Nanomechanical Analysis of High Performance Materials

Polymers are chemical compounds or mixture of compounds consisting of repeating structural units created through a process known polymerization. These are important groups of materials made up of long chain carbon, covalently bonded together. Polymerization is a process in which monomeric molecules react together chemically to form macromolecules. Polymers are now finding increasing use in engineering applications due to unique properties. Mechanical strength of polymers is of prime importance in engineering applications. Polymers in their service life are exposed to different mechanical and thermal stresses. Durability of polymer strongly depends on the resistance of these materials against environmental condition. In order to assess the strength of material, good knowledge on mechanic of materials is imperative. In this manner, this section aims at introducing mechanical properties of polymers.

Development of PeakForce QNM^® a new, powerful scanning probe microscopy (SPM) method for high resolution, nanoscale quantitative mapping of mechanical properties is described. Material properties such as elastic modulus, dissipation, adhesion, and deformation are mapped simultaneously with topography at real imaging speeds with nanoscale resolution. PeakForce QNM has several distinct advantages over other SPM based methods for nanomechanical characterization including ease of use, unambiguous and quantitative material information, non-destructive to both tip and sample, and fast acquisition times. This chapter discusses the theory and operating principles of PeakForce QNM and applications to measure mechanical properties of a variety of materials ranging from polymer blends and films to single crystals and even cement paste.

In the last twenty years or so, the development of hard thin coatings has progressed to the state that hardness testing based on an instrumented technique has become very popular since for this application, the depth of penetration has to be kept within a small percentage of the overall coating thickness and the resulting impressions are too small for an accurate traditional optical measurement. Despite the well-known methods of analyzing instrumented indentation data, considerable problems arise when this test is applied to very hard materials. The underlying boundary conditions for instrumented indentation analysis are often ignored by practitioners who are sometimes accepting of the results at face value, since often they provide a very pleasing and desirable estimation of hardness of their samples. This chapter reviews the essential features of instrumented indentation analysis and points out the significance of those issues that can affect the computed values of both hardness and elastic modulus. In particular, the significance of the geometry factor ε, the indenter area function, and the mean pressure elastic limit. These interrelated factors can conspire to increase the computed value of hardness by up to a factor of 2 if not properly taken into account. This chapter educates and informs the reader so that results of hardness for very hard materials may be properly interpreted when either viewed in the literature or obtained experimentally so as to avoid incorrect conclusions and results.

The ever-increasing popularity of nanomechanical testing is being accompanied by the development of more and more novel test techniques and adaptation of existing techniques to work in increasingly environmentally challenging test conditions. Considerable progress has been made and reliable mechanical properties of materials can now be obtained at a range of temperature and surrounding media, greatly aiding development for operation under these environmental conditions. In this chapter several of these developments are reviewed, focussing on their use in the non-ambient nanomechanical testing of polymers and nanocomposites.

As material and device length scales decrease, there must be a corresponding increase in the instrumentation resolution for accurate measurements. For these small length scale systems, including thin films, fine grained structures, and matrix composites, nanoindentation experiments provide a proven method for mechanical property measurements. Additionally, when nanoindentation is combined with scanning probe microscopy, individual tests can be placed directly in the regions of interest. However, these tests do not have infinite resolution, as they are limited by the volume probed during a test and the resulting residual damage. Here, an investigation of elastic and plastic mechanical properties is made in relation to the lateral test spacing and the mechanically probed volume. The results clearly show that closely spaced tests having residual plasticity adversely affect neighboring tests, having both poor accuracy and precision in the measurement. This is in contrast to purely elastic tests, which can be closely spaced without affecting accuracy or precision.

This chapter describes the basic fundamental principles that are required to understand the operation of modern nanoindentation techniques. Special attention has been paid to explain the terms that an experimentalist should know while analyzing the data from nanoindentation. Studies conducted by different researcher using nanoindentation techniques have been briefly mentioned as examples. Additionally, studies conducted on silicone quasi-ceramic coatings are also provided.

