Arc-melting

Solidification. The heat of the electric arc melts a portion of the base metal and any added filler metal. The force of the arc produces localized flows within the weld pools, thus providing a stirring effect, which mixes the filler metal and that portion of the melted base metal into a fairly homogeneous weld metal. There is a very rapid transfer of heat away from the weld to the adjacent, low temperature base metal, and solidification begins nearly instantaneously as the welding heat source moves past a given location. 

Rhenium hexafluoride is a cosdy (ca 3000/kg) material and is often used as a small percentage composite with tungsten or molybdenum. The addition of rhenium to tungsten metal improves the ductility and high temperature properties of metal films or parts (11). Tungsten—rhenium alloys produced by CVD processes exhibit higher superconducting transition temperatures than those alloys produced by arc-melt processes (12). 

Arc melting also can be used to consoHdate bars of metal that are pressed from powder or sponge and used as consumable electrodes in a low voltage, high current arc. The bar is suspended vertically and the molten metal falls from the bottom of the bar onto a water-cooled copper cmcible, from which it is removed as an ingot. 

Fusion-Cast Shapes. Refractory compositions are arc-melted and cast into shapes, eg, glass-tank flux blocks as large as 305 X 610 X 1219 mm. After casting and annealing, the blocks are accurately diamond ground to ensure a precise fit. 

Component Consumable vacuum-arc melt Plasma Plasma cold-hearth melt melt Electron-beam cold-hearth melt Induction melt... 

Consolidation. ConsoHdation by the consumable-electrode electric-arc melting technique is ideally suited for vanadium and is used extensively... 

Multiple-arc melting for a minimum of two melts is conventionally used to ensure a homogeneous ingot. Although conventional arc-melt practice involves a negative electrode, improved alloying is achieved with a positive electrode for at least one of the several melts and usually the first melt. 

Zirconium is a hard, shiny, ductile metal, similar to stainless steel in appearance. It can be hot-worked to form slabs, rods, and rounds from arc-melted ingot. Further cold-working of zirconium with intermediate annealings produces sheet, foil, bar wire, and tubing. Physical properties are given in Table 3. 

Consolidation and Fabrication. Chromium metal may be consoHdated by powder metallurgy techniques or by arc melting in an inert atmosphere (8,13,24,25) (see Metallurgy Metallurgy, powder). 

Arc-melted titanium has excellent fluidity and lends itself readily to the creation of thin margins. Spmes must be carefully placed and abundant venting provided, however, to avoid holes and porosity ia the casting. The detection of defects by radiography is faciUtated by the low density of titanium, and conventional dental x-ray units may be used ia many cases. 

By tire coiTect choice of the metal oxide/carbon ratio in the ingoing burden for the furnace, the alloy which is produced can have a controlled content of carbon, which does not lead to the separation of solid carbides during the reduction reaction. The combination of the carbon electrode, tire gaseous oxides and the foamed slag probably causes tire formation of a plasma region between the electrode aird the slag, and this is responsible for the reduction of elecU ical and audible noise which is found in this operation, in comparison with tire arc melting of scrap iron which is extremely noisy, and which injects unwanted electrical noise into the local electrical distribution network. 

The carbides of the lanthanoids and actinoids can be prepared by heating M2O3 with C in an electric furnace or by arc-melting compressed pellets of the elements in an inert atmosphere. They contain the C2 unit and have a stoichiometry MC2 or M4(C2)3. MC2 have the CaC2 structure or a related one of lower symmetry in which the C2 units lie at right-angles to the c-axis of an orthogonal NaCl-type cell. They are more reactive than the alkaline-earth metal... 

Alloys were prepared by arc melting high purity starting materials followed by homogenisation. Transmission electron microscopy specimens were prepared by... 

The materials for solid solutions of transition elements in j3-rh boron are prepared by arc melting the component elements or by solid-state diffusion of the metal into /3-rhombohedral (/3-rh) boron. Compositions as determined by erystal structure and electron microprobe analyses together with the unit cell dimensions are given in Table 1. The volume of the unit cell (V ) increases when the solid solution is formed. As illustrated in Fig. 1, V increases nearly linearly with metal content for the solid solution of Cu in /3-rh boron. In addition to the elements listed in Table 1, the expansion of the unit cell exceeds 7.0 X 10 pm for saturated solid solutions " of Ti, V, (2o, Ni, As, Se and Hf in /3-rh boron, whereas the increase is smaller for the remaining elements. The solubility of these elements does not exceed a few tenths at %. The microhardness of the solid solution increases with V . Boron is a brittle material, indicating the accommodation of transition-element atoms in the -rh boron structure is associated with an increase in the cohesion energy of the solid. 

A pellet is pressed of an intimate mixture of finely divided reactants and reaction induced either by arc melting and high-T annealing or by solid-state sintering in an electrical or high-frequency furnace. Isolating the borides from reactive container components can be a problem. The use of boron nitride liners has proved effective. In some cases the protective liner is made of sintered boride containing the same elements as the boride in preparation. 

A series of Be-Pt intermetallic compounds arc prepared during the electrodeposition of Be on Pt from a solution of BeCl2 in an equimol NaCl-KCl mixture at 710°C. X-Ray diffraction of the electrode surface shows the presence of BePt, BcjPt. Electrolytic methods are also used to extract single crystals of Be,V from alloys prepared by arc melting Be and the transition metal in the proportion 15 1. 

Ti02 particles, the benzene-thermal reaction of TiCLi. and NaN3, chemical vapor reactions, plasma syntheses, or arc-melting [15-20], The optical properties of low-concentrated TiN nanoparticle systems were studied by Quinten [21], Highly dispersed TiN was used as an additive to improve the mechanical properties of titanium carbide-based cermets [22],... 

---