The effects of heat treatments on hardness and wear resistance in Ni-W alloy coatings

The relationship of processing parameters, microstructure, and mechanical responses of the electrodeposited nickel-tungsten alloys exposed to elevated temperatures in the range 700-1100 °C are investigated. Reverse pulse electrodeposition technique is employed to control the tungsten content and nanocrystalline grain size of the deposits. The application of heat treatment at 700 °C on the alloy with high tungsten content (22 at.%) and small grain size (3 nm) gives hardness enhancement and a small decrease in wear resistance. Prolonging annealing duration and increasing annealing temperature promote more grain growth and reductions of both hardness and wear resistance, despite the formations of secondary phases. For alloys with lower tungsten contents (6% and 13%) and larger grain sizes (13 and 56 nm), higher degrees of grain growth coupled with monotonic decline of hardness are observed. The study indicates that the electrodeposited nickel-tungsten alloys with a high tungsten content potentially serve as strong candidates for high temperature applications.     

Effects of strut geometry and pore fraction on creep properties of cellular materials

A set of analytical models based on engineering beam analysis is developed to predict creep behavior of cellular materials over a broad range of relative density. Model predictions, which take into account the presence of mass at strut nodes and consider different possible deformation mechanisms and foam architectures, are compared to experimental creep results for a replicated nickel-base foam and a reticulated aluminum foam. As porosity decreases, the controlling creep mechanism in the foams changes from strut bending, to strut shearing, and ultimately to strut compression.     

Corrosion Behavior of Reverse-Pulse Electrodeposited Zn-Ni Alloys in Saline Environment

The study investigates the relationship of the reverse-pulse electrodeposited zinc-nickel alloy coatings’ characteristics and their corrosion behaviors in a saline environment, using both anodic polarization and electrochemical impedance analysis. The introduction of anodic pulsation gives deposits of more refined grain sizes and increased nickel contents, resulting in improvement of the corrosion resistance. High anodic current densities employed in the reverse-pulse electrodeposition, however, modulate crystallographic orientations of the grains, introduce porosity to the structure, and hence adversely affect the corrosion resistance of the coating deposits.     

Electroless Ni-based coatings for biodiesel containers

Biodiesel commonly experiences oxidative and hydrolytic degradations, leading to problems of low storage stability and corrosion of fuel containers. The present study investigates the fabrication and use of electroless-deposited nickel alloys, containing phosphorus and tungsten, as potential coating materials that effectively protect steel-based biodiesel containers from corrosion. Through long-term static immersion and high-temperature oxidation tests, coupled with surface analyses of the coatings and assessments of the biodiesel’s acidity and storage stability, it is determined that a nickel coating with 15 wt% of phosphorus is favorably compatible with biodiesel, both in terms of corrosion protection and fuel stability.     

Electrochemical Codeposition and Heat Treatment of Nickel-Titanium Alloy Layers

The fabrication of nickel-titanium (Ni-Ti) alloy layers via the electrochemical codeposition and heat treatment is proposed and investigated herein. The codeposition of a Ti-dispersed Ni-matrix layer on an indium tin oxide-coated glass substrate was systematically conducted over varied current densities, Ti-particle loadings in an electrolyte and Ti particle sizes to investigate their effects on the Ti content and morphology of the layers. A moderate particle loading of approximately 2 to 6 g/dm³ led to relatively high Ti contents, whereas a decrease of particle size gave a dense and uniform layer with relatively low Ti contents. Following heat treatment, the Ni-Ti composite layers completely transformed into the Ni-Ti alloys with varying dominant phases of NiTi, Ni₃Ti, and Ni solid solution depending on the alloy compositions. The assessment of the Ni-Ti phase diagram and the Ni-Ti interdiffusivity are discussed to verify the resultant phases present in the post-annealed layers. The results and analyses from this work entail the construction of the codeposition’s mechanistic views and the interaction of the hydrodynamic, gravitational, and electrophoretic forces on particles suspended in an electrolyte, which are critical to the development of the Ni-Ti component fabrication via the combined codeposition-heat treatment route.     