Metals, oxides and alloys are widely used in transport and industry-engineering applications, due to their functionality. In this work, the nanomechanical properties (namely hardness and elastic modulus) and nanoscale deformation of metals, oxides and alloys (elastic and plastic deformation at certain applied loads) are investigated, together with pile-up/sink-in deformation mechanism analysis, subjected to identical condition parameters, by a combined Nanoindenter—Scanning Probe Microscope system. The study of discrete events including the onset of dislocation plasticity is recorded during the nanoindentation test (extraction of high-resolution load–displacement data). A yield-type pop-in occurs upon low applied load representing the start of phase transformation, monitored through a gradual slope change in the load–displacement curve. The ratio of surface hardness to hardness in bulk is investigated, revealing a clear higher surface hardness than bulk for magnesium alloys, whereas lower surface hardness than bulk for aluminium alloys; for metals and oxides, the behavior varied. The deviation from the case of Young’s modulus being equal to reduced modulus is analyzed, for all three categories of materials, along with pile-up/sink in deformation mechanism. Evidence of indentation size effect is found and quantified for all three categories of materials.

This chapter reviews the creep or viscoelastic deformation behavior of soft materials under nanoindentation-type testing. Analysis protocols of nanoindentation based on the Hertzian elastic contact theory, linear viscoelasticity analyses, and a more recent rate-jump method, are described and assessed. In addition to continuous viscoelasticity, a special type of discrete creep deformation, often observed in a wide range of materials during nanomechanical testing, is also highlighted.

The chapter is devoted to the assessment of effective elastic properties of an aluminium alloy appearing on cell walls of a closed-cell foam system Alporas. The methodology used for this purpose is based on a bottom-up approach which includes identification of mechanically distinct material phases by means of combination of several analyses. Electron microscopy and image analyses are employed at first to identify miscrostructural and chemical entities. Mechanical properties of the distinct phases are studied by grid nanoindentation. Phase separation is performed using statistical deconvolution. Microstructural information is then used for the assessment of effective cell wall stiffness. Several analytical and numerical tools are tested and compared for this purpose. Good mutual agreement is achieved between the methods due to the close-to-isotropic nature of the phase dispersion within the cell wall volume.

Nano-indentation and nano-scratch tests are appropriate methods for measuring the mechanical and tribological properties of bulk samples, thin films and coatings. Using nano-scale tests, numerous properties like modulus of elasticity, hardness, fracture toughness, elastic–plastic behavior and wear resistance can be obtained. Macro-scale tests are conventional methods for determining the mechanical properties of biomaterials, but they are often expensive and require rather large test samples. In this article, the mechanical and tribological properties of hand-mixed and vacuum-mixed bone cements and a dental nano-composite determined by using nano-indentation and nano-scratch tests will be described and discussed. It is shown that bone cement mixed using the vacuum mixing exhibits significantly improved mechanical and tribological properties compared with the hand-mixed bone cement. Moreover, it is demonstrated that thermocycling affect the mechanical properties of dental nano-composite considerably.

After an introduction describing the indentation techniques traditionally applied to the study of micromechanical properties of minerals and rocks, phenomena induced by the diamond tip’s penetration into crystalline rocks are analyzed. Crystalline rocks are characterized by low values of the critical breakage load, i.e. the threshold load corresponding to the transition from a ductile to a brittle behavior. As a consequence, it seems more convenient to examine the mechanical behavior of crystalline rocks by using instrumented nanoindentations. Above the critical load, ranging from rock to rock, fractures occur, affecting the indentation results and thus invalidating the values of the rock mechanical properties obtained by indentation data processing. In order to determine the correct values of the hardness and elastic modulus of brittle rocks, an innovative measurement modality for rocks, i.e. Continuous Stiffness Measurement mode, is proposed. By providing the continuous evolution of the hardness and of the elastic modulus as a function of the indentation depth, it has proven particularly suited to analyze the effects of induced fracturing on the load versus displacement curve.

