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Nanoindentation for measuring thin film mechanical properties is probably the most popular yet ill-understood method due to its inherent complexities. As opposed to burst pressure or microtensile tests of lithographed structures, where relatively uniform stress fields may be generated, the indentation-induced stress gradients can produce unique challenges. Because of the test's simplicity and ability to mechanically probe the smallest of scales, it is becoming increasingly applied. Five possible stages of deformation are suggested from Hertzian elastic to film delamination and double buckling. In particular metal films on harder substrates are emphasized where it is shown that dislocation nucleation and arrest are only partially understood. Later stages of film delamination are illustrated with Cu/SiO 2 /Si where it is shown that the true work of adhesion is 0.6 J/m 2 . Current limitations of indentation-induced delamination measures of toughness involve large scatter associated with sensitivity of the fracture radius to the contact radius ratio.

Sputtered copper and tungsten thin films both with and without tungsten and chromium superlayers were tested by using nanoindentation probing to initiate and drive delamination. The adhesion energies of the films were calculated from the induced delaminations using the analysis presented in “Quantitative adhesion measures of multilayer films: Part I. Indentation mechanics.” Copper films ranging in thickness from 150 to 1500 nm in the as-sputtered condition had measured adhesion energies ranging from 0.2 to 2 J/m2, commensurate with the thermodynamic work of adhesion. Tungsten films ranging in thickness from 500 to 1000 nm in the as-sputtered condition had measured adhesion energies ranging from 5 to 15 J/m2. The superlayer was shown to induce radial cracking when under residual tension, resulting in underestimation of the adhesion energy when the film was well adhered. Under conditions of weak adherence or residual compression, the superlayer provided an excellent means to induce a delamination and allowed an accurate and reasonably precise quantitative measure of thin film adhesion.

The deformation of thin layers of glass on crystalline materials has been examined using newly developed experimental methods for nanomechanical testing. Continuous films of anorthite (CaAl2Si2O8) were deposited onto Al2O3 surfaces by pulsed-laser deposition. Mechanical properties such as Young's modulus and hardness were probed with a high-resolution depth-sensing indentation instrument. Nanomechanical testing, combined with AFM in situimaging of the deformed regions, allowed force-displacement measurements and imaging of the same regions of the specimen before and immediately after indentation. This new technique eliminates any uncertainty in locating the indentation after unloading. Emphasis has been placed on examining how the Al2O3 substrate crystallographic orientation will affect mechanical composite response of silicate-glass film/Al2O3 system.

In this study we combined nanoscratch testing with a multilayer sapphire and aluminum nitride single-substrate system to determine the effects of interface composition and structure on susceptibility to fracture of hard, thin tantalum nitride films. Nanoindentation tests showed that the elastic moduli of the tantalum nitride and aluminum nitride films, as well as the sapphire substrate, were essentially equal at 400 GPa. On both portions of the substrate, these tests also showed that near surface hardness was near 35 GPa. Nanoscratch tests triggered long blisters and circular spalls on both the sapphire and aluminum nitride portions of the substrate. The blisters showed that the tantalum nitride film was subjected to a compressive residual stress of {minus}6.7 GPa. The spalls showed that failure occurred along the tantalum nitride film-substrate interface regardless of substrate composition. Most importantly, the blisters and spalls showed that the mode I component of the fracture energies were essentially equal on both substrate materials at a value near 3.1 J/m{sup 2}. These energies are on the order of the energies for metallic bonding. {copyright} {ital 1999 Materials Research Society.}

A simple superposition solution for a point-loaded elastic plate on a soft substrate is proposed. The solution considers a “drumhead” being elastically bent into a compliant substrate that is viscoelastic-plastic. With simplifying assumptions it is found that the drumhead and substrate support loads proportional to δ1/2 and δ3/2, respectively, where δ is the vertical point displacement. At fixed displacement, relaxation proceeds at high loads, but if sufficiently unloaded, recovery or increased load results with time. Qualitative verification of the time-dependent drumhead solution is shown by relaxation and recovery data on polycarbonate covered by polysiloxane, composite or diamondlike carbon (DLC) coatings, and films.

Mechanical characterization combined with micro feature observations provide a successful method in elucidating micromechanisms of plastic deformation. As such, the present study is centered on some aspects as related to slip/twinning mechanisms in uranium base systems. Most of the findings emerged from a broad experimental/theoretical program particularly in a lean U-Ti alloy. Within this framework, the interrelationship between slip and mechanical twinning onset was mainly developed. In fact, the key issue remains in defining the critical role of plasticity on the local stress field. Better understanding of this concept has already been explored through several types of failure events in elastic-plastic solids. For such material of low crystal structure symmetry, better understanding of concomitant slip/twinning behavior is essential regarding deformation and fracture resistance. Thus, incentives to shed light on these basic issues becomes apparent. At least it is desirable to follow the sequence of micro-events as the level of plasticity proceeds in this U-Ti alloy which is characterized by a DBT. To assist this extrinsic dominant variables such as state of loading, temperature and strain rate were included.

