In this research, the influences of the oxygen impurity contained in the commercially available nitrogen gas on the reactions of chromium pellets with nitrogen were investigated in the temperature range 600–1350 °C. A small amount of oxygen competed with the majority N2 to react with chromium in the annealing process. Analyzing the in situ oxygen partial pressure changes during annealing proved that the dissolution of oxygen in Cr and/or resultant CrxN (CrN or Cr2N) was exothermic and the solubility decreased with increasing temperature. It was found that the oxygen partial pressure decreased drastically to about 10−22 atm when specimens were annealed at 600 °C compared to a mere 10−5 atm for a blank test, while its value increased with temperature. The oxidation involved simultaneous dissolution of oxygen in specimens and formation of oxide scale. Moreover, comparing the aforementioned results with those obtained from additional annealing experiments preformed in argon gas showed that the formation of Cr2O3 might stem mainly from oxidation of the resultant nitrides instead of the metallic chromium.

Oxidation behavior of Ni-toughened reactively sputtered composite thin films of nanocrystalline TiN and amorphous SiNx [denoted as nc-TiN/a-SiNx(Ni)] was explored to understand the oxidation mechanism. The films were deposited on silicon substrate using a magnetron sputtering technique. Oxidation was carried out from 450 °C up to 1000 °C. The nature of the oxidation was determined using x-ray photoelectron spectroscopy. The microstructure of the oxidized films was studied using grazing incidence x-ray diffraction. The topography was characterized using atomic force microscopy. It was determined that the oxidation of the nc-TiN/a-SiNx(Ni) thin film proceeds primarily through a diffusion process, in which nickel atoms diffuse outward and oxygen ions inward. The oxidation takes place by progressive replacement of nitrogen with diffused oxygen. Five regions were identified in the oxidized layer from surface into the film. For films doped with 2.1 at.% Ni, a threshold temperature of 850 °C was determined, below which, excellent oxidation resistance prevails but above which, oxidation takes place at exponential rate, accompanied by abrupt increase of surface roughness.

The anodic films formed on AZ91D magnesium alloy after heat treatment were analyzed and their electrochemical properties were investigated. The results showed that the cooling rate had a significant influence on the microstructure evolution of the AZ91D magnesium alloy after solution heat treatment at 440 °C for 20 h in N2 atmosphere. A single-phase microstructure was observed when the alloy was quenched in water after solution heat treatment. However, a duplex structure consisting of both α and β phases was found if the solution-annealed alloy was cooled in air. The differences in microstructure of the heat treated AZ91D magnesium alloy gave rise to a significant change in the property of the anodic film formed in 3 M KOH + 0.21 M Na3PO4 + 0.6 M KF + 0.15 M Al(NO3)3 electrolyte. During the early stage of anodization, for the as-cast alloy, inhomogeneous anodic films were formed exhibiting relative rough surface appearances. A rather smooth anodic film was formed for the solution-annealed AZ91D magnesium alloy either followed by air cooling or water-quenched. The surface and cross section appearance was almost the same regardless of the prior heat treatment after anodizing for 20 min. The corrosion resistances of the various anodized AZ91D magnesium alloy were evaluated and compared by employing electrochemical impedance spectroscopy (EIS). The results demonstrate that the anodic film formed on the water-quenched AZ91D magnesium alloy had a slightly higher polarization resistance than that formed on the as-cast alloy. The highest polarization resistance of anodic film was found for that formed on annealed and air-cooled alloy. The presence of Al-rich β phase on the surface gave rise to the formation of a more protective anodic film which consisted of a great amount of Al2O3.

