Nano Hardness Research Articles

Highly translucent nanostructured glass-ceramic

Transparent and translucent glass-ceramics (GCs) are found in an increasing number of domestic and high-technology applications. In this paper, we evaluated and optimized the effects of two-stage heat treatments on the resulting crystalline phases and microstructure of a glass of the SiO2–Li2O–P2O5–TiO2–CaO–ZnO–Al2O3 system. The objective was to develop a transparent nanostructured glass-ceramic (GC). After numerous heat treatment trials, we found that a long nucleation period of 72 h at 455 °C followed by a crystal growth treatment at 660 °C for 2 h resulted in a highly translucent GC having homogenously distributed nanocrystals. The relatively high amount of P2O5 (2.5 mol%) induced the formation of lithium disilicate as the main crystal phase. We thus developed a GC having crystals under 50 nm, with a high crystallized fraction (52%vol. Li2Si2O5 and 26% vol Li2SiO3), transmittance of approximately 80% in the visible spectrum for 1.2 mm thick specimens, nano hardness of 8.7 ± 0.1 GPa (load of 400 mN), a high elastic modulus of 138 ± 3 GPa as measured by nanoindentation, and good flexural strength (350 ± 40 MPa) as measured by ball-on-3 balls tests. Due to its high content of Li+, this GC has the potential to be chemically strengthened and can be further developed to be used in a number of applications, such as on displays of electronic devices.

Corrosion effects on the granular nano mechanical properties of buried cast iron

Considerable research reported in literature shows that corrosive soil degrades the bulk mechanical properties of buried cast iron pipes due to cracks anddegradation of microstructure. The nanomechanical properties of the grains of cast iron pipes can also be affected by the corrosion before bulk mechanical properties. However, the influence of soil corrosivity on the nanomechanical properties at the granular level is remained unresolved to date. This paper addresses this gap and presents the nanomechanical measurements performed on the corroded cast iron specimens and the maximum degradation was quantified.Specimensafter 545 days of burial in corrosive soil conditions were tested by nanoindentation for determining the degradation of their nanomechanical properties. The analysis of the test results showed a significant reduction in the nano elastic and nano hardness of the grains of the cast iron due to the diffusion of hydrogen from the surrounding corrosive soil environments. The high corrosion rates were found proportional to inducing the maximum degradation of the nano elastic modulus of the grains. A relation for the prediction of maximum degradation of the nano elastic modulus of the grains as a function of corrosion rates, pH and moisture content of the clay soil was also developed. The finding of the current research is significant as it shows that apart from bulk mechanical properties, the nanomechanical properties of cast iron grains can be degraded by corrosive environments which in turn can affect the service life. Furthermore, understanding the mechanical science of the degradation of the grains can assist in manufacturing sustainable ferrous pipes resistive to corrosion soils.

Nanoindentational and conventional mechanical properties of spark plasma sintered Ti–Mo alloys

The densification behavior and mechanical properties of spark plasma sintered titanium-molybdenum alloys were investigated in this paper. All Ti-(4, 8, 12, 16, and 20 wt%) Mo samples were sintered at 1200 °C for 5 min under 50 MPa. A significant relative density of 99.9% was secured for the Ti-based alloy with 16 wt.% Mo. The overall trend of hardness was similar to that of the relative density as Ti-16 wt.% Mo alloy showed the highest hardness values of 372 HV30 and 592 HV0.3 in macro (30 kg) and micro scales (300 g), respectively. Maximum ultimate tensile strength values (852 MPa at room temperature and 600 MPa at 600 ℃) belonged to the Ti-8 wt.% Mo sample. Such an observation was related to the formation of β-Ti phase and the strain-induced transformation phenomenon. The highest flexural strength of ∼2 GPa belonged to the Ti-12 wt.% Mo alloy, which may be a result of solid solution formation between Ti and Mo. Finally, average values of nano hardness, elastic modulus, and stiffness of various phases available in the samples with 12 and 20 wt% Mo were calculated through nano-indentation technique and the former specimen presented higher values in all the mentioned qualities.

