Atom probe tomography and transmission electron microscopy are used to analyze magnetron-sputtered MoS2 films containing Ti and Au/Sb2O3 as a model system for tribological coatings. Transmission electron microscopy characterization showed that the Ti–MoS2 film is dense and featureless whereas Sb2O3/Au–MoS2 film is less dense and have columnar morphology. Three-dimensional atom probe reconstructions revealed that the Ti–MoS2 films have a homogeneous composition and contain about 15 at.% Ti, which is uniformly distributed throughout the MoS2 matrix without any evidence of Ti precipitation. Sb2O3/Au–MoS2 films also showed homogeneous distribution of Sb2O3 throughout the MoS2 matrix and the presence of Au-rich precipitates. The complementary techniques of atom probe tomography and transmission electron microscopy indicate that Ti and Sb2O3 incorporation in the deposition of MoS2 produces amorphous microstructures, whereas the addition of Au forms nano-sized and well-dispersed precipitates.

Field trials were conducted to evaluate the season long population dynamics and location (in leaf or on leaf surface) of an antibiotic resistant strain of the bacterium Pseudomonas syringae pv. tagetis (PST) applied to Canada thistle leaves. An application preceding 2 to 3 d of hot dry weather was compared to an application preceding 2 to 3 d of cool wet weather. Leaf samples were taken weekly to assess the population of PST found inside the leaves and on the leaf surface. While PST populations initially differed, populations were similar for both treatments one week after application. While this suggests that environment did not have a major impact, weather conditions for testing this hypothesis were not ideal. Over the first 35 d of the experiment, little rainfall was observed. PST populations were low and stable. However, rain events over the 40 d that followed resulted in great oscillations in mean PST populations and in some cases significant population increases. During dry periods, internal and total PST populations differed significantly, suggesting the external populations played a major part in population composition. However, the two sampling periods that closely followed three consecutive days of rainfall indicated internal populations were not significantly different from the total, suggesting that internal populations played the primary role in population composition. The results of this research provide evidence that rain events lead to overall PST population increases and to greater proportions of PST inside Canada thistle leaves, suggesting that it is better to apply PST during wet periods than dry.

Canada thistle is resilient to many control tactics, especially in undisturbed sites. Such sites are suitable for slow acting biological control agents, such as the bacterium Pseudomonas syringae pv. tagetis (PST), because complete control is usually not required in the short term. A new method of introducing or intensifying PST infection of Canada thistle was investigated. Sap of naturally infected Canada thistle was extracted and applied in water plus Silwet L-77 organosilicone surfactant with a backpack sprayer to healthy Canada thistle plants in the field. Application variables of time of the season, spray volume, concentration, and frequency were studied. When practical field rates were applied, infected sap concentration and spray volume did not affect the level of disease observed. This suggests that PST applications could be practical at the field scale because a single application caused apical chlorosis. However, multiple applications proved beneficial because four consecutive weekly applications caused greater disease incidence (50%) than one or two applications (28% and 30%, respectively). Disease symptomology was greatest when PST was applied in mid-July rather than mid-June or mid-August. However, the levels of disease expression were not adequate to effectively suppress Canada thistle. Increased toxin production, either by finding ways to support higher PST populations or by selecting strains that produce more toxin per bacterial cell, would improve this system.

Hardness, elastic modulus, and stress directly influence the ability of tantalum carbide/amorphous hydrocarbon (TaC/a-C:H) thin films to enhance the wear-resistance of steel tribological component surfaces. Designed factorial experiments enabled an evaluation of the effects of acetylene flow rate (QC2H2), direct current bias voltage level (Vb), and substrate rotation rate (ωRot) during deposition on the mechanical properties of reactively sputtered TaC/a-C:H films. Significant relationships were found between compressive stress level and Vb, whereas hardness and elastic modulus were dependent primarily on Vb and secondarily on QC2H2 within the studied parameter space. It is proposed that effects of ion bombardment on the a-C:H phase during growth are responsible for property dependencies on Vb. Decreases in hardness and elastic modulus with increasing QC2H2 are attributed to increased hydrogen concentration and a concomitant decreased volume fraction of TaC crystallites in the films.

The properties of nanocomposite tantalum carbide/amorphous hydrocarbon (TaC/a-C:H) thin films depend closely on reactive magnetron sputtering deposition process conditions. The chemical composition and structure trends for TaC/a-C:H films were obtained as a function of three deposition parameters: acetylene flow rate, applied direct current (dc) bias voltage, and substrate carousel rotation rate. Films were deposited according to a 23 factorial experimental design to enable multiple linear regression modeling of property trends. The Ta/C atomic ratio, hydrogen content, total film thickness, TaC crystallite size, and Raman spectra were statistically dependent on acetylene flow rate, applied dc bias voltage, or both. Transmission electron microscopy revealed a nanometer-scale lamellar film structure, the periodicity of which was affected mostly by substrate carousel rotation rate. The empirical property trends were interpreted with respect to hypothesized growth mechanisms that incorporate elements of physical vapor deposition and plasma-enhanced chemical vapor deposition.

The friction and wear performance were correlated with the thermal stability of reactively sputtered Si–aC:H thin films containing various Si and H concentrations. The average steady-state friction coefficients as measured by dry sliding pin-on-disk tests decreased with increasing Si and H content. Furthermore, the films with high Si and H formed thick transfer films as compared to the films with little or no Si and H content. Minimums in average ball abrasion rate and average film wear rate were observed at the Si/C = 0.10 film composition. The most intense and distinct “graphitic” Raman peaks were collected from the Si/C = 0.10 transfer film debris. In addition, the Si/C = 0.10 film also had the most distinguishable graphitic Raman signature after annealing in air at 500 °C compared to the other Si–aC:H films, suggesting a possible relationship between the nature of transfer films resulting from dry sliding in air and the bulk films that were annealed in air.

The performance of rolling element bearings is enhanced by the application of nanocomposite coatings that are composed of metal carbides incorporated into an amorphous hydrogenated carbon matrix (MC/a-C:H). When applied to the rolling elements in tapered roller bearings, MC/a-C:H coatings were found to help increase fatigue life, rib-roller end scuffing resistance, and false brinelling resistance in poorly lubricated environments. This series of performance tests were conducted with both coated and uncoated rollers. The results are attributed to the minimization of adhesive interactions and desirable counterface micro-polishing due to the presence of the thin hard coatings on rollers in the bearings.

Silicon-incorporated amorphous hydrocarbon (Si-aC:H) films with varying Si contents were deposited onto a Ti interlayer on Si and steel substrates by reactive sputtering in an unbalanced magnetron sputtering system. The objective of this study was to measure and relate the structural, chemical, and mechanical properties of these Si-aC:H films. Transmission electron microscopy revealed that the Si-aC:H phase is amorphous and TiC exists at the Si-aC:H/Ti phase boundary for all compositions. Mechanical properties such as hardness, indentation modulus, and intrinsic stress decreased with increasing Si and H content in the films, for Si/C ≥ 0.04. XPS measurements suggested that this is most likely due to the decreasing presence of a C-C sp3 interlinked network, accompanied by an increase in C-H and Si-H bonds. This conclusion was supported by radial distribution functions obtained using extended electron energy-loss fine structure analysis (EXELFS).