Volume 96, Issue 11

Various sources of errors in the standard procedure according to the ISO 14577 draft for the iteration of elastic modulus and hardness of solid materials, with reference to fused quartz with its particular and unique indentation response, are pointed out on the basis of practical examples. Similar objections exist towards the use of the S 2 F N – 1 parameter, where S is the stiffness and F N is the normal force. It is suggested to use unambiguous mechanic characterization (at least additionally) by quantitative analysis of the loading curves in nanoindentations. These exhibit a general dependence between normal force and (displacement) 3/2 , the proportionality constant k being a non-iterated nanoindentation coefficient with dimension [force/length 3/2 ] and unit [μN/nm 3/2 ] that depends on the indenter tip geometry (pyramidal or conospherical) and is a characteristic material’s property. The validity has been demonstrated for virtually all types of materials (metals, semimetals, oxides, salts, organic molecular crystals, polymers) independent of their different bonding states. Pressure-induced phase transitions are detected by kinks in the linear plots for the loading curves well in the nanoindentation region. Crystalline materials, such as strontium titanate, exhibit far-reaching anisotropic effects along lattice axes that would strongly forbid the reference to an amorphous standard. The nanoindentation coefficient characterizes the different polymorphs and the face anisotropies. Another unambiguous mechanical characterization is given by the full work of indentation (as differentiated from the less secure plastic work of indentation). It also characterizes the face anisotropies with high precision for a given indenter as it is found proportional to (normal force) 3/2 , which allows for useful extrapolations.

III-V semiconductor alloys have been grown onto lattice-matched substrates. These systems correspond to In x Ga 1 – x As with x ≈ 0.5 grown on InP, and to In y Ga 1 – y P with y ≈ 0.5 grown on GaAs and were used in order to produce epitaxial layers free of structural defects (threading dislocations). InGaP alloys, in contrast to InGaAs, are known to order partially to a degree η that can be controlled by the growth temperature and substrate orientation (here, η could be adjusted in the range 0 – 0.5). Nanoindentation tests were carried out to measure the mechanical response of the heteroepitaxial layers. Transmission electron microscopy was used to characterize the structure as well as the plastic zones generated into the specimen by nanoindentation. Comparison of the alloys with binary references (InAs, InP, GaAs, GaP bare substrates) showed strengthening, with the hardness and flow-stress values being much larger than those of binary softer reference materials (InP and InAs).

An extensive comparison between the conventional Vickers hardness at 500 mN and indentation hardness measured with Vickers indenters at 500 mN is presented for up to 20 different materials and for three different instruments. Additionally, the indentation modulus is compared to Young’s modulus, which was measured with alternative methods or taken from the literature. It is shown that the agreement between the results from depth-sensing indentation and the reference values can be improved by additional corrections, for the calculation of the indentation area. With corrections the mean hardness difference to the Vickers hardness reference as average of all investigated materials can be reduced to about 10 % although disturbing pile-up or sink-in effects can still not be considered. For the modulus, the mean difference was only about 6 %.

The influence of the pressure distribution beneath a spherical indenter onto the resulting penetration depth and consequently its impact onto the derived apparent indentation modulus has been modelled theoretically. It turns out that the pressure distribution has the same effect as a constant hydrostatic pressure of one half of the contact pressure within the entire sample. The effect is particularly important in situations of high contact pressure as during elastic indentation loading before the occurrence of the first popin. Furthermore, for all materials with a high ratio between hardness and elastic modulus the indentation modulus should differ from the “zero-pressure elastic modulus” in an experimentally verifiable way. A quantitative assessment delivers a possible increase up to 15 %.

This work presents a review on recent methodologies for the analysis of data obtained through instrumented indentation testing. Experimental tests, using a Vickers indenter, were carried out on low-carbon and bearing steels and indents were later analyzed in a laser interferometer. The results were used to verify the accuracy of methods proposed to predict the indentation morphology, pile-up or sink-in, and the accuracy of routines proposed to extract the mechanical properties of the indented materials. The occurrence of pile-up in all tested materials indicated that models may fail in predicting this behavior and, consequently, in determining the yield stress and strain-hardening exponent.

