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In this paper, a predictive multi-scale model based on a cellular automaton (CA)-finite element (FE) method has been developed to simulate thermal history and microstructure evolution during metal solidification for the Direct Metal Deposition (DMD) process. The macroscopic FE calculation that is validated by thermocouple experiment is developed to simulate the transient temperature field and cooling rate of single layer and multiple layers. In order to integrate the different scales, a CA–FE coupled model is developed to combine with thermal history and simulate grain growth. In the mesoscopic CA model, heterogeneous nucleation sites, grain growth orientation and rate, epitaxial growth, re-melting of pre-existing grains, metal addition, grain competitive growth, and columnar to equiaxed phenomena are simulated. The CA model is able to show the entrapment of neighboring cells and the relationship between undercooling and the grain growth rate. The model predicts the grain size, and the morphological evolution during the solidification phase of the deposition process. The developed “decentered polygon” growth algorithm is appropriate for the non-uniform temperature field. Finally, the single and multiple-layer DMD experiment is conducted to validate the characteristics of grain features in the simulation.

To obtain efficient metalization of the surface and cell walls of carbon foam, an electroless silver displacement deposition method was investigated, in which a copper layer was first electroless-deposited and then displaced by silver. The purity of the silver coating, and the morphology, microstructure, mechanical strength and electrical conductivity of the resulting carbon foams were characterized by SEM, EDS, XRD, mechanical and conductivity tests. Results indicate that a uniform and continuous silver film is formed on the cell walls of the carbon foam with a better adhesion to the carbon compared to that obtained using the traditional one-step silver plating method. The coating is crystalline silver without copper or silver oxide. The conductivity and mechanical strength of these carbon foams increase from 700 to 2055 S/cm and 0.54 to 1.05 MPa, respectively when the silver content is increased from 0 to15.5 wt%.

Hollow microstructure always exhibits some special properties in the field of electrochemistry. Here, this study reports the rational design and preparation of TiNb2O7 nanofibers with one dimensional hollow structure via co-electrospinning. The as-electrospun TiNb2O7 hollow nanofibers show high intercalation potential, low charge-charge resistance and fast electrochemical kinetics. The electrochemical results exhibit that the TiNb2O7 hollow nanofibers deliver a reversible capacity of 210.1 mAh g−1 after 150 cycles at a current rate of 0.4 C, and 158.4 mAh g−1 after 900 cycles even at a current rate of 10 C with an outstanding capacity retention of 80.6%. The excellent electrochemical performance of nanofibers can be related to the unique morphology of hollow structure. Furthermore, the lithium ions storage mechanism of TiNb2O7 hollow nanofibers is also systematically analyzed, which is related to one two-phase coexistence and two solid-solution processes during the whole charge-discharge cycle. In addition, it is also demonstrated by in situ and ex situ observations that TiNb2O7 hollow nanofibers have outstanding structural stability and electrochemical reversibility. Therefore, the TiNb2O7 hollow nanofibers can be applied as an alternative promising electrode material for the next rechargeable lithium ions batteries.

In this paper, low-valent titanium ions were prepared by a redox reaction between TiCl4 and a titanium sponge. After dissolving the precursors in NaCl-KCl mixed molten salt, the electrochemical behaviours of Ti(III) and Ti(II) ions in the NaCl-KCl molten salt system were studied by cyclic voltammetry at 750 °C on a Mo electrode. The valence state of titanium ion in molten salt was confirmed by X-ray photoelectron spectroscopy (XPS), and the microstructure of the titanium powder was characterized via scanning electron microscopy (SEM). The main findings are that the titanium powder with a small particle size and coralloid shape was obtained via the production of a complex of Ti(III) and halogen elements, followed by a one-step reduction. However, the titanium powder prepared by the one-step reduction of Ti(II) had a large particle size and was dense.

High entropy alloys are multicomponent alloys that have at least five different principal elements as alloying elements. Each of these elements has an atomic percentage between 5% and 35%. Typically, they form body-centered cubic (bcc) or face-centered cubic (fcc) structure and are known to possess excellent mechanical properties, corrosion resistance, excellent electric and magnetic properties. Owing to their excellent corrosion and wear resistance, researchers are focusing on employing these materials as coatings. In this research, Laser Metal Deposition (LMD) was used to fabricate AlxCoFeNiCu1−x (x = 0.25, 0.5, 0.75) high entropy alloys from elemental powder based feedstocks. Thin wall claddings fabricated via LMD were characterized by a variety of techniques. Data from X-ray Diffraction (XRD) and Electron Back Scatter Diffraction (EBSD) suggested that with increase in Al content and decrease in Cu content, a change in crystal structure from a predominantly fcc to a combined fcc and bcc structure can be observed. The microstructure of the material was observed to be columnar dendritic. Data from standard less EDS analysis showed that the dendritic phase was Fe and Co enriched while the matrix was Cu and Al enriched in all the considered high entropy alloy fabrications. The Vickers hardness data was used to estimate the mechanical properties of these deposits. Results also showed that with the increase in aluminum content, AlxCoFeNiCu1−x displayed higher hardness. The high hardness values imply potential applications in wear resistant coatings.

Good stoichiometry of cadmium sulfide (CdS) film facilitates its application in photovoltaic devices; however, traditional thermal evaporation usually results in a Cd-deficient CdS film at a low-substrate temperature. In this study, Cd-rich CdS quantum dots (QDs) were synthesized by a facile co-precipitation method and used as the precursor to thermally evaporate CdS film on indium tin oxide-coated glass (ITO/glass). As a consequence, the stoichiometry of CdS film was greatly improved with atomic ratio of Cd to S restored to unity. More importantly, the newly developed CdS film, with its rod-like surface microstructure, acted as an efficient photoanode in a photoelectrochemical (PEC) cell. Its properties, including surface morphology and roughness, crystal structure, chemical composition, film thickness, energy-level structure and photosensitivity, are studied in detail.