Ta-based alloys

P.-Y. Lee, J.-L. Yang, Solid-State Amorphization in Ta-based alloy system by mechanical alloying technique, Mater. Sci. Eng.,... 

The influence of alloying Ta with W is illustrated in Fig. 3.1-164 for Ta2.5W and TalOW, which are the main commercial Ta-based alloys. 

After deformation both Nb- and Ta-based alloys are usually heat treated in high vacuum before delivering in order to achieve a fine grained primarily recrystallized microstructure. 

The heating of the winding insulation will lead to the outgassing of the organic materials which make up the Insulation. Since the coolant in the alternator is in thermodynamic contact with all the other components in the primary loop, it is important that the alternator does not outgas any material which can lead to material damage of other components. For example, Nb- and Ta> base alloys cannot be exposed to sources of carbon and oxygen as they suffer from rapid... 

Researchers have tried to fabricate plates using many different metals— mainly, stainless steel, aluminum alloys, titanium alloys, nickel alloys, copper alloys, intermetallic alloys, and metal-based composites such as carbon fiber-reinforced aluminum alloys, carbon fiber reinforced copper alloys, etc. [26]. Although Ta, Hf, Nb, Zr, and Ti metals show good corrosion resistance and chemical stability [6], the cost of fhese metals is too high for them to be used as materials in metal plates. That is why relatively cheaper iron-based alloys, particularly stainless steel, have been popularly studied as plate material. In the following secfions, we will infroduce sfainless sfeel (SS) and SS plates, which have been extensively investigated and show promise for the final applications [6,11]. 

Chromizing and Related Diffusion Processes. Chromizing is similar to aluminizing. A thin corrosion and wear resistant coaling is applied to low cost steels such as mild steel, or to a nickel-based alloy. In the related boroni/ing process, a thin boron alloy is produced for extreme hardness, wear, and corrosion resistance. Siliconizing is yet another process used especially lor coaling of the refractory metals Ti. Nb. Ta. Cr. Mo. and W. 

Molybdenum, niobium, and tantalum (bcc crystal structure) form a continuous series of solid solutions with tungsten, but only Nb and Ta additions lead to a strong straining effect. Higher additions of Nb and Ta raise the recrystallization temperature but also increase the DBTT and thus decrease the workability. Therefore, none of these binary or ternary tungsten base alloys developed in the past [6