Influence of flavonoids on long-term bonding stability on caries-affected dentin

To evaluate the effect of experimental dentin pre-treatment solutions formulated with different flavonoids on microtensile bond strength (μTBS), nanohardness (NH) and ultra-morphological characteristics of artificial caries-affected dentin (CAD) bonded using a universal bonding system. A microbiological method was used to create an artificial CAD in 91 human molars. Five experimental pre-treatment solutions were created using the following flavonoids: quercetin (QUE); hesperidin (HES); rutin (RUT); naringin (NAR), or proanthocyanidin (PRO). A placebo solution (PLA) with no flavonoids added was also evaluated. The flavonoids or placebo solutions were applied to the CAD prior to the application and photoactivation of a universal adhesive (Scotchbond Universal, 3M Oral Care). A control group (CON), in which only the bonding agent was applied without any flavonoid solution, was also evaluated. A 3-mm-thick block of resin composite (Opallis, FGM) was built up on the flat bonded CAD surfaces and was light-cured following the manufacturer's instructions. Specimens were sectioned to obtain resin-dentin slices and sticks (cross-sectional area of 0.8 mm2). The μTBS, NH, and confocal ultramorphology analysis of resin-dentin interface was evaluated at 24 h and after thermo-cycling aging (25,000 cycles). The results were analyzed using 2-way ANOVA followed by Bonferroni's post hoc test (pre-set α = 0.05). The specimens from groups QUE, NAR, and RUT presented greater μTBS values than those from CON group (p<0.05). Specimens from some of these experimental groups presented greater nanomechanical properties (p<0.05), and no morphological degradation at the resin-dentin interface after aging. The use of exogenous cross-linkers as dentin pre-treatment before bonding procedures may represent a suitable strategy to improve the longevity of universal adhesive systems applied to caries-affected dentin.

Evaluation of effect of two different functionalized nanoparticle photodynamic therapy on nanohardness of root dentin-An in vitro study.

The aim of this study was to evaluate the effect of functionalized nanoparticle photodynamic therapy on Nano hardness of root dentin METHODOLOGY: Fifty single rooted lower premolars were decoronated and sectioned into two halves. Then the samples were embedded horizontally in to the acrylic resin to expose the dentin surface. Baseline nanohardness was done at midroot level using a Nanohardness tester. Exposed dentin surfaces were immersed in the following irrigating solutions Post treatment nanohardness testing was done and results were analyzed statistically RESULTS: In general, all the samples in their respective groups had significant change in nanohardness following immersion in irrigant solutions except in NaOCl + EDTA and saline group. CSRB-np and PLGA-MBnp showed increased nanohardness (P = 0.005 and P = 0.007 respectively). Whereas NaOCl + EDTA + CHX showed decrease in nanohardness (P = 0.04). With regards to Modulus of elasticity (MOE), CSRB-np showed significant difference (P = 0.002) compared to the other groups. MOE increased in CSRB-np and PLGA-MBnp while it decreased in all the other groups. In this study, the improvement of nanohardness and modulus of elasticity following the immersion of root dentin in CSRB-np solution was demonstrated.

Effect of hot isostatic pressing on densification, microstructure and nanoindentation behaviour of Mg\u2013SiC nanocomposites

The production of fully dense nanocomposites with a homogeneous distribution of nanoparticles through powder metallurgy (PM) techniques is challenging. Additionally to mechanical milling, pressing and sintering, a final consolidation process is needed to fully densify the nanocomposite. Hot isostatic pressing (HIP) is a promising alternative method to other hot forming processes to eliminate porosity in these PM parts. In contrast to hot extrusion, for instance, isotropic properties are achieved, and textures, as they are usually observed in Mg after uniaxial deformation, are avoided. Here, we evaluate the effect of HIP on the densification, microstructure and (nano)hardness of Mg–SiC nanocomposites. Even though density increased indeed, we observed no increase in the mechanical properties, due to significant heterogeneity in the microstructure. SiC-free regions with a higher grain size developed. Local nanohardness measurements of the HIPed Mg nanocomposite revealed that these regions had a significantly lower nanohardness than the SiC-containing regions. Under consideration of mechanisms reported to be active in Mg in the pressure and temperature regime we used, we conclude that grain growth is the most likely mechanism leading to the microstructure observed after HIP. This is driven by the thermodynamic pressure to decrease the grain boundary energy and facilitated by a slightly inhomogeneous distribution of SiC nanoparticles in the sintered nanocomposite.

