Nanoindentation and Nanoscratching

Since the early 1980s, the study of mechanical properties of materials on the nanometre scale has received much attention, as these properties are size dependent. The nanoindentation and nanoscratch are the important techniques for probing mechanical properties of materials in small volumes. Indentation load-displacement data contain a wealth of information. From the load-displacement data, many mechanical properties such as hardness and elastic modulus can be determined. The nanoindenter has also been used to measure the fracture toughness and fatigue properties of ul- 

A most recent commercial Nano Indenter (Nano Indenter XP (MTS, 2001)) consists of three major components [66] the indenter head, an optical/atomic force microscope, and x-y-z motorized precision table for positioning and transporting the sample between the optical microscopy and indenter (Fig. 28). The load on the indenter is generated using a voice coil in permanent magnet assembly, attached to the top of the indenter column. The displacement of the indenter is measured using a three plate capacitive displacement sensor. At the bottom of the indenter rod, a three-sided 

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The two mechanical properties measured most frequently using indentation techniques are the hardness, H, and the elastic modulus, E. A t5pical load-displacement curve of an elastic-plastic sample during and after indentation is presented in Fig. 30, which also serves to define some of the experimental quantities involved in the measurement. 

The key quantities are the peak load, the displacement at peak load, and the initial unloading contact stiffness, 

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In order to study microscale friction and wear, scientists have developed the friction force microscope (FFM), nanoindentation and nanoscratch tester which serve as excellent tools in micro tribological research [1,6-9]. In this chapter, we first compare the differences between macro and micro friction and wear, and then introduce some results of our research group on microscale friction and wear of ordered films, thin solid films, and multilayers. 

M.M. Shokrieh, M.R. Hosseinkhani, M.R. Naimi-Jamal, and H. Tourani, Nanoindentation and nanoscratch investigations on graphene-based nanocomposites, Polymer Testing, 32 (1), 45-51,2013. 

Nanoindentation and nanoscratch measurements were taken to determine hardness and modulus distributions with respect to depth as well as the shear strength and friction coefficient of the tribofilms on a nanometer scale [1, 32]. Both measurements were combined with in situ AFM observations to find a flat film area less influenced by roughness and to confirm the indent or scratch made on the tribofilms from topographic images after the test. In these observations, the same diamond tip was used as the stylus for indentation or scratching as well as the AFM probe for obtaining in situ AFM images. 

The H/E ratio is a key parameter determining the type of behaviour observed in nanoindentation and nanoscratching wear. Si has a lower H/E ratio than Si02 which explains why the transition from elastic to plastic behaviour occurs at higher contact pressure on this material. 

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. 

NANOINDENTATION, NANOSCRATCH AND NANOIMPACT TESTING OF SILICON-BASED MATERIALS WITH NANOSTRUCTURED SURFACES... 

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