Nanostructured silicon carbide films have been deposited on molybdenum substrates by hypersonic plasma particle deposition. In this process a thermal plasma with injected reactants (SiCl4 and CH4) is expanded through a nozzle leading to the nucleation of ultrafine particles. Particles entrained in the supersonic flow are then inertially deposited in vacuum onto a temperature-controlled substrate, leading to the formation of a consolidated film. In the experiments reported, the deposition substrate temperature Ts has ranged from 250°C to 700°C, and the effect of Ts on film morphology, composition, and mechanical properties has been studied. Examination of the films by scanning electron microscopy has shown that the grain sizes in the films did not vary significantly with Ts. Micro-X-ray diffraction analysis of the deposits has shown that amorphous films are deposited at low Ts, while crystalline films are formed at high Ts. Rutherford backscattering spectrometry has indicated that the films are largely stoichiometric silicon carbide with small amounts of chlorine. The chlorine content decreases from 8% to 1.5% when the deposition temperature is raised from 450°C to 700°C. Nanoindentation and microindentation tests have been performed on as-deposited films to measure hardness, Young's modulus and to evaluate adhesion strength. The tests show that film adhesion, hardness and Young's modulus increase with increasing Ts. These results taken together demonstrate that in HPPD, as in vapor deposition processes, the substrate temperature may be used to control film properties, and that better quality films are obtained at higher substrate temperatures, i.e. Ts≈700°C.

The mechanical properties of solution deposited lead zirconate titanate (PZT) thin films; including the hardness, modulus, and fracture behavior, have been studied using continuous indentation methods. Comparisons are made between the behavior of the thin films and a bulk PZT ceramic. The thin films exhibit a hardness between 5 and 8 GPa, slightly lower than the hardness measured in a bulk PZT, ≈9 GPa. The increased grain boundary area in the thin films, which have 100 nm grain sizes, may act to accommodate plastic deformation. Fracture caused by indentations appears to be constrained to the sub-surface regions of the film, and no evidence of indentation induced delamination was observed. Traditional indentation analysis cannot accurately determine the elastic modulus of thin film PZT materials due to non-linear elastic behavior. The apparent modulus of the thin film PZT is insensitive to processing methods that alter the electrical properties of the film.

The current study is centered on elastic-plastic solid interaction with hydrogen. Here, the environment isfree hydrogen, from either external or internal origins providing as such aggressive effects. In this context, near surface displacement occurred, beside microcracking onset or growth, significant interfacial weakening, as critical forms of mechanical degradation. Metastable austenitic stainless 316L steel was selected, in order to provide a comprehensive study on bulk surfaces. Globalfindings on hydrogen effects were supplemented by nanoscale information. Only for the nanosection, Ti/Cu thinfilms were also included, namely an additional small-volume case. Samples have been charged with hydrogen under lowfugacity conditions and the outcoming effects have been sorted out by mechanical response tracking assisted by contact mechanics methodology. Nanoindentation and continuous scratch tests were utilized supplemented by Scanning Probe Microscopy (SPM) visualization. Local resolution provided remarkable input to the globalfindings, in terms of dislocation nucleation aspects, near surface modification, plastic localization and microfracture onset. In thin layers, the effective work of the adhesion was reduced indicating significant degradation that could be expressed quantitatively. Global/local benefits of the stainless steel system under study made it possible to apply multiscale models describing complex micro­mechanical processes. Рассматривается взаимодействие упруго­-пластического твердого вещества с водоро­дом. Средой служит свободный водород от внешнего или внутреннего источника, что создает агрессивный эффект. В результате происходило приповерхностное смещение, кроме начала образования микротрещин или их роста и значительного межфазного раз­упрочнения, что является основными причи­нами потери механической прочности. Для всестороннего изучения внутренней струк­туры поверхности была выбрана метастабильная аустенитная нержавеющая сталь 316Л. Общие данные о действии водорода были дополнены информацией на наноуровне. Для получения данных на нано­уровне были изучены тонкие пленки Ti/Cu, т.е. проведены испытания на малом объеме материала. Образцы обрабатывали водоро­дом в условиях низкой летучести, а ре­зультаты классифицировали по механи­ческому отклику методом контактной меха­ники. Применяли наноиндентирование и непрерывное царапанье с использованием сканирующей микроскопии. Результаты ло­кальных исследований послужили значи­тельным вкладом в общие выводы, включая зарождение дислокаций, приповерхностную модификацию, начало пластической локали­зации и микроразрушения. Эффективная работа адгезии в тонких слоях уменьшилась, что свидетельствует о существенном сниже­нии механических свойств, выражаемом ко­личественно. Преимущества глобального и локального подходов при изучении нержа­веющей стали позволили использовать многоуровневые модели, описывающие комплексные микромеханические процессы.

