Mechanical Properties Microprobe Research Articles

Microstructure and properties of ceramic coatings produced on 2024 aluminum alloy by microarc oxidation

The microstructures of the microarc oxidation coatings and 2024 aluminum alloy substrate were observed using the scanning electron microscope (SEM) and the phase composition of the coatings was analyzed by X-ray diffraction (XRD). Furthermore, the profiles of the nanohardness, H, and elastic modulus, E, along the coating depth were first determined using the mechanical properties microprobe. The microarc oxidation coatings consist of two layers—a loose layer and a compact layer. The H and E in the compact layer are about 18–32 GPa, 280–390 GPa, respectively. The H and E profiles are similar, and both of them exhibit a maximum value at a same depth of the coatings. The distribution of α-Al2O3 phase content determines the H and E profiles in the coatings. The changes of α-Al2O3 and γ-Al2O3 contents result from the different cooling rates of the molten alumina in the microarc discharge channel at the different depths of the coatings. After the microarc oxidation treatment, the microstructure of the alloy substrate, even near the Al/Al2O3 interface, has not been changed.

Mechanical properties and fracture behavior of interfacial alumina scales on plasma-sprayed thermal barrier coatings

The mechanical properties and fracture behavior of Y-doped Al2O3 scales were investigated by furnace thermal cycling (to 1,150°C) of plasma-sprayed thermal barrier coatings (TBCs) with vacuum plasma-sprayed (VPS) or air plasma-sprayed (APS) Ni–22Cr–10Al–1Y bond coatings. No significant alterations in Al2O3 hardness or Young’s modulus (as measured by mechanical properties microprobe) were detected as a function of bond coat type, exposure time, or number of thermal cycles. The interfacial Al2O3 scales on VPS NiCrAlY exhibited progressive increases in localized fracture, buckling, and delamination during thermal cycling. The concentration of arrayed lenticular voids in the columnar Al2O3 grain boundaries significantly increased during cyclic oxidation (as compared to isothermal oxidation), but only in scales which formed on convex surfaces, suggesting internal void growth was stress-related. The amount and frequency of scale damage was higher on convex surfaces with a relatively large radius of curvature as compared to convex surfaces with a very small radius of curvature. Although the thermo-mechanical fracture resistance of Al2O3 scales on APS NiCrAlY was superior to scales on VPS NiCrAlY, TBC lifetimes on VPS NiCrAlY were greater by a factor of 2. Apparently, severe interfacial scale damage did not rapidly degrade the adherence of the ceramic top coatings.

Longitudinal hardness and Young's modulus of spruce tracheid secondary walls using nanoindentation technique

Using a mechanical properties microprobe, measurements of hardness and elastic modulus of tracheid walls in the longitudinal direction of spruce wood were obtained by continuously measuring force and displacement as a diamond indenter impressed a cell wall. Maximum mechanical properties were found at the edges of the walls of angular shaped tracheids. Both the hardness and elastic modulus of latewood cell walls were higher than cell walls in the earlywood. The high spatial resolution of this new concept of mechanical testing allows a direct comparison with ultrastructural and microchemical parameters of lignified cells which opens a wider area of applications for the understanding of intrinsic wood properties.

Comparing Mechanical Properties of Secondary Wall and Cell Corner Middle Lamella in Spruce Wood

Mechanical characterizations of the S2 layers and the cell corner middle lamella in the axial direction were investigated in spruce wood, A mechanical properties microprobe capable of measuring hardness and Young's modulus on a spatially resolved basis similar to that of an electron beam microprobe was used. Hardness of the cell comer middle lamella was found to be almost as high as that of the secondary wall, but the Young's modulus of the cell corner middle lamella was 50% less than that of the S2' The S2 showed constant hardness over its range of Young's modulus, but the cell corner middle lamella exhibited a strong correlation (R2 = 0.55) between hardness and the Young's modulus. Further investigations are needed to directly combine chemical and micromechanical properties and also to investigate the mechanical effects of the high variability of cell corner middle lamella chemistry.

High resolution characterisation of tribochemical films on alumina

This paper presents the results of the characterisation of tribochemical films produced by the sliding wear of alumina in a humid environment. The techniques that were used were field emission scanning electron microscopy (FESEM) mechanical properties microprobe or nanoindentor (MPM), atomic force microscopy (AFM), frictional force microscopy (FFM) and non-contact optical profilometry. It was found that the tribochemical films were softer than the remnant alumina on the worn surfaces, and were liable to fracture and cracking under the indenter. The FESEM showed similar features to the AFM, but because of its direct height imaging, the AFM was better at resolving and imaging small MPM indentations. The AFM also showed that the tribochemical films were composed of small rounded particles which were pressed together to form the films. Some FFM contrast is attributed to steep gradients or edges, and some to variations in surface roughness. There is, however, some contrast which cannot easily be explained by simple geometric interactions and appears to be associated with variations in surface chemistry and structure.

