Nanoindentation has been widely used for measuring mechanical behavior of nanocrystalline (nc) metals that cannot be measured by tensile and compressive test. The hardness and elastic modulus are usually obtained by Oliver and Pharr method. However, this may not be true for materials showing viscoelastic characteristics. This study aims at clarifying the effect of testing parameters, especially loading rate and holding time, on the hardness and elastic modulus of a nanocrystalline Fe-51Ni coating obtained in nanoindentation tests as the material exhibits anelastic and creep characteristics. An analytical method based on the correspondence principle for linear viscoelasticity was developed. The holding displacement-time data obtained in indentation creep tests at a high loading rate of 20 mN/s were analyzed and material parameters related to the elastic, anelastic and creep characteristic were derived using a model containing one Maxwell unit and two Kelvin units. The anelastic deformation thus contains at least two relaxation processes having relaxation times of 0.37 s and 6.8 s, respectively and the creep deformation is described by a viscosity value of 4.2x104 GPa.s for the alloy in an as-deposited state. Moreover, electrodeposited (ED) Ni was analyzed by electron backscatter diffraction. Results indicated that the ED Ni exhibits a bimodal distribution of grain size. The grains having sizes larger than 2 £gm shows a strong fiber texture of <100>//ND, whereas the small grains (<2 £gm) are mainly randomly oriented.

The Pd77Cu6Si17 (PCS) thin film metallic glasses (TFMGs) with high glass forming ability and hardness are selected as a hard coating for improving the surface hardness of the AZ31 magnesium alloy. Both micro- and nano-indentation tests are conducted on the specimens with various PCS film thicknesses from 30 to 2000 nm. The apparent hardness and the relative indentation depth (£]) are integrated by a quantitative model. The involved interaction parameters and relative hardness values are extracted from iterative calculations. According to the results, surface hardness can be enhanced greatly by PCS TFMGs in the shallow region, followed by gradual decrease with increasing £] ratio. In addition, the specimens with thinner coating (for example, 200 nm) show greater substrate-film interaction and those with thick coating (for example, 2000 nm) become prone to film cracking. The optimum TFMG coating thickness in this study is estimated to be around 200 nm. Keywords: Magnesium alloys, hardness, sputtering, thin film metallic glass, nanoindentation

The existing researches on interface properties between heterology materials mainly focus on semiconductor-metal and dielectric materials, but little on organic-inorganic ones. In recent years, the nanometer scale phenomena of interfaces between organic-inorganic is gaining a lot of attentions and becoming new frontier regions of nano-related research. Since gold exhibits excellent optical, electrical and mechanical properties, which can be applied to nano-optics, mechanics and electronics. Therefore this study aims to investigate the deformation behavior of nanaoindentation using molecular dynamics simulation and nanoindentation experiments. The nano-effect of mechanical properties between the interface of gold and heterologous Polymethyl Methacrylate (PMMA) with different side groups; i.e., Isotactic-PMMA, Syndiotactic-PMMA and Atactic-PMMA, are explored, respectively. The molecular structures of those side groups of the different PMMAs are identified and characterized. Those PMMA isomer thin films are prepared using spin-coater to deposit the different side groups of PMMA upon Au thin film. Sputter technique is used to form gold thin film with different thickness. The morphology on the surface of samples is characterized by using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The indenter equipment is applied to realize the interface mechanical properties. The time-dependent properties of viscoelastic materials in nanoscale are measured using continuous stiffness measurement (CSM) nanoindentation technique. The effects of displacement rates on the hardness and modulus behavior of PMMA-based are investigated by nanoindentation. The mechanical properties are correlated with the side groups of the PMMA. The hardness of the PMMA-based increases with the raising displacement rate of the Berkovich tip. On the other hand, the modulus of the variation PMMA-based with the varied displacement rate of the Berkovich tip is not significant. The nanoindentation test shows different constituents in nanocomposite systems with a stronger material properties of the interface region than the matrix in each material.

