D. L. Olson

Variation of color in titanium and zirconium nitride decorative thin films

The color variation in zirconium and titanium nitrides was investigated with respect to the atomic ratio between nitrogen and transition metals and with oxygen as the contaminant. The nitride thin films were deposited using cathodic arc evaporation. The stoichiometry of the films was varied through changes in nitrogen gas flow rate and total pressure in the deposition chamber. Thickness of all nitride films was controlled at 0.5 μm. Oxygen content in the thin films was correlated to their color. The reflectivity spectra of ZrN and TiN thin films were measured in the visible region of the spectrum and their color was quantified in the L*a*b* color system. Increasing the atomic ratio of nitrogen to transition metals causes the overall reflectivity of the gold-like color to decrease and the yellowness to increase. A change of the stoichiometry without a noticeable change of thin film color is wider for TiN than ZrN. The variation in oxygen contents results in the color change in the same direction as that of the variation of nitrogen content. Therefore, oxygen found in the nitride thin films behaves as nitrogen; it consumes free electrons from transition metal.

Hydrogen trapping in ferritic steel weld metal

Abstract A brief overview is given of the role of hydrogen trapping in hydrogen management of steel welding. The concept of hydrogen trapping is introduced in conjunction with efforts in reducing hydrogen cracking in steel welding. Appropriate selection of hydrogen traps offers the potential to control the content and distribution of hydrogen in steel weldments. The effectiveness of hydrogen traps through selective alloying in reducing the concentration of diffusible hydrogen during welding thermal cycles is evaluated, particularly in its use as a substitute for costly weld heat treatment practices. The relationship of weld metal microstructure and hydrogen contents to the effective use of hydrogen trapping elements is discussed. The fundamental aspects which control hydrogen content as well as hydrogen distribution in steel are discussed, such as the statistical thermodynamics and the transport of hydrogen in steel containing traps. As tools for investigating potential hydrogen traps, several experimental methods are discussed in relation to their applicability to characterise the physical nature of hydrogen traps. These methods include the hydrogen permeation technique and hydrogen thermal desorption analysis. Recent efforts to prevent hydrogen cracking in steel weldments through numerical computations require consideration of hydrogen trapping in the weld microstructure, and hence knowledge of applicable data of hydrogen trapping parameters is necessary for welding engineers to improve hydrogen management in steel welding.

Effect of Microstructure on Corrosion of Steels in Aqueous Solutions Containing Carbon Dioxide

Abstract The influence of microstructure on the corrosion rate of steels in a carbon dioxide (CO2)-containing aqueous solution was measured experimentally as a function of pH, temperature, and part...

Modeling of infiltration kinetics for liquid metal processing of composites

An equation for modeling the kinetics of liquid-metal infiltration into a porous compact has been developed. The model is based on considering a bundle of capillary tubes as an analog for the porous compact. A solution which describes a limiting form of behavior has been shown to be valid for small extents of infiltration relative to a hypothetical static state. The numerical solutions of the dimensionless infiltration-equation have been used to delineate conditions for which limiting solutions are valid. A dimensionless group λ has been shown to be capable of classifying the behavior into two limiting cases: either “inviscid-flow“, λ 10-2, or “viscous-flow“, λ > 102. It would appear that for capillary-tube (pore) radii less than 100 µ-m and for conditions where the compact is wetted by the liquid metal, A is likely to be >100 and therefore correspond to a “viscous-flow system“. Also, an infiltration-rate parameter, ϕ, has been selected which can be used to assess the effects of alloying additions to the liquid-metal infiltrant. This parameter can therefore provide for the selection of alloy infiltrants, surface preparation modification, and processing parameters such as temperature, time of infiltration, and pore size of compact in regard to the processing of composites. Although the model concept (capillary-tube bundle) is recognized as being deficient in not treating the compact as what it really is (a porous medium), the work presented was intended to quantify the limiting behavior of the capillary-tube-bundle approach which has been used in the past.

Hydrogen-assisted processing of materials

Abstract Under certain conditions, hydrogen can degrade the mechanical properties and fracture behavior of most structural alloys; however, it also has some positive effects in metals. Several current and potential applications of hydrogen for enhancing the production and processing of materials are reviewed. These include thermohydrogen processing (THP) and forming of refractory alloys, processing of rare earth-transition metal magnets by hydrogen decrepitation (HD) and hydrogenation–decomposition–desorption–recombination (HDDR), hydrogen-induced amorphization (HIA) and microstructural refinement, extraction of elements from ores and alloys, and the use of hydrogen as a reducing gas for welding and brazing. Hydrogen is found to enhance the formability, microstructure and properties of a large variety of materials, including steels, Ti-based alloys and metal matrix composites (MMCs), refractory metals and alloys, rare earth-transition metal alloys, metalloid-containing metallic glasses, etc.