Residual Stress, Mechanical Behavior and Electrical Properties of Cu/Nb Thin-Film Multilayers

ABSTRACTThe effect of compositional wavelength on the residual stress, electrical resistivities and mechanical properties of Cu/Nb thin-film multilayers sputtered onto single-crystal Si substrates was evaluated. Electrical resistivities were measured down to 4 °K using a standard four-point probe measurement system. A differential specimen-curvature technique was used to detennine residual stress, and a mechanical-properties microprobe was employed to obtain hardness and elastic modulus. Characterization techniques included profilometry, Ion-Beam Analysis (IBA) and Transmission Electron Microscopy (TEM). The hardness of the Cu-Nb multilayers increased with decreasing compositional wavelength so that the layered structures had hardness values in excess of either of the constituents and the hardness predicted by the rule of mixtures. A peak in the net residual compressive stress of the multilayers was observed at a compositional wavelength of 100 nm. No resistivity plateau was observed within the composition wavelength range studied.

Hardness and elastic modulus of zircon as a function of heavy-particle irradiation dose:

Abstract Synthetic single-crystals of zircon [(100) growth surfaces] were implanted at 77K with 540 keV Pb ions with fluences of 3.3 × 1011 to 5 × 1015 ions/cm2 —a dose range that completely spans the crystalline-to-amorphous transition as determined by Rutherford backscattering/ion-channeling measurements. A chemically unzoned, natural crystal [polished (100) section] was similarly implanted. Both the natural and synthetic crystals, as examined by mechanical-properties microprobe (MPM) methods, exhibited an overall radiation-induced softening (70% reduction) and decrease in modulus (42%) through the crystalline-to-amorphous transition. This transition occurs over a narrow range of dose, i.e. 1 × 1013 to 1 × 1014 Pb ions/cm2. Moreover, below the transition, a pronounced radiation-induced hardening occurs in the near-surface region of the synthetic crystals. This radiation hardening may be due to the accumulation of interstitials. In contrast, the natural zircon showed no hardening; however, its initially ...

Hardness and modulus measurements on oxide scales

This paper provides a comparison between hardness and elastic modulus data measured using a mechanical properties microprobe (MPM), the acoustic microscope and two techniques based on resonant frequency to measure the elastic moduli of oxide systems. Measured values for bulk oxides, namely AI2O3 and Cr2O3, have been used to compare the various measurement systems. The comparison is then extended to measurements on oxide scales. In general, hardness values measured using the MPM technique agree with reported bulk values, although differences between laboratories have been identified which may be attributable to the position of indentation within the scales. Hardness values for scales are found to be similar to hardness values for the bulk, lying in the range 21–30 GPa for A12O3 scales and 18–33 GPa for Cr2O3 scales. Young's moduli for recrystallized AI2O3 have been measured using the mechanical properties microprobe, acoustic microscopy and resonance methods. Data determined using the MPM technique give th...

Use of the mechanical properties microprobe for characterization of oxide scales

A mechanical properties microprobe (MPM) based on low-load, depth-sensing submicrometre indentation testing is an extremely powerful instrument for examining surface mechanical behaviour and offers several advantages for determining the elastic and plastic properties of protective oxide scales. Its high spatial and force resolutions allow measurements on thin scales and, for thicker surface oxides, determination of gradients in properties. Under optimal conditions, hardness and modulus values can be determined with an overall accuracy of about 10%. A key factor in analysis of the load-displacement data is an accurate determination of the indenter contact area. Because of this, companion indentations into bulk oxides using the same indenter reduce uncertainties associated with comparing the elastic and plastic properties of such materials with their corresponding scales. Use of a standard MPM is currently limited to near room temperature. More effective depth-sensing indentation testing of oxide scales at ...

Single-Fiber Push-In vs. Single-Fiber Push-Out: A Comparison Between Two Test Methods to Determine the Interfacial Properties of Brittle Matrix Composites

ABSTRACTInterfacial properties of Nicalon™-reinforced brittle matrix composites were determined from single-fiber load-controlled push-in tests using a Mechanical Properties Microprobe (Nanoindenter) and single-fiber displacement-controlled push-out tests using the Interfacial Test System (ITS). A comparison between the results from these two tests is presented along with a discussion of data analysis techniques.

