deformation and finally to abrasive wear. The addition of Ph4Sn particles reduces the sensitivity of the Ph4Sn/UHMWPE composites to water and transfers the load to the UHMWPE network, resulting in the wear resistance improved.

MWCNTs doped GFRPs drilling: crosscheck among holes obtained by alternative manufacturing methods

In this study, the holes of glass fiber reinforced polymer (GFRP) and multi-walled carbon nanotubes (MWCNTs) doped GFRP composite materials were drilled using abrasive water jet (AWJ), CO2 laser cutting, orbital drilling, and punching methods; the effects of these methods on hole quality were determined. The hole entry and exit dimensions were obtained equal and in the desired size by orbital drilling; thus, kerf formation was prevented due to the lateral and face milling of the end mill. The surface hardness change was not observed in the hole circles obtained with the orbital drilling and punching methods. However, epoxy hardening was observed in the hole circles obtained by laser cutting due to the heat effect of laser beam. In AWJ method, matrix-fiber integrity was disrupted, and delamination was observed due to the effect of water pressure and kinetic energy; consequently an increase in material thickness was observed and surface hardness decreased. It was determined that MWCNTs additive increased the surface hardness of composites and maintained its hardness and durability in post-cutting measurements. Splintering and burring were not seen in any method, but fiber carbonization was observed in the inner parts of the hole due to thermal effects in laser cutting.

Spark Plasma Sintering of Aluminum-Based Powders Reinforced with Carbon Nanotubes: Investigation of Electrical Conductivity and Hardness Properties.

This paper focuses on reporting results obtained by the spark plasma sintering (SPS) consolidation and characterization of aluminum-based nanocomposites reinforced with concentrations of 0.5 wt%, 1 wt% and 2 wt% of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Experimental characterization performed by SEM shows uniform carbon nanotube (CNT) dispersion as well as carbon clusters located in the grain boundary of the Al matrix. The structural analysis and crystallite size calculation were performed by X-ray diffraction tests, detecting the characteristic CNT diffraction peak only for the composites reinforced with MWCNTs. Furthermore, a considerable increment in the crystallite size value for those Al samples reinforced and sintered with 1 wt% of CNTs was observed. Hardness tests show an improvement in the composite surface hardness of about 11% and 18% for those samples reinforced with 2 wt% of SWNCTs and MWCNTs, respectively. Conductivity measurements show that the Al samples reinforced with 2 wt% of MWCNTs and with 0.5 wt% SWCNTs reach the highest IACS values of 50% and 34%, respectively.

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.

Tribological properties of PAANa/UHMWPE composite materials in seawater lubrication

Abstract To prepare a high-performance anti-friction and wear-resistant composite material for friction sub-components in marine equipment, a modification was made by adding different amounts sodium polyacrylate (PAANa) to ultra-high molecular weight polyethylene (UHMWPE). PAANa/UHMWPE-blended powders were prepared at individual weight ratios of 0/100, 3/97, 5/95, 8/92, 13/87, and 18/82 with hot-press molding. In seawater, experiments of PAANa/UHMWPE composites sliding against GCr15 have been conducted with a ball-on-disk configuration in this study. The results show the surface hardness of composites was almost the same with the increase in PAANa proportion, however, the friction coefficient and wear scars of PAANa/UHMWPE composites/GCr15 sliding pairs firstly decrease and then increase. Scanning electron microscopy (SEM) results show that wear mechanism of the composites is mainly plastic deformation and spalling. The composites with PAANa content of 3% and 5% achieves better tribological properties than the pure UHMWPE material.