Hot-dip galvanization with pulse-electrodeposited nickel pre-coatings

The galvanizing process whereby steel is electrodeposited with nickel using pulsed current waveforms and hot-dipped in a molten zinc bath at 450 °C is investigated here as a potential route to mitigate the coating overgrowth problem. The influences of processing parameters, including electroplating and galvanizing durations, on the evolutions of microstructure and phase structures, and polarization characteristics of galvanized steels are explored. The results from the polarization study and salt spray tests indicate that the galvanized coating prepared with a nickel pre-coating, comprising zinc–nickel intermetallic layers, exhibits significantly better corrosion resistance than the conventionally-galvanized steel.     

Effects of WC addition on structure and hardness of electrodeposited Ni-W

Nickel-tungsten/tungsten carbide composites (Ni-W/WC) are fabricated by co-electrodeposition. Processing parameters including current density, particle content, and particle size are found to influence surface morphology and consequently the apparent hardness of the co-deposits. A cathodic current density below 0.2 A/cm² and solid loading between 1 and 2 g/l are essential for providing deposits with non-porous and uniform structure. The use of 0.5 µm tungsten carbide particles and a current density of 0.1 A/cm² results in a Ni-W/WC composite of fine and dense nodular structure with hardness of about 10 GPa, exceeding those of nanocrystalline nickel-tungsten alloys and comparable to that of hard chromium coating.     

Early development of a shaftless horizontal axis wind turbine for generating electricity from air discharged from ventilation systems

The air discharged from ventilation systems is a high potential wind resource for generating electricity in countries where wind speed is unreliable or weak, such as in Thailand. The air discharged from ventilation systems produces consistent and high-speed wind when benchmarked against natural wind. However, the limitations of conventional wind turbines are that they have negative impacts on the ventilation system and are inconvenient to install in many areas. The innovative shaftless horizontal axis wind turbine (SHWT) introduced in this article has been designed to close the gap between the wind source and the conventional wind turbines in this process. The concept design shows how it could be mounted next to sources of waste wind, requiring only a small space for installation. An open hole is provided to enable airflow to be discharged into the environment. This SHWT has high market potential for utilizing man-made wind to generate electricity from an alternative source which supports sustainable energy development. The purpose of this study is to demonstrate the concept design of a prototype SHWT used for energy recovery from the discharged air of a ventilation system. How the rotor and stator design of the SHWT optimize wind turbine performance and minimize the negative effects on the ventilation system efficiency are also addressed in this study. The performance of the SHWT is demonstrated in a lab-scale test using the type of propeller fan that is generally applied in many sectors in Thailand. The results showed that the SHWT was successful in generating electricity and produced minimal negative effects on the ventilation system's performance. The maximum power output of the prototype SHWT is 7.4 W at a rotational speed of 1644 rpm using eight sets of magnets and 5.1 m/s wind speed. The maximum wind turbine efficiency is 51%. However, it still requires further optimization to enhance the SHWT performance.     

Effects of low-content activators on low-temperature sintering of tungsten

Tungsten compacts are processed by the activated sintering technique at low temperatures near 1200 °C, whereby either nickel, iron or a combination of the two are employed as additives. Despite very small contents of additives of a few monolayers and below, the processing technique is found viable for providing enhancing effects to the sintering kinetics of tungsten, and the sintered materials remain in the partially densified stage. Nickel is proved to be a superior activator, which induces a reduction of the activation energy as its content increases.     

Crack initiation and propagation of galvanized coatings hot-dipped at 450 °C under bending loads

Crack initiation and propagation behaviors in the intermetallic layers of galvanized coatings subjected to bending loads are characterized and numerically simulated. Coating structure of galvanized steel prepared by hot dipping at 450 °C is a laminate composite consisting of δ, ζ, and η phases, with an infinitesimal layer between the coating and steel article speculatively representing a Γ phase. The specimens were deformed in a four-point bending configuration, and the evolution of cracks was investigated as a function of bending angles. Through-cracks were found to develop in the δ layer of the coatings after thermal cooling due to thermal stresses and propagate toward the outer surface under increments of bending loads. Finite element simulations of galvanized steels were subsequently developed with an initial crack tip located in the δ layer to determine the controlling parameters of the crack propagation and to assess the coatings' fracture parameter, critical far field stress, and stress distributions. The analysis highlights the enhancement of fracture resistance of the galvanized coatings owing to the presence of the ζ layer.