Microstructure and properties of sintered components produced from nanoparticulate materials are critically dependent on degree of deagglomeration of particulates prior to their consolidation. While all nanoparticulate materials have an inherent tendency to agglomerate owing to attractive Van der Waals forces the impact of agglomeration on sintering behavior/sintered density of powder compacts and associated properties is significant. Although a lot of work has been carried out on developing approaches to deagglomeration of nanopowders it is a challenging task to evaluate the extent of deagglomeration by examining powder compacts. Microscopy of powders (TEM) or of compacts (SEM) is unable to provide any clear distinction between powders with different degrees of particulate agglomeration/deagglomeration. The present chapter cites two case studies from processing of dye sensitized solar cells and synthesis of nanocrystalline yttria stabilized zirconia (YSZ) powders respectively to illustrate that nanoindentation can be an effective way of characterizing the impact of deagglomeration approaches and the consequent deagglomeration extent on powders and compact characteristics. Electrical characterization of the titania based dye-sensitized solar cells, characteristics of green and sintered compacts prepared from synthesized nano YSZ powders are supported by observations from nanoindentation studies.

The aim of this work is to find optimal fillers for nano-layered foils of Ti/Al, Ti/Ni, Ni/Al, Al/Cu for diffusion joining of hard-weldable γ-TiAl alloy by means of nanoindentation test. Nano-layered foils have the non-equilibrium state of structure and are prone to the development of self-propagating high-temperature synthesis reaction during heating. Reaction propagates extremely fast and can be characterized by exothermal effect with a transformation of material structure and with a change in micro/nano mechanical properties.

In this chapter, we present an overview of an optimized method for the determination of surface elastic residual stress in thin ceramic coatings by instrumented sharp indentation. The methodology is based on nanoindentation testing on focused ion beam (FIB) milled micro-pillars. Finite element modeling (FEM) of strain relief after FIB milling of annular trenches demonstrates that full relaxation of pre-existing residual stress state occurs when the depth of the trench approaches the diameter of the remaining pillar. Under this assumption, the average residual stress present in the coating can be calculated by comparing two different sets of load-depth curves: the first one obtained at the center of stress-relieved pillars, the second one on the undisturbed (residually stressed) surface. The influence of substrate’s stiffness and pillar’s edges on the indentation behavior can be taken into account by means of analytical simulations of the contact stress distributions. Finally, the effect of residual stress on fracture toughness and deformation modes of a TiN PVD coating is analyzed and discussed here.

Nanoindentation revealed a number of effects, like pop-in behavior or indentation size effects, that are very different from the classical mechanical behavior of bulk materials and that have therefore sparked a lot of research activities. In this contribution a multiscale approach is followed to understand the mechanisms behind this peculiar material behavior during nanoindentation. Atomistic simulations reveal the mechanisms of dislocation nucleation and multiplication during the very start of plastic deformation. From mesoscale dislocation density based models we gain advanced insight into how plastic zones develop and spread through materials with heterogeneous dislocation microstructures. Crystal plasticity models on the macroscale, finally, are able to reproduce load-indentation curves and remaining imprint topologies in a way that is directly comparable to experimental results and, thus, allows for the determination of true material properties by inverse methods. The complex interplay of the deformation mechanisms occurring on different length scales is described and the necessity to introduce the knowledge about fundamental deformation mechanisms into models on higher length scales is highlighted.

This chapter describes the large-displacement indentation test method for examining elastic–plastic behaviors of vertically aligned carbon nanotube arrays (VA-CNTs). The principle of this test is explained by using a cavity expansion model. The experiments have been performed on VA-CNTs synthesized by the chemical vapor deposition (CVD) method. Under a cylindrical, flat indenter, the VA-CNTs exhibit two distinct deformation stages: a short, elastic deformation at small displacement and a plateau-like, plastic deformation at large displacement. The critical indentation stress, a measure of yield stress or collapsing stress of the VA-CNT arrays, has been obtained. The deformation mechanism of the VA-CNTs at large displacement is revealed with scanning electronic microscope (SEM) images of the deformed VA-CNTs and finite element simulations.