Nanoindentation Hardness Measurements Research Articles

Effects of dose rate change under irradiation on hardening and microstructural evolution in A533B steel

Iron-ion irradiations were carried out for 0.09wt%Cu A533B steel specimens at 290°C to investigate effects of dose rate change during irradiation; the irradiations consisted of the base irradiation (with an unchanged dose rate) and an additional one with changed dose rates from 1 to 50 times that of the base one. Nano-indentation hardness measurements showed that the increase in hardness was higher for lower dose rate of the base irradiation. A similar trend was identified during the additional irradiation. Transmission electron microscope (TEM) and three-dimensional atom probe (3DAP) analyses were carried out for the quantitative characterization of defect features. Mn/Ni/Si/Cu-enriched clusters and dislocation loops were observed in all specimens. The increase in hardness mainly depended on the formation of the solute atom clusters. The square root of the volume fraction of the solute atom clusters provided a good correlation with the increase in hardness. The effects of dose rate and dose rate change during irradiation were explained by the formation of solute atom clusters.

Microstructural studies of electrospark deposited aluminide coatings on 9Cr steels

Electrospark deposition (ESD) technique has been used to apply an iron aluminide coating on 9Cr reduced activation steel, which is a structural material for test blanket modules of fusion reactors. Phase identification and microstructural analysis of the aluminide coating along with the interface region were performed with the support of X-ray diffraction technique, optical microscopy, scanning electron microscopy and nanoindentation hardness measurements. Microstructural examination indicated prominent changes in the near interface microstructure of the steels processed by the ESD process. The substrate side of the coating/substrate interface consisted of a soft zone that is possibly of quasi-amorphous nature and of an M23C6 type carbide segregation rich area below this interface. The coating, however, showed extensive crack defects that need to be removed for reliably assessing its suitability as a barrier layer for blanket applications.

Investigation of the surface of a laser-treated cast iron cylinder bore

AbstractThe pollution materials emission standards in Europe are going to be more strict. In order to meet the environmental standards, a European automotive manufacturer performs a finishing laser treatment on the honed cylinder bores of their V-engine blocks. Samples of laser treated cast iron cylinder bores with lamellar graphite were investigated. In order to evaluate the microstructure and grain size of the laser-treated layer, scanning electron micrographs were taken on cross-sectioned samples with a scanning electron microscope/focused ion beam dual-beam instrument. The samples were found to be ultra-fine grained. Nanoindentation hardness measurements of the surface layer showed a clear linear trend between the laser power density in the applied range and the measured hardness. Additional microhardness measurements suggest an annealed region beneath the surface.

Structural and mechanical properties of Cr–Al–O–N thin films grown by cathodic arc deposition

Coatings of (CrxAl1−x)δ(O1−yNy)ξ with 0.33⩽x⩽0.96, 0⩽y⩽1 and 0.63⩽δ/ξ⩽1.30 were deposited using cathodic arc evaporation in N2/O2 reactive gas mixtures on 50V negatively biased WC–10wt.% Co substrates from different Cr and Al alloys with three different Cr/Al compositional ratios. For N2<63% of the total gas, ternary (Cr,Al)2O3 films containing <1at.% of N forms; as determined by elastic recoil detection analysis. Increasing the N2 fraction to 75% and above results in formation of quaternary oxynitride films. Phase analyses of the films by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy show the predominance of cubic Cr–Al–N and cubic-(Cr,Al)2O3 solid solutions and secondary hexagonal α-(Cr,Al)2O3 solid solution. High Cr and Al contents result in films with higher roughness, while high N and O contents result in smoother surfaces. Nanoindentation hardness measurements showed that Al-rich oxide or nitride films have hardness values of 24–28GPa, whereas the oxynitride films have a hardness of ∼30GPa, regardless of the Cr and Al contents. Metal cutting performance tests showed that the good wear properties are mainly correlated to the oxygen-rich coatings, regardless of the cubic or corundum fractions.