Interface Degradation in CAS/Nicalon During Elevated Temperature Aging

ABSTRACTA CaO-Al203-SiO2 (CAS)/Nicalon glass-ceramic matrix composite has been subjected to elevated temperature oxidation heat-treatments between 375 and 1200°C, for up to 100 hours. Micro- and macro-mechanical properties have been determined by fiber push-down, using a mechanical properties microprobe, and flexure testing, respectively. Aging between 450 and 800°C results in significant property degradation, with reduced bending modulus and flexure strength, increased fiber sliding stress, and a transition to a purely brittle failure mode. Aging degradation is due to oxidative removal of the carbon interlayer, with the subsequent formation of a silica bond between fiber and matrix. At higher temperatures, carbon is retained due to the formation of a protective silica plug at exposed fiber ends, with the subsequent retention of composite properties. Short duration pre-treatment schedules, at 1000 or 1100°C, were developed to prevent intermediate temperature property degradation.

Evaluation of the Mechanical Properties of Tribochemical Films on Alumina

AbstractThis paper presents the results of the mechanical characterisation, by a mechanical properties microprobe or nanoindenter, of tribochemical films produced by the sliding wear of alumina in a humid environment.It was found that the tribochemical films were softer than the remnant alumina on the worn surfaces, and were liable to fracture and cracking under the indenter.

Evaluation of Interfacial Properties of Fiber‐Reinforced Ceramic Composites Using a Mechanical Properties Microprobe

The application of a mechanical properties microprobe to evaluate the interfacial properties of fiber‐reinforced ceramic composites is addressed. The stress–displacement relation of the embedded fiber, which is subjected to an axial loading–unloading cycle, is analyzed. The interfacial bonding, Coulomb friction at the debonded interface, Poisson's effect of the loaded fiber, and residual stresses are included in the analysis, and closed‐form analytical solutions are obtained. Based on the analytical solutions, a methodology is established to extract the interfacial properties from experimental stress–displacement curves. The roles of interfacial bonding, Poisson's effect, and residual axial stresses on the residual fiber displacement after complete unloading are also addressed in the present study.

Characterization of the mechanical properties of a–SiC: H films

Amorphous hydrogenated silicon carbide (a–SiC: H) thin films (t < 1 μm) were grown from two different precursor gases, a methane/silane mixture and silacyclobutane (SiC3H8). Plasma enhanced chemical vapor deposition was used to deposit a–SiC: H thin films on silicon substrates at temperatures of 175 °C and 600 °C. These a–SiC: H films were characterized using the mechanical properties microprobe (nanoindenter) and by scratch testing. Data and mechanical properties information collected from these measurements have been correlated with film process conditions and materials characteristics. A simplified approach was used to calculate the average nanoindentation hardness from shallow indentations. Using this technique, results for a silicon wafer are in good agreement with that previously reported. Analysis of the substrate influence on the thin film nanoindentation data implies that the measured hardness is relatively unaffected by the substrate, while the measured elastic properties are somewhat influenced by the substrate. The a–SiC: H film hardness is shown to depend on the precursor gas and molecular bonding, while the elastic properties vary with precursor gas, composition, and density, as influenced by the plasma source deposition power. The MPM data and scratch test data show similar correlations to plasma source power, film structure, and film composition.

Evaluation of interfacial mechanical properties in SiC fiber-reinforced macro-defect-free cement composites

The application of a micro-indentation technique for the measurement of interfacial mechanical properties in a fiber-reinforced cement composite has been examined. The composite was formed by placing aligned SiC fiber tows between macro-defect-free (MDF) cement sheets after which the compact was warm pressed at 6·89 MPa (1000 psi) at 80°C. The interfacial characteristics of the composite were varied by modifying the surfaces of the fibers prior to their incorporation into the matrix. These modifications included either an application of a stearic acid film or 1000°C gas phase treatments in air, oxygen, or nitrogen for one hour. These four fiber surface treatments served as the independent parameter for the mechanical testing analysis. The interfacial characteristics, including the shear, the residual axial fiber, and debond stresses, were evaluated with a mechanical properties microprobe by measuring the force/displacement curves generated during load-unload cycling. Estimates of these three stress values were obtained by matching the experimental force/displacement curves with data predicted from an existing model. For two of the four systems investigated, relatively high residual axial fiber compressive stresses were required adequately to describe the large fiber displacement recovery obtained after complete unloading. The stresses were believed to have resulted from the large differential shrinkage between the fibers and matrix during processing. The shear and debond stress values were highest for those fibers oxidized in air and lowest for fibers coated with stearic acid. The calculated interfacial shear stress value becomes significantly overestimated when the residual axial stress has a large magnitude and is not taken into account in the calculation.

Characterization of YBa 2Cu 3O 7-x in a mechanical properties microprobe

Early after the discovery of the high Tc superconductors several authors indicated severe limitations of these materials for many possible industrial applications. The extreme brittle behavior of sizable samples has impaired the mechanical characterization of the ceramic superconductors. Recent developments in small scale hardness testing have now made it possible to make hardness indents in materials and derive meaningful mechanical properties data. This has largely been accomplished by instrumenting specialized hardness testing equipment with high resolution devices to monitor continuously the loads and displacements experienced by the contact of the indenter on the material. By proper analysis of the load displacement data, it is also possible to determine a number of material properties which cannot normally be obtained using conventional microhardness testing such as the elastic modulus. In this paper the authors characterized the mechanical properties of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} crystallites by employing a Nanoindenter.

