Ultra-micro Hardness Research Articles

Evaluation of degree of conversion, microtensile bond strength and mechanical properties of three etch-and-rinse dental adhesives

Abstract This study evaluated microtensile bond strength (µTBS), degree of conversion, modulus of elasticity and ultramicrohardness of three etch-and-rinse adhesives systems. The materials evaluated were: Ambar (FGM), Optibond (Kerr) and Magic Bond (Vigodent). The degree of conversion was analyzed by FTIR/ATR. To evaluate bond strength (μTBS) in dentin, 15 teeth (n = 5) were restored and sliced to obtain the specimens (0.8mm2). The dynamic ultra microhardness tester was used to evaluate the hardness and modulus of elasticity. The Magic Bond adhesive system showed lower µTBS than Ambar and Optibond (p <0.001). For degree of conversion, comparisons between groups of adhesive systems evaluated showed statistically significant difference (p<0.001), with higher values for Ambar and Optibond when compared a Magic Bond. For modulus of elasticity and ultramicrohardness, Ambar and Magic Bond showed lower values than Optibond. The best results in all properties evaluated were obtained by the Optibond adhesive system.

Biodegradation of anti-microbial titanium-magnesium-silver coatings on polyetheretherketone for bone-contact applications

In addition to high bonding between bone and implant, suppressing bacterial infection at the implant site is an extremely high surgical request. For spinal implants the effects of infection can be much worse due to risks for the patient by nerve damage resulting in paralysis. The main problem of nosocomial multiresistant bacteria is connected to biofilm formation, which efficiently protects against infiltration of pharmaceutical antibiotic drugs. In such a case, a fast revision surgery for exchange of the implant is mandatory, because osseointegration is stopped by bacterial endotoxins. Mostly silver is used on the market, possessing a wide spectra of anti-microbial activity for the majority of nosocomial bacteria and viruses at very low ppb concentration by destroying their cell walls. In this study, it is aimed to improve the antibacterial behavior of PEEK implants by developing a layered, biofunctional coating which consists of titanium as a stiff and osteoconductive base layer, magnesium as bioresorbable intermediate layer to increase the bioactivity and silver as an antibacterial top layer. Platinum is doped to silver to increase the release of silver. XRD, SEM/EDS and AFM, ultra-micro hardness indentation test and immersion tests are carried out to identify the coating properties. In order to clarify the release mechanism, electrochemical tests are also performed. Results reveal that doping Pt increases the mechanical properties of the coating whereas it decreases the release of silver by enhancing its passivation behavior.

Influence of carbon nanotubes functionalization on the mechanical properties of polymethacrylate nanocomposites

Nanocomposites based on poly (methyl methacrylate) (PMMA) and a copolymer of methyl methacrylate and hexyl methacrylate were investigated. The fillers were: multi walled carbon nanotubes (MWCNTs) and functionalized MWCNTs (oxidized). The samples were studied by the depth sensing indentation methods (DSI) based on measurement of load–displacement curves at a constant loading speed. The tests were performed on a dynamic ultra microhardness tester DUH-211S in accordance with ISO 14577-1. The dynamic hardness, Martens hardness, indentation hardness, indentation modulus and elastic part of the deformation work were measured. Classical Vickers hardness was also determined.It was established that the mechanical properties of the polymer matrices have been improved by adding 1% of MWCNTs in spite of their being or not functionalized. The presence of functionalized nanotubes had a particular effect upon the different polymer composites. They improved the micromechanical characteristic for PMMA composites and worsened those of copolymer composites. The following assumptions about the structural peculiarities of the composites investigated have been proposed: the reason for the different effect of the modified carbon nanotubes are the length of the side chains and different interaction; the long hexyl groups spatially hinder the contact of the ester groups with functionalized MWCNTs and thus facilitate the agglomeration of the latter.

Influence of the Brittle Behavior of Work Materials on Microgrooving

An electroplated diamond wire tool is frequently used for the machining of hard and brittle materials such as silicon ingots, magnetic materials, ceramics, and sapphires. This study aims to examine the influence of brittle behavior of work materials on machinability (including tool wear); therefore, we conduct dynamic ultramicro hardness measurements and microgrooving experiments for three types of ceramics. The results indicate that the groove depth of a work material tends to increase with the processing time. Moreover, material properties of a work material, such as hardness and toughness, have a significant impact on the fluctuations in its groove depth. However, kerf width of a work material does not depend on the processing conditions and material properties. In addition, a faster relative velocity improves processing efficiency but also increases tool wear.