Nickel has been widely used as an under-bump metallization (UBM) material in the microelectronics industry. The solid-state reaction between the eutectic SnAg solder bumps and three thicknesses of Ni/Cu UBM was investigated, with 5 μm-Cu/3 μm-Ni, 3 μm-Cu/2 μm-Ni, and 0 μm-Cu/1 μm-Ni. It was found that the shear strength of the solder bumps decreased after the solid-state aging at 150 °C for 200 h, and it did not change much after it was prolonged for 500 and 1000 h. Aging of the Ag3Sn intermetallic compound (IMC) and grain growth of the solder are responsible for the decrease in the shear strength. Furthermore, the shear test results indicated that the fracture mode switched from ductile to brittle for the solder bumps with 1 μm Ni after aging longer than 200 h, causing the strength of the solder to decrease abruptly. This is attributed to the consumption of the peripheral Ni layer after the solid-state aging for 1000 h. The Ni consumption rate was measured to be 0.02 μm/h1/2 at 150 °C.

Eu3+-doped zirconia nanopowders were prepared by the sol-gel technique using two different methods, based on the hydrolysis of zirconium n-propoxide, producing tetragonal and monoclinic zirconia under different preparation conditions. A detailed microstructure characterization was performed through wide angle x-ray scattering, small angle x-ray scattering, trasmission electron microscopy, and nitrogen physisorption measurements. The possible influence of the zirconia crystalline phases and particle sizes on the luminescence properties of the lanthanide ion was investigated. A detailed analysis of the emission spectra of the samples suggested that the dopant Eu3+ ions replace the Zr4+ ions in the zirconia crystal lattice. Moreover, samples prepared by the two different methods were characterized by different decay times of the Eu3+ ion luminescence.

A preceding study of the competition between fracture modes in monolithic brittle materials in cyclic loading with curved indenters in liquid environments is here extended to brittle layers on compliant substrates. The fracture modes include outer and inner cone cracks and radial cracks that initiate from the near-contact zone and penetrate downward. Outer cone cracks are driven by stresses from superposed Hertzian and plate flexure fields; inner cone cracks also grow within these fields but are augmented by mechanical driving forces from hydraulic pumping into the crack fissures. Radial cracks are augmented by mechanical driving forces from developing quasiplasticity zones beneath the indenter. Basically, the crack-growth rates are governed by a crack velocity relation. However, the hydraulic and quasiplastic mechanical forces can cumulate in intensity with each cycle, strongly enhancing fatigue. Plate flexure generates compressive stresses at the top surface of the brittle layer, somewhat inhibiting the initiation, and tensile stresses at the lower surface, strongly enhancing the far-field propagation. The tensile stresses promote instability in the crack propagation, resulting in through-thickness penetration (failure). Experiments on a model bilayer system consisting of glass plates bonded to thick polycarbonate bases are presented as an illustrative case study. In situ observations of the crack evolution from initial growth to failure reveal that each fracture mode can dominate under certain test conditions, depending on plate thickness, maximum load, and sphere radius. Implications concerning the failure of practical layer systems, notably dental crowns, are discussed.

Numerical analysis is conducted to clarify the formation mechanisms of silicide nanoparticles synthesized in an induction thermal plasma maintained at atmospheric pressure. The induction thermal plasma is analyzed by an electromagnetic fluid dynamics approach, in addition to a multi-component co-condensation model, proposed for the silicide nanoparticle synthesis. In the Cr–Si and Co–Si systems, silicon vapor is consumed by homogeneous nucleation and heterogeneous condensation processes; subsequently, metal vapor condenses heterogeneously onto liquid silicon particles. The Mo–Si system shows the opposite tendency. In the Ti–Si system, vapors of silicon and titanium condense simultaneously on the silicon nuclei. Each system produces nanoparticle diameters of around 10 nm, and the required disilicides, with the stoichiometric composition, are obtained. Only the Ti–Si system has a narrow range of silicon content. The numerical analysis results agree with the experimental findings. Finally, the correlation chart, predicting the saturation vapor pressure ratios and the resulting silicon contents, is presented for estimation of nanoparticle compositions produced in the co-condensation processes.