Grain boundary doping strengthens nanocrystalline copper alloys

Nanoindentation hardness measurements were performed on nanocrystalline (nc-) Cu alloys to test recent molecular dynamics predictions that (i) solute segregation to grain boundaries can lead to significant strengthening and (ii) solutes with large size mismatch with Cu are most effective. Results show that the hardness of nc-Cu90Nb10 is greater than 5 GPa, more than double that of pure nc-Cu, whereas similar additions of Fe solute have nearly no effect. These results are in good agreement with simulations.

Investigation of radiation damage and hardness of H- and He-implanted SiC

In this study, an investigation was conducted in order to determine the effects of high-dose H and He ion implantation on the structure of 3C-SiC and 6H-SiC as well as the effects on material hardness in order to understand the role of H and He produced in SiC by neutron-induced transmutations as described by Heinisch et al. [J. Nucl. Mater. 2004, 327, 175–181.]. H and He ions were implanted into polycrystalline 3C-SiC on a Si substrate and single-crystal bulk 6H-SiC, respectively, at an ion energy of 100 keV, and the total dose that was used for both species was 1017 ions/cm2 in the temperature range of 473–573 K. The specimens were annealed at 1000°C for 20 min in an inert Ar atmosphere. The damaged region in the He-implanted 6H-SiC had a high density of small bubbles, but no cracks were observed. Severe cracking was observed along the damaged region in the H-implanted 3C-SiC specimens as well as a high density of hydrogen platelets. Neither specimen displayed any amorphization. Nanoindentation hardness measurements showed a marked increase in the hardness of the annealed He-implanted 6H-SiC, which was ascribed to the creation of point defects inhibiting interplanar slip. There was also a large decrease in hardness corresponding to the depth of the ion damage.

Influence of Low‐Temperature Environmental Exposure on the Mechanical Properties and Structural Stability of Dental Zirconia

The effect of dental fabrication procedures of zirconia monolithic restorations and changes in properties during low-temperature exposure in the oral environment is not completely understood. The purpose of this study was to investigate the effect of procedures for fabrication of dental restorations by low-temperature simulation and relative changes of flexural strength, nanoindentation hardness, Young's modulus, surface roughness, and structural stability of yttria-stabilized zirconia. A total of 64 zirconia specimens were prepared to simulate dental practice. The specimens were divided into the control group and the accelerated aging group. The simulated group followed the same procedure as the control group except for the aging treatment. Atomic force microscopy was used to measure surface roughness. The degree of tetragonal-to-monoclinic transformation was determined using X-ray diffraction. Nanoindentation hardness and modulus measurements were carried out on the surface of the zirconia specimens using a nanoindenter XP/G200 system. The yttria levels for nonaged and aged specimens were measured using energy dispersive spectroscopy. Flexural strength was determined using the piston-on-three-ball test. The t-test was used to determine statistical significance. Means and standard deviations were calculated using all observations for each condition and evaluated using a group t-test (p < 0.05). The LTD treatment resulted in increased surface roughness (from 12.23 nm to 21.56 nm for Ra and 15.06 nm to 27.45 nm for RMS) and monoclinic phase fractions (from 2% to 21%), with a concomitant decrease in hardness (from 16.56 GPa to 15.14 GPa) and modulus (from 275.68 GPa to 256.56 GPa). Yttria content (from 4.43% to 4.46%) and flexural strength (from 586 MPa to 578 MPa) were not significantly altered, supporting longer term in vivo function without biomechanical fracture. The LTD treatment induced the tetragonal-to-monoclinic transformation with surface roughening in zirconia prepared using dental procedures.

Performance of melamine modified urea–formaldehyde microcapsules in a dental host material