Effect of Fluoride-Releasing Adhesive Systems on the Mechanical Properties of Eroded Dentin.

The aim of the study was to evaluate the effect of erosive pH cycling with solutions that simulate dental erosion on Martens hardness (HMV) and elastic modulus (Eit) of dentin restored with fluoride-releasing adhesive systems. Twenty-seven bovine dentin slabs were restored with three adhesive systems: Adper Single Bond 2 total-etch adhesive system, One Up Bond F and Clearfil SE Protect fluoride-containing self-etching adhesive systems. The restorations were made with Filtek Z250. The HMV and Eit values at distances of 10, 30, 50 and 70 µm from the interface were evaluated using a dynamic ultra microhardness tester before and after immersion in deionized water, citric acid and hydrochloric acid (n=9). Data were submitted to repeated-measures ANOVA and Fisher's PLSD tests (=0.05). After erosive cycling, HMV values of dentin decreased in all groups. For dentin restored with Adper Single Bond 2, the lowest values were found closer to the hybrid layer, while for One Up Bond F and Clearfil SE Protect, the values remained unaltered at all distances. For dentin restored with fluoride-releasing adhesive systems, a decrease in Eit was found, but after 30 µm this difference was not significant. The acid substances were able to alter HMV and Eit of the underlying dentin. For fluoride-releasing adhesives, the greater the distance from bonded interface, the lower the Eit values. The fluoride in One Up Bond F and Clearfil SE Protect was able to protect the underlying dentin closer to the materials. In this way, the fluoride from adhesive systems could have some positive effect in the early stages of erosive lesions.

Characteristics of micro-arc oxidation and laser melting modified compound film on Ti alloy surface

In order to obtain and enhance the excellent performance of films with porous microstructure through the micro-arc oxidation (MAO) process on TC4 alloy (Ti–6Al–4V) surface, the composite technology included in MAO and laser remelting (LSM) process was introduced. Two kinds of specimens were fabricated, one was prepared only by MAO process in silicate electrolyte system; the other was treated by LSM process after MAO. Then, subsequently, MAO and MAO+LSM films were fabricated. Scanning electron microscopy, X-ray diffraction, ultra microhardness tester and electrochemical analyzer were used to analyze the microstructure, phase composition, surface hardness and corrosion resistance of two kinds of films. The results show that the film, after LSM from inside to outside, exhibits dense layer, middle layer and remelting layer; the former MAO loose layer is replaced by remelting layer with compact structure and low porosity, as well as the proportion of rutile phase in MAO+LSM film is improved, the hardness and corrosion resistance is also increased and the combination mode of MAO film and the substrate is still kept. Therefore, for improving the properties of MAO film on the Ti alloy surface, the LSM technology plays a promoting role.

Scratch adhesion characteristics of PVD Cr/CrAlN multilayer coating deposited on aerospace AL7075-T6 alloy

Purpose – The purpose of this study is to design and develop a new functional coating system for aerospace AL7075-T6 alloy that would evaluate the mechanical properties of the coating. Design/methodology/approach – This paper outlines the scratch adhesion characterisation of Cr/CrAlN coating using a combination of radio frequency (RF) and direct current (DC) physical vapour deposition (PVD) magnetron sputtering. The surface morphology, microstructure and chemical composition of the Cr/CrAlN film were evaluated by optical microscopy (OM), field emission scanning electron microscopy (FESEM) integrated with energy-dispersive X-Ray spectroscopy (EDX) and atomic force microscopy (AFM). The film-to-substrate adhesion was measured by a scratch test machine manufactured with a detection system, motorized stages, penetration depth sensors, optical microscope and tangential frictional load sensors. Findings – The AFM and ultra-micro hardness results showed an increase in surface roughness to about 20 per cent and hardness to about 74 per cent. Moreover, the film-to-substrate adhesion strength of 1,814 mN was obtained with PVD deposition process. Research limitations/implications – The main limitation of this work is caused by PVD deposition process. Besides, surface defects such as pinholes contribute to a decrease in adhesion strength. Practical implications – The higher hardness of CrAlN coating is used to improve the properties of softer aluminium substrates. This hardness prevents ploughing-induced wear and provides greater adhesion strength by preventing coating delamination. Originality/value – Until now, CrAlN is coated only on ferrous alloys. It has not yet been tried on aluminium alloys. Moreover, coating functionality depends on higher adhesion and failure mechanisms involved in the film-to-substrate system, which is significant in aerospace applications.