Improving the Tribological Properties and Biocompatibility of Zr-Based Bulk Metallic Glass for Potential Biomedical Applications.

Zr-based bulk metallic glasses (Zr-BMGs) are potentially the next generation of metallic biomaterials for orthopaedic fixation devices and joint implants owing to their attractive bulk material properties. However, their poor tribological properties and long-term biocompatibility present major concerns for orthopaedic applications. To this end, a novel surface modification technology, based on ceramic conversion treatment (CCT) in an oxidising medium between the glass transition temperature and the crystallisation temperature, has been developed to convert the surface of commercially available Zr44Ti11Cu10Ni11Be25 (Vitreloy 1b) BMG into ceramic layers. The engineered surfaces were fully characterised by in-situ X-ray diffraction, glow-discharge optical emission spectroscopy, scanning electron microscopy, transmission electron microscopy, and scanning transmission electron microscopy. The mechanical, chemical, and tribological properties were evaluated respectively by nano-indentation, electrochemical corrosion testing, tribological testing and the potential biocompatibility assessed by a cell proliferation assay. The results have demonstrated that after CCT at 350 °C for 40 h and at 380 °C for 4.5 h the original surfaces were converted into to a uniform 35–55-nm-thick oxide layer (with significantly reduced Ni and Cu concentration) followed by a 200–400-nm-thick oxygen-diffusion hardened case. The surface nano hardness was increased from 7.75 ± 0.36 to 18.32 ± 0.21 GPa, the coefficient of friction reduced from 0.5–0.6 to 0.1–0.2 and the wear resistance improved by more than 60 times. After 24 h of contact, SAOS-2 human osteoblast-like cells had increased surface coverage from 18% for the untreated surface to 46% and 54% for the 350 °C/40 h and 380 °C/4.5 h treated surfaces, respectively. The significantly improved tribological properties and biocompatibility have shown the potential of the ceramic conversion treated Zr-BMG for orthopaedic applications.

Effect of interfacial characteristics on magnesium to steel joint obtained using FAST

Friction-stir Assisted Scribe Technique (FAST) was used to join AZ31 magnesium alloy to Zn-coated steels including hot-dipped galvanized 590 and electroplated 270 steel with and without coating. The mechanical properties and performance of a FAST joint are governed by its underlying interfacial and microstructural characteristics, which in turn are determined by the FAST tool and process parameters. The FAST tool was utilized to create a different scribe engagement depth that can vary the extent of chemical intermixing and size of mechanical hooks. Microstructure and chemistry investigations on the weld interface were assessed using scanning electron microscopy and electron dispersive spectroscopy. Mechanical properties including lap shear tensile strength and micro and nano hardness at different interfacial regions were correlated to the local microstructures. A finite element-based modeling approach was developed to identify optimal interfacial characteristics that lead to a desired mechanical performance. The results of the computational model were compared to the experimental observations. A sensitivity analysis was conducted to study the variation in the mechanical response and failure modes of the joint with respect to the interfacial characteristics. Results indicate that interfacial characteristics including hook shape can have a significant impact on the joint strength and failure modes.

