Laser melting process

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... 

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. 

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... 

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. 

A ruby laser pulsed irradiation of Ge/Si heterostructures with Ge nanoclusters (quantum dots) at the irradiation energy density near the melting threshold of Si surface has been studied by means of Raman spectroscopy and by numerical simulation of the laser-induced processes. Two types of the structures have been tested. They differ mainly in the depth of nanoclusters occurence (0.15 and 0.3 pm). From the RS analysis one may conclude that laser irradiation results in different changes of QD properties. The decrease of QD size dispersion is observed in the samples with QDs at 0.3 pm, this effect is not observed in the samples with QDs at 0.15 pm. The numerical simulation of laser heating shows that the QDs are in a molten state for the same time, but the induced temperatures of nanoclusters for the two depths differ by -100 K. This result indicates that qualitatively different effects of the laser irradiation may be connected with different temperatures of QDs during laser irradiation. 

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). 

Laser Beam Machining, Fig.1 Overview of laser machining processes and their typical laser-matter interaction times and power densities. The red line marks the 1 kJ/cm energy density level, where most processes are distributed. The dotted line indicates the melt boundary of metals (Reprinted from Meijer et al. (2002), with permission from Elsevier)... 

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. 

One inviscid melt spinning process, the containerless laser heated melt process (Chapter 4.4.4) is believed to facilitate the formation of fibers by increasing the viscosity of the inviscid melt (and jet lifetime) at a normal quench rate of IC K/s, i.e., without increasing the quench rate to -10 K/s. 

Figure 13. Containerless laser-heated melt process. Redrawn from J. K. Weber, J. J. Felton, B. Cho and P. C. Nordine, Glass fibres of pure and erbium- or neodymium-doped yttria-alumina compositions. Nature, 393,769-771 (1998).

The economics and scalability of the new process are not known. The materials cost and the cost of operating a laser process are probably about the same for an amorphous YAG sensor fiber made by the containerless laser heated melt process and a for single crystal YAG sensor fiber made by laser heated pedestal growth (Chapter 4.5.2). And both are containerless processes. However the higher process speed may favor the laser heated melt process (1.5 m/s) over the laser heated pedestal process (1 mm/s). 

Three processes are known to fabricate continuous yttrium aluminum garnet (YAG) fibers. Single crystal YAG fibers are obtained by the edge defined film fed growth process and by the laser heated float zone process (Chapter 4.5). Both are slow processes. Amorphous YAG glass fibers have recently been demonstrated by a containerless laser heated melt process (Chapter 4.4). Polycrystalllne YAG fibers can be obtained with sol-gel and related processes (this chapter). These are potentially fast processes. 

---