Nanoindentation testing Indentation test

Nanoindentation testing by CDR does not give values of absolute microhardness directly. This is because microhardness is usually defined as load divided by indent area projected onto the plane of the surface, and this area is not explicitly measured in nanoindentation testing. However, the data can be processed on the basis of well established assumptions (Loubet et al, 1984) to yield relatively direct information that is of value in quality control. 

The hardening and embrittlement of polyimides by ion implantation has been also studied (Pivin, 1994). Nanoindentation tests performed using a sharp diamond pyramid of apical angle 35° provided very quantitative depth profiles of microhardness in polyimides implanted with C, N, O, Ne or Si ions. In all cases the microhardness increased steeply when the amount of deposited energy reached the order of 20 eV atom". For energies of 200 eV atom" the polymer is transformed into an amorphous hydrocarbon and the microhardening factor saturates at a value of 13-20. However, the carbonized layer is poorly adherent, as is evidenced by reproducible discontinuities in the depth vs load curves, when the indenter tip reached the interface. 

Pellicle and tea-immersed pellicle were analyzed using nanoDMA (dynamic mechanical analysis) to see if the tannins had an effect on the viscoelasticity of the pellicle. NanoDMA is a technique used to study and characterize mechanical properties in viscoelastic materials. The method is an extension of nanoindentation testing [58, 59], An analysis of the nanoindentation load-depth curve gives the hardness (H) and reduced elastic modulus (E ), provided the area of contact, A, between the indenter tip and the sample is known [ 13]. By... 

In Figure 6.8, the histogram is adduced, which shows elasticity modulus E change, obtained in nanoindentation tests, as a function of load on indenter P or nanoindentation depth /r. If the dependences E P) or EQi) are identical qualitatively for all the three considered nanocomposites, then the dependence E h) for nanocomposite BSR/TC was chosen, which reflects the indicated scale effect quantitative aspect in the most clearest way. 

Load (P) versus depth of penetration (h) curves, also called compliance curves, are the output from a nanoindentation test. The curves are obtained as load is applied to the indenter tip up to some maximum value and then back to zero. 

The scratch tests are very similar to the nanoindentation tests and can be considered side by side. In both teclmiques, a prime tip is used for the adhesion measurements by dragging across the measuring surface under an increasing load, which results in an indentation. Scratch and indentation tests are suitable for the analyses of the coatings and thin films [100]. Sharp diamond indenters are usually used for the adhesion and scratch resistance determination between the substrate and coating. These techniques can fail for the analyses of hard coatings on soft substrates due to no detectable failures as a result of small critical loads. Therefore,... 

The elastic moduli of the as-sintered porous LSCF cathode film samples were measured using a NanoTest nanoindentation platform (Micromaterials, UK) with a spherical diamond indenter tip of 50pm diameter. Compared with sharp indenters like Berkovich tips, benefits of using spherical tips include less sensitivity to surface condition. At least 20 measurements were conducted in different locations for each sample in order to measure the variability of the mechanical response of the sample. Prior to nanoindentation tests, the NanoTest platform was precisely calibrated using a standard sihca sample to establish the system frame compliance. 

In nanoindentation tests of thin films, one of the key difficulties is to avoid errors in measuring film properties caused by influence of the substrate. To do so, an appropriate indentation depth (hmax) and/or an indent load (Pmax) are desired by taking into account the test film s thickness and the nature of the substrate (whether it has higher or lower elastic modulus than the film). Indenting to a depth less than 10% of the thickness of a film (namely hmax/tf < 0.1) has been empirically considered as a safe condition to avoid effects from substrate and extract intrinsic film properties in routine nanoindentation tests " . However, it can be found in our case that the effect from substrate was much less significant for indentation depth up to 0.2tf, as shown in Figure 3. Moreover, the influence of the substrate was not as marked for films sintered at 1100 and 1200 °C, as the plots stabilised as plateaus after indentation depth increased beyond 0.2tf. This was most probably because the stiffness of these films was closer to that of the substrate. 

Nanoindentation is regarded as a good method to evaluate hardness in materials. In the nanoindentation test, a diamond indenter is forced into... 

During nanoindentation testing, a set load in the miUinewton range is applied to the indenter in contact with the specimen (Fig. 6.2). The penetration depth in the... 

Figure 6.2 Schematic diagram of a nanoindentation test (a) and commonly used indenter type (b) Vickers indenter (c) elongated diamond-shaped indent formed on the sample by Knoop indenter (d) spherical indenter and (e) Berkovich indenter.

Characterization of the mechanical properties of these thin silica layers, unreinforced or reinforced, is usually conducted by using the nanoindentation technique [33-37] to determine the hardness (H) of the layer and the elastic modulus ( ) using the Oliver-Pharr method [38]. In these tests, a Berkovich indenter is used and low maximum loads are applied (in the range of mN) to avoid the influence of the mechanical response of the substrate. A complete review of how to calculate different key mechanical parameters ( , H, fracture toughness, residual stresses, and adhesion) of thin sol-gel coatings using nanoindentation tests and scratch testing with nanoindenter equipment can be found in the work of Malzbender et al. [39]. 

Indentation tests are performed to evaluate the elastic modulus and the hardness of the coating. In macroscopic test, the radius of residual impression is easily measured with an optical observation, while it is difficult to measure in micro- or nanoindentation tests. In such a case, a method to estimate the residual impression radius is proposed. 

The depth of the print, created during nanoindentation test, hereafter called residual displacement, e is a function of the applied load W, and of the local elastic plastic behaviour of the material, that can be represented by the value of Xe, E and v. Therefore, since the load is known and the elastic parameters are constant in die depth of the nitrided layer (E=210 GPa, v = 0.3 [8]), there is a direct relation between e, and Xe. To measure the depth of the print, the indentation head is loaded and unloaded at increasing maximum load, following the procedure shown in figure 3. The displacement is recorded at the same time. The residual displacement is calculated as the difference between displacement for a low load after unloading and before the first load. In a single test, 0, is then determined for several loads W and for the same local elastic plastic behaviour. 

Another approach is nanoindentation tests where the Young s modulus can then be obtained through probing the localised curvature created on the fibre surface after indentation [246, 247]. Although this method is easy to perform, many factors should be considered with some uncertainties [222]. In shear modulation force... 

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

To measure the hardness and elastic modulus of thin films while avoiding the influence of the substrate, peak indentation depth cannot exceed about 30% of the film thickness.Because commercial nanoindenters can make a minimum penetration depth of 10-15 nm, hardness and elastic modulus of films thinner than 30 nm cannot be measured. Clearly, new techniques for fabricating sharper indenters and new nanoindentation theories are needed to extend this technique. For film thicknesses less than 30 nm, nanoscratch tests are widely accepted to evaluate the mechanical properties (discussed later). Alternatively, assuming the hardness and elastic modulus of a film do not change with thickness, thicker films can be used. 

Nanoscratch tests have been used to simulate the effect of third-body particulate wear debris on component surface scratching during use. The load at which the co-efficient of friction or friction force suddenly increases is identified as the critical load, and is used to evaluate scratch resistance and adhesion strength. The depth-sensing nanoindenter, usually equipped with a conical indenter, can elucidate the mode of failure, whether elastic/plastic deformation, cracking, or delamination. 

---