Microstructure and properties of aluminum silicon/short fibre carbon composites fabricated by semi-solid thixomixing

A novel method was developed, based on thixotropic nature of semi-solid slurry of aluminum silicon alloy, for the effective dispersion and distribution of short carbon fibers (Csf) under intensive shear stress (τ) into the eutectic without physical or chemical damage. The Csf were distributed homogeneously into the matrix at optimum conditions: a temperature of 576–580°C, around 48% of solid fraction, and rotation speed of mixing was at 100rpm. The gas entrapment and porosity was a challenge in the fabrication the aluminum composite by thixomixing, and its size increased when the samples were heat treated. The extruded and heat treated composites had around 24% improvement of mechanical strength as assessed by tensile tests. The predominant deposition of silicon and its intermetallics at the interfacial region improved the wettability and adherence to achieve good mechanical properties. The formation of some intermetallics can be helpful to overcome low wettability effects and their structural evolutions were impressive. The fractography analysis illustrated the ductile fracture with some plastic deformation as the results of dimples and some fiber pull-out in the fractured surface. Ultra-micro hardness evaluation showed good interfacial bonding after heat treatment. The thixomixing process can be developed to produce various composites with different reinforcement.

Torsional Fretting Wear Behavior of Duplex DLC Coatings Deposited on Ion Nitriding Treated LZ50 Steel

Duplex ion nitriding/DLC coatings were prepared on LZ50 steel. Characterizations were detected by scanning electron microscopy, atomic force microscope, Raman spectroscopy, dynamic ultra-micro hardness tester, and profilometer. The torsional fretting wear behaviors of DLC coatings and substrate LZ50 steel against GCr15 steel ball in dry conditions were studied under angular displacement amplitudes within a range of 0.1°–5°, constant normal load of 50 N, and rotational speed of 0.8° s−1. DLC coatings presented dense structure and high hardness. Compared with the substrate, DLC coatings removed the mix fretting regime and shifted the slip regime to low angular displacement amplitudes. The friction torques of DLC coatings were lower than that of the substrates. In the partial slip regime, the damage of DLC coatings was low. In the slip regime, the damage mechanism combined with delamination, abrasive wear, and graphitization. The DLC coatings exhibited good capability for anti-torsional fretting damage.

Evaluation of Mechanical Properties of a Polymer Matrix Thermosetting (Epoxi)

This research objective evaluate the main mechanical properties of epoxy resin, used in composite matrices. The tests carried out (according to standards of ASTM - American Society for Testing and Materials) tensile, compression, bending, Charpy and ultra-micro hardness for determining the following properties: modulus of elasticity, tensile strength, compression and bending, toughness (strain energy) and hardness. Preliminary results showed that the modulus of elasticity in compression is significantly greater than in tension, reaching a difference of more than 100%.The values of module in bending were slightly lower than in compression. This difference of stiffness between tensile and compression of the matrix phase cannot be ignored during the development of the composite. Knowledge of this behavior and allow a better orientation distribution of fibers (or particles) during the development of the composite in order to achieve optimal performance of the final product.

Effects of radiation on spinodal decomposition of ferrite in duplex stainless steel

Abstract Duplex stainless steel specimens embrittled by temperature-accelerated thermal aging at 400 °C for 40,000 h were irradiated at 300 °C to 1 dpa with 6.4 MeV Fe3+ ions to study the effects of radiation on spinodal decomposition of ferrite. The microstructural change was examined by atom probe tomography, and the hardness change was measured with an ultra-micro hardness tester. Hardening of the ferrite in thermal aged specimens was reduced by irradiation, whereas the ferrite of the unaged specimen was hardened by it. The spinodal decomposition of the ferrite into Fe-rich α phase and Cr-rich α′ phase, and G-phase precipitation occurred after the thermal aging. Fluctuation of the Cr concentration based on the formation of Cr-rich α′ phase decrease by irradiation. This suggested that irradiation caused the disappearance of spinodal decomposition. The decrease in spinodal decomposition correlated with a decrease in hardness.