Effect of Tool Shoulder Diameter on the Surface Hardness of Aluminum-Molybdenum Surface Composites Developed by Single and Double Groove Friction Stir Processing

Molybdenum (Mo), possessing higher hardness compared to aluminum (Al), is used for the surface hardness improvement in Al 1050 alloy. Al-Mo surface composites are developed using friction stir processing with different tool shoulder diameters. Single groove composite (SGC) and double groove composite (DGC) samples are processed with 22-, 20-, and 18-mm shoulder diameter tools to study the effect of tool shoulder diameter and Mo content on the surface hardness of Al-Mo surface composites. Microhardness increased from 26 to 51 Hv on the top surface and 52 Hv on the cross section surface, in 18 DGC. The surface hardness of the composite samples increased with decrease in tool shoulder diameter due to the combined effect of grain refinement and Mo reinforcement particles. Unprocessed Al 1050 base alloy possessed an average grain size of ~ 99 µm. The grain size in the processed samples reduced with decrease in tool shoulder diameter. Surface composites processed with 22-, 20-, and 18-mm tools exhibited an average grain size of ~ 23, ~ 22, and ~ 21 µm, respectively. The amount of Mo particles incorporated in the composite material increased with decrease in tool shoulder diameter. Microstructural analysis confirmed that the FSP groove method incorporated about ~ 8 wt pct Mo in 22 SGC and ~ 12 wt pct in 22 DGC, respectively. The amount of Mo particles in 20 SGC and 20 DGC is ~ 17 wt pct and ~ 22 wt pct, respectively, whereas 18 SGC and 18 DGC possessed ~ 27 wt pct and ~ 31 wt pct Mo particles. Mechanical shearing through severe plastic deformation during the friction stir processing reduced the average Mo particle size in the surface composites. Molybdenum is distributed in its elemental form in the Al-Mo surface composites without any intermetallic formation.

The evaluation of the surface micro-hardness values in different depth of resin blocks

Objective: Computer-aided design and manufacturing technology has shown great improvement in dentistry since the 1980s. This technology is based on a one-stage restoration using prefabricated blocks. Two main types of materials are used during CAD / CAM indirect restorations: glass-ceramic / ceramic and resin composite. CAD / CAM resin blocks are polymerized under high temperature and pressure. Polymerization depth affects the surface hardness of composite resins. When preparing a restoration, different depth layers of the resin block are used. The aim of this study is to show that adequate polymerization is achieved in each layer of the resin blocks and that the hardness of each layer is the same. Two composite resin block materials and one hybrid resin block material were included in this study. Material and method: The CAD/CAM block materials evaluated in this study were Cerasmart, Lava and Vita Enamic Square specimens (n=5/material) of approximate dimensions 10×10×2 mm blocks were sectioned (5 slices/block) from commercially available CAD-CAM materials using a diamond saw (exakt 300 cl Apparatebau, Norderstedt, Germany) with water cooling. All specimens were abraded followed by 500,1200,2500 grid using SiC abrasive paper (exakt 400 cs Apparatebau, , Norderstedt, Germany). After storage in distilled water at 37 °C for 24 hours the Knoop hardness test was performed using a hardness testing machine (Buehler MMT 3 digital micro hardness tester, Lake Bluff, IL, USA) using a load of 500 gf and a loading time of 10s. Results: The material with the highest hardness number was Vita Enamic block, whereas the lowest numbered group was the Cerasmart. The rank order of surface hardness was as follows: Vita Enamic> Lava Ultimate >Cerasmart. Conclusion: The hardness measurements of the layers of blocks were similar.

Surface Hardness of Dental Composite Resin Restorations in Response to Preventive Agents