Effect of pulsating water jet disintegration on hardness and elasticity modulus of austenitic stainless steel AISI 304L

The presented article is focused on the evaluation of mechanical properties of stainless steel disintegrated using an ultrasonically modulated pulsating water jet. The experimental procedure was performed using a nozzle with a circular orifice with an equivalent diameter of 1.6 mm. The mechanical properties evaluation was based on indentation elasticity modulus Ep and nano hardness H, which were measured using nanoindentation technique. Influence of ultrasonic power and plunger pressure change on disintegrated material was evaluated. Changes in mechanical properties in dependence on distance from the disintegrated surface were evaluated. Elasticity modulus and nano hardness change were observed below and on the sides of the disintegrated surfaces. Measurements were performed until the distance of 930 μm. The indentation was carried in three series of 10 indents with 100 μm spacing located below the affected area, next to the affected area and in the unaffected material. Results of experimental testing show changes of nano hardness (generally an appreciable decrease) and elasticity modulus (limited increase) of material under and to the side of the newly created surface.

Effects of combining ultrasonic micro-forging treatment with laser metal wire deposition on microstructural and mechanical properties in Ti–6Al–4V alloy

Ultrasonic micro-forging treatment (UMFT) is a novel grain refinement and properties improvement technique based on plastic deformation and ultrasonic vibration, and it can be applied to the manufacture of large components. The effects of the different amplitudes and loads of UMFT on microstructure and mechanical properties of laser metal wire deposition (LMwD) Ti–6Al–4V alloy were researched in this paper. The microstructural evolution and properties improvement were investigated by means of optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, surface roughness tester, vickers hardness tester and nano indentor. Experimental results showed that amplitudes and loads can significantly affect geometric dimensioning, surface roughness and constituent phases of the deposited layers. The microstructure of un-treated sample consists of epitaxial growth columnar β grains and a certain volume fraction of equiaxed β grains. A large volume fraction of equiaxed β grains appeared in UMFTed samples and the area percentage of equiaxed grain can be controlled by deposition parameters. The evolution of grain morphology should be attributed to recrystallization. Moreover, after UMFT, vickers hardness increased from 360 HV to 520 HV, nano hardness increased by 1.54 times and Young's modulus reached to 170 GPa. The increase of hardness and Young's modulus are likely to be caused by grain refinement.

Annealing behavior of hardening and ductility loss of a 16Cr–4Al ODS ferritic steel irradiated with high energy Ne ions

Annealing behavior of the hardening and ductility loss of an oxide-dispersion-strengthened (ODS) ferritic steel (16Cr–4Al) irradiated with high-energy heavy ions is studied. 20Ne ions with 123.4 MeV supplied by a cyclotron was used to produce a quasi-uniform atomic region of atomic displacement damage and Ne concentration from surface to a depth of 33 μm in the specimens. Two atomic displacement levels (0.16dpa, 0.70dpa) were approached at about 220 K. The irradiated specimens were subsequently thermally annealed at room temperature, 473 K and 673 K, respectively. Hardness and ductility of the specimens were investigated with nano-indentation technique and small-punch test. The data of the nano hardness were fitted by Nix-Gao model to obtain the bulk equivalent hardness values. The irradiated specimens show observable hardening, which recedes monotonously with the increase of annealing temperature. The Arrhenius plots show a good linearity in the entire temperature range investigated, with an apparent activation energy of 0.13 ± 0.01 eV for both the two damage levels. Assuming that the hardening is caused by the self-interstitial-atom (SIA) clusters initially produced by the cascade damage, an activation energy of 0.70 ± 0.05 eV is deduced for the migration and coalescence process of the SIA-clusters. The small punch test (SPT) of the high-dose specimens shows that a minor ductility loss occurred under conditions as-irradiated or subsequently thermally annealed at 473 K, while a remarkable increase of the ductility loss was observed after the thermal annealing at 673 K, which coincides with the formation of nano-scale gas bubbles in high density in the specimen. It is indicated that the formation of bubbles has minor on the irradiation hardening. A comparison of three ODS ferritic steels Ne-ion-irradiated to 0.7 dpa/260 appm(Ne) shows that the ductility loss decreases with the increase of the sink strength of the oxide dispersoids/ferritic substrate interfaces.

