Niobium-molybdenum alloys

M. Mazzolai (2001). J. Alloys Compounds, 316, 189-192. A neutron spectroscopy study of the local vibrations, the interstitial sites and the solubility limit of hydrogen in niobium-molybdenum alloys. 

Si-20Ci-20Fe foi niobium alloys and MoSi foi molybdenum alloys (see Mol denumand mol denum alloys Niobiumand niobium compounds Refractory coatings) (33). 

Nitrogen and carbon are the most potent solutes to obtain high strength in refractory metals (55). Particulady effective ate carbides and carbonitrides of hafnium in tungsten, niobium, and tantalum alloys, and carbides of titanium and zirconium in molybdenum alloys. 

Because several of the superalloys contain very little iron, they are closely related to some of the non-ferrous alloys. Some of the second- and third-row transition metals possess many of the desirable properties of superalloys. They maintain their strength at high temperatures, but they may be somewhat reactive with oxygen under these conditions. These metals are known as refractory metals, and they include niobium, molybdenum, tantalum, tungsten, and rhenium. 

In the cuse of refractory metals, coalings generally arc silicidcs, applied by pack cementation or slurry processes. Typical silieidc compositions arc Si—20Cr-2DFe for niobium alloys and MoSiy for molybdenum alloys. 

There are transition metals in many of the products that people use in daily life. Some of these metals have obvious roles, such as the coin metals of gold, silver, and copper. Iron, which makes up 90% of all metal that is refined, or purified for use, is found in everything from tools to paper staples to washing machines. The most important iron product is steel, an iron-based metal alloy. Most steel made for manufacturing purposes is iron alloyed with the element carbon, which makes the steel much harder than iron alone. Several other transition metals are alloyed with iron to make different kinds of steel for different uses. Vanadium, niobium, molybdenum, manganese, chromium, and nickel are all used in steel alloys. For instance, chromium and nickel are alloyed with iron to create stainless steel, a type of steel that does not rust and is used in surgical instruments, cookware, and tools. Some famous landmarks such as the top of the Chrysler skyscraper in New York City and the St. Louis Gateway Arch are covered in stainless steel. 

FP-4 (zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony)—are only slightly soluble (<1 wt %) in the process alloy, thus will partition between both product streams. The process, as presented, offers no method of FP-4 removal and possibly an unwanted increase in these products would occur if the fuel were to be recycled. However, it would be possible to separate the FP-4 from the plutonium/thorium stream by recovering the plutonium/thorium by hydriding. The FP-4 do not form stable hydrides and would remain in solution. 

The method based on the use of DAM has been applied for determining titanium in biological materials [11], silicate rocks [32,99,100], cast iron and steel 33], molybdenum and tungsten [6,18], vanadium [18], zirconium, hafnium, and niobium [101], lithium fluoride [102], nickel, aluminium, and molybdenum alloys [11], and ferrotitanium [103]. Titanium was determined in aluminium alloys with the use of DAM in the presence of SnCh [35,104]. 

Most of these are carbon-manganese-molybdenum alloys with small additions of chromium and/or nickel plus vanadium or niobium. Vanadium or niobium acts as a carbide stabilizer and grain refiner, improving both elevated temperature strength and notch ductility. An exception is Fortiweld (MOBO 45 is the same steel), which is a boron-treated 1/2% molybdenum steel. This alloy is the cheapest of the group, but has hardly been used for reactors in the U.K., possible because its impact properties in thick sections are not so attractive as alternative steels. 

A thermal treatment is utilized to intentionally precipitate phases, causing a strengthening of the alloy. An alloy addition of one or more of titanium, niobium, molybdenum, copper, or aluminum generates the precipitating phase. The final alloy can be solution treated because all alloying elements are in solid solution and the material is in its softest or annealed state. In this condition, the material can be formed, machined, and welded. After fabrication, the unit is exposed to an elevated temperature cycle (aging) that precipitates the desired phases to cause an increase in mechanical properties. 

Alloy 625, also known as Inconel alloy 625, is used both for its high strength and aqueous corrosion resistance. The strength of alloy 625 is primarily a solid solution effect from molybdenum and niobium (Columbian). Alloy 625 has excellent weldability. The chemical composition is shown in Table 15.7. 

Although columbium (niobium) stabilized alloy G from formation of chromium-rich carbides in the heat-affected zones of the welds, secondary carbide precipitation still occurred when the primary columbium carbides dissolved at high temperatures, and the increased carbon in the matrix increases the tendency of the alloy to precipitate intermetallic phases. Alloy G-3 has lower carbon (0.015% maximum vs. 0.05% maximum for alloy G) and lower columbium (0.3% maximum vs. 2% for alloy G). The alloy also possesses slightly higher molybdenum (7% vs. 5% for alloy G). 

Biocompatible materials that have been successfully used for implantable medical device packaging include titanium and its alloys, noble metals and their alloys, biograde stainless steels, some cobalt-based alloys, tantalum, niobium, titanium-niobium alloys, Nitinol, MP35N (a nickel-cobalt-chromium-molybdenum alloy). 

Antonova et al. (33) discuss different fluxing agents in combination with combustion in a tube furnace at 1250 to 1300°C in an oxygen stream of 200 ml/min. Carbon dioxide is determined by titrimetry. For niobium alloys they propose copper as fluxing agent, for molybdenum alloys a mixture of zinc oxide and copper, and for tungsten alloys copper oxide. 

There were two different liner material classes under consideration a refractory metal alloy and a Ni-base superalloy. The refractory options consist of niobium, tantalum, or molybdenum alloys. The Ni-base superalloy options are the same as those for the outer pipe Inconel 617, Haynes 230, and Nimonic PE-16. -Considerations that would have affected liner selection include the performance of the material at high temperatures, material compatibility with the insulation, reactor core materials, and turbine, as well as the interface with the reactor and turbine. 

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