Using a simplified version of Johnson’s core model analysis of the plastic zone, one may determine the plastic zone size around a contact or, alternatively, determine the yield strength by measuring the plastic zone. The theoretical model contains three parameters: indentation load, yield strength and zone size so that knowing any two gives the third. This is experimentally demonstrated for a series of single crystals (Fe–3wt%Si, tungsten, zinc) and polycrystals (1100-0 Al, copper and 2024-T6 aluminum). In addition, two of these are evaluated in several work-hardened states. Plastic zone sizes are estimated principally by atomic force microscopy and Zygo interferometry imaging with some verification by transmission electron microscopy. On the theoretical side, verification of the relationship is obtained by elastic–plastic numerical analysis of a bi-material system based upon an Fe–3wt%Si single crystal with a thin oxide film. It is shown that in general predictions are reasonable down to nanometer level contacts except for two cases where an indentation size effect may dominate. The proposed relationship is suggested to be an alternative measure of yield strength compared to the often cited value of H /3, particularly at light contacts.

The adhesion of sputtered copper thin films was measured with a quantitative indentation technique utilizing refractory superlayers to trigger and promote delamination. Adhesion energies of the indentation-induced delaminations were analyzed in terms of the critical strain energy release rate. Two groups of films were investigated. Group I ranged in thickness from 225 to 1000 nm in both the as-deposited and annealed condition. Adhesion energies ranged from 2 to 15 J/m 2 , with higher adhesion for the annealed condition. Group II films had nominal thicknesses of 430 and 1100 nm, some with 7–10 nm interlayers of either titanium or chromium. Adhesion energies of these films ranged from 4 to 30 J/m 2 , increasing by a factor from 1.3 to 7.5, as a function of the interlayer presence and type, with the increase in energy due to a chromium interlayer exceeding that of titanium. Adhesion energies increased with film thickness for all films, with interlayers and annealing producing a larger increase. These quantitative results were compared to previous semi-quantitative and quantitative results, and shown to have comparable magnitudes and trends.

Active-passive potential steps have been applied during continuous microindentation into 300 μ m thick Fe3%Si sheets exposed to 1 M H 2 SO 4 . First, samples were allowed to deflect in the indentation direction whereby the indenter penetration changed due to local metal dissolution and sample deflection resulting from passive film stress induced bending. Samples were then constrained to eliminate stress induced deflection. A distinct difference between the indentation curves for the above two types of tests allowed separation of the effects of film stress and local dissolution. Indenter tip displacement correlated with the current behavior and was consistent with the salt film evolution and resulting electrostrictive film stress. A theoretical model allows estimates of the time dependent film thickness (3.5 μ m at maximum) and electrostrictive film stress (330 MPa at maximum).

In this study we combined nanoscratch testing with a multi-layer aluminum oxide and aluminum nitride single substrate system to determine the effects of interface composition and structure on susceptibility to fracture of hard, thin tantalum nitride films. Nanoscratch tests showed that the film on aluminum oxide and on aluminum nitride portions of the substrate failed readily along the tantalum nitride film-substrate interface regardless of substrate composition. Most importantly, the fracture energies were essentially equal on both substrate materials. These results strongly suggest that a sputter deposited interface structure controls susceptibility to fracture.

The use of nanoindentation techniques to measure nanoscale mechanical behavior is a new path of interest to researchers today. Load drops and displacement excursions can be utilized to measure activation volumes for dislocation events in single crystals, thin films, and nanoposts. Through the introduction of a new length-scale parameter, the dislocation wall spacing, a mechanism describing staircase yielding, is presented. The dislocation wall spacing can also be used to estimate activation volumes. Molecular dynamics simulations of nickel film indentation have been used to validate the origin of staircase yielding and also show consistent dislocation wall spacings. Additionally, stress relaxation experiments have been used to estimate activation volumes.

A dynamic mechanical analyzer equipped with a diamond indenter tip was used to measure the elastic modulus of polymeric coatings as well as various bulk materials. A fabricated indenter probe was used to indent bulk samples of aluminum and fused quartz, as well as gelatin and polystyrene films in order to compare the micron-level indentation measurements with sub-micron (nanoindentation) techniques. The measured moduli were in agreement for ductile materials and thick films (> 20 μm), but limited displacement resolution, material cracking, and hydrostatic pressure effects led to diverging values for thinner coatings and more brittle materials.

