In this article, we review recent advances in the understanding and analysis of damage initiation and evolution in laminate structures with brittle outerlayers and compliant sublayers in concentrated loading. The relevance of such damage to lifetime-limiting failures of engineering and biomechanical layer systems is emphasized. We describe the results of contact studies on monolayer, bilayer, trilayer, and multilayer test specimens that enable simple elucidation of fundamental damage mechanics and yet simulate essential function in a wide range of practical structures. Damage processes are observed using post mortem (“bonded-interface”) sectioning and direct in situ viewing during loading. The observations reveal a competition between damage modes in the brittle outerlayers—cone cracks or quasiplasticity at the top (near-contact) surfaces and laterally extending radial cracks at the lower surfaces. In metal or polymeric support layers, yield or viscoelasticity can become limiting factors. Analytical relations for the critical loads to initiate each damage mode are presented in terms of key system variables: geometrical (layer thickness and indenter radius); material (elastic modulus, strength and toughness of brittle components, hardness of deformable components). Such relations provide a sound physical basis for the design of brittle layer systems with optimal damage thresholds. Other elements of the damage process—damage evolution to failure, crack kinetics (and fatigue), flaw statistics, and complex (tangential) loading—are also considered.

Ordered PbSe crystalline nanowire arrays have been successfully fabricated in the nanochannels of porous anodic alumina membrane by direct current electrodeposition. X-ray diffraction and selected area electron diffraction investigations demonstrate that the PbSe nanowires have a uniform cubic structure. Electromicroscopy results show that the nanowires are quite ordered with diameters of about 50 nm and lengths up to 5 micrometers. X-ray energy dispersion analysis indicate that Pb:Se is very close to 1:1. The optical absorption spectrum of these PbSe nanowires show that there exist two peaks at 280 and 434 nm, respectively, attribute to excitonic absorption peaks.

Interfacial phase and microstructure, solder hardness, and joint strength of Sn–3.5Ag–X (X = Cu, In, Ni; compositions are all in wt% unless specified otherwise) solder alloys were investigated. Considering the melting behavior and the mechanical properties, five compositions of Sn–3.5Ag–X solder alloys were selected. To examine the joint characteristics, they were soldered on under bump metallurgy isothermally at 250 °C for 60 s. Aging and thermal cycling (T/C) were also performed on the solder joint. The interfacial microstructure of the joint was observed by scanning electron microscopy. X-ray diffraction and energy dispersive x-ray analyses were made toidentify the type of solder phase and to measure compositions. Excessive growth of an interfacial intermetallic layer in the Sn–3.5Ag–6.5 In solder joint led to a brittle fracture. In the other four solder joints, ductile fractures occurred through the solder region and the solder hardness was closely related with the joint strength.

The epitaxial growth of KTiOPO4 (KTP) films on different natural faces of KTi1-xGexOPO4 substrates was studied. The growth on faces (100) and (201) is generally of high quality, irrespective of the growth time or concentration of germanium in the substrates. On the other hand, the epitaxial growth on the face (101) is always of poor quality, and the defects are pyramids, even when the germanium content in the substrate is low and the growth time is short. The films on faces (011) and (110) generally have small hillocks as defects and for high concentrations of Ge in the crystals some cracks begin to appear. The film thickness, depending on the growth time and the face considered was measured by scanning electron microscopy (SEM) using backscattered electrons. The diffusion of germanium from the substrate to the film is very low, as demonstrated by electron probe microanalysis measurements and SEM observations. The difference in the refractive indices ny and nz of KTP and KTi0.92Ge0.08OPO4 are on the order of 0.01, which could be enough to produce wave guides. Finally, it was observed that the second harmonic generation response of KTP substituted with Ge decreases as the Ge content in the crystal increases.

Ni/8 mol% Y2O3-stabilized zirconia cermets are used in thin-film electrolyte solid-oxide fuel cells as support substrates. Rapid oxidation of the metallic Ni can cause failure of the substrate and of the whole system. The rate of Ni oxidation in air and in an inert atmosphere containing water vapor was determined as a function of temperature between 500 and 950 °C. A logarithmic rate law describes the oxidation kinetics in air, whereas a linear rate law fits the first branch of the curve of the experimental data in a humidified inert atmosphere. The substrate exhibits no significant mechanical degradation after uniform oxidation under moderate conditions. However, the observed bending of the samples after oxidation in humidified argon, due to the nonuniform oxidation, can cause damage to fuel cell