To assess the impact of using preventive mouthwash agents on the surface hardness of various resins composites. Hundred specimens were prepared from five types of composite resin material in a Teflon mold. Five specimens from each type of restorative materials (Herculite XRV Ultra, Estelite Σ Quick, Z Hermack, Versa Comp Sultan, and Empress Direct IPS) were evaluated posttreatment with immersion in four types of preventive mouthwashes gels and rinses - group 1: Flocare gel (0.4% stannous fluoride), group 2: Pascal gel (topical APF fluoride), group 3: Pro-relief mouthwash (Na fluoride), and group 4: Plax Soin mouthwash (Na fluoride) - at 37°C in a dark glass container at 24, 48, and 72 hours. Surface hardness measurement was made for each tested material. Statistically, we analyzed the mean values with one-way analysis of variance (ANOVA) and Tukey's test, with significance level of p < 0.05. All composite resin materials showed decrease in their surface hardness with the time elapsed (24, 48, and 72 hours) postimmersion in the preventive mouthwashes and gels except the Herculite XRV Ultra and Versa Comp Sultan materials. Flocare gel group showed increase in the surface hardness after 48 hours of immersion than the other periods and in Estelite Σ Quick after 72 hours. There was significant differences in all materials tested with the immersion in the preventive mouthwashes and gels, such as Flocare gel (0.4% stannous fluoride), Pro-relief mouthwash (Na fluoride), and Plax Soin mouthwash (Na fluoride) except Pascal gel (topical APF fluoride) (p > 0.05), at time intervals mentioned earlier (p < 0.05). The effect of preventive mouthwashes and gels on resin composite materials was decreased surface hardness with the time elapse of immersion for all materials except the Flocare gel group, which contains 0.4% stannous fluoride as a preventive ingredient increases the surface hardness after 48 h for Herculite XRV Ultra and Versa Comp Sultan and Estelite Σ Quick after 72 hours. The preventive agents in the form of mouthwash and gel are used to prevent oral diseases that affect the surface hardness of composite resin, and this leads to occlusion, color stability, and surface roughness.

Effect of glycerin on the surface hardness of composites after curing

Objectives: The purpose of this study was to examine the effect of glycerin topical application on the sur- face hardness of composite after curing. Materials and Methods: A composite (Z-250, 3M ESPE) was packed into a disc-shaped brass mold and light cured according to one of the following protocols. Group 1 (control) was exposed to air and light cured for 40 sec, group 2 was covered with a Mylar strip and light cured for 40 sec, group 3 was surface coated with glycerin and light cured for 40 sec, and group 4 was exposed to air and light cured for 20 sec and then sur- face coated with glycerin and cured for additional 20 sec. Twenty specimens were prepared for each group. The surface hardnesses of specimens were measured with or without polishing. Five days later, the surface hardness of each specimen was measured again. Data were analyzed by three-way ANOVA and Tukey' s post hoc tests. Results: The surface hardnesses of the unpolished specimens immediately after curing decreased in the follow- ing order: group 2 > 3 > 4 > 1. For the polished specimens, there was no significant difference among the groups. Within the same group, the hardness measured after five days was increased compared to that imme- diately after curing, and the polished specimens showed greater hardness than did the unpolished specimens. Conclusions: The most effective way to increase the surface hardness of composite is polishing after curing. The uses of a Mylar strip or glycerin topical application before curing is recommended.

Effect of solvent composition on transparency and surface hardness of poly(methyl methacrylate)‐silica nanocomposites provided on polycarbonate

AbstractPoly(methyl methacrylate)‐silica nanocomposites with 49 vol % of silica were prepared by blending poly(methyl methacrylate‐co‐2‐hydroxyethyl methacrylate) [content of 2‐hydroxyethyl methacrylate: 15.1 mol %] with perhydropolysilazane in a ethylacetate/cyclohexane/xylene mixture, casting on polycarbonate (PC) substrates and drying for 24 h at room temperature. When the cyclohexane content in the solution was in a range from 21.7 to 32.3 vol %, composites were transparent in a wide range from 400 to 1000 nm of wavelength, the maximum surface hardness of composites on the substrate measured by nanoindentation was 1.07 GPa. Dynamic light scattering and viscometric analysis indicated that aggregates of poly(methyl methacrylate‐co‐2‐hydroxyethyl methacrylate) was formed in the mixture when the transparent composites were obtained on the PC substrates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Power Distribution across the Face of Different Light Guides and Its Effect on Composite Surface Microhardness