Nanochemical testing techniques were used to quantitatively assess the adhesion of thin film-substrate systems. These techniques utilized micron-scale diamond tips with instrumentation continuously measuring to sub-nanometer and sub-millinewton resolutions. Delamination was modeled as an interfacial crack propagation problem, utilizing linear elastic fracture mechanics and characterized by the critical strain energy release rate. A 9.1 μm thick phenol–formaldehyde polymer film on stainless steel was tested with indentation, scratching and edge-loading of fine lines. Also, sputtered copper and tungsten–copper bilayer films on SiO2, 150 to 1500 nm thick, were tested with indentation.

Experiments involving the indentation of single crystals of both tungsten and an iron alloy show that the observed yield phenomena can be predicted using a superdislocation model driven by the change in shear stress between the elastically and fully plastic loading conditions. A low density of dislocation multiplication sites is required to support elastic loading which approaches applied shear stresses on the order of the theoretical shear strength of the material. Oxide film thickness and crystal orientation are examined as parameters in controlling the yield phenomena. A model based on activation of dislocation multiplication sources is suggested to explain the initiation of the yield point during indentation and the overall load–depth relationship during indentation.

A commercial piezoelectric acoustic emission transducer has been used in conjunction with nanoindentation techniques to study the relationship between acoustic emission signals and discrete physical events to identify the type and strength of an event. Indentations into tungsten and iron single crystals have been used to study dislocation generation and passive film failure. In addition, indentations made into a thin nitride film on sapphire have been used to cause film delaminations. Parameters such as signal rise time and frequency for a piezoelectric sensor are related to sample geometry, and not to the type of event which caused the acoustic emission signal. As a possible calibration for acoustic emission sensors, the most meaningful parameter is the acoustic emission energy, which has been shown to scale with the elastic energy released during the event. The measured values of elastic energy released correspond very closely to those calculated using Hertzian contact mechanics.

We have modified the microscratch test to create a near plane strain loading condition. In the Microwedge Scratch Test (MWST), a wedge-shaped diamond indenter tip is drawn along a fine line (i.e., narrow strip of film), while simultaneously being driven into the line. We compare microwedge scratching of zone 1 (voided grain boundaries) and zone T (metallurgical grain boundaries) thin film specimens of sputtered tungsten on thermally grown SiO2. Symptomatic of its weak grain boundaries, the zone 1 film displays three separate crack systems. Because of its superior grain boundary strength, the zone T film displayed only one of these—an interfacial crack system. By correlating fracture phenomena to signature events in the load-displacement curve, we develop governing equations for propagating interfacial cracks, including expressions for strain energy release rate, bending strain, and mode mixity. Grain boundary fracture causes zone 1 films to spall before a stable crack is formed. Zone T films survive the bending strains, and hence adhesions may be inferred from stable crack growth mechanics. We conclude by contrasting and comparing experimental results for plane strain indentation versus plane strain scratching.

A new method for evaluating modulus and hardness from nanoindentation load/ displacement curves is presented. As a spherical indenter penetrates an elastoplastic half-space, the elastic displacement above the contact line is presumed to diminish in proportion to the total elastic displacement under the indenter. Applying boundary conditions on the elastic and plastic displacements for elastic and rigid plastic contacts leads to an expression that can be best fit to the entire unloading curve to determine E*, the reduced modulus. Justification of the formulation is presented, followed by the results of a preliminary survey conducted on three predominantly isotropic materials: fused quartz, polycrystalline Al, and single crystal W. Diamond tips with radii ranging from 130 nm to 5 μm were used in combination with three different nanoindentation devices. Results indicate that the method gives property values consistent with accepted values for modulus and hardness. The importance of surface roughness and indentation depth are also considered.

Modulus and yield strength determinations from nanoindentation experiments of thin poly(methyl methacrylate) (PMMA) polymer films have been investigated. The modulus was calculated from flat punch theory and showed a large effect of the substrate, hydrostatic pressure, and surface topography. Substrate corrections were possible in some cases but often resulted in erroneous or negative values due to large penetration depths with respect to the film thickness and differences in the stiffness of the coating and substrate. Hydrostatic pressures up to 600 MPa were exerted by a conical and cube corner indenter tip and influenced the modulus and yield strength measurements. Due to the non-linear deformation behavior of the PMMA films, however, hydrostatic pressure corrections tended to underestimate the modulus. The yield strength was measured based on Tabor's approximation using the unloading curve and was compared with measurements using plastic zone predictions and compression test data. Yield strength calculations from plastic zone images were lower in every case than those calculated from compliance, showing the viscoelastic nature of the material.