AbstractUrea–formaldehyde (UF) microcapsules filled with dicyclopentadiene (DCPD) show potential for making self‐healing dental restorative materials. To enhance the physical properties of the capsules, the urea was partially replaced with 0–5% melamine. The microcapsules were analyzed by different microscopic techniques. DSC was used to examine the capsule shell, and the core content was confirmed by 1H NMR spectroscopy. Capsules in the range of 50–300 μm were then embedded in a dental composite matrix consisting of bisphenol‐A‐glycidyl dimethacrylate (Bis‐GMA) and triethylene‐glycol dimethacrylate (TEGDMA). Flexural strength, microhardness, and nanoindentation hardness measurements were performed on the light‐cured specimens. Optical microscopy (OM) examination showed a random distribution of the microspheres throughout the host material. The incorporation of small amounts of the microcapsules did not affect the performance of the matrix material. Scanning electron microscopy (SEM) analysis revealed excellent bonding of the microcapsules to the host material which is a characteristic of utter importance for maintaining the very good mechanical properties of a dental composite with self‐healing ability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Deformed Microstructure and Hardness of Hadfield High Manganese Steel

Hadfield high manganese steel, with a full austenite microstructure at room temperature, has been receiving much attention, and it is used in a variety of applications such as railway crossings, crawler treads for tractors and impact hammers, because of its excellent work-hardening rate, high toughness and high wear resistance. Many efforts have been made to study the deformation mechanisms of Hadfield steel, with an attempt to correlate the excellent work hardening properties of the steel with its evolved microstructures. 1–5) Deformation and work-hardening properties of Hadfield steel are often assessed by uniaxial tension or compression tests and also by hardness measurements; 6,7) such assessments are essentially averaged results of deformation over a whole specimen or over a relatively large volume of material. Nevertheless, microscopic observations revealed that the evolved substructures of the Hadfield steel subjected to deformation are mostly non-homogeneous, 8) indicative of non-uniform deformation and work hardening that has occurred in the deformed steel. The understanding of non-uniform deformation and work hardening of materials is of critical importance, especially in failure analysis of practical industrial products, since locally concentrated straining associated with non-uniform work hardening tends to initiate damage and cracking. 9,10) Some researchers have, indeed, evaluated the degree of straining heterogeneity due to mechanical twinning of Hadfield steel by a digital image correlation method; 8) however, not much attention has been paid to the local-scale hardness in deformed Hadfield steel. A non-uniform distribution of hardness on the local scale, which may be influenced by a number of factors such as grain boundary, grain orientation of the indentation plane as well as the microstructures under the indentation tip, 11–13) can be expected in the deformed Hadfield steel. The aim of the present work is to study the non-uniform work hardening of a practical deformed Hadfield steel crossing by characterizing the local-scale hardness distribution by means of Vickers and nanoindentation hardness measurements, and to explore the origin of the hardness non-uniformity by investigating the local microstructural features in the deformed Hadfield steel by means of optical microscope, electron back-scattered diffraction (EBSD) and transmission electron microscope (TEM).

Nano mechanical properties of an automotive clear-coats containing nano silica particles with different surface chemistries

Different nano-silica particles were incorporated in an automotive OEM clear-coat based on acrylic-melamine chemistry. A neat and three silane-treated nano-silica particles were added to the clear-coat. Treated grades were coated by dimethyl dichloro silane, hexamethyl disilane and methacryl silane, respectively. The scratch/mar resistances of the heat-cured films were investigated using nano-indentation hardness measurements. It was found that there is a close relationship between the surface chemistry of silica nano-particles and nano mechanical behavior of the baked films. Adding the above-mentioned nano-silica particles to the clear coat resulted in higher elastic modulus and indentation hardness. The most significant effect was observed in samples containing silica particles coated with dimethyl dichloro silane and carrying acidic surface hydroxyl groups.

Effect of leaser treatment on the surface of cast iron cylinder bores

The environmental and pollution materials emission standards in Europe are going to be more strict. In order to meet the standards, a European automotive manufacturer performs a finishing laser treatment on the honed cast iron cylinder bores of their V-engine blocks. Samples of laser treated cast iron cylinder bores with lamellar graphite were investigated. Due to the growing popularity and high efficiency of fiber lasers, samples treated with Yb-fiber lasers were investigated. In order to evaluate the microstructure and grain size of the laser treated layer, scanning electron microscopic images were taken on cross sectioned samples with a scanning electron microscope/focused ion beam dual beam electron microscope. The samples were found to be ultra fine grained. Nanoindentation hardness measurements of the surface layer showed a clear linear trend between the laser power density in the applied range and the measured hardness. Additional micro hardness measurements suggest an annealed region beneath the surfa ce.