The evolution of interfacial microstructure of eutectic SnAgCu and SnPb solders on Al/Ni(V)/Cu thin films was investigated after various heat treatments. In the eutectic SnPb system, the Ni(V) layer was well protected after 20 reflow cycles at 220 °C. In the SnAgCu solder system, after 5 reflow cycles at 260 °C, the (Cu,Ni)6Sn5 ternary phase formed and Sn was detected in the Ni(V) layer. After 20 reflow cycles, the Ni(V) layer disappeared and spalling of the (Cu,Ni)6Sn5 was observed, which explains the transition to brittle failure mode after ball shear testing. The different interfacial reactions that occurred in the molten SnAgCu and SnPb systems were explained in terms of different solubilities of Cu in the two systems. The dissolution and formation of the (Cu,Ni)6Sn5phase were discussed on the basis of a Sn–Ni–Cu phase diagram. In the solid-state aging study of the SnAgCu samples annealed at 150 °C for up to 1000 h, the Ni(V) layer was intact and the intermetallic compound formed was Cu6Sn5 and not (Cu,Ni)6Sn5, which is the same as was observed for the eutectic SnPb system.

The morphology and composition of MgO films grown on single-crystalline diamond (100) have been studied. MgO thin films were deposited in the substrate temperature range from room temperature (RT) to 723 K by means of electron beam evaporation using a MgO powder source. Atomic force microscopy images indicated that the film grown at RT without O2 supply was relatively uniform and flat whereas that deposited in oxygen ambient yielded higher growth rates and rough surface morphologies. X-ray photoelectron spectroscopy analyses demonstrate that the MgO film deposited at RT without O2 has the composition closest to that of the stoichiometric MgO and that a thin contaminant layer composed mainly of magnesium peroxide (before etching) or hydroxide (after etching) was unintentionally formed on the film surface, respectively.These results will be discussed in relation to the interaction among the evaporated species and intentionally supplied oxygen molecules at the growth front as well as the interfacial energy between diamond and MgO.

In this work, (Ba1−xCex)Ti1−x/4(VTi)x/4O3 ceramics with x = 0.02, 0.04, 0.06, and 0.08 (VTi denotes titanium vacancies) were synthesized by the mixed-oxide method. The results of x-ray diffraction analysis and scanning electron microscopy show that all the samples are monophasic. The crystalline structure can be indexed as tetragonal for the samples with x ≤ 0.06, but as cubic for x = 0.08. Three phase transitions were observed in the temperature dependence of the dielectric permittivity, similar to those observed in pure BaTiO3, and the three phase transition temperatures (Tc, T1, and T2) shifted to lower temperatures with the rates of −18, −12, and −7 K per molar percentage of Ce3+, respectively. This is quite different from that observed in BaTiO3 with Ce substitution at the Ti-site, in which Tc shifted to a lower temperature, and T1 and T2 to higher temperatures. The permittivity maximum increased with increasing Ce content, which is mainly attributed to an increase in the grain size.

GaN films were produced by the chemical solution deposition method (CSD) using two different precursors—gallium dimethyl amide (GDA; containing gallium–nitrogen bonds) and gallium isopropoxide (GIP; containing gallium–oxygen bonds). Pyrolysis of the GDA film at 600 °C produced a continuous layer of GaN grains with a single orientational relation with the substrate [GaN (0001) ∥ Al2O3 (0001) and GaN (1010) ∥ Al2O3 (1120)], and an overlying polycrystalline film. At temperatures greater than 600 °C, the oriented grains consumed the polycrystalline layer via an evaporation–condensation mass transport. Pyrolysis of the GIP films at 600 °C produced a continuous layer of gallium oxynitride having the corundum structure [i.e., α–Ga2O(3−x)N2/3x] with an epitaxial relation to the substrate (α–Ga2O(3−x)N2/3x[0001] ∥ Al2O3 [0001] and α–Ga2O(3−x)N2/3x [1010] ∥ Al2O3 [1120]), and an overlaying polycrystalline gallium oxynitride film with a spinel structure. Increasing temperature caused growth of oriented grains in contact with the substrate and conversion of the oxynitride to wurtzite GaN at 800 °C. Room-temperature (300 K) and low-temperature(77 K) photoluminescence measurements behaved similarly to metal-organic chemical vapor deposition based GaN with additional photoluminescence most likely due to nitrogen vacancy impurities.