Surface structural features and wear analysis of a multilayer Ti6Al4V-B4C thin film coated AISI 1040 steel

The deprived wear resistance of AISI 1040 steel often results in higher wear rates. The best ways to upgrade their wear resistance are to introduce hard particle reinforcement to produce a metal matrix composite which can be used as a coating. In the present study Ti-6Al-4V-4B4C metal matrix composite coatings were coated on AISI 1040 steel using the magnetron sputtering process and their dry sliding wear behavior was studied at room temperature. The coating morphology was explored by SEM, XRD, FT-IR, and AFM. The constant coating thicknesses of 80 nm and 115 nm were achieved for 0.5 h and 1 h coating duration, respectively. The effects of introducing B4C on the hardness, thermal behavior, wear, and friction characteristics were studied. The nano hardness and elastic modulus were attained by AFM nanoindentation technique which showed a maximum of 21.7 GPa and 218.4 GPa, respectively. It was proven that the adding of B4C increases the thermal stability of Ti-6Al-4V-4B4C coatings as well as modifies the oxidation mechanism. It is expected that the addition of B4C will improve the thermal behavior of thin film coatings for their practical application. Wear tests were executed by ball-on-disc wear tester with E-52100 sphere as the counterface at a sliding velocity of 2 m s−1 with 3 N load. Wear rate and coefficient of friction (CoF) reduced with an increase in load and sliding distances also composite coatings exhibited higher wear resistance within entire loading conditions, hereafter suggesting that it could be a favorable substitute to other hard coatings.

Microstructure and mechanical stability of Bi doped Mg2Si0.4Sn0.6 thermoelectric material

Bi doped Mg2Si0.4Sn0.6 had been synthesised in a high energy ball mill followed by compaction using a sintering hot press. The structural and compositional characterization of sintered mass indicated the formation of a highly densified single-phase product. The microstructure of the hot-pressed samples had been critically assessed. Thermoelectric properties were measured between room temperature and 723 K. A decrease in electrical conductivity was found with the increase in temperature but the Seebeck coefficient showed a reverse trend justifying the attainment of degenerate semiconducting behaviour. Meanwhile, the lattice thermal conductivity was subdued to 1.5 W/mK at 623 K. However, the highest zT value of 0.8 was achieved at 723 K. Moreover, the detailed X-ray photoelectron spectroscopic analysis was carried for the determination of binding energy of the constituent elements in the experimental alloy; it also provided the correct estimation of atomic percentage of the concerned elements. The Raman spectrum revealed a shift in F2g peak with respect to that of Mg2Sn and Mg2Si in correspondence with the composition of the synthesised alloy. The synthesised alloy showed micro and nano hardness of 3.7 and 4.03 GPa respectively, which implies that good mechanical strength could be achieved in the synthesised alloy.

Behavior to wear and corrosion of steel with chromium silicon nitride coatings

Chromium silicon nitride coatings were deposited via physical vapor deposition using a reactive sputtering magnetron, on steel specimens, with a chromium silicate target, purity of 99.5% and argon/nitrogen gas ratio (%) of 80/20. The coating characterization was carried out by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and nano hardness. The erosion-corrosion analysis was performed with a pin on disc tribometer, with a zircon pin, load of 1 N, applying three rotation speeds of the system (250 rpm, 400 rpm and 500 rpm) with an electrolyte composed of water, silica sand (0.05 mm, 0.1 mm and 0.15 mm) and 1% of sodium chloride. The electrochemical techniques used were resistance to polarization, electrochemical impedance spectroscopy and potentiodynamic polarization. The coating decreases the rate of substrate wear between 32% and 56%. The coefficient of friction decreases by almost 50% with the application of the film. Finally, the coating reduces by an order of magnitude the corrosion rate of steel in systems subject to wear and in 3 orders of magnitude in steel systems in static conditions, increasing the useful life of industrial facilities.