Chemical resistance of DLC thin film deposited PMMA substrates

DLC thin films were deposited on silicon and poly(methyl methacrylate) (PMMA) substrate using a plasma chemical vapor deposition method with a negative bias voltage of 200 V applied to the substrate, and investigated for the chemical resistance to acetaldehyde, acetone, acetic acid and sodium hydroxide by an immersion test. Raman spectra and nano-indentation hardness measurement showed high stability in the DLC structure and mechanical property against the immersion into organic solvents, acid and alkali solutions. The decrease in Raman spectra peak intensities, before and after the immersion into acetaldehyde and acetone, was reduced by the DLC thin film deposition on the PMMA substrate, and the effect of DLC coating was revealed. A scanning electron microscope (SEM) observation from the PMMA substrate surface and cross section, with and without the DLC coating and before and after the immersion into acetone, suggested that the DLC layer protected the dissolution of PMMA into acetone by preventing the molecules of acetone from contacting with the surface of PMMA and penetrating into the PMMA.

Combination of surface nanocrystallization and co-rolling: Creating multilayer nanocrystalline composites

This paper describes a combination of surface mechanical attrition treatment and co-rolling performed at 550 °C. This duplex method leads to the formation of a semi-massive multilayer structure of alternating nanocrystalline layers, transition layers and coarse-grained layers. Transmission electron microscopy observations correlated with nanoindentation hardness measurements demonstrate that the nano- and subnanocrystalline layers are preserved after the process. Tensile tests showed improved yield and ultimate strengths, and acceptable ductility.

Area function calibration in nanoindentation using the hardness instead of Young's modulus of fused silica as a reference value

AbstractFor nanoindentation hardness and Young's modulus measurements the area function of the indenter has to be calibrated carefully since direct measurement of the contact area is not possible. Most often this is done by making a series of indentations into a material with known Young's modulus, e. g. fused silica. In this paper it will be shown that this method may lead to significant deviations in hardness values found over the lifetime of the indenter due to successive rounding of the tip. Additionally, depth-dependent hardness values may apparently be found which would falsify all hardness determinations. Using instead the hardness of fused silica as a reference value these problems will be avoided. Additionally, the calibration becomes independent of material constants such as the Young's modulus of the diamond tip and the Poisson ratios of both indenter and sample, which enter into the conventional calibration method.Finally, this paper discusses whether the indentation modulus determined by nanoindentation and the Young's modulus determined by, for example, tensile testing, are quantitatively equal. This is a precondition for the traceability of the Young's modulus method often mentioned as its main advantage.

Helium effects on mechanical properties and microstructure of high fluence ion-irradiated RAFM steel

Reduced-activation ferritic/martensitic steels, RAFS, are leading candidates for the blanket and first wall of fusion reactors, and effects of displacement damage and helium production on mechanical properties and microstructures are important to these applications. Because it is the most effective way to obtain systematic and accurate information about microstructural response under fusion environment, single-(Fe 3+) and dual-(Fe 3+ + He +) irradiations were performed followed by TEM observation and nano-indentation hardness measurement. Dual-ion irradiation at 420 °C induced finer defect clusters compared to single-ion irradiation. These fine defect clusters caused large differences in the hardness increase between these irradiations. TEM analysis clarified that radiation induced precipitates were MX precipitates (M: Ta, W). Small defects invisible to TEM possibly caused the large increase in hardness, in addition to the hardness increment produced by radiation induced MX. In this work, radiation hardening and microstructural evolution accompanied by the synergistic effects to high fluences are discussed.

Comparison between nanoindentation and scratch test hardness (scratch hardness) values of copper thin films on oxidised silicon substrates

In this paper we measured for the first time the scratch hardness of copper thin films and compared this with hardness measured from nanoindentation. Copper films with thicknesses in the range 100 nm to 500 nm were deposited by rf magnetron sputtering on silicon substrates. Scratch hardness was determined by CSM™ scratch tester using scratch widths at low loads. The measured hardness values were compared with conventional nanoindentation hardness measurement by CSM™ nanohardness tester. At these low indentation depths there is a good correlation between the scratch hardness and the nanoindentation hardness, with an increase in hardness as the film thickness decreases.