Interfacial fracture has been induced between a tantalum nitride film with an aluminum interlayer on a sapphire substrate using nanoindentation. To identify failures for which a model calculation is valid a commercial acoustic emission sensor has been used to study the details of the failure event. The interfacial fracture energy of the system with an aluminum interlayer under the loading conditions at the crack tip is approximately 8 J/m2. Within narrow bounds, this toughness value is reproducible using three different theoretical approaches. The acoustic emission signal is used to determine a lower bound interfacial crack velocity of 5 m/s. The majority of the failure occurs at the aluminum-sapphire interface, suggesting that the fracture energy and crack velocity determined are related to the toughness of this interface and not the nitride-aluminum interface.

Continuous microindentation has been carried out on an iron–3% silicon single crystal in 1 M sulfuric acid. The ability of the material to support elastic loading is directly linked to the presence of thermally grown oxide films and passive films applied through potentiostatic control of the sample. When the passive film is removed, either by chemical or electrochemical means, the iron alloy can no longer sustain pressures on the order of the theoretical shear strength of iron. Instead, the metal behaves in a traditional elastic-plastic manner when no film is present. The oxide film at the edges of the indentation can sustain applied tensile stresses up to 1.2 GPa prior to failure. Indentation in materials undergoing dissolution must account for the rate of material removal over the remote surface and the resulting plastic deformation around the contact of the indentation.

We have investigated mechanical probing of a precracked fine line structure as a new type of thin film fracture mechanics specimen. An idealized mechanics analysis is first presented. Experimentally, two types of precracks are formed. A thin carbon layer to which other layers weakly adhere creates a “processed precrack” by integrated circuit processing techniques. An “indented processed precrack” is formed by precision alignment of a sharp microwedge. The processed precrack is found to reduce the critical tangential load by 50% from a non-precracked line, while the indented processed precrack lowers the load by 200%. From this, a reasonable value of adhesion may be directly calculated. Crack path behavior is observed to depend on strength of the interface. In the case of a weak interface, the crack remains in the interface as it extends. For a strong interface, it kinks into the substrate if the crack is initially short, but remains in the interface if it is initially long. Given the experimental evidence, the mechanics are slightly modified to quantitatively model the experimental data.

Nanoindentation data on single-crystal Au(111), Au(110), and Au(100) are presented and show an interesting yielding phenomenon---this yielding behavior is composed of a series of discrete yielding events separated by elastic deformation. The onset of this behavior is in agreement with calculations for the theoretical shear strength of gold. Good quantitative agreement is found between the experimental results and a model developed for the nucleation and multiplication of dislocations by a simple Frank-Read source under the indenter tip.

The atomic force microscope (AFM) has been used to observe and characterize for the first time surface steps and grooves on the faces of Cr2O3 grains formed as an oxide scale on Ni−30Cr and Ni−30Cr−0.5Y alloys during high temperature oxidation. The very high spatial resolution of the AFM is required to characterize these features. We propose that these surface features, whose dimensions are in the range of nanometers and tens of nanometers, may be interpreted as evidence of highly localized plastic deformation of the oxide scale. The size and spacing of the steps and grooves are consistent with models of plastic deformation based on slip bands derived from dislocation climb or dislocation glide. Mechanical twinning and the models for stress-driven surface instability are also possibly responsible for some surface features. The addition of yttrium to the alloy seemed to enable enhanced plastic deformation of the scale. The strain corresponding to the observed features, estimated by simple models, could relax a significant part of oxide growth and thermal stresses.

Mechanical properties of cold-worked molybdenum, grade 4 titanium, and an α-β titanium alloy are measured with tensile tests and by indentations using conical indenters with 105, 120, and 137 deg included angles. The extent of plastic deformation and pileup around an indentation is measured using profilometry. Various models predicting the extent of plastic deformation and pileup are compared to the actual measured values. As inferred from indentation, the calculated yield strength of the material from the mean pressure does not correlate well to the yield strength measured by tensile testing. The plastic zone size surrounding an indentation can also be used to determine the yield strength of the material, and this does correlate to the yield strength measured by tensile tests. Furthermore, the extent of plastic deformation is relatively independent of the included angle of the indenter for the range of materials used in this system. Models predicting the amount of pileup at the edges of the indentation appear to approach but overestimate the actual amount of pileup in the materials tested.

Using a continuous microscratch technique, the adhesion strengths of Pt, Cr, Ti, and Ta2N metallizations to NiO and Al2O3 substrates have been characterized. The practical work of adhesion was determined as a function of both thickness and annealing conditions. For all except the Ta2N films, the practical work of adhesion increases nonlinearly from a few tenths of a J/m2 to several J/m2 as the thickness of the thin film is increased, indicating that a greater amount of plastic work is expended in delaminating thicker films. Further, the practical work of adhesion also increases with increasing annealing temperature, indicating stronger bonding at the interface. In the limit that the film thickness tends to zero, the plastic energy dissipation in the film tends to zero. As a result, the extrapolation to zero thickness yields the true work of adhesion for that system.

