Rapid manufacturing of metal components by laser forming

This overview will focus on the direct fabrication of metal components by using laser-forming techniques in a layer-by-layer fashion. The main driving force of rapid prototyping (RP) or layer manufacturing techniques changed from fabrication of prototypes to rapid tooling (RT) and rapid manufacturing (RM). Nowadays, the direct fabrication of functional or structural end-use products made by layer manufacturing methods, i.e. RM, is the main trend. The present paper reports on the various research efforts deployed in the past decade or so towards the manufacture of metal components by different laser processing methods (e.g. selective laser sintering, selective laser melting and 3-D laser cladding) and different commercial machines (e.g. Sinterstation, EOSINT, TrumaForm, MCP, LUMEX 25, Lasform). The materials and applications suitable to RM of metal parts by these techniques are also discussed.     

Preparation and properties ofX-sialon

X-sialon has been produced by hot pressing Si₃N₄-Al₂O₃-SiO₂ powder mixtures and Si₃N₄ Powder-mullite gel mixtures at 1650 °C. The formation mechanism ofX-sialon has been studied and is correlated with the processing technique for the two preparation routes. Microprobe analysis of the obtainedX-sialon phase, combined with previous observed compositions and literature formulae suggests that, at 1650 °C,X-sialon exists as a narrow solid solubility region on the Si₃N₄-mullite line in the Si₃N₄-SiO₂-Al₂O₃-AIN phase diagram. The physical, mechanical and chemical properties ofX-sialon have been evaluated.X-sialon has a modest hardness of 1280 kg mm^–2, a fracture toughness of 1.7 Mpa m^1/2, and an elastic modulus of 213 GPa.X-sialon exhibits excellent chemical stability in contact with iron-based alloys at 1200 °C.     

Synthesis,characterizations, photo-electrochemical,and physical properties of a new 0D copper(II) complex

Journal of Materials Science: Materials in Electronics - A new hybrid single crystal was synthetized by chemical route. The binuclear complex containing N-donor ligand...     

Nonequilibrium behavior in the Al-Ge alloy system: Insights into the metastable phase diagram

The competitive formation of metastable and stable phases during nonequilibrium processing of Al-Ge alloys and the corresponding metastable phase equilibria have been investigated. For germanium concentrations in the range 30 to 50 at. pct, it is shown that the four metastable phases can be ranked in order of decreasing stability as follows: monoclinic (P2₁/c), rhombohedral (R-C), orthorhombic (Pbca), and hexagonal (P6/mmm). Their formation depends not only on the transformation temperature(e.g., the liquid undercooling), but also on the presence of appropriate heterogeneous nucleation sites. For example, the orthorhombic phase has only been observed in amorphous films after rapid annealing/crystallization treatments. It is also shown that all of these phases form metastable equilibria with α-aluminum only,i.e., no metastable phase equilibria appear to exist between any metastable phase and β-germanium or between any two metastable phases. Consequently, it is not possible to draw a single metastable phase diagram that incorporates all of these phases with phase boundaries that represent their metastable equilibria; rather, separate diagrams should be drawn for each metastable phase. It is noted that these diagrams should extend only to the metastable phase field rather than all the way to pure germanium: for compositions richer in germanium, the results indicate that the metastable phase forms and then remelts upon the formation of germanium or a more stable, germanium-enriched metastable phase. Furthermore, it is proposed that this behavior is rather general in nature. Finally, it is concluded that the production of metastable phases in bulk form, in systems such as this where so many reactions occur simultaneously and competitively, might be impossible using solidification processing approaches. Formerly with the Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195     

The Effect of Variable Binder Content and Sintering Temperature on the Mechanical Properties of WC–Co–VC/Cr3C2 Nanocomposites

WC powders with an average crystallite size of 10 nm were successfully prepared by ball milling of micron-sized tungsten carbide powders. Grain growth inhibitors (VC and Cr₃C₂) with concentrations of 0.6 wt% each were added to nanocomposites of WC–9Co and WC–12Co, in both as-received and milled WC. Powder mixtures were then consolidated using spark plasma sintering technique at 1200 and 1300 °C for 10 min under high vacuum and pressure of 50 MPa. The influence of WC crystallite size, Co content, and sintering temperature over microstructure and mechanical properties of the resulting composites were studied through XRD and FESEM. Densification and attained grain sizes of the sintered products were measured by Archimedes principle and Scherrer procedure, respectively. Moreover, microhardness (H_v30) and fracture toughness were measured and compared for each composition to comparatively assess the individual effect. It was observed that the addition of VC and Cr₃C₂ resulted in decreased densification of the synthesized composites. These grain growth inhibitors were found to limit grain sizes to 131 nm with an average hardness of 1592 H_v30 and fracture toughness of 9.23 Mpam^1/2.     

Nanostructured materials for water desalination

Desalination of seawater and brackish water is becoming an increasingly important means to address the scarcity of fresh water resources in the world. Decreasing the energy requirements and infrastructure costs of existing desalination technologies remains a challenge. By enabling the manipulation of matter and control of transport at nanometer length scales, the emergence of nanotechnology offers new opportunities to advance water desalination technologies. This review focuses on nanostructured materials that are directly involved in the separation of water from salt as opposed to mitigating issues such as fouling. We discuss separation mechanisms and novel transport phenomena in materials including zeolites, carbon nanotubes, and graphene with potential applications to reverse osmosis, capacitive deionization, and multi-stage flash, among others. Such nanostructured materials can potentially enable the development of next-generation desalination systems with increased efficiency and capacity.     

Fabrication of polysulfone nanocomposite membranes with silver‐doped carbon nanotubes and their antifouling performance

In this study, polysulfone (PSf)/silver‐doped carbon nanotube (Ag‐CNT) nanocomposite membranes were prepared by a phase‐inversion technique; they were characterized and evaluated for fouling‐resistant applications with bovine serum albumin (BSA) solutions. Carbon nanotubes were doped with silver nanoparticles via a wet‐impregnation technique. The prepared Ag‐CNT nanotubes were characterized with scanning electron microscopy (SEM)/energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, Raman spectroscopy, and thermogravimetric analysis. The fabricated flat‐sheet PSf/Ag‐CNT nanocomposite membranes with different Ag‐CNT loadings were examined for their surface morphology, roughness, hydrophilicity, and mechanical strength with SEM, atomic force microscopy, contact angle measurement, and tensile testing, respectively. The prepared composite membranes displayed a greater rejection of BSA solution (≥90%) and water flux stability during membrane compaction with a 10% reduction in water flux values (up to 0.4% Ag‐CNTs) than the pristine PSf membrane. The PSf nanocomposite membrane with a 0.2% Ag‐CNT loading possessed the highest flux recovery of about 80% and the lowest total membrane resistance of 56% with a reduced irreversible fouling resistance of 21%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44688.     

Direct Selective Laser Sintering of Hard Metal Powders: Experimental Study and Simulation

Direct selective laser sintering (SLS) technology can be used to produce 3D hard metal functional parts from commercial available powders. Unlike conventional sintering, it does not require dedicated tools, such as dies. Hence, total production time and cost can be reduced. The large shape freedom offered by such a process makes the use of, for example, sintered carbides components viable in domains where they were not applied before. Successful results have been obtained in the production of sintered carbide or hard metal parts through SLS. The investigation focuses on tungsten carbide–cobalt (WC-Co) powder mixture. This material is characterised by its high mechanical properties and its high wear resistance and is widely used in the field of cutting tools. This paper is devoted to the experimental study and the simulation of direct selective laser sintering of WC-Co hard metal powders.