The hardness and Young's modulus of bulk YBa2Cu3O7−x (1:2:3) and YBa2Cu4O8 (1:2:4) as determined by ultra low load indentation

Using a highly-spatially-resolved mechanical properties microprobe, the Young's modulus and hardness of bulk YBa2Cu3O7−x (1:2:3) and YBa2Cu4O8 (1:2:4) have been determined. The Young's modulus of a superconductor is an important parameter in determining critical grain sizes above which microcracking will occur due to anisotropic thermal stresses that arise during processing. This phenomenon of microcracking has been determined to cause a decrease in the attainable critical current densities in bulk superconductors. The mechanical properties data for these two materials show that the Young's modulus of 1:2:3 is approximately 35% greater than the modulus of 1:2:4. This along with available anisotropic thermal expansion data for 1:2:3 and 1:2:4 suggests that the critical grain size for 1:2:4 is about 7 times greater than the critical grain size for microcracking in 1:2:3.

Hardness and elastic modulus of zircon as a function of heavy-particle irradiation dose: I.In situα-decay event damage

Abstract For a natural single crystal of zircon, ZrSiO4, from Sri Lanka, exhibiting zonation in U and Th contents, the hardness and elastic modulus have been determined as a function of α-decay dose using a mechanical properties microprobe (MPM). The zones vary in thickness from one to hundreds of micrometers, and have uranium and thorium concentrations such that the α-decay dose varies between 2 × 1015 and 1 × 1016 α-decay events/mg (0.15 to 0.65 dpa, displacement per atom). The transition from the crystalline to the aperiodic metamict state occurs over this dose range. For a traverse of 75 indent pairs across layers sampling a large portion of the crystalline-to-metamict transition (3.7 × 1015 to 9.7 × 1015 α-decay events/mg) both the hardness and elastic modulus decrease linearly with increasing α-decay dose. The radiation-induced softening follows a behavior similar to other radiation-induced changes, that is with the expansion of the unit cell parameters there is a decrease in density, birefringence, hardness and bulk modulus.

Mechanical properties of highly aligned YBa 2Cu 3O 7−δ effect of Y 2BaCuO x particles

The elastic modulus and hardness of highly aligned YBa 2Cu 3O 7−δ obtained by melt processing was determined using a highly spatially resolved mechanical properties microprobe. Ultra-low load indentation measurements on the (001) cleavage plane of aligned 123, indicated a Young's modulus of 143 ± 4 GPa and a hardness of 10.0 ± 1.9 GPa. For measurements on a plane perpendicular to the cleavage plane, values of 182 ± 4 GPa for the modulus and 10.8 ± 1.7 GPa for the hardness were obtained. A lower modulus in the c-direction is perhaps a result of the layer-like structure of 123, with weak coupling between the layers. Measurements on the trapped single crystal 211 particles yielded a modulus of 213 ± 5 GPa and a hardness of 14.4 ± 2 GPa. Considerations of the thermal and elastic mismatch effects between the 211 particles and the 123 matrix, the large thermal expansion anisotropy of aligned 123, and microstructural examination of polished and fracture surfaces of the aligned samples indicate that the 211 particles perhaps serve to enhance the fracture resistance behavior of 123 by energy dissipation due to interfacial delamination and crack bridging.

The indentation and wear properties of a thermal-diffusion-boronized CoCrWC alloy

Vickers and ultralow-load indentation and unlubricated sliding wear properties of a commercially produced, diffusion-boronized layer deposited over a wrought CoCrWC alloy have been investigated using both commercially available and custom-built instruments. Cross-sectional micro- and ultralow-load indentation measurements using commercially available Vickers and mechanical properties microprobe (MPM) apparatus respectively, demonstrated the extreme hardness of the diffusion layer; the latter technique produced an elastic modulus maximum of 420 GPa. Typical modulus values were found to depend on the coating microstructure and measurement depth beneath the free surface and ranged from 366 to 410 GPa. Vickers microhardness measurements of the boronized layer yielded an average hardness value of 3200 kg mm −2 (31 GPa), compared with a maximum MPM hardness of 38 GPa at a depth of 6 microm beneath the free surface. The presence of the boronized layer resulted in great improvements in the unlubricated sliding wear performance against monolithic Al 2O 3, reducing the extent of wear attributable to the mechanisms of abrasion and adhesion through increases in hardness and modifications to the surface chemistry and structure respectively.