The effect of local defect on thin film mechanical properties is studied in this thesis. The molecular dynamics (MD) is employed to simulate and analyze the relation between intermolecular strength and deformation in the nanoindentation test. The variation of hardness and elastic modulus are simulated from the load-displacement response and the projected area of contact at the maximum load. In this study, Tersoff potential function is employed to describe the molecular behavior of nano-scale carbon and silicon films. The MD models of the diamond indenter and film are applied in the simulation. Due to the hardness different, the diamond indenter can be assumed rigid when silicon thin film was test. However, the indenter¡¦s wear and compressive effects can not be ignored when diamond film were studied under nanoindentation simulation. The indentation parameter in the simulation includes substrate size, indentation velocity, peak hold time, system temperature, indentation depth, local void size, void position and vacancy rate. The results show that the hardness and elastic modulus of thin film may decrease significantly with considering the existence of local defect. The results also elucidated that the elastic modulus and hardness for perfect lattice structure thin films should be the upper bond value of the real bulk material.

<p>In the past two decades depth-sensing indentation has becomea widely used technique to measure the mechanical properties ofmaterials. This technique is particularly suitable for thecharacterisation of materials at sub-micro or nano scale thoughthere is a tendency to extend its application to the micro ormacro scale. The load-penetration depth curve of depth-sensingindentation is a characteristic of a material and can be usedfor analysing various mechanical properties in addition tohardness. This thesis deals with the mechanicalcharacterisation of bulk materials, thin films and coatings,gradient materials, and composites using depth-sensingindentation. Finite element method has been resorted to as atool to understand the indentation behaviour of materials.</p><p>The piling-up or sinking-in behaviour of materials plays animportant role in the accurate determination of materialsproperties using depth-sensing indentation. Finite elementsimulations show that the piling-up or sinking-in behaviour isdetermined by the material parameters, namely<i>E/σ</i><i>y</i>ratio and strain hardening exponent orexperimental parameter<i>h</i><i>e</i><i>/h</i><i>max</i>ratio, and the contact friction. Anempirical model has been proposed to relate the contact area ofindentation to the<i>E/σ</i><i>y</i>ratio and the<i>h</i><i>e</i><i>/h</i><i>max</i>ratio and used to predict thepiling-up orsinking-in of materials. The existence of friction is found toenhance the sinking-in tendency of materials. A generalrelationship between the hardness and the indentationrepresentative stress valid for both soft and hard materialshas been obtained. A possible method to estimate the plasticproperties of bulk materials has been suggested.</p><p>Measuring the coating-only properties requires theindentation to be done within a critical penetration depthbeyond which substrate effect comes in. The ratio of thecritical penetration depth to the coating thickness determinedby nanoindentation is independent of coating thickness andabout 0.2 for gold / nickel, 0.4 for aluminium / BK7 glass, and0.2 for diamond-like-carbon / M2 steel and alumina / nickel.Finite element simulations show that this ratio is dependent onthe combination of the coating and the substrate and moresensitive to differences in the elastic properties than in theplastic properties of the coating/substrate system. Thedeformation behaviour of coatings, such as, piling-up of thesoft coatings and cracking of the hard coatings, has also beeninvestigated using atomic force microscope.</p><p>The constraint factors, 2.24 for WC phase and 2.7 for WC-Cocemented carbides, are determined through nanoindentation andfinite element simulations. A modified hardness model of WC-Cocemented carbides has been proposed, which gives a betterestimation than the Lee and Gurland hardness model. Finiteelement method has also been used to investigate theindentation behaviour of WC-Co gradient coatings.</p><p><b>Keywords:</b>depth-sensing indentation, nanoindentation,finite element method, atomic force microscope, mechanicalproperties, hardness, deformation, dislocations, cracks,piling-up, sinking-in, indentation size effect, thin coatings,composite, gradient materials, WC-Co, diamond-like-carbon,alumina, gold, aluminium, nickel, BK7 glass, M2 steel.</p>

