Refractory alloying elements

F. S. Pettit and G. H., Meier, The effects of refractory elements on the high temperature oxidation and hot corrosion properties of superalloys. In Refractory Alloying Elements in Superalloys, eds. J. K Tien and S. Reichman, Metals Park, OH, ASM, 1984, p. 165. 

Niobium is important as an alloy addition in steels (see Steel). This use consumes over 90% of the niobium produced. Niobium is also vital as an alloying element in superalloys for aircraft turbine engines. Other uses, mainly in aerospace appHcations, take advantage of its heat resistance when alloyed singly or with groups of elements such as titanium, tirconium, hafnium, or tungsten. Niobium alloyed with titanium or with tin is also important in the superconductor industry (see High temperature alloys Refractories). 

In both atomization modes, as thin unstable ligaments, and/ or sheets disintegrate into round droplets, atomization gas may plausibly be trapped into the droplets under certain conditions. For alloys with alloying elements which readily react with atomization gas, for example, oxidize to form refractory oxides, solidification may be delayed and spheroidization is prevented so that rough flakes may form. For such alloys, the atmosphere in the spray chamber must be inert and protective to avoid the formation of any refractory and to foster spheroidal shape of droplets. 

Two different kinds of metals are found in chondrites. Small nuggets composed of highly refractory siderophile elements (iridium, osmium, ruthenium, molybdenum, tungsten, rhenium) occur within CAIs. These refractory alloys are predicted to condense at temperatures above 1600 from a gas of solar composition. Except for tungsten, they are also the expected residues of CAI oxidation. 

More Mo is consumed annually than any other refractory metal. The major use for Mo is as an alloying element in alloy steels, tool steels, stainless steels, Ni-based and Co-based superalloys. In these materials, it increases the hardenability, toughness, high-temperature strength, and corrosion resistance. Molybdenum is important in the missile industry, where it is used for high-temperature structural parts, such as nozzles, leading edges of control surfaces, support vanes, struts, reentry cones, radiation shields and heat sinks. In the electrical and electronic industries. Mo is... 

Alloying elements, electrode mass, minerals, ores, oxidizers, refractories, fluxes. 

Such carbon exchange can be observed between alkali metals and ferritic or austenitic steels as well as alloys based on vanadium, niobium, or other refractory alloys. Carbon dissolved in alkali metals also has the ability to react with other dissolved nonmetallic elements. In some cases, rather surprising reaction products have been observed. 

Part 3 Classes of Materials starts with the selective treatment of metals that are applied as base and alloying elements of metallic materials. The next class of materials discussed are ceramics. Detailed groupings and definitions of technical ceramics are given and traditional ceramics and cements, silicate ceramics, refractory ceramics, oxide ceramics, and nonoxide ceramics are treated. The physical and physicochemical properties of those polymers, copolymers, and polymer blends which are widely used for scientific applications and in industry are described in the next chapter. The last chapter serves as a source of data and commercial product information on glasses as engineering materials of practical importance. 

Niobium is similar in nature to the other psissivating reactive-refractory metals (titanium, zirconium, and tantalum) and has an inherent resistance to a wide range of chemicals. In general, compared to Zr and Ti, Nb has better corrosion properties in acids with small amounts of metal or organic contaminants. Niobium alloys with alloying elements such as Zr and Ti have been evaluated surd have shown increased reactive tendencies in rough proportion to their compositional content as might be expected with solid solution alloys. 

Large efforts were given to assess compatibility of refractory alloys with liquid Li in space nuclear power applications. The compatibility issue has commonality with that of V-alloys with liquid Li. Those alloys which easily oxidize may have the benefit of using Li as a coolant because Li may remove impurity O in the alloys. However, high O level in the matrix of the refractory alloys may induce reduction corrosion [75]. Addition of O getters such as Hf, Zr, or Y were recommended for Nb-alloys [76]. Corrosion in liquid Li proceeds by dissolution of elements followed by mass transfer and impurity pick-up/extraction. Both processes are highly influenced by the circulation condition (delta T and flow distribution) and impurity levels of both Li and the alloy being tested. 

Silicon. Silicon is typically present only in minor amounts in most nickel-base alloys. In alloys containing significant amounts of iron, cobalt, molybdenum, tungsten, or other refractory elements, the level of silicon must be carefully controlled because it can stabilize carbides and harmful intermetallic phases. However, the use of silicon as a major alloying element has been found to greatly improve the... 

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