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Joost J Vlassak - One of the best experts on this subject based on the ideXlab platform.
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determining the elastic modulus and hardness of an ultra thin film on a substrate using nanoIndentation
Journal of Materials Research, 2009Co-Authors: Joost J VlassakAbstract:A data analysis procedure has been developed to estimate the contact area in an elastoplastic Indentation of a thin film bonded to a substrate. The procedure can be used to derive the elastic modulus and hardness of the film from the Indentation load, displacement, and contact stiffness data at Indentation depths that are a significant fraction of the film thickness. The analysis is based on Yu’s elastic solution for the contact of a rigid conical punch on a layered half-space and uses an approach similar to the Oliver-Pharr method for bulk materials. The methodology is demonstrated for both compliant films on stiff substrates and the reverse combination and shows improved accuracy over previous methods. Since 1992, the analysis method proposed by Oliver and Pharr 1 has been established as the standard procedure for determining the hardness and elastic modulus from the Indentation load-displacement curves for bulk materials. In the Oliver-Pharr method, the projected contact area between indenter tip and material is estimated using the equations for the elastic contact of an indenter of arbitrary shape on a uniform and isotropic half space. 2 The Indentation modulus and hardness of the material can thus be calculated without the necessity of imaging the Indentation after the experiment. The Oliver-Pharr method was initially developed for analyzing Indentations in bulk materials, not for films on substrates, and no information about a possible substrate is included in the analysis. The Oliver-Pharr method is, however, frequently used by researchers to interpret Indentations performed on thin films in an attempt to obtain approximate film properties regardless of the effect of substrate properties on the measurement. The accuracy of such a measurement depends on the film and substrate properties and on the Indentation depth as a fraction of the total film thickness. In general, the error due to the substrate effect increases with increasing Indentation depth and with increasing elastic mismatch between film and substrate. 3–7 To minimize the effect of the substrate on the measurement, the Indentation depth is often limited to less than 10% of the film thickness. 5 This empirical rule is not always reliable, especially if the elastic mismatch between film and substrate is large. The 10% rule is also not useful for thin films when experimental issues make it difficult to obtain accurate results for shallow Indentations. Evidently there exists a need for a method that can be used to analyze thin-film Indentation data for Indentation depths where the substrate effect cannot be ignored. A number of studies with several different approaches to modeling the substrate effect have been reported. 7–13 King used numerical techniques to model the elastic Indentation of a layered half space with flat-ended punches of various cross sections. 8 The depth dependence of the effective Indentation modulus of the composite system Meff was represented numerically as a function of the punch size a normalized by the film thickness t using the following phenomenological formula
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Indentation plastic displacement field part ii the case of hard films on soft substrates
Journal of Materials Research, 1999Co-Authors: Ting Y Tsui, Joost J VlassakAbstract:The plastic displacements around Knoop Indentations made in hard titanium/aluminum multilayered films on soft aluminum alloy substrates have been studied. Indentations were cross-sectioned and imaged using the focused-ion-beam (FIB) milling and high-resolution scanning electron microscopy (SEM), respectively. The FIB milling method has the advantage of removing material in a localized region without producing mechanical damage to the specimen. The micrographs of the cross-sectioned Indentations indicate that most of the plastic deformation around the Indentation is dominated by the soft aluminum substrate. There is a very small change in the multilayered film thickness around the Indentation{emdash}less than 10{percent}. The plastic deformation of the thin film resembles a membrane being deflected by a localized pressure gradient across the membrane. Stress-induced voids are also observed in the multilayered film, especially in the area around the Indentation apex. The density and the size of the voids increase with Indentation depth. Indentation sink-in effects are observed in all of the Indentations inspected. Based on the experimental results, the amount of sink-in of the hard film{endash}soft substrate composite is larger than the bulk substrate and film alone. This is confirmed by the finite element analyses conducted in this work. {copyright} {ital 1999 Materials Research Society.}
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Indentation plastic displacement field: Part II. The case of hard films on soft substrates
Journal of Materials Research, 1999Co-Authors: Ting Y Tsui, Joost J Vlassak, William D. NixAbstract:The plastic displacements around Knoop Indentations made in hard titanium/aluminum multilayered films on soft aluminum alloy substrates have been studied. Indentations were cross-sectioned and imaged using focused-ion-beam (FIB) milling and high-resolution scanning electron microscopy (SEM), respectively. The FIB milling method has the advantage of removing material in a localized region without producing mechanical damage to the specimen. The micrographs of the cross-sectioned Indentations indicate that most of the plastic deformation around the Indentation is dominated by the soft aluminum substrate. There is a very small change in the multilayered film thickness around the Indentation—less than 10%. The plastic deformation of the thin film resembles a membrane being deflected by a localized pressure gradient across the membrane. Stress-induced voids are also observed in the multilayered film, especially in the area around the Indentation apex. The density and the size of the voids increase with Indentation depth. Indentation sink-in effects are observed in all of the Indentations inspected. Based on the experimental results, the amount of sink-in of the hard film–soft substrate composite is larger than the bulk substrate and film alone. This is confirmed by the finite element analyses conducted in this work.