Yield points have been detected in both GaAs and Fe3wt%Si single crystals when contacting the surface with sharp diamond tips. The present study concentrates mostly on Fe3wt%Si and demonstrates that a unique point in the load-displacement curve can be associated with the first dislocation nucleated. This occurs at loads in the vicinity of 100 μN for a 66 nm radius tip. Subsequently, this produces an avalanche of dislocations estimated to range from about 15 to 74 in number depending on the magnitude of the yield point load. A model, based upon discretized dislocations is proposed for both the initiation of yielding at an upper yield point (UYP) and the arrest of the indenter at a lower yield point (LYP). The UYP is interpreted in terms of Rice's unstable stacking energy concept, previously applied to crack tips, and accounts for tip radius, oxide film thickness and image force effects. The LYP is interpreted in terms of the back forces provided by previously emitted shielding dislocations. These two approaches provide first order solutions of the upper and lower yield points which both vary from test to test by as much as a factor of four. The large variation in nucleation load is proposed to be due to point to point differences in oxide thickness which might range from 4.5 to 8.5 nm.

Analytical calculations of mechanics for strain energy release rate, bending strain and phase angle are reported for a new procedure to test thin film mechanical properties. In the Microwedge Indentation Test (MWIT), a symmetric wedge-shaped probe extends fully across a wide thin film interconnect line, so that analysis under the assumption of plane strain is appropriate. As the indentation proceeds, an interfacial crack between the interconnect line and the substrate develops if the interface is weak. From this, adhesion can be calculated. Eventually, the interfacial crack becomes long enough that buckling ensues, giving rise to large thin film bending strains. Consequently the phase angle changes continuously from 53 to −37°. Depending on whether spallation occurs by fracture in the center of the beam or at the end of the beam at the interfacial crack tip, a thin film critical bending strain or grain boundary fracture toughness may be determined.

Experimental results of microwedge indentation are presented in order to evaluate the thin film fine line on a thick substrate as a fracture mechanics test specimen. Crack length is found to be proportional to indentation volume, allowing assessment of adhesion. The amplitude of single-buckles is used to estimate induced residual stress in the fine line and adhesion is independently assessed. The phenomena of double-buckling and spallation during indentation are experimentally verified, and are used to estimate fracture toughness of the thin film columnar grain boundaries. Although values of adhesion are unreasonably high, cracking of the substrate occurred, violating the critical assumption of negligible substrate compliance. The amplitude assessment gives a more reasonable value. A hypothesis for the complete sequence of events is proposed.

A transmission electron microscopy study of the dislocation distribution under an indentation has revealed first that a complex sequence of loop nucleation, cross-slip and renucleation results in a cross-like network at the free surface and a square-like network underneath. These dislocation distributions are made up of two types of dislocation: redundant dislocations responsible for general plasticity and work hardening, and shielding dislocations responsible for the equilibrium of forces. The former are roughly an order of magnitude more prevalent. The total number of dislocations are consistent with continuum plasticity theory while the shielding density is consistent with a proposed superdislocation pile-up model.

The interfacial fracture energy of Ti/Al2O3 composites was measured with and without a diffusion barrier at different bonding temperatures by using four-point bending tests. It was found that the interfacial fracture energy increases with increasing bonding temperature up to 950 °C. When the bonding temperature was further raised to 1000 °C, the interfacial fracture energy drops. The decrease of the interfacial fracture energy is due to the formation of the continuous intermetallic compound, Ti3Al, at the interface between Ti and Al2O3. By using a diffusion barrier, the interfacial fracture energy decreases from 25.4 to near O J/m2 and 32.9 to 8.7 J/m2 for applied bonding temperatures of 800 and 900 °C, respectively. This is because the diffusion barrier reduced the diffusion of Al across the interface and into the Ti, thereby preventing a strong chemical bond at the interface. For the composite bonded at 900 °C, the crack propagation was found to occur at the interface between the Ti and Al2O3. The interfacial failure was found to be in the Ti3Al reaction layer for the composite processed at 1000 °C. With a diffusion barrier, the crack propagation path follows several interfaces. Evaluation of the processing temperature on the mechanical properties of the Ti was also obtained by using a nanoindentation technique.

Nanomechanical devices constitute an important and growing field, as they allow for new understanding of the mechanical properties at interfaces and surfaces. As an example, a newly developed nanoindentation device has been used to accomplish μN load indents into GaAs. First, it is shown that a plastic zone can be measured and is comparable to theory. Also, it is shown that the rate of indentation affects both the depth and upset zone of low load indents, implying a strain-rate sensitivity effect at room temperature. This is reinforced by observation of what appears to be a glide-based relaxation process.