<p>In this Thesis Ti-Al-C thin films deposited by cathodic arc at 700, 800 and 900 °C were investigated with respect to composition, structure and mechanical properties. The highest growth temperature resulted in close to single crystalline Ti₂AlC MAX phase.</p><p> </p><p>A high oxygen incorporation of 7-12 at.% was detected in all the films, likely originating from residual gas and the Al₂O₃ substrate. It was evident that the characteristic nanolaminated MAX phase structure was retained upon deflection from the ideal MAX phase stoichiometry.</p><p> </p><p>Hardness and elastic modulus of the sample grown at 900 °C were 16 and 259 GPa, respectively, as determined by nanoindentation using a Berkovich tip. Nanoindentation measurements with a cube corner tip were also performed on all three samples in order to extract elastic moduli.</p><p> </p><p>Analysis of loading-unloading curves and SPM images revealed no relation between pop-in events and pile-ups around the residual imprints, indicating that other mechanisms than formation of kink bands may be responsible for formation of pile-ups. This was also confirmed by cross-sectional TEM investigation of an indent: Ti₂AlC MAX phase deformed without kinking and delamination, as opposed to the observations in single crystalline Ti₃SiC₂ films. Several possible reasons for the different deformation mechanism observed are discussed. </p><p> </p><p>These results are of importance for the fundamental understanding of the origin of material characteristics, and serve as an initial study initiating further investigations of the influence of defects on MAX phase properties.</p>

TiNi shape memory alloy is characterized by shape memory and superelastic effects which occur due to reversible martensite transformation. It has been recently found that TiNi alloy has superior dent and wear resistance compared to other conventional materials. The stress-induced martensite transformation exhibited by this alloy contributes to its dent and wear resistance. Much work is required to establish the fundamental principals governing the superelastic behavior of TiNi under wear and indentation conditions. Understanding the superelastic behavior helps to employ superelastic TiNi in applications where high impact loading is expected as in gears and bearings. In this study the superelastic behavior of shape memory alloys under reciprocating sliding wear and indentation loading conditions was investigated. The deformation behavior of superelastic Ti-Ni alloys was studied and compared to AISI 304 stainless steel. Dominant wear and deformation mechanisms were identified.

Microscale bi-material lattices with near zero thermal expansion are designed to create a thermally stable optical surface for applications in a space telescope. To facilitate the design, the thermal expansion of a unit cell with spacers is derived analytically and validated via finite element studies. Predicting the lattice behaviour also requires knowledge of the constituent properties. To this end, molecular dynamics simulations are performed to determine the thermal expansion and recrystallization behaviour of aluminum and titanium thin films, and nanoindentation experiments are conducted to extract their elastic-plastic properties. Unit cell configurations giving near zero thermal expansion are obtained through iterative analysis. The resulting designs are analyzed and validated via finite element simulations and shown to exhibit long term stability.

Microscale bi-material lattices with near zero thermal expansion are designed to create a thermally stable optical surface for applications in a space telescope. To facilitate the design, the thermal expansion of a unit cell with spacers is derived analytically and validated via finite element studies. Predicting the lattice behaviour also requires knowledge of the constituent properties. To this end, molecular dynamics simulations are performed to determine the thermal expansion and recrystallization behaviour of aluminum and titanium thin films, and nanoindentation experiments are conducted to extract their elastic-plastic properties. Unit cell configurations giving near zero thermal expansion are obtained through iterative analysis. The resulting designs are analyzed and validated via finite element simulations and shown to exhibit long term stability.

High Temperature Polymer Matrix Composites (HTPMCs) are widely used by the aerospace industry today because of their high specific strengths, light weight, and the ability to custom tailor their mechanical properties to individual applications. Because of the harsh environmental conditions these materials experience during service use, these composite structures are susceptible to a high rate of thermo-oxidative degradation that ultimately causes premature failure in service. The current knowledge base is lacking in the fundamental spatial variability of the constituent materials upon aging, which precludes composite developers from predicting lifetime mechanical properties of the composites in use. The current study summarizes state of the art techniques in characterizing the thermally oxidized matrix resin system (PMR-15 polyimide), and develops novel techniques in direct mechanical measurement of the spatial variability of mechanical properties. Works to date and future advances in the field with respect to in situ testing are presented.