A study was made of radial crack evolution in curved brittle layers on compliant support substrates. Three-dimensional boundary element analysis was used to compute the stepwise growth of radial cracks that initiate at the bottom surfaces of glass on polymeric support layers, from initiation to final failure. The algorithm calculates reconstituted displacement fields in the near-tip region of the extending cracks, enabling direct evaluation of stress-intensity factors. Available experimental data on the same material systems with prescribed surface curvatures were used to validate the essential features of the predicted crack evolution, particularly the stability conditions prior to ultimate failure. It was shown that the critical loads to failure diminish with increasing surface curvature. Generalization of the ensuing fracture mechanics to include alternative brittle-layer/polymer-substrate systems enabled an explicit expression for the critical load to failure in terms of material properties and layer thicknesses. Implications concerning practical layer systems, particularly dental crowns, are briefly discussed.

With the potential to map mechanical properties of heterogeneous materials on a micrometer scale, there is growing interest in nanoindentation as a materials characterization technique. However, nanoindentation has been developed primarily for characterization of hard, elasto-plastic materials, and the technique has not been validated for very soft materials with moduli less than 5 MPa. The current study attempted to use nanoindentation to characterize the elastic moduli of soft, elastomeric polydimethylsiloxane (PDMS) samples (with different degrees of crosslinking) and determine the effects of adhesion on these measurements using adhesion contact mechanics models. Results indicate that nanoindentation was able to differentiate between elastic moduli on the order of hundreds of kilo-Pascals. Moreover, calculations using the classical Hertz contact model for dry and aqueous environment gave higher elastic modulus values when compared to those obtained from unconfined compression testing. These data seem to suggest that consideration of the adhesion energy at the tip-sample interface is a significantly important parameter and needs to be taken into account for consistent elastic modulus determination of soft materials by nanoindentation.

Measurement of electromigration parameters in the lead-free solder SnAg3.5 was carried out by utilizing U-groove solder lines and atomic force microscopy in the temperature range of 100–150 °C. The drift velocity was measured, and the threshold current densities of the SnAg3.5 solder were estimated to be 4.4 × 104 A/cm2 at 100 °C, 3.3 × 104 A/cm2 at 125 °C, and 5.7 × 103 A/cm2 at 150 °C. These values represent the maximum current densities that the SnAg3.5 solder can carry without electromigration damage at the three stressing temperatures. The critical products for the SnAg3.5 solder were estimated to be 462 A/cm at 100 °C, 346 A/cm at 125 °C, and 60 A/cm at 150 °C. In addition, the electromigration activation energy was determined to be 0.55 eV in the temperature range of 100–150 °C. These values are very fundamental for current carrying capability and mean-time-to-failure measurement for solder bumps. This technique enables the direct measurement of electromigration parameters of solder materials.

Barium titanate zirconate, Ba(Ti1−xZrx)O3 (0 ≤ x ≤ 0.25), thin films were deposited via the chemical solution deposition (CSD) method directly on copper foils. The films were processed in a reductive atmosphere containing nitrogen, water vapor, and hydrogen gas at 900 °C to preserve the metallic copper substrate during crystallization. Increasing the fraction of BaZrO3 revealed several effects, including an increase in unit cell dimensions, a decrease in both the temperature and value of the maximum permittivity, as well as a decrease in the average grain size of the films. The decrease in the relative permittivity was attributed to a grain size effect as opposed to zirconium substitution. In film compositions containing 25 mol% BaZrO3, the permittivity below Tmax became dispersive, and the ferroelectric transitions became increasingly diffuse. These characteristics suggest relaxor-like behavior. The dielectric tunability of Ba(Ti1−xZrx)O3 was studied at room temperature and at Tmax for each composition. There was little variation in the tunability with measurement temperature; however compositions that were ferroelectric at room temperature saw a decrease in hysteresis at Tmax, and all compositions showed an increase in permittivity.