Surface slip upset and grain boundary displacement can be measured with considerable precision by AFM. For HSLA steel, measurement of surface damage by determination of the damage parameter, f, in conjunction with characterization of environmental effects on threshold criterion is sufficient to predict initiation. Plasticity at the grain boundaries is the dominant mechanism controlling initiation in HSLA; hydrogen embrittlement accelerates initiation in marine environments. For α-titanium, initiation behavior is apparently controlled by mechanical oxide rupture. Surface damage increases in aqueous chloride environments where repassivation is prevented and metal is effectively softened. As in the HSLA steel, the fraction of the cumulative plasticity emerging at the surface is critical in predicting initiation.

In U-Ti alloys, a simplified dislocation shielding model might represent the lower shelf regime of fracture toughness as a function of microstructure, temperature and strain rate. This proposed shielding model centers on the local back-stress for shielding and, as such, depends on the friction stress and its strain rate sensitivity. Shielding concepts might be applicable to some brittle lower symmetry crystal structures obeying similar trends typical to thermally activated deformation mechanisms.

Under shear stress, silicon nanocrystals become amorphous through an intermediate hexagonal crystalline phase.

Diamond indentation of a surface with a thin passive film require s loads an order of magnitude smaller for Ni〈100〉 crystals than for Fe-3 wt% Si〈100〉 crystals. The load bearing capacity of the Fe-3 wt% Si can be reduced by two orders of magnitude by removing the 1- nm thick native oxide film. These phenomena can be explained by considering the equilibrium of forces associated with tip, image and friction stresses acting on dislocations emitted from the indenter tip. The key ingredient to this model is the nucleation and growth of dislocation loops at loads of only tens of micronewtons. Three types of critical contact experiments demonstrate that dislocations can be initiated at loads well below those previously thought to represent elastic loading only.

A microscratch technique for determining the fracture toughness of brittle intermetallics is presented. Advantages include very small sample sizes and multiple tests on a single, flat polished surface. The fracture toughnesses of single-crystal NiAl in {001}〈100〉, {001}〈110〉, {110}〈110〉, and {110}〈100〉 crack orientations were evaluated using this technique. The results of the scratch testing are compared with measurements on small compact tension samples. Also, transmission electron microscopy is used to help explain the dislocation character of the resulting plastic zones in samples tested. Lastly, a model for determining the dislocation velocity during nanoindentation is presented to help understand the ductile-brittle transition temperature of semibrittle materials.

The effect of interfacial reactions on the fracture toughness of the bond between a reactive metal, Ti, and a relatively stable oxide αAl 2 O 3 , was studied for heat treatments at different temperatures. The microstructure, chemistry and fracture toughness of the interfaces were characterized using transmission electron microscopy and a continuous microscratch test. The formation of intermetallic compounds resulted in a deterioration in the interfacial fracture toughness, relative to an unreacted interface. The decrease in fracture toughness was related to the presence along the interface of a brittle intermetallic phase and cavities. The cavities were produced as a result of the volume change and the oxygen released during the formation of intermetallic compounds at temperatures of 600°C and above. The strongest interface exhibited little if any reaction between the Ti and the Al 2 O 3 .

Teflon amorphous fluoropolymer (TAF) multi-walled carbon nanotube (MWCNT) suspensions have the potential for creating conductive coatings on insulating films for numerous applications. However, there are few studies on polymer MWCNT suspension properties and even fewer that use Teflon. To define mechanical and electrical property relationships, bilayer films of TAF-MWCNT were created with differing concentrations of MWCNTs. Nanoindentation revealed that addition of 8 wt% MWCNTs to TAF increased the elastic modulus by about 25% and hardness by about 15%. Conducting indentation showed 8 wt% MWCNT films exhibit uniform stable conductance once indentation depth exceeds several hundred nanometers. Films with lower concentrations of CNTs were insulating. The two techniques provide a unique description of structure property relationships in this suspension film system.

Localized heating of metals and alloys using a focused laser beam in ambient atmosphere produces dielectric oxide layers that have characteristic optical appearances including different colors. Nanoindentation probed the deformation and fracture of laser-fabricated oxides on 304L stainless steel. Conductive nanoindentation measured electrical contact resistance (ECR) of the same colored oxides indicating a correlation between laser exposure, conductance during loading, current-voltage (I-V) behavior at constant load, and indentation response. Microscopy and X-ray diffraction examined the microstructure and chemical composition of the oxides. Combining techniques provides a unique approach for correlating mechanical behavior and the resulting performance of the films in conditions that cause wear.