THE EFFECT OF TiN, TiAlN, CrAlN, AND TiAlN/TiSiN COATINGS ON THE WEAR PROPERTIES OF AISI H13 STEEL AT ROOM TEMPERATURE

TiN, TiAlN, CrAlN and TiAlN/TiSiN films were deposited on AISI H13 hot work steel substrate by cathodic arc evaporation method. Each coating was optimized in laboratory conditions and the highest hardness and wear resistance coatings were taken into consideration for this study. Morphological properties, chemical compositions, crystallographic structure, nano hardness and adhesion strength of coatings were analyzed with SEM, AFM, EDS, XRD, nano indentation and scratch resistance tester. Wear experiments were performed using ball-on-disk tribometer against Al2O3 ball of 6[Formula: see text]mm diameter and wear volume of coatings were measured using optical profilometer. Wear experimental results revealed that all coated samples showed higher wear resistance and hardness than uncoated AISI H13 steel substrate. The highest wear and scratch resistances as well as nano hardness were attained for CrAlN coating. TiAlN coating has the lowest scratch resistance and wear resistance. Adhesive wear mechanism was the dominant wear mechanism for CrAlN coatings which is the highest wear resistant coating. Abrasive wear mechanism was the dominant wear mechanism for TiAlN coatings which is the lowest wear resistant coating.

Nanoindentation and nanoscratch tests of YAG single crystals: An investigation into mechanical properties, surface formation characteristic, and theoretical model of edge-breaking size

Nanoindentation and nanoscratch tests of YAG single crystals were systematically performed. The mechanical properties including elastic recovery rate, elastic modulus, nano hardness and fracture toughness of YAG single crystals were obtained by the nanoindentation tests. The surface morphologies of the scratched grooves were analysed using scanning electron microscopy. The formation characteristics of YAG single crystals induced by varied-depth nanoscratch indicated that there was distinct brittle-to-ductile transition phenomenon during the scratching process. Surface radial cracks occurred prior to the edge-breaking phenomenon, and transverse cracks extending to the surface of the work material dominated the brittle removal of YAG single crystals. A theoretical model of the edge-breaking size during the nanoscratch process was developed by considering the stress intensity factor, elastic recovery rate, and residual force. This model indicated that the edge-breaking size increased as the normal force, average elastic recovery rate and elastic modulus increased, but decreased as the nanoindenter tip radius, fracture toughness and nano hardness increased. When the average elastic recovery rate was within 17.5%–20% (the maximum elastic recovery rate was within 35%–40%), the values predicted by the theoretical model agreed well with the experimental values, and the average error was less than 5%. The model could provide theoretical guidance for analysing the surface generation characteristics of brittle solid materials during the abrasive processing at brittle removal regime.

Improving bonding to eroded dentin by using collagen cross-linking agents: 2years of water storage.

The aim of this study was to investigate the effects of collagen cross-linking agents on nanomechanical and bonding properties of eroded dentin (ED), 24h and 2years after water storage. Human molar dentin surfaces, eroded by soft drinks or citric acid, were acid-etched and treated with primers containing proanthocyanidin (PA) and riboflavin (RI) or were untreated (control) and tested after 24h and 2years. After acid etching and adhesive application (Prime&Bond Elect (PBE); Scotchbond Universal (SBU); Tetric n-bond Universal (TEU)), specimens were sectioned into beams and tested for microtensile bond strength (μTBS) and silver nitrate deposition (NL) after 24h and 2years. The beams were used to evaluate the 24-h in situ conversion of degree (DC). Nanohardness (NH) and Young's modulus (YM) were evaluated via resin-bonded dentin slices after 24h and 2years. A three-way ANOVA and Tukey's test were used for statistical analysis (5%). For both storage times, ED with citric acid resulted in lower μTBS, NH, and YM and higher NL for each adhesive system than soft drink ED (p < 0.05). After 2years of water storage, cross-linking primers maintained the μTBS, NH, and YM (p < 0.05) when compared with the control group. Althougth, the NL values decreased for all groups after 2 years of water storage, PA and RI treatments showed NI values lower than control group (p < 0.001). No significant differences were observed between PA and RI treatments (p > 0.05). Cross-linking primers maintain or improve DC (p < 0.03). In general, TEU and SBU yielded higher μTBS, DC, NH, and YM and lower NL than PBE. Cross-linking agents improved the results and maintained the resin-ED interface bonding and nanomechanical properties, without jeopardizing adhesive polymerization. Cross-linking agents are a viable alternative for improving and maintaining resin-ED interface bonding and nanomechanical properties.

