Formation of amorphous electrodeposited Ni-W alloys and their nanocrystallization

Nowadays, application of nanocrystalline nickel-tungsten (Ni-W) alloys is receiving a great interest because they are an efficient replacement for hard chromium coatings owing to their premium hardness, wear, and corrosion properties. Moreover, heat-treated nanocrystalline Ni-W alloys demonstrate proper mechanical properties as well as thermal stability at high temperatures. The current paper reviews different aspects of electrodeposition, microstructure, corrosion, oxidation, wear, and mechanical properties Ni-W alloys and nano/micro composites. Besides, heat treatment effects on properties and thermal stability of these alloys are also reviewed.

With the miniaturization of a solid, effects of surface strain and quantum trapping become increasingly important in determining its properties. As a result, low-dimensional materials manifest unusual features, especially in their energetic and mechanical behavior. The establishment of a consistent understanding on an atomic-level of the mechanism behind the fascinating behaviors of low-dimensional systems, which include monatomic chains, hollow tubes, liquid and solid surface skins, nanocavities, nanowires, and nanograins, as well as interfaces, has long been a great challenge. In this report, a literature survey is presented, followed by a theoretical analysis culminating in the development of a local bond average (LBA) approach that may complement existing approximations in terms of continuum medium and quantum computations. The LBA approach correlates the measurable quantities of a specimen to the identities of its representative bonds, and the energetic responses of these bonds (bond nature, order, length and strength) to external stimuli, such as changes in temperatures and coordination environments. It is shown that the shortened and strengthened bonds between under-coordinated atoms and the consequent local strain and quantum trapping dictate, intrinsically, the mechanical behavior of systems with a high proportion of such atoms. The thermally driven softening of a substance arises from bond expansion and lattice vibrations that weaken the bonds. The competition between the energy density gain and the residual atomic cohesive energy in the relaxed surface of skin depth determines, intrinsically, the mechanical performance of a mesoscopic specimen; the competition between the activation and inhibition of the motion of atomic dislocations motion dominates, extrinsically, the yield strength of the specimen during plastic deformation. Therefore, the mechanical behavior of a specimen depends on its shape, size, the nature of the bonds involved, surface and interface conditions, and the temperature at which the physical properties of the specimen is measured. Excellent agreement with existent measurements of temperature dependence of surface tension, size and temperature dependence of elasticity and extensibility, and the inverse Hall–Petch relationship in nanograins have been established. Furthermore, these agreements have led to quantitative information regarding the bond identities in monatomic chains and carbon nanotubes, as well as the factors dominating the sizes at which a grain is strongest. In addition, the interface electric repulsion between nanocontacts due to the skin trapping and the associated local charge densification may provide feasible mechanism for the superfluidity, superlubricity and superhydrophobicity as widely observed. The progress made insofar evidences the essentiality of the LBA approach from the perspective of bond formation, dissociation, relaxation and vibration and the associated energetics for the exposition of thermo-mechanical behavior of low-dimensional materials. Extending the application of the approach to junction interfaces, liquid surfaces, defects and impurities, chemically adsorbed systems, amorphous states, and substances under other applied stimuli such as pressure and electric field would contribute to better knowledge of such systems and could lead to the development of even more fascinating and profitable materials.

In this review we address the electrochemical growth of metals and alloys with nanometric structures controlling the functional properties of electrodeposited coatings and freestanding electroforms. Electrodeposition is starting to be regarded as a viable process for nanofabrication and - even though electrocrystallisation has received considerable attention from both the theoretical and experimental viewpoints - it is now worth focussing systematically on the role of processing and electrochemical engineering factors, in the tailoring of nanosized structural features. This information is currently scattered in the literature and a specific review would fill an information gap. This paper offers: (i) an overview of the tools currently avaliable for the description and in-situ and ex-situ assessment of the nanostructure of electrodeposited metals; (ii) a systematic discussion of the relationships among their nanostructure and mechanical and chemical properties; (iii) a rationalisation of the mechanisms of formation of the different types of nanoelectrodeposits; (iv) a critical presentation - ordered by chemical composition - of specific systems. An updated and comprehensive literature coverage is provided, based on over 300 papers.

Of late, nanotechnology seems to be rapidly thrusting its applications in all aspects of life including engineering and medicine. Materials science and engineering has experienced a tremendous growth in the field of nanocomposite development with enhanced chemical, mechanical, and physical properties. A wide array of research has been conducted in the processing of nanocomposites. Consolidation of these systems from loose particles to bulk free form entities has always been a challenge. To name a few, traditional consolidation techniques such as cold pressing and sintering at high temperatures, hot pressing, and hot isostatic pressing have strong limitations of not being able to retain the nanoscale grain size due to the excessive grain growth during processing. This article reviews in detail the results from numerous studies on various methods for manufacturing nanocomposites with improved properties and retained nanostructures. Both challenges and recent advances are discussed in detail in this review.

In recent years, near-nano (submicron) and nanostructured materials have attracted increasingly more attention from the materials community. Nanocrystalline materials are characterized by a microstructural length or grain size of up to about 100 nm. Materials having grain size of ∼0.1 to 0.3 μm are classified as submicron materials. Nanocrystalline materials exhibit various shapes or forms, and possess unique chemical, physical or mechanical properties. When the grain size is below a critical value (∼10–20 nm), more than 50 vol.% of atoms is associated with grain boundaries or interfacial boundaries. In this respect, dislocation pile-ups cannot form, and the Hall–Petch relationship for conventional coarse-grained materials is no longer valid. Therefore, grain boundaries play a major role in the deformation of nanocrystalline materials. Nanocrystalline materials exhibit creep and super plasticity at lower temperatures than conventional micro-grained counterparts. Similarly, plastic deformation of nanocrystalline coatings is considered to be associated with grain boundary sliding assisted by grain boundary diffusion or rotation. In this review paper, current developments in fabrication, microstructure, physical and mechanical properties of nanocrystalline materials and coatings will be addressed. Particular attention is paid to the properties of transition metal nitride nanocrystalline films formed by ion beam assisted deposition process.