Elastic moduli diamond

A fully automated microscale indentor known as the Nano Indentor is available from Nano Instmments (257—259). Used with the Berkovich diamond indentor, this system has load and displacement resolutions of 0.3 N and 0.16 nm, respectively. Multiple indentations can be made on one specimen with spatial accuracy of better than 200 nm using a computer controlled sample manipulation table. This allows spatial mapping of mechanical properties. Hardness and elastic modulus are typically measured (259,260) but time-dependent phenomena such as creep and adhesive strength can also be monitored. 

The high elastic modulus, compressive strength, and wear resistance of cemented carbides make them ideal candidates for use in boring bars, long shafts, and plungers, where reduction in deflection, chatter, and vibration are concerns. Metal, ceramic, and carbide powder-compacting dies and punches are generahy made of 6 wt % and 11 wt % Co ahoys, respectively. Another apphcation area for carbides is the synthetic diamond industry where carbides are used for dies and pistons (see Carbon). 

Diamond has the highest atom-number density of any known material at terrestrial pressures. Because of its high atom-number density and strong covalent bonding, diamond has the highest hardness and elastic modulus of any material and is the least compressible substance known. 

The elastic modulus, measured in units of pressure (1 gigapascal = 1 GPa = 10 1 Pa) indicates the stiffness of a material when it is subjected to a load. The larger the value, the stiffer the material. Numbers on the Mohs hardness scale range from 1 for talc, a very soft material, to 10 for diamond, the hardest known substance. 

Figure 5 Scaling of the elastic modulus cii of aerogels versus density p. Materials Si02 (triangles) sintered Si02 (dots) carbon (diamonds) MF (circles) RF (squares). Open symbols denote evacuated aerogels filled symbols denote aerogels in air.

Why should we be interested in carbon nanotubes For one thing, there are not very many materials that have structural perfection at a molecular level as ideal as a single carbon nanotube. One can think about using their aspect ratio and small diameter for imaging applications. Also, they have very good mechanical properties and thermal properties. Theoretical calculations and measurements performed on individual carbon nanotubes have shown that their elastic modulus is as high as that of diamond, on the order of one terapascal. Indeed, if we could make a defect-free cable—one as long as we wanted—then a cable to connect the Earth and the moon would be within the realm of possibility. 

Here, Nq) is the average coordination number and A is the polarity of the bond, B is in GPa and is given in Angstroms [6]. For nonpolar, covalent bonds in diamond A = 0, whereas in other compounds, such as cBN, Si3N4 and C3N4 A > 0 which decreases the value of the elastic modulus. The expected high theoretical hardness of C3N4 is based on the small bond distance and relatively small polarity A. 

The universal hardness , is obtained from the same formula if h is inserted instead of Aplastic- The universal hardness includes both the elastic and plastic deformation. The hnear part of the unloading curve corresponds to the elastic recovery when the diamond pyramid is in a constant area contact with the material. Therefore it represents Hooke s law and allows one to calculate the corresponding elastic modulus E/ — i/) which is a complicated function of the bulk, shear, and tensile moduli is the Poisson ratio). The details of the apparatus, the measuring procedure and possible errors are given in the relevant papers to which we refer here [25-28]. If done correctly, the plastic hardness measured by the indentation agrees within about 10-15% reasonably well with that from the classical Vickers method at least in the range H < 1500kgmm [25]. 

The nanoindentation experiments were conducted at room temperature with a Nano Indenter XP system (MTS Nanoinstruments, Knoxville, TN) using a Berkovich-type diamond tip. Before each test, the system was calibrated using a fused silica. The continuous stiffness mode (CSM) was used in the tests. Thirty randomly selected different fiber and CVI matrix locations were indented for each component of C/C composites. The method of Oliver and Pharr was employed for the elastic modulus calculations. ... 

PEEK can be coated with diamond-like carbon by plasma inunersion ion implantation and deposition to enhance its surface properties [89]. The elastic modulus of diamond-like carbon is closer to that of cortical bone than PEEK. Therefore, the combination of PEEK and diamond-like carbon has been proposed to enhance the stability and surface properties of PEEK in bone replacements. 

Diamond, however, is a metastable phase of carbon, with lower binding energy (15 eV/mol) [23], Its compact lattice has sp hybridization (tetrahedral structure) that gives an extreme hardness, rather than electrical conductivity. Diamond is an excellent insulator (band gap 8 eV) due to a orbitals (sp ), which, among other properties, will provide a more cohesive and elastic modulus. 

A Berkovich diamond tip with a total included angle of 142.3° and a radius of around 150 nm was used for the nanoindentation measurements [1-2]. Indentation load-displacement curves were obtained by applying loads ranging from 1 pN to 1 mN. The hardness and reduced elastic modulus of the tribofilms were determined with Oliver s method [35,36], where fused silica with a Young s modulus of 69.7 GPa was used as a standard sample for tip-shape calibration to determine the function of the contact area with respect to the contact depth in a range of 1.5-50 nm. Figure 9.5 shows indentation load-displacement curves obtained for the MoDTC/ZDDP and ZDDP tribofilms at a maximum load of 600 pN and in situ AFM images of the residual indent. A plastic pileup was clearly observed around the indent on both the MoDTC/ZDDP and ZDDP tribofilms. 

A 1 jim thick diamond-like carbon film is deposited at 500 °C on a Ti alloy substrate. The film with elastic modulus Ef = 500 GPa and Poisson ratio Ui = 0.2, is essentially free of any internal stress at the deposition temperature. When cooled to the temperature 20 °C, however, an equibiaxial compressive mismatch stress of 5 GPa is expected to exist in the film as a consequence of thermal mismatch with the substrate. An unbonded circular patch, 30 gm in diameter, developed at the film-substrate interface during film deposition. Determine whether the film buckles upon cooling to 20 °C If so, determine the temperature at which buckling begins. 

The characteristic time defined in (9.21) establishes a time scale for surface evolution of the kind discussed in the preceding section. Its definition depends on a number of parameter values that are not measurable and, therefore, are not known with any certainty. To get some idea of its magnitude, estimate the value of the characteristic time for the particular case of a Si surface with a mismatch strain of Cin = 0.008 at a temperature of T = 600 °C. Base the estimate on the unit cell dimension of a = 0.5431 nm for the diamond cubic crystal structure, and on the following values of macroscopic material parameters an elastic modulus of E = 130 GPa, a Poisson ratio of = 0.25, a mass density oi p = 2328kg/m, and the surface energy of 70 = 2J/m. Assume that 10% of the surface atoms are involved in the mass transport process at any instant so that = 0.1. 

Load cycle indentation was performed using a commercial ultra microindentation system (UMlS-2000) with a spheroconical diamond indenter with 3 pm radius. The radius of the indenter was calibrated using silica glass, of which the elastic modulus and Poisson s ratio were known. The initial contact force was 0.1 mN, and load controlled tests are performed. Each test was repeated ten times at different positions on the polished surface of the specimen. 

HaU effect measurement, 467 hardness measurement in sol-gel coatings aluminium alloy, use of, 304 antireflex coatings, 305 Berkovich indenter, 303, 304 defomation mechanisms, 302 diamond indenter, 302 elastic modulus, 303 indentation testing, 302 indium-tin-oxide coatings, 305 loading-unloading cycle, 303 pencil hardness, 305 Poisson s ratio, 303 silica, 304... 

When a rigid indenter compresses a soft flat sample such as a gasket sample, d is the depth of the indentation because the diamond or steel indenter s deformation is negligible relative to that of the sample. Based on Eqn (11.14) and experimental indentation load and indentation depth, the elastic modulus of the sample can be obtained. 

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