We have obtained the first atomic force microscope (AFM) images of cell like boundaries and slip band emergence of fatigued metals surfaces (titanium and high strength-low alloy steel). The AFM has been used to obtain quantitative information about slip spacings and slip height displacements. Using these measurements we have determined the fraction of plastic strain that contributes to surface displacement upset. Values of 1.6% for Ti and 0.9% for HSLA resulted for completely reversed plastic strain cycling. We introduce a model for fatigue crack initiation based on slip band spacings, slip height displacement, and cumulative plastic strain. To first order these compare well with experimental initiation data obtained by other investigators. The relative ease of sample preparation for AFM, along with its outstanding height resolution, offers a higher degree of simplicity and precision in fatigue crack initiation studies compared to more conventional techniques.

This paper presents the development of a higher-order direct boundary integral-displacement discon- tinuity method for crack propagation in layered elastic materials. The method is based on the dual boundary integral equations of linear elasticity which are solved by means of a quadratic boundary element formulation. The analytical solution for a point force within a bonded half-plane region is used to derive the kernel functions of the boundary integral equations. Square-root displacement-discontinuity elements are used to model the crack tips, and stress intensity factors may be computed using the numerically predicted values of the displacement discontinuity components at the midpoints of these crack-tip elements. An algorithm based on the maximum tensile-stress criterion is then developed and incorporated into the boundary element model to predict the paths of cracks propagating in layered elastic materials. In the experimental part of this study, crack profiles for straight-through-cracked, compact-tension specimens of the anodically bonded silicon/Pyrex glass system are measured by profilometry. The plane strain prediction of the crack-propagation path is compared with the experimentally measured crack profiles. Consistent with the prediction, the interfacial crack is observed to kink away from the strong, anodicaUy-bonded interface and propagate into the more compliant glass layer. The predicted initial kink angle of 26 ° agrees very well with the average measured value of 280 . The measured path of the crack is also in very good agreement with the predicted path over about the first 120 microns of crack growth with increasing deviation observed beyond that.

A discretized dislocation model is used to assess the quasi-state equilibrium, crack tip emission and shielding of near-tip dislocations for Mo single crystals. As in a previous study for Fe-3 wt% Si, based partly on the Rice-Thomson criterion [12], this model leads to a failure prediction for Mo both consistent with the absence of an expected dislocation free zone and the observed toughness transition over the test temperature range. While cleavage is the failure mode in the semibrittle regimes of these two b.c.c. crystals, KIc values vary from 5 up to 60 MPa-m1/2 with an increase in test temperature. The equilibrium solution for both metals from the discrete dislocation model is reconnected with ordinary continuum theory through the CTOD and plastic zone size, as well as Weertman's hypothesis [19] of the nonredundant/redundant dislocation decomposition for near-tip microplasticity. The similarities in zeroth order successive approximation solutions derived for these two metals, with very disparate elastic anisotropies, suggests that such approaches may also be applicable to semibrittle ordered intermetallics.

Grain oriented 3 wt% silicon steel of 0.3 mm thickness was subjected to fracture toughness evaluation in the transition temperature regime at cross-head rates of 10−2, 10−4 and 10−6 ms−1. The observed values were compared to the Microscopically-Shielded Griffith Criterion (MGC) model [Acta metall. mater.40, 2861 (1992)] which had previously predicted fracture toughness for plasticity induced cleavage of single crystals. From this, it is shown that the MGC model gives reasonable predictions of fracture toughness for cleavage at different loading rates and test temperatures. An analytical approximation of the computer simulation gives the interesting result that fracture toughness predominantly has a two-parameter dependence for a given material. It is directly proportional to an exponential function of the true surface energy and inversely proportional to an exponential function of the yield strength. It is also demonstrated that grain oriented 3 wt% silicon steel represents a useful experimental material for fundamental fracture toughness investigations.

The in situ mechanical properties of the fibers, matrices and interfaces in an Al2O3 fiber-reinforced β-21S Ti alloy have been evaluated by using two nanoscale indentation tests. The Al2O3 fibers were coated with a refractory metal and Y2O3 duplex coating which served as a diffusion barrier during the HIPing used to produce the metal matrix composites. The hardness of the fibers, interfaces and matrix were obtained by performing a series of indentations across the fiber/matrix interface. The hardness decreases from the Al2O3 fiber to the Ti matrix. Additionally, by doing fiber pushout tests, the interfacial shear strength, interfacial frictional stress and mode II interfacial fracture energy were obtained. Scanning electron microscopy and X-ray mapping were used for microstructural and chemical analysis. The mechanical properties of the interfaces were related to their chemical composition. The interfacial fracture was found to occur at the interface between the refractory metal and the Y2O3. The mode II interfacial fracture energy in this system is more than two orders of magnitude lower than the interfacial fracture energy of Ti/Al2O3 without the diffusion barrier.