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Indentation plastic displacement field part i the case of soft films on hard substrates
Journal of Materials Research, 1999Co-Authors: Ting Y Tsui, Joost J VlassakAbstract:The plastic deformation behavior of Knoop Indentations made in a soft, porous titanium/aluminum multilayered thin film on a hard silicon substrate is studied through use of the focused-ion-beam milling and imaging technique. Pileup is observed for Indentations with depths larger than 30% of the total film thickness. Analysis of the Indentation cross sections shows that plastic deformation around the Indentation is partly accommodated by the closing of the pores within the multilayers. This densification process reduces the amount of pileup formed below that predicted by finite element simulations. Experimental results show that the pileup is formed by an increase of the titanium layer thickness near the edges of the Indentation. The thickness increase is largest near the film/substrate interface and decreases toward the surface of the multilayered film. The amount of normal compression near the center of the indenter is characterized, and it is demonstrated that the deformation becomes more nonuniform with increasing Indentation depth.
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A New Technique for Visualizing The Displacement Field of Indentations: The Case of A Soft Film on A Hard Substrate
MRS Online Proceedings Library, 1997Co-Authors: Joost J Vlassak, T. Y. Tsui, W. D. NixAbstract:We have developed a new technique for visualizing displacement fields of Indentations in thin films. In this technique, the indented film consists of alternating layers of two different materials. One of the materials serves as a marker for visualizing the plastic flow induced by the Indentation. Focused Ion Beam (FIB) milling is used to cross-section the Indentation, revealing the deformed layers. This technique can be used to study how the presence of the substrate affects the plastic displacement field around the Indentation. The technique is applied to a multilayered film of aluminum and titanium nitride on a silicon substrate. The titanium nitride layers are much thinner than the aluminum layers and serve the function of marker. Pile-up of the film material around the indenter and the effect of the hard substrate are easily revealed and a mechanism for pile-up is suggested. The technique also shows that the grain structure in the deformed zone around the Indentation is altered profoundly.
William C. Lacourse - One of the best experts on this subject based on the ideXlab platform.
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Environment-dependent Indentation recovery of select soda-lime silicate glasses
Ceramics International, 2012Co-Authors: Mirabbos Hojamberdiev, Harrie J. Stevens, William C. LacourseAbstract:Abstract Indentations made on silicate glasses can easily be affected by the environment. In the present work, Indentations were made on select commercial float glasses as well as on experimental soda-lime silicate glasses using a 1 mm diameter spherical tungsten carbide ball-mounted Brinell indenter. Recovery of Indentations made on the glass samples was measured in different environments, namely, 100 °C, room temperature/room humidity and 100% relative humidity, as a function of time by using a Zygo laser non-contact profiliometer. Elastic (Young's modulus, bulk modulus, shear modulus and Poisson's ratio) and Indentation (Vickers hardness, fracture toughness, brittleness and fracture surface energy) properties of the glasses were also determined by a pulse-echo and Vickers Indentation methods, respectively, to correlate with the recovery of Indentations. The elastic properties and Vickers hardness are directly proportional to the packing ions present in the glass structure and the strength of an individual bond, whereas the brittleness and fracture toughness more likely depend on molar volume of the glasses. According to the applied environment, a recovery rate of Indentations follows the order: room temperature/room humidity
Zhengren Huang - One of the best experts on this subject based on the ideXlab platform.