Thermal Degradation and Microhardness Analysis of Polyene with Modified Oil Resin

Thermal degradation of polyene synthesized from recycle polyvinyl chloride (PVC) and hardness of polyene coated with modified oil has been studied by thermogravimetric analysis (TGA) and microhardness test. The synthesized polyene from reaction of recycle PVC were varied from 30 minutes, 1 hour, 2 hours and 4 hours and their thermal stability has been analyzed. From differential thermal gravimetric, DTG curve, polyene from two hours reaction showed the highest degradation temperature up to 445°C due to degradation of polyene sequences. Microhardness test performed by Shimadzu DUH 211/DUH-211S dynamic ultra microhardness tester according to ASTM E384 showed that polyene derived from 2 hours PVC with modifed oil resin resulted in the highest microhardness ~ 107.99 MPa.

Influence of Nanostructured Fibers on Properties of Building Composites

Currently, interest in nanotechnology concept for cement composites is steadily growing. Results of investigations of the concrete surface, reinforced with nanostructured mineral fibers by using atomic force microscopy (AFM) and dynamic ultra-micro hardness tester (DUMHT) of the specific areas of surface are presented. For comparison plain concrete and concrete with addition of single mineral fibers investigated as well. The analysis of the obtained data has shown that as a result of the directed microdisperse structurization provided by nanoinitiators on a surface of fibers, increase strength and deformation characteristics of a material. The main objective of this paper is to research the mechanisms of pattern formation surface of the concrete contained the High-modulus basalt microfiber (HMBMF) as a solid carrier for nanoparticles.

Calculation of the Mechanical Properties of FeB Layer's by Finite Element Method

Surface treatments of engineering materials are important for serviceable engineering components. One of the thermo-chemical surface treatments of steel based materials is the boriding process. In this study, low alloy steel substrates were borided by pack boriding process at 900 °C. Experimental indentation tests were conducted on Dynamic Ultra-micro Hardness test machine, under applied peak loads of 800 mN, 1000 mN, 1200 mN and 1400 mN. To get the mechanical properties of FeB layers, the resulting load–unload test data of the samples obtained from the experimental indentation tests were analyzed and curve-fitted in Kick’s and Meyer’s law for the loading and the unloading part of the load-unload curve respectively. Then, a set of analytical functions that take the pile-up and sink-in effects into account during instrumented sharp indentation were solved using numerical methods. These analytical functions were defined within an identified representative plastic strain, εr, for the Vickers indenter geometry as a strain level that allows for the description of the indentation loading response independent of strain hardening exponent, n. The mechanical characterization of samples, finite element modeling was applied to simulate the mechanical response of FeB layer on low alloy steel substrate by using ABAQUS software package program.

A Model for the Calculation of Mechanical Properties of Hydroxyapatite Coatings on Ti6Al4V Substrate Using Finite Element Methods

The scope of this study is to find out yield curve on the coating-substrate system of hydroxyapatite (HA) by finite element modeling. With this regard, Hydroxyapatite (HA) coatings were successfully formed on Ti6Al4V substrates by using biomimetic technique. Experimental indentation tests were conducted on Dynamic Ultra-micro Hardness test machine. In finite element modeling (FEM), mechanical properties of coatings were determined by using ABAQUS software package. This numerical study was carried out using an axisymmetric FEM model. To calculate the mechanical properties of coating, the resulting load–unload test data of the samples obtained from the experimental indentation tests were analyzed and curvefitted in Kick’s and Meyer’s law for the loading and the unloading part of the loadunload curve respectively. Then, a set of analytical functions that take the pile-up and sink-in effects into account during instrumented sharp indentation were solved using numerical methods These analytical functions were defined within an identified representative plastic strain, εr, for the Vickers indenter geometry as a strain level that allows for the description of the indentation loading response independent of strain hardening exponent, n.

Co-deposited Zn-submicron sized Al 2O 3 composite coatings: Production, characterization and micromechanical properties

In this study, co-deposition of zinc (Zn)-submicron sized alumina (Al 2O 3) particles via electrodeposition method was investigated. Composite coatings were produced using different coating parameters such as current density, pH, temperature, agitation type, and ceramic powder content of the bath solution. Structural and microstructural properties of the coatings were characterized by X-ray diffractometer (XRD) and scanning electron microscopy with electron dispersive spectroscopy (SEM–EDS). Mechanical properties of the coatings were evaluated by dynamic ultra-micro hardness (DUH) tester, a micro-indentation technique, in detail. It was found that, co-deposition of submicron sized Al 2O 3 particles and Zn metal was successfully achieved via electrodeposition method without any chemical interaction between the ceramic particles and the electrolyte. Comparison of SEM images belonging to the coatings fabricated to those of the reference coatings revealed that homogenous grain structure was obtained. Finally, a boost in the micromechanical properties of the coatings was gained by changing the effective co-deposition parameters such as current density and particle content in the electrolyte.