Development of a Predictive Model for Activation-Controlled Corrosion of Steel in Solutions Containing Carbon Dioxide

Abstract Corrosion of steel in carbon dioxide (CO2)-containing solutions is considered a chemical reaction-controlled process. A corrosion rate equation was derived on the basis of fundamental reaction rate theory and compared to empirically determined relationships reported in the literature. The predictive equation was developed as a function of pH, partial pressure of CO2 (PCO2), and temperature. The equation allows the inclusion of other variables, such as flow, impurities, inhibitors, and steel microstructure, through the reaction constant. The application limit for this equation extends to the point where corrosion becomes diffusion-controlled as a result of the formation of stable corrosion products on the steel surface.

A thermodynamic criterion to predict wettability at metal- alumina interfaces

Metals are known to wet ceramics by chemical bond formation. Existing theories, using reaction thermodynamics, can predict the relative wetting trends in wetting systems but fail to distinguish between the wetting and non wetting systems. Wetting is considered as a surface phenomenon, and the spontaneity of wetting is controlled by ΔGW, a thermodynamic term defined here as the Gibbs free energy of wetting. A model that treats wetting as a reaction between the surface phase of the ceramic and the molten metal is presented to calculate ΔGW. The model is used to predict wetting tendencies of various molten metals on α-alumina surfaces. The predictions are compared with previously published results, as well as with the experimental results of this study. Experimental wettability parameters were measured using a capillary rise apparatus. Measurements were made for various metals wetting an aluminum-oxide surface. Based on this model, a thermodynamic wetting map that delineates wetting and non wetting regimes is drawn. A map of this nature can be used advantageously in ceramic joining and metal-matrix composites applications.

A review of extractive processes for lithium from ores and brines

A review of the methods and techniques used to win lithium from pegmatites, natural brines and clays. Additionally, the present procedures for extracting lithium metal from the chloride are outlined with purification and analytical methods discussed. Areas where research would be of benefit are pointed out in those circumstances where additional information will improve process efficiency or increase reserves.

Influence of solidification on the microstructural evolution of nickel base weld metal

Abstract The effect of segregation resulting from solidification on the microstructural evolution of nickel base alloys was investigated. Two different groups of alloys were produced to simulate either the Hastelloy C type or the Inconel 625/718 type of alloys. Gravitational thermal analysis welding was performed on these experimental alloys and the extent of microsegregation in the weld metal was determined. Using composition profiles obtained from solidified microstructures, predictions of the phase stability of these microstructures were made based on metal d-level (Md) calculations. The maximum Md values obtained in these microstructures were compared with those critical to the formation of topologically close-packed (TCP) phases such as sigma, P, and Laves. These profiles showed an increase in the Md level in the interdendritic regions which was correlated to the formation of TCP phases.

Characterization of hard chromium nitride coatings deposited by cathodic arc vapor deposition

Abstract CrN coatings of various stoichiometries, were deposited on 304 stainless steel and M4 tool steel by planar cathodic arc vapor deposition (CAVD). This investigation concentrated on the effects of the CAVD process parameters and the resulting mechanical properties. To achieve this, several properties of the deposited films were studied; hardness, adhesion, coefficients of friction, residual stress, texture and stoichiometry. Hardness and adhesion were measured by low load Vickers indentation and diamond scratch testing respectively. The adhesion exhibited an inverse relationship with respect to the hardness of the CrN coatings. Hardness values averaged 17.7 GPa while maximum adhesion values of the CrN coatings exceeded 85 N using a 0.2 mm diamond stylus. Typical values for the coefficients of friction remained lower than 0.10 (diamond against CrN). Residual stress was measured by glancing incidence X-ray diffraction (GIXRD). Residual stress measurement indicated a transition from compressive to tensile stresses for midrange levels of both nitrogen partial pressure (e.g., 3.33 Pa) and substrate bias (e.g., −150 V). The stoichiometry of the films (N:Cr) ranged from 0.7 to 1 for nitrogen partial pressures of 2.00 and 5.32 Pa, respectively.