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Effects of Vickers Cracks on the Mechanical Properties of Solid-phase-sintered Silicon Carbide Ceramics: Effects of Vickers Cracks on the Mechanical Properties of Solid-phase-sintered Silicon Carbide Ceramics
Journal of Inorganic Materials, 2012Co-Authors: Xiao Yang, Zhengren HuangAbstract:In order to study the effects of Vickers cracks on the mechanical properties of solid-phase-sintered silicon carbide (SSiC for short) ceramics, the Indentation cracks and the crack profiles were observed after loading 0.1–100 N loads on the SSiC samples by SEM. The critical Indentation load for Vickers crack initiation in SSiC ceramics lies between 0.1 N and 0.2 N. Indentations by loads lower than 0.5 N have limited influence on bending strength. And if the Indentation loads is higher than 10 N, the obtained hardness floats around 24.2 GPa and the cracks are half-coin type. The proper Vickers Indentation load range for SSiC ceramic hardness and toughness tests are determined to be 10 N or above
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Vickers Indentation crack analysis of solid-phase-sintered silicon carbide ceramics
Ceramics International, 2012Co-Authors: Xiao Yang, Zhengren HuangAbstract:Abstract Solid-phased-sintered silicon carbide ceramics were prepared by traditional process with carbon and boron carbide as additives. The crack initiation and the profiles of the samples after Vickers Indentation were observed in order to analyze the crack system. The typical characterizations of Vickers Indentation, crack length c and diagonal 2 a were used to determine the crack system. The surface cracks appear when the Indentation load surpasses 0.1–0.2 N or the Indentation diagonal length is over 3 μm. Clear and typical half-penny cracks formed after 10 N or above Indentations. Within the 3–10 N range, the expected radial crack was not observed; but the relation between the crack length and Indentation load told that the crack system after 3–10 N Indentation is still half-penny. As to the critical c/a value for crack system transition, if it exists, it does not exceed 2.2. The fact that the toughness by IF method after 3–10 N strongly differs from that after 10–100 N may suggest that the determination of fracture toughness by Indentation fracture method is not related to crack system. In addition, it is found that a more precise fracture toughness test of SSiC ceramics by IF method requires an Indentation force larger than 10 N.
Karsten Durst - One of the best experts on this subject based on the ideXlab platform.
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influence of dislocation density on the pop in behavior and Indentation size effect in caf2 single crystals experiments and molecular dynamics simulations
Acta Materialia, 2011Co-Authors: Matthias A Lodes, Mathias Goken, Alexander Hartmaier, Karsten DurstAbstract:Abstract In this work, the Indentation size effect and pop-in behavior are studied for Indentations in undeformed and locally pre-deformed CaF 2 single crystals, using both nanoIndentation experiments and molecular dynamics simulations. To study the influence of dislocation density on the Indentation behavior, small-scale Indentations are carried out inside the plastic zone of larger Indentations. This experiment is mimicked in the simulations by indenting a small sphere into the center of the residual impression of a larger sphere. The undeformed material shows the well-known pop-in behavior followed by the Indentation size effect. Pre-deforming the material leads to a reduction in the Indentation size effect both for experiments and simulations, which is in accordance with the Nix–Gao theory. Furthermore, the pop-in load is reduced in the experiments, whereas a smooth transition from elastic to plastic deformation is found in the simulations. There, plasticity is initiated by the movement of pre-existing dislocation loops in the vicinity of the plastic zone. The simulations thus give a detailed insight into the deformation mechanism during Indentation and highlight the importance of the dislocation microstructure for the Indentation size effect and dislocation nucleation.
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study on the Indentation size effect in caf2 dislocation structure and hardness
Acta Materialia, 2009Co-Authors: P Sadrabadi, Karsten Durst, Mathias GokenAbstract:Abstract In this study nanoIndentations have been performed on a cleaved surface of a CaF2 single crystal and the dislocation structure has been investigated by the etch pit technique using atomic force microscopy. The deformation during Indentation is first purely elastic until dislocations are created observable in a pop-in in the load displacement data, as well as in a dislocation rosette around the Indentation. After pop-in a relatively high hardness is observed, which gradually decreases, until at 3 μm a nearly constant hardness is found. By using sequential polishing, etching and imaging, the dislocation structure underneath Indentations with Indentation depths of 300 nm and 110 nm (load: 5 mN, 1 mN) is quantified. The dislocation density and radial distribution of dislocation density depend on the Indentation depth, where a smaller Indentation depth leads to a higher dislocation density, which is in qualitative agreement with the observed increase in hardness.