The aim of this study was to examine the influence of light guide type on the distribution of irradiant emission from a light-emitting diode (LED) curing light and to measure the effect of light dispersion on surface microhardness across the top and bottom surfaces of two types of composite resins. A laser beam analyzer (LBA-700, Spiricon) was used to evaluate light distribution (Top Hat factor [THF]) across the distal surface of a standard and turbo light guide from an LED curing light (Bluephase, Ivoclar Vivadent). Composites (Z100 [hybrid], A110 [microfill]; 3M ESPE) were placed in blackened rings (2 x 11 mm) and exposed at 0 mm for 5 seconds (Z100) or 15 seconds (A110) using the light guides at similar irradiance, energy density, and exit diameters (N = 5). Similar irradiance values were produced by using the turbo light guide on the "low power" setting of the curing light and the "high power" setting when using the standard light guide. THF values were analyzed with an unpaired t-test. Knoop hardness (KHN) was determined on the top and bottom surfaces (Leco) in 1-mm lateral increments from the specimen center and proceeding 4 mm in both east-west and north-south directions. The effects of the major factors (light guide type and lateral distance) on the hardness of each composite were analyzed using multiple analysis of variance (ANOVA), and a two-tailed, unpaired Dunnett's t-test determined when lateral hardness values significantly differed from that at the specimen center. The percentage difference between maximum and minimum (max-min) hardness values for each specimen, with respect to distance from specimen center, and the percentage decrease for the standard and turbo light guides, with respect to both composite resin types, were compared using ANOVA and the Tukey's post-hoc test. The standard guide had a significantly higher (i.e., more uniform light distribution) THF than did the turbo tip (p < 0.001). For the microfill, significant differences in hardness were found based on the distance from the specimen center (p < 0.0001), and with respect to the top or bottom surfaces (p < 0.0001). However, no difference was found between the two types of light guides (p = 0.939). For the hybrid, significant differences in hardness were found based on lateral distance (p < 0.001), surface (p < 0.001), and light guide type (p = 0.045).However, for both composites, significant interactions were present. Significant differences were found between hardness at the specimen center and at various lateral distances, depending on composite type, surface, and light guide type. The percent age max-min hardness decrease across the surface was significantly less for the standard light guide (p < 0.0001) and at the top surface (p < 0.02) with both composite resin types. Also, the least percentage max-min hardness decrease occurred on the top surface of the microfill material (p < 0.001). The standard light guide produced a more homogeneous distribution of light across the tip end compared with the turbo light guide, based on the THF. Composite surface hardness patterns correlated with the applied irradiance distribution profiles, yielding greater hardness at higher irradiance locations for both top and bottom surfaces. Light guide selection may influence the uniformity of surface and subsurface hardness when light-curing composite resin restorations.

Improvements in the understanding and application of duplex coating systems using arc plasma technology

There has been interest for some years now in the development of duplex treatments involving plasma nitriding coupled with the deposition of a hard coating. Although this coating system has in service use for various applications, there are still however many underlying uncertainties with regard to how treatment parameters affect coating performance, for example the deposition temperature and the related substrate softening. Different duplex treatments are applied to SKH 51 and SKH 2 steel by changing the nitriding atmosphere and TiN deposition temperature. The nitride layers with the ε-Fe 3N phase are more prone to denitriding than those consisting of either an α or γ′-Fe 4N phase during deposition of the hard coating. The black layer formed through denitriding of the SKH 51 alloy is thinner than that of the SKH 2 alloy. This is considered to be a result of the presence of nitride forming elements. Regardless of the nitride phases that are formed, the diffusion of nitrogen atoms is enhanced at increased substrate temperatures, induced by ion bombardment characteristics during coating growth, causing a significant decrease in the nitrogen content of the original prenitrided layer. The composite surface hardness of the treated specimens is found to be most dependent on substrate softening effects, as opposed to factors such as black layer formation. The adhesion of the TiN coating to the underlying nitrided layer again appears to be influenced more by softening of the substrate during higher temperature deposition as opposed to the formation of a black layer. This is indicated by the fact that the adhesion to the samples with an initial ε-Fe 3N nitrided surface is greater than those with an α phase, even though the black layer is only present for the former. These studies reveal that avoiding substrate softening is essential in producing high performance hard coating/nitride duplex coatings.