A New Plasma Surface Alloying to Improve the Wear Resistance of the Metallic Card Clothing

A new surface strengthening process: Plasma surface chromizing was implemented on the metallic card clothing to improve its wear resistance based on double glow plasma surface metallurgy technology. A chromizing coating was prepared in the process, which consisted of a deposited layer and diffusion layer. The surface morphologies, microstructure, phase composition, and hardness were analyzed in detail. The friction behaviors of the metallic card clothing before and after plasma surface alloying were comparatively analyzed under various sliding speeds at room temperature. The results showed that: 1. The chromizing coating on the surface of metallic card clothing was dense and homogeneous without defects, and the metallic card clothing still maintained its integrity and sharpness. 2. The chromizing coating consist of [Fe,Cr], Cr, Cr23C6, and Cr7C3, which contribute to the high hardness. 3. The average microhardness of metallic card clothing increased from 365.4 HV0.05 to 564.9 HV0.05 after plasma surface chromizing. Nano hardness of the chromizing coating was approximately 1.87 times than the metallic card clothing. 4. At various sliding velocities of 2 m/min, 4 m/min, and 6 m/min, the specific wear rates of metallic card clothing were 16.38, 9.06 and 6.26 × 10−4·mm3·N−1·m−1, and the specific wear rates of metallic card clothing after plasma surface chromizing were 2.91, 3.30, and 2.95 × 10−4·mm3·N−1·m−1. Furthermore, the wear mechanism of the chromizing coating gradually changed from adhesive wear to abrasive wear as the sliding velocity increased. The results indicate that the wear resistance of metallic card clothing was improved obviously after plasma surface chromizing.

Nano-scale hardness and elastic modulus of WC-Co composites and their relationship to the tools life during particleboard milling

Nano-scale hardness and elastic modulus of WC-Co composites and their relationship to the tool life during particleboards milling. The paper summarizes the results of the technique of hardness and elastic modulus determination using a load and displacement sensing indentation experiments. During the tests these properties were measured in nano-scale for different types of WC-Co composites using the Anton Paar TriTec Ultra Nano Hardness Tester (UNHT). In addition, durability examination of WC-Co tools during milling of particleboard was carried out. In the final stage, the correlation of the studied properties with the lifetime of tools was analyzed. The studies have revealed a relationship between micro-hardness and the total cutting length of the WC-Co tools.

Comparative analysis of third generation leds used for photoactivation of nanoparticulated compound resins of different colors

Properties of composite resins compared to activation sources that emit double wavelengths. This study evaluated the nanohardness (ND), the modulus of elasticity (ME) and degree of monomeric conversion (GC) of two colors (A2 and WE) of the nanoparticulate composite resin Z350XT (3M/ESPE) polymerized by two photoactivating units (Bluephase, Ivoclar/Vivadent and VALO, Ultradent). 24 specimens (CP) were made with a split polypropylene circular matrix surrounded by an aluminum ring (5 mm x 2 mm). The PCs were photoactivated with a light intensity of 1,200 mW / cm2 for 30 seconds and stored in an oven at 37o C, for 24 hours. The ND and ME tests were performed on the DUH211S nanodurometer Shimadzu, with a force of 10 mN and a waiting time of 0 s and the GC test was performed on the IR Prestige21 FTIR Shimadzu, considering 20 scans, 2 cm-1 resolution and wavelength from 4000 to 400. The data were analyzed by ANOVA and Kruskall-Wallis (α = 0.05). The WV group showed superior nanohardness, with a statistically significant difference (p=0.0284). The ME values did not show statistically significant results both when comparing the color effect (p=0.0975 and 0.0777) and that of the activating source (p=0.2189 and 0.1814). The results of the CG showed to be very similar when related to the two variables. Polymerization with the VALO photoactivator unit led to improvements in the nanohardness in the light-colored resin, not being the same observed in relation to the degree of monomeric conversion and the elasticity module.