Preferred-orientated 4H–SiC nanocrystalline films on silicon substrates were successfully prepared by the pyrolysis of the polyimide Langmuir–Blodgett films containing nanometer-sized amorphous silicon nitride powders. Fourier-transform infrared spectra revealed 4H–SiC nanoparticles with interfacial silicon oxide. Ultraviolet photoluminescence with energies above the band gap of bulk 4H–SiC was observed from the films in which the mean size of 4H–SiC particles was 10 nm, while no photoluminescence was observed from the films in which the mean size of particles was 17 nm. A quantum confinement/luminescence center model is suggested to explain the origin of the ultraviolet luminescence.

The microstructure of BaTiO3 thin films, epitaxially deposited on (001) MgO by pulsed laser ablation, has been investigated by transmission electron microscopy. The films are always c-axis-orientated, but dislocations, {111} stacking faults, and antiphase boundaries are frequently observed. Conventional TEM and high-resolution microscopy allow one to deduce the Burgers vectors of dislocations as b1 = 〈100〉 or b2 = 〈110〉, both being perfect dislocations. Most extrinsic stacking faults are ending at 1/3〈112〉 or 1/3〈111〉 partial dislocations; the displacement vector of the antiphase boundaries is 1/2〈101〉. Studying the interfacial structure by means of zone images taken along [100] and [110] shows that the misfit is mainly released by dislocations with Burgers vectors of 1/2〈110〉 and 1/2〈101〉.

Phase transformations in synthetic hexacelsian were investigated by hot-stage transmission electron microscopy. A second phase transformation from an orthorhombic to hexagonal structure was identified in the synthetic hexacelsian at approximately 700 °C. The hexacelsian was found to exhibit a sequence of phase transformations on heating of hexagonal (P63/mcm)–orthorhombic (Immm)–hexagonal (P6/mmm). Antiphase domain boundaries, which were observed in P63/mcm and Immm phases, were absent in the P6/mmm phase. Crystal symmetries of the three phases were determined by convergent beam electron diffraction, and space group symmetries were derived by comparison of experimental selected area electron diffraction patterns with computer-simulated patterns.

Cold isostatic pressing (CIP) is often used in the compaction of nano-sized powders. For technological reasons, however, uniaxial pressing prior to CIP takes place. This paper reveals the first quantitative measurements of density gradients within and the asymmetric sintering response of nanoscale zirconia compacts formed by (i) simple uniaxial compaction and (ii) specific ratios of uniaxial and CIP pressure. We find that CIP forms an exterior “skin” of higher but variable surface density and decreases the width of the density distribution. It does not eliminate density gradients; nonuniform shrinkage still occurs during sintering. The high- and low-density zones (the moving and fixed ram ends, respectively) that form during uniaxial compaction are reversed during CIP. Considering both density distribution width and spring-back cracking, the “best” uniaxial-CIP pressure combination is 1–20 ksi for this particular powder and an L/D of 1.0. The greater final compaction of the low-density zone during CIP causes relatively large variations in final dimensions (nearly 400 microns) in spite of the smaller density distribution width. The usually neglected uniaxial pressing step has definite technological impacts on the production of nanostructured components via compaction.

A novel approach was undertaken in producing porous AlN microelectronics tapes with high thermal conductivity and low dielectric constant. This method involved polymer microspherical powders used as a sacrificial mold to introduce controlled porosity into the green tapes during pyrolysis. The Al2O3-rich porous green tapes were then reaction sintered at 1680 °C for 12 h to create porous AlN tapes. This work builds upon a previously developed novel reaction sintering process that densified and converted Al2O3-rich tapes (Al2O3–20 wt% AlN–5 wt% Y2O3) to AlN tapes at a relatively low sintering temperature of 1680 °C. The sintering behavior of the porous tapes was investigated, and the effects of the microsphere particle size and volume addition were studied. The microspheres successfully contributed to the significant reduction of tape density by porosity, and this contributed to lowering its dielectric constant. Dielectric constants of the AlN tapes were reduced to about 6.8 to 7.7 while thermal conductivity values were reasonable at about 46 to 60 W/mK. Coefficient of thermal expansion (CTE) values showed a linear trend according to phase composition, with the porous AlN tapes exhibiting CTE values of 4.4 × 10−6 to 4.8 × 10−6/°C, showing good CTE compatibility with silicon at 4.0 × 10−6/°C. The added porosity did not significantly affect the CTE values.