Different layers of different thicknesses were coated on the same polymethyl methacrylate (PMMA) substrate. For each of these bilayered systems, quasi-static and dynamic instrumented indentations using continuous stiffness measurement have been made. We verified if data from indentation tests performed on a given sample obey a power law relationship. The aim was to calculate the viscoplasticity index n with sufficient accuracy (by taking into account the viscoelastoplastic properties of the studied samples), since this value is characteristic of the viscoplastic properties of a material and, therefore, allows evaluating the plastic scratch resistance of the surface. Thanks to both indentation methods the viscoplasticity index could be calculated and its value compared to the different bilayered systems one. As n is supposed to be intrinsic to a material, its value should not depend on the characterization technique.

Sputtered aluminium layers from 250 to 2000 nm thick on (100) silicon have been indented to various depths and the nanoindentation load – displacement curves recorded. The loading curves were then simulated by finite element analysis and the results compared to identify the yield properties of the coating. Modelling data for thicker samples closely follows experimental data, but for thinner coatings there is a considerable gradient in properties through the film thickness.

Both the hardness and modulus values obtained by nanoindentation depend on knowledge of the area of contact between the test material and the indenter. Significant errors can be introduced into the measurement if the projected area of the indentation contact is not known with sufficient accuracy. The state-of-the-art for user validation of indenter area function is to use materials of known Young’s modulus in the ‘two reference materials method’. However, the area function is best measured directly by traceably calibrated metrological atomic force microscopy. An area function for a standard Hysitron indenter was generated, using both atomic force microscopy and indentation. The results are compared, and the effect of data fitting techniques and measurement uncertainty are discussed.

The paper deals with the application of Pharr’s concept of the effectively shaped indenter as well as an extension of that concept – referred to as extrapolation method – on the determination of the yield strength of porous thin films. As an example, a 1066 nm thick porous SiO 2 xerogel film having a porosity of about 50% and an average pore size in the range 3 – 4 nm was investigated. Three different spherical indenters with radii of 1.4, 3.11 and 110 lm were used in this investigation. Depending on the indenter radius and the applied load the physical nature of the sample deformation was different making the one or the other of the two methods more suitable for analysis. We found that the data received with the large indenter could be well analysed using Pharr’s concept, while for the two smaller indenters the extrapolation method had to be used. The yield strength values obtained with the two methods were in remarkable agreement (109 vs. 99 MPa).

Indentations and scratch tests using a Nano Indenter ® XP have been carried out to characterize the mar and wear resistance properties of polymeric bilayer systems. These systems were composed of a transparent coating on a thermoplastic polymer (PMMA) substrate. The different thin films were deposited using several coating technologies. Nanoindentation tests with a Berkovich indenter were performed at different peak loads from 0.625 to 10 mN, to determine the mechanical properties both of thin films and of the PMMA substrate, such as the elastic modulus and the hardness. A new analysis of the loading curve was applied to extract the viscoplasticity index. Then, scratch tests using a conical indenter truncated with a spherical tip (radius R = 5 μm) were realized with increasing progressively applied load (from 0 to 40 mN) to create irreversible damages (crack or delamination). The distinction between ductile and brittle behaviour in a scratch process leads to the definition of some specific parameters. For all tested specimens, we estimated the average contact pressure, the strain rate and the average strain beneath the indenter at which the fracture occurs. We propose a complete method to estimate with accuracy these differents parameters, from data supplied experimentally by the depth sensing instrument. This method takes into account the piling-up phenomenon and the viscoelastic recovery of the polymeric surface at the rear of the contact. No direct relationship was found between the viscoplasticity index and the ductile/brittle transition determined by the scratch test. Different criterions related to mar and scratch resistance were tested and compared to results obtained with macroscopic tests.

Ultrathin polymeric films devoted for nanoimprint lithography were tested. Atomic force microscopy was used to study the surface topography, and the adhesive and nanomechanical/tribological behaviour. The wetting properties of the films were also evaluated, using a special test rig for the contact angle measurements.

Silicone polymeric films were deposited on silicon substrate, and their adhesive and nanomechanical properties were studied. The surface characterization and tribological (wear) behaviour were investigated using atomic force microscopy. The surface Gibbs energy was estimated locally, using a special test rig where the contact angle of very small (with a diameter of about 100 μm) sessile drops was measured by processing of the image from a camera. The nanomechanical properties of the films were tested by using Hysitron’s test instruments. Such films seem to be interesting for application on contact surfaces of microgrippers used in assembly processes in micro electro mechanical systems and nanotechnologies.