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Indentation size effect in spherical and pyramidal Indentations
Journal of Physics D: Applied Physics, 2008Co-Authors: Karsten Durst, Mathias Goken, George M. PharrAbstract:The Indentation size effect (ISE) is studied for spherical and pyramidal Indentations on a Ni poly-crystal. The Indentation experiments were conducted using a Berkovich geometry as well as different spherical indenters with radii of 0.38, 3.8 and 51.0??m. A strong ISE is observed for the material yielding a higher hardness at smaller depths or smaller sphere radii. The transition from elastic to plastic behaviour is associated with a pop-in in the load?displacement curve, in contrast to the conventional elastic?plastic transition as discussed by Tabor. The Indentation response is modelled using Tabor's approach in conjunction with the uniaxial macroscopic stress?strain behaviour for calculating the statistically stored dislocation density for a given indenter geometry. The geometrically necessary dislocation (GND) density is calculated using a modified Nix/Gao approach, whereas the storage volume for GNDs is used as a parameter for the measured depth dependence of hardness. It will be shown that the ISE for both pyramidal and spherical Indentations is related and can be understood within the same given framework. The Indentation response of metallic materials can thus be modelled from pop-in to macroscopic hardness.
Ting Y Tsui - One of the best experts on this subject based on the ideXlab platform.
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Indentation plastic displacement field part ii the case of hard films on soft substrates
Journal of Materials Research, 1999Co-Authors: Ting Y Tsui, Joost J VlassakAbstract:The plastic displacements around Knoop Indentations made in hard titanium/aluminum multilayered films on soft aluminum alloy substrates have been studied. Indentations were cross-sectioned and imaged using the focused-ion-beam (FIB) milling and high-resolution scanning electron microscopy (SEM), respectively. The FIB milling method has the advantage of removing material in a localized region without producing mechanical damage to the specimen. The micrographs of the cross-sectioned Indentations indicate that most of the plastic deformation around the Indentation is dominated by the soft aluminum substrate. There is a very small change in the multilayered film thickness around the Indentation{emdash}less than 10{percent}. The plastic deformation of the thin film resembles a membrane being deflected by a localized pressure gradient across the membrane. Stress-induced voids are also observed in the multilayered film, especially in the area around the Indentation apex. The density and the size of the voids increase with Indentation depth. Indentation sink-in effects are observed in all of the Indentations inspected. Based on the experimental results, the amount of sink-in of the hard film{endash}soft substrate composite is larger than the bulk substrate and film alone. This is confirmed by the finite element analyses conducted in this work. {copyright} {ital 1999 Materials Research Society.}
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Indentation plastic displacement field: Part II. The case of hard films on soft substrates
Journal of Materials Research, 1999Co-Authors: Ting Y Tsui, Joost J Vlassak, William D. NixAbstract:The plastic displacements around Knoop Indentations made in hard titanium/aluminum multilayered films on soft aluminum alloy substrates have been studied. Indentations were cross-sectioned and imaged using focused-ion-beam (FIB) milling and high-resolution scanning electron microscopy (SEM), respectively. The FIB milling method has the advantage of removing material in a localized region without producing mechanical damage to the specimen. The micrographs of the cross-sectioned Indentations indicate that most of the plastic deformation around the Indentation is dominated by the soft aluminum substrate. There is a very small change in the multilayered film thickness around the Indentation—less than 10%. The plastic deformation of the thin film resembles a membrane being deflected by a localized pressure gradient across the membrane. Stress-induced voids are also observed in the multilayered film, especially in the area around the Indentation apex. The density and the size of the voids increase with Indentation depth. Indentation sink-in effects are observed in all of the Indentations inspected. Based on the experimental results, the amount of sink-in of the hard film–soft substrate composite is larger than the bulk substrate and film alone. This is confirmed by the finite element analyses conducted in this work.
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Indentation plastic displacement field part i the case of soft films on hard substrates
Journal of Materials Research, 1999Co-Authors: Ting Y Tsui, Joost J VlassakAbstract:The plastic deformation behavior of Knoop Indentations made in a soft, porous titanium/aluminum multilayered thin film on a hard silicon substrate is studied through use of the focused-ion-beam milling and imaging technique. Pileup is observed for Indentations with depths larger than 30% of the total film thickness. Analysis of the Indentation cross sections shows that plastic deformation around the Indentation is partly accommodated by the closing of the pores within the multilayers. This densification process reduces the amount of pileup formed below that predicted by finite element simulations. Experimental results show that the pileup is formed by an increase of the titanium layer thickness near the edges of the Indentation. The thickness increase is largest near the film/substrate interface and decreases toward the surface of the multilayered film. The amount of normal compression near the center of the indenter is characterized, and it is demonstrated that the deformation becomes more nonuniform with increasing Indentation depth.