CdTe:Zn:V crystals grown by the seeded Bridgman method in microgravity conditions during the STS95-Spacelab-AGHF-1 mission and in the ground laboratory (l-g) were analyzed and compared. The results obtained clearly show that the structural quality of the space crystal is better. Density of inclusions, concentration of dislocations, and presence of stresses are lower in the microgravity-grown (μ-g) crystal. The l-g crystal contains twins and grains from the beginning of the growth process, that is, from the near-seed region. In general, the concentration of inclusions and amount of segregated impurities on the l-g crystal are larger than in the μ-g crystal. X-ray rocking curves and low-temperature photoluminescence spectra demonstrate the relatively high quality of both crystals on a microscale at the beginning of the growth and show that the l-g conditions were worse at the end. The results of this investigation demonstrate a positive role of contactless growth and μ-g conditions in the melt in suppressing the creation of inclusions and dislocations.

The joining of a Ti3SiC2 ceramic with a Ti–6Al–4V alloy was carried out at the temperature range of 1200–1400 °C for 15 min to 4 h in a vacuum. The total diffusion path of joining was determined to be Ti3SiC2/Ti5Si3Cx/Ti5Si3Cx + TiCx/TiCx/Ti. The reaction was rate controlled by the solid-state diffusion below 1350 °C and turned to the liquid-state diffusion controlled with a dramatic increase of parabolic rate constant Kp when the temperature exceeded 1350 °C. The TiCx tended to grow at the boundarywith the Ti–6Al–4V alloy at a higher temperature and longer holding time. TheTi3SiC2/Ti–6Al–4V joint is expected to be applied to implant materials.

A statistical method of the design of experiments and analysis of variance (ANOVA) was used to obtain optimized sputtering conditions for oriented ZnS thin films doped with 5% manganese on glass substrates. The effects on the five sputtering factors—substrate temperature, radio frequency power, sputtering pressure, sputtering time, and pre-sputtering time—were simultaneously investigated by using the design of experiments and ANOVA. Through only 16 experiments, it was proved statistically at the 5% level that the substrate temperature was the only significant control factor. ZnS films were then deposited under the optimized sputtering conditions on fused quartz and thermally annealed in a reducing ambient (5% H2 diluted in Ar) at 500, 600, 700, and 800 °C. It was found that the crystallinity and triboluminescence intensity of the films were enhanced by postannealing up to 700 °C.

The growth and structure of the Co1−xNixO series of single crystals with 0 ≤ x ≤ 1 were investigated with the goal of achieving a single-phase crystal over several centimeters of bulk growth. The single crystals were grown via the floating zone method controlling the partial pressure of oxygen to prevent secondary phase precipitation. The resulting crystals were single phase for all compositions. CoO was a single-domain crystal but contained microvoids. The lattice parameters followed a rule-of-mixtures trend, but the coefficient of thermal expansion exhibited a maximum in the middle of the solid solution, which was attributed to enhanced vacancy formation.

Nanostructured montmorillonite/poly(diallyldimethylammonium chloride) multilayer thin films were fabricated up to 100 layers thick by stepwise alternating polyelectrolyte and clay deposition from solution. The structure and morphology of the films were characterized by x-ray diffraction, ellipsometry, atomic force microscopy, and quartz crystal microbalance ex situ and in situ measurements. The mechanical properties were tested by nanoindentation. The hardness of the multilayer thin film was 0.46 GPa. The thin film's modulus was correlated to its ordering and anisotropic structure. Both hardness and modulus of this composite film were higher than those of several other types of polymer thin films.

The fundamental relations used in the analysis of nanoindentation load–displacement data to determine elastic modulus and hardness are based on Sneddon's solution for indentation of an elastic half-space by rigid axisymmetric indenters. It has been recently emphasized that several features that have important implications for nanoindentation measurements are generally ignored. The first one concerns the measurement of the contact depth, which is actually determined by using a constant value ε = 0.75 for the geometry of a Berkovich indenter and for any kind of material, whereas the reality is that ε is a function of the power law exponent deduced from the analysis of the unloading curve. The second feature concerns the relation between contact stiffness, elastic modulus, and contact area, in which a correction factor γ larger than unity is usually ignored leading to a systematic overestimation of the area function and thus to errors in the measured hardness and modulus. Experimental measurements on fused quartz are presented that show the variation of ε with the geometry of the tip–sample contact; that is to say with the contact depth, as well as the existence of the correction factor γ, as predicted in some recent articles. Effects of both ε and γ on harness and modulus measurements are also shown.