A model of the nanoindentation process was elaborated using the finite-element method. The ADINA software was used in the computation of the load – displacement curve. The distribution of stresses in the TiN film on a smooth substrate (Si) was found. The influence of mechanical material properties of the film and substrate on the process of indentation and the stress distribution was considered. The effect of yield stress, tip’s radius and hardening modulus was discussed. The results were compared with the results of experimental nanoindentation tests performed for ultrathin films.

A thermodynamic optimization for the Be– Si system has been performed using the CALPHAD (CALculation of PHAse Diagrams) technique applied to newly measured phase diagram data. The description for this binary system is then combined with the thermodynamic parameters in the Al –Be and Al –Si systems to synthesize a thermodynamic description for the Al –Be –Si ternary system. To verify the reliability of the extrapolated ternary phase diagrams, 11 decisive ternary alloys are prepared by are melting Al, Be and Si pieces and annealing at 530 °C for 8 days. Water-quenched samples are analyzed using differential thermal analysis (DTA), X-ray diffraction (XRD), optical microscopy, and scanning electron microscopy with energy dispersive X-ray (SEM/EDX) techniques. The calculated isopleths at 94 wt.% Al, 88 wt.% Al, 50 at.% Al, and 2 wt.% Be are compared with the experimental data from the present work and the literature. The comparisons show that no ternary interaction parameter is needed for the ther-modynamic description of this ternary system. The liquidus projection and reaction scheme are also presented.

Thermodynamic modelling of the Ca–Sn binary system was carried out. The thermodynamic parameters related to this system were determined from experimental phase diagram and thermodynamic information available in the literature. In this system the liquid phase was modelled by the association model with the “Ca 2 Sn” associated complex. This consideration permits to well restore experimental values. A set of thermodynamic interaction parameters, the calculated phase diagram as well as the comparison with experimental data are presented.

Interfacial reaction between Cu and Ti 2 SnC during the processing of Cu–Ti 2 SnC composite was investigated by using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It is shown that the reaction is closely related to the reaction temperature, reaction time, and relative ratio of Cu and Ti 2 SnC. The reacting products are Cu(Sn) solid solution and TiC x , and the transporting process during interfacial reaction is described. The interfacial reaction products are further confirmed by measuring the hardness across the interface using nanoindentation test. It is shown that the reaction is controlled by the de-intercalation of Sn from Ti 2 SnC to form Cu(Sn) solid solution and TiC x , and crystallographic relations of [01̅1] TiC x // [010] Ti 2 SnC and (11̅1̅) TiC x // (001) Ti 2 SnC were observed at the interface. The effect of interfacial reaction on the mechanical and electrical properties of the composite is also discussed.

This investigation presents the observations made pertaining to the lubricated sliding wear response of a zinc-based alloy containing nickel over a range of applied pressures and sliding speeds. Properties studied were wear rate and frictional heating. The varying wear response of the samples under different material and test conditions has been substantiated through the features of wear surfaces, subsurface regions, and debris. The role of various microconstituents in the material and their specific features have been correlated with the observed wear behaviour of the alloy in different material and test conditions. The wear rate and frictional heating increased with pressure and speed. The data plots in general comprised initially low slope followed by a higher slope at larger applied pressures. Heat-treated samples performed better than the as-cast one except at the maximum sliding speed; a reverse trend was noted in the latter case. The study suggests the benefits of heat treatment in terms of improved wear response of the alloy under specific test conditions. Moreover, the wear behaviour of the samples for different material and test conditions could be explained in terms of the features of their microconstituents and the predominance of one set of factors causing improved wear behaviour over the other producing a reverse effect.

Tungsten alloy white cast iron (TAWCI) exhibits strong brittleness and a narrow application scope. The influences of Ce, K and Na on the microstructure and performance of TAWCI have been studied, and the idea to estimate the spheroidization effect of carbides using circular degree ( C . D .) is put forward. The results show that eutectic carbides turn from network into sphericity after the modification. Carbide is refined and uniformly distributed and the C . D . of eutectic carbides increases. The mechanism of carbide spheroidization has been analyzed. The impact toughness and wear resistance of TAWCI obviously improves with the rise of C . D . of carbides. The service life of a modified TAWCI roll is 35 % higher than that of high-chromium cast-iron roll, its production cost is reduced by 25 %.