Additive manufacturing of metallic components – Process, structure and properties

Additive manufacturing of metals

Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.

The metallurgy and processing science of metal additive manufacturing

In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

Selective Laser Melting (SLM) is a particular rapid prototyping, 3D printing, or Additive Manufacturing (AM) technique designed to use high power-density laser to melt and fuse metallic powders. A component is built by selectively melting and fusing powders within and between layers. The SLM technique is also commonly known as direct selective laser sintering, LaserCusing, and direct metal laser sintering, and this technique has been proven to produce near net-shape parts up to 99.9% relative density. This enables the process to build near full density functional parts and has viable economic benefits. Recent developments of fibre optics and high-power laser have also enabled SLM to process different metallic materials, such as copper, aluminium, and tungsten. Similarly, this has also opened up research opportunities in SLM of ceramic and composite materials. The review presents the SLM process and some of the common physical phenomena associated with this AM technology. It then focuses on the following a...

/pdf/review-of-selective-laser-melting-materials-and-applications-2gpgz4zp60.pdf

Review of selective laser melting : materials and applications

Solidification Features of Ti45Al Alloys with Different Boron Addition

Microstructure characteristics and acoustic properties of laser repaired Chinese bronze bells 2300 years ago

Here, novel magnetic imprinted porous foams (MIFs) were prepared by Pickering oil-in-water high internal phase emulsion polymerization, using renewable cellulose nanocrystals (CNCs) derived from cotton source as the stabilizer, and surfactant Tween 85 and iron oxide magnetic nanoparticles as additive in aqueous phase, for selective adsorption of 4-nitrophenol (4-NP). Interconnected porous foam structure was formed and optimized by controlling the addition amount of solid stabilizer CNCs, Tween 85, and oil phase volume, the optimum value of which was 7.5 wt%, 5.0 wt%, and 85 %, respectively. The as-synthesized imprinted material had the good thermal stability and magnetic responsivity. The adsorption equilibrium data was fitted well by the Langmuir isothermal model with a maximum adsorption capacity of 287.5 µmol/g. Pseudo-second-order kinetics model could better describe the kinetics data. MIFs showed excellent selective ability for 4-NP as compared with these structural analogues. Besides, Thomas model explained the dynamic breakthrough curves better. The regeneration ability of MIFs was also satisfying after several reuse.

Magnetic Interconnected Macroporous Imprinted Foams for Selective Recognition and Adsorptive Removal of Phenolic Pollution from Water

Fabrication of fluorinated polyimide optical waveguides by micropen direct writing technology

The σ-phase precipitation in 20% cold-worked 15Cr–15Ni titanium-modified austenitic stainless steel was studied during long-term aging treatment. During the isothermal aging stage, the amount of σ-phase was significantly increased at beginning and gradually became constant. The aging time only slightly affected the size and morphology of the σ-phase. Conversely, during the isochronal aging stage, the amount of σ-phase grew rapidly with the increase in the aging temperature. The σ-phase with a large amount of stacking faults was prone to nucleate around the (Ti, Mo)C particles or at the grain boundaries. The (Ti, Mo)C particles can act as effective nucleation sites, where the σ-phase directly precipitates from the austenitic matrix. From this work, the growth of σ-phase is found to be influenced by the aging temperature, and a new mechanism of σ-phase precipitation from austenite has been proposed.

Ming Gao

Papers

Solidification Features of Ti45Al Alloys with Different Boron Addition

Microstructure characteristics and acoustic properties of laser repaired Chinese bronze bells 2300 years ago

Magnetic Interconnected Macroporous Imprinted Foams for Selective Recognition and Adsorptive Removal of Phenolic Pollution from Water

Fabrication of fluorinated polyimide optical waveguides by micropen direct writing technology

σ -Phase Precipitation Mechanism of 15Cr–15Ni Titanium-Modified Austenitic Stainless Steel During Long-Term Thermal Exposure