High melting temperature metals

Rotating electrode atomization may be applied to almost all metals and alloys since it does not require a crucible for melting and/ or pouring. In particular, high melting-temperature metals and alloys, such as Ti and Zr, are well suited for the process. However, the production cost is still a drawback associated with the process, since electrode production is generally more expensive than a metal melt. In addition, production rates are relatively low compared to other atomization processes such as gas atomization and water atomization. 

While convenient, it should be noted that most of these approximations require the same precision of measurement as do curve fitting techniques and obviously lead to less accurate results. They have been particularly used to derive values for high melting temperature metals and alloys, yielding values that have an author to author reproducibility of typically 10%, as demonstrated by examination of collected data for Cu and Fe, (lida and Guthrie 1988). It is, however, often difficult when making such comparisons to decide whether the differences reflect varying precisions of measurement, differences in experimental procedure or qualities of materials. 

Cold-chamber die casting shot cylinder filled with a ladle for each cycle. Used for high melting temperature metals. 

You may be wondering why we did not mention the pure refractory metals Nb, Ta, Mo, W in our chapter on turbine-blade materials (although we did show one of them on Fig. 20.7). These metals have very high melting temperatures, as shown, and should therefore have very good creep properties. 

Alloys with rhenium, another high melting point metal (3180°C) exhibit outstanding high temperature properties insofar as they have a higher recrystallisation temperature than pure tungsten and are still ductile in the recrystallised condition. Common alloys with rhenium contain 3%, 5% or 26% rhenium. The 3% and 5% alloys combine ductility with reasonable... 

Although UV powder coatings can be applied to a variety of substrates, including metals and plastics with high melting temperatures, their primary advantage is for coating of substrates, which ared ... 

The skutterudites do not melt congruently and involve pnicogens (P, As, Sb) that generally have high vapor pressures at the formation temperatures of the compounds. The high melting temperatures of Fe, Ru and Os coupled with the reactivity of the lanthanide metals with convenient crucible materials (e.g., Si02) makes the synthesis of many of these compounds difficult. As a result, variations in the reported properties of a particular lanthanide skutterudite compound can often be traced to differences in sample composition and quality. 

Only the two first methods allow measurement of the temperature coefficient of the surface energy. The maximum bubble pressure technique is well-adapted for metals with low and intermediate melting points and specially for oxidizable metals, while the sessile drop technique has been applied with success to measure ctlv values up to 1500°C. The drop weight method is particularly useful for very high melting-point metals because it avoids liquid contact with container materials. This is also true for the recently developed levitation drop technique that analyses the oscillation spectrum of a magnetically levitated droplet. 

The fuels for fast breeder reactors include alloys such as U-Pu-Zr and the ceramic materials UO2-PUO2, UC-PuC, and UN-PuN, but the mixed oxides, UO2-PUO2, are the choice for prototype fast breeder fuel elements because of their high melting temperature, compatibility with cladding and coolants, and relatively good irradiation stability and fission product retention. The disadvantages are the relatively low metal density, the... 

---