Surface hardness of the dental composite cured by light that penetrate tooth structure according to thickness of tooth structure, light intensity and curing time

In this study we measured the amount of light energy that was projected through the tooth material and analyzed the degree of polymerization by measuring the surface hardness of composites. For polymerization, Optilux 501 (Demetron, USA) with two types of light guide was used: a 12 mm diameter light guide with 840 nW/ light intensity and a 7 mm diameter turbo light guide with 1100 nW/. Specimens were divided into three groups according to thickness of penetrating tooth (1 mm, 2 mm, 0 mm). Each group was further divided into four subgroups according to type of light guide and curing time (20 seconds, 40 seconds). Vickers' hardness was measured by using a microhardness tester. In 0 mm and 1 mm penetrating tooth group, which were polymerized by a turbo light guide for 40 seconds, showed the highest hardness values. The specimens from 2 mm penetrating tooth group, which were polymerized for 20 seconds, demonstrated the lowest hardness regardless of the types of light guides (p

The effect of machining on the surface properties of SiC/Al composites

The machined surface quality of composites is one of the most important factors affecting the actual application of the composites. In this paper the hardness and residual stress of composites in the surface layer affected by machining are investigated. The results indicate that the work-hardening and residual stress of composites in the machined surface layer have some peculiarities. The machined surface hardness of composites reinforced by SiC particles may be lower than that of the unaffected interior material, but the subsurface is hardened evidently, and the average hardening is more remarkable for composites reinforced by fine particles. In the surface of composites reinforced by coarse particles the residual stress may be released due to structural defects, but for composites reinforced by fine particles there is a tendency for compressive residual stress in the surface. Cutting with a larger removal rate increases the possibility for tensile residual stress in the machined surface layer of the composites.

Characterization and hardness modelling of alternate TIN/TICN multilayer cathodic arc PVD coating on tool steel

TiCN coatings on the market today are in general multi-layer TiN/ Ti(C x N 1− x ) coatings. Such multilayered film configuration enables optimisation of the film/substrate as well as the film/worked material interactions, by controlling the internal stress state, fatigue toughness, hardness and superficial composition of these Ti(C x N 1− x ) coatings. This paper presents the results of the investigations on a wear resistant coating made by alternate layers of TiN and Ti(C x N 1− x ) (nominal 0.5 μm each), deposited on S600 tool steel by reactive cathodic arc evaporation using a reactive gaseous mixture of methane and nitrogen. Microstructural and compositional characterisation were carried out using ball crater tests, Optical Microscopy, Scanning Electron Microscopy associated with Energy Dispersive Microanalysis and Image Analysis. Micro hardness measurement were evaluated by means of the Chicot and Lesage volume law of mixture model to cope with the problem of the multiple influence of the different layers and the substrate on the real multilayer surface hardness. In order to predict the surface hardness, the model needs the knowledge of the properties of each type of layers and of the substrate (Young modulus, H 0=hardness at infinitely small load and n=strain hardening coefficient, or ISE index). These properties were measured using microindentation tests from ad hoc samples of single TiN 0.5 μm layer film, single Ti(C x N 1− x ) 0.5 μm layer film and the uncoated substrate. Young modulus for the TiN and TiCN were evaluated with load–displacement nanoindentation tests; Young modulus for the substrate is from manufacturer. Thickness, composition profiles and microstructure of each film were used to qualify the data input for the model. Experimental measurements on the composite surface hardness allowed then the verification of the predictions.