1501 マイクロ試験によるFe-Sn合金の粒界強度評価(OS15-1 ナノ・マイクロの視点からの変形と破壊の力学)

Bending tests were performed for a micro-sized cantilever specimen that made at Fe-2wt%Sn alloy by using focused ion beam and the root of the specimen was set to a grain boundary to investigate strength for grain boundary fracture by using an atomic force microscope with ultramicro hardness tester. The alloy was heated at 600℃ for 5 h in argon gas atmosphere to cause grain boundary segregation of Sn. Three specimens were prepared for a random grain boundaiy and each specimen had a notch with different depth from 0.7μm to 2.3μm on the grain boundary. The three specimens were fractured at the grain boundary in the bending tests. The J integrals evaluated around the notch tips of three specimens by finite element analysis were between 158 J/m^2 and 171 J/m^2. The J integrals were equal within 5% independent the notch depth, indicating that the quantitative evaluation for the strength of grain boundaries as J integral can be attained by adopting this experimental method.

Mechanical properties of in situ Al 2O 3 formed Al–Si composite coating via atmospheric plasma spraying

In this study, mechanically alloyed Al–12Si/SiO 2 composite powder was deposited onto an aluminum substrate by atmospheric plasma spraying. The composite coating consisting of in situ formed Al 2O 3 reinforced hypereutectic Al–18Si matrix alloy was achieved. The produced coatings were extensively analyzed with respect to X-ray diffraction (XRD). The XRD patterns of the coatings include Al, Si and Al 2O 3 phase formation. Mechanical properties of layers were examined by Dynamic Ultra-micro hardness test machine for estimating Young’s modulus due to load–unload sensing analysis. The hardness and Young’s modulus of the composite coatings sprayed at different plasma current and the distance were measured under 200, 400, 600, 800 and 1000 mN of applied peak loads by indentation technique. The effects of spray distance and arc current on the hardness and Young’s modulus have been investigated. Additionally, it was observed that the arc current and spray distance strongly influence the mechanical properties of the coatings.

Indentation size effect on mechanical properties of HVOF sprayed WC based cermet coatings for a roller cylinder

The present paper concerns the determination of mechanical properties such as hardness, elastic modulus and yield strength of WC-based cermet coatings for a roller cylinder. With this regard, Co and Ni containing WC-based coatings were sprayed on Ni–Al deposited 316 L stainless steel substrates by using High Velocity Oxygen Fuel (HVOF) technique. These HVOF sprayed coatings were analyzed by Scanning Electron Microscopy (SEM) with an Energy Dispersive Spectroscopy (EDS) system attachment. Mechanical properties of the coatings were examined by Shimadzu Dynamic Ultra-micro hardness test machine in order to determine the Young's modulus through load–unload sensing analysis. In addition to mechanical investigation, hardness–depth and hardness–force curves of WC-based coatings were investigated. It was found that both of these characteristics exhibit significant peak load dependency. Experimental indentation studies were carried out to determine load–unload curves of WC-Co and WC-Ni based coatings under 300 mN, 350 mN, 400 mN and 450 mN applied peak loads. Hardness and Young's modulus of WC-based coatings were calculated from experimental indentation test data of samples. It has been observed that the hardness and Young's modulus of the coating depends on the contact area and indentation size. The originality of this study is to determine the indentation size effect and contact area variations on mechanical properties of HVOF sprayed WC-based coatings.

T0301-1-1 マイクロ試験による粒界強度評価手法の開発(マイクロ・ナノ構造体の強度・力学特性)

Bending test was performed for a micro-sized cantilever specimen that made at Fe-2wt%Sn alloy and the root of the specimen was set to a grain boundary to investigate a condition for grain boundary fracture as a preliminary test for evaluation of grain boundary strength by using an ultramicro hardness tester. The alloy was heated at 600℃ for 5h to cause grain boundary segregation of Sn. The grain boundary was fractured in the bending test for the specimen made at large angle grain boundary; whereas the specimen made at small angle grain boundary was not. This result indicates the possibility that quantitative evaluation for the strength of embrittled grain boundaries can be attained by adopting this experimental method.