Laser melting

The laser spray process uses a high power carbon dioxide laser focused onto the surface of the part to be metallized. A carrier gas such as belium blows metal particles into the path of the laser and onto the part. The laser melted particles may fuse to the surface, or may be incorporated into an aHoy in a molten surface up to 1-mm thick. The laser can be used for selective aHoying of the surface, for production of amorphous coatings, or for laser hardening. 

Onion-like graphitic clusters have also been generated by other methods (a) shock-wave treatment of carbon soot [16] (b) carbon deposits generated in a plasma torch[17], (c) laser melting of carbon within a high-pressure cell (50-300 kbar)[l8]. For these three cases, the reported graphitic particles display a spheroidal shape. 

In particular, the laser melting experiment produced two well-differentiated populations of carbon clusters (a) spheroidal diamond particles with a radial texture... 

G.E. Jellison, Jr., Optical and Electrical Properties of Pulsed Laser-Annealed Silicon R.F. Wood and G.E. Jellison, Jr., Melting Model of Pulsed Laser Processing R.F. Wood and F.W. Young, Jr., Nonequilibrium Solidification Following Pulsed Laser Melting... 

Continuous laser melt quenching of hypoeutectic Ag-Cu alloys has been performed and discussed by Copley et al. (1995) nano-phase coupled growth structures (with spacing of 10 nm) have been observed in banded nano-structures. 

Brandner, J.J., Hansjosten, E., Anurjew, E., Pfleging, W. and Schubert, K. (2007) Microstructure devices generation by selective laser melting. Proceedings of... 

Janai and Moser (1982) have used chemical-vapor-deposited amorphous silicon films that were deposited at 600°C on silica (fused quartz) substrates. Information was recorded in films with thickness d between 2500 and 5000 A by irradiation with a ruby laser pulse of 50 nsec duration and an energy density ranging from 0.4 to 1.5 J cm-2. The upper energy limit is known to be above the threshold for laser melting in a-Si (Baeri et al., 1980). To determine the optical transmission density difference... 

R. F. Wood and F. W. Young, Jr., Nonequilibrium Solidification Following Pulsed Laser Melting... 

Rapid solidification 10 -10 Pulsed laser melting of a solid surface Amorphous and nanocrystaUine thin films... 

Nucleation has a number of important practical consequences. In metallurgy, the rate of nucleation of molten metals and metal alloys affects the structural and mechanical properties of the solid metals that are formed upon casting. In the preparation of high-quality crystalline semiconductors through laser melting and resolidification the nucleation step affects the resulting microstructures. In the atmospheric sciences, nucleation of ice in clouds is a widely studied process, while biologists are interested in the ways in which certain plants appear to inhibit nucleation of ice from water and thus show increased resistance to cold. 

SIMS has also been used to determine the As concentration profile after liquid state diffusion from laser melted spin-on arsenic glass. In this case laser diffusion was desireable because It avoided the thermal stress-induced damage to large thinned wafers that could occur during heating In a furnace. (41). 

X Xu, G P. Grigoropoulos, and R. E. Russo, Heat Transfer in Excimer Laser Melting of Thin Polysilicon Layers, / Heat Transfer, 117, pp. 708-715,1995. 

Stuart FM, Persano C (1999) Laser melting of apatite for (U-Th)/He chronology Progress to date. EOS Trans Am Geophys Union 80 F1169... 

Example Solid freeform fabrication (SFF) techniques such as selective laser melting (SLM) and sintering (SLS) are often prized for being much cleaner than conventional machining processes and being able to fabricate products with minimum waste (e.g., Bourell et al. 2009). 

Figure 3a and b show two different laser melting machines with sealed build chambers for the processing of reactive materials such as titanium. The machine (Fig. 3b) cannot just do AM but engraving and marking due to exchangeable modules as well. 

Rapid Tooling, Fig. 3 (a) Laser melting machine with sealed build space (Realizer SLM 100). (b) Laser melting machine with exchangeable generating modules (Concept, Cusing, M3 linear)... 

In summary, continuous sapphire fibers are commercially available, and new YAG fibers are readily achieved with the Saphikon process, or the LHPG process (see Chapter 6), or else by the new containerless laser melt process (Chapter 4). Currently however, there is only one route known, i.e., HP-LCVD, that might eventually be capable of yielding continuous, single crystal fibers such as SiC or titanium carbide fibers. A single crystal SiC fiber by LCVD has... 

In the last year, the application of selective laser melting (SLM) to ceramics has also been tried, and proved to work. The principle of this technique was described above. First preliminary experiments showed promising results [23]. 

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