The mechanical alloying method was used to synthesize a single glassy phase of Co65Ti20W15 alloy powders, using a high-energy ball mill. The glass transition temperature of the end-product, which was obtained after 173 ks of milling time, lies at 786 K, whereas the crystallization takes place at 878 K through a single sharp exothermic peak with an enthalpy change of crystallization of −4.37 kJ/mol. The reduced glass transition temperature was found to be 0.51. This glassy alloy powders exhibit a very large supercooled liquid region (92 K) for a ternary metallic system. The spark plasma sintering method was used to consolidate the glassy powders under an argon gas atmosphere at 843 K with a pressure of 19.6–38.2 MPa. The sample that was consolidated within 180 s maintains its chemically homogeneous glassy structure with a relative density of above 99.6%. Neither the supercooled liquid region nor crystallization temperature was affected by such a rapid consolidation procedure. Thus, the thermal stability of the bulk glassy sample is almost identical with the original glassy powders. The Vickers microhardness of the bulk glassy Co65Ti20W15 reveals high values, ranging between 8.69 and 8.83 GPa. The fabricated bulk glassy alloy shows high compressive strength of 2.44 GPa with a Young’s modulus of 176.81 GPa. Neither yielding stress, nor plastic strain could be detected for this glassy alloy, which its elastic strain is 1.33%.

Sn–8Zn–3Bi solder paste and Sn–3.2Ag–0.5Cu solder balls were reflowed simultaneously on Cu/Ni/Au metallized ball grid array (BGA) substrates. The correlation between microstructural evolution and the electrical resistance of the joints under various testing conditions of reflow cycles and heat treatment was investigated. The electrical resistance of the Sn–Ag–Cu joints without Sn–Zn–Bi was also conducted for comparison. The average resistance values of Sn–Ag–Cu and Sn–Ag–Cu/Sn–Zn–Bi samples changed, respectively, from 7.1 (single reflow) to 7.3 (10 cycles) mΩ and from 7.2 (single reflow) to 7.6 (10 cycles) mΩ. Furthermore, the average resistance values of Sn–Ag–Cu and Sn–Ag–Cu/Sn–Zn–Bi samples changed, respectively, from 7.1 (aging 0 h) to 7.8 (aging 1000 h) mΩ and from 7.2 (aging 0 h) to 7.9 (aging 1000 h) mΩ. It was also noticeable that the average resistance values of Sn–Ag–Cu/Sn–Zn–Bi samples were higher than those of Sn–Ag–Cu samples in each specified testing condition. The possible reasons for the greater resistance exhibited by the Sn–Zn–Bi incorporated joints were discussed.

Zinc oxide (ZnO) films doped with aluminum (Al) were deposited with a pulsed laser deposition technique to characterize the charge compensation phenomena in ZnO. In particular, oxygen radical (O*) irradiation during film deposition was used to modify the oxygen stoichiometry. Irradiation with O* decreased electron concentration in Al-doped ZnO. The lattice parameter of the resultant films also varied with the growth conditions. However, no obvious correlation between electron concentration and lattice parameter was found. The self-diffusion coefficients indicated the presence of non-equilibrium defects. The properties of the films are discussed from the viewpoint of non-equilibrium compensated defects detected in the diffusion measurements.

The one-step synthesis of barium titanate (BaTiO3) nanoparticles was studied by employing a low-pressure spray pyrolysis (LPSP) method. The effects of temperature, pressure, and the addition of urea to the precursor were investigated experimentally. The results were compared with the experimental data of the conventional (atmospheric) spray pyrolysis method. It was shown that the BaTiO3 nanoparticles could be synthesized by the low-pressure method, while only spherical hollow particles with smooth surfaces could be produced by the conventional spray method. The addition of urea greatly improved the crystal growth and particle breakup due to extra heat supplied during the combustion reaction coupled with the evolution of gases. The dispersity of nanoparticles increased with the quantity of urea and with a decrease in pressure. The possible mechanism of the formation of BaTiO3 nanoparticles in the LPSP process was also proposed.