Effects of deposited nuclear and electronic energy on the hardness of R7T7-type containment glass

The effects of elastic and inelastic interactions induced by cumulative alpha decay on the hardness of R7T7-type nuclear containment glass were investigated on actinide-doped glass specimens and by external irradiation of inactive glass by light and heavy ions. Vickers microindentation and nanoindentation hardness measurements showed that in the deposited energy range investigated (below 3 × 10 22 keV/cm 3) inelastic effects have no influence on the plastic response of the glass. Conversely, identical hardness variations versus the nuclear energy deposited in the material were observed on curium-doped glass and on glass irradiated by ion bombardment. The observed hardness variation stabilized after the deposited energy reached about 3 × 10 20 keV nucl/cm 3. These findings indicate that the change in the plastic response of the glass is a consequence of ballistic effects.

Structure and mechanical behavior of a toucan beak

The toucan beak, which comprises one third of the length of the bird and yet only about 1/20th of its mass, has outstanding stiffness. The structure of a Toco toucan ( Ramphastos toco) beak was found to be a sandwich composite with an exterior of keratin and a fibrous network of closed cells made of calcium-rich proteins. The keratin layer is comprised of superposed hexagonal scales (50 μm diameter and 1 μm thickness) glued together. Its tensile strength is about 50 MPa and Young’s modulus is 1.4 GPa. Micro and nanoindentation hardness measurements corroborate these values. The keratin shell exhibits a strain-rate sensitivity with a transition from slippage of the scales due to release of the organic glue, at a low strain rate (5 × 10 −5/s) to fracture of the scales at a higher strain rate (1.5 × 10 −3/s). The closed-cell foam is comprised of fibers having a Young’s modulus twice as high as the keratin shells due to their higher calcium content. The compressive response of the foam was modeled by the Gibson–Ashby constitutive equations for open and closed-cell foam. There is a synergistic effect between foam and shell evidenced by experiments and analysis establishing the separate responses of shell, foam, and foam + shell. The stability analysis developed by Karam and Gibson, assuming an idealized circular cross section, was applied to the beak. It shows that the foam stabilizes the deformation of the beak by providing an elastic foundation which increases its Brazier and buckling load under flexure loading.

The toucan beak: Structure and mechanical response

The structure and mechanical response of a Toco toucan ( Ramphastos toco) beak were established. The beak was found to be a sandwich composite with an exterior of keratin scales (50 μm diameter and 1 μm thickness) and a core composed of fibrous network of closed-cells made of collagen. The tensile strength of the external shell is about 50 MPa. Micro- and nanoindentation hardness measurements corroborate these values. The keratin shell exhibits a strain-rate sensitive response with a transition from slippage of the scales due to release of the organic glue, at a low strain rate (5 × 10 − 5 s − 1 ) to fracture of the scales at a higher strain rate (1.5 × 10 − 3 s − 1 ). The closed-cell foam consists of fibers having a Young's modulus (measured by nanoindentation) of 12.7 GPa. This is twice as high as the keratin shells, which have E = 6.7 GPa. This is attributed to their higher calcium content. The compressive collapse of the foam was modeled by the Gibson–Ashby constitutive equations. There is a synergistic effect between foam and shell evidenced by a finite-element analysis. The foam stabilizes the deformation of the keratin shell by providing an internal support which increases its buckling load under compressive loading.

Work hardening in rolled nanolayered metallic composites

The strength of room temperature rolled sputter deposited nanolayered Cu–Nb composites is evaluated. Self-supported Cu–Nb foils with initial individual layer thickness varying from 32 to 75 nm were rolled to the same final layer thickness of 30 nm. Nanoindentation hardness measurements were used to study the change in hardness with rolling strain. The resulting work hardening rate is compared to bulk Cu and mechanisms that give rise to work hardening in nanolayered metals, in the absence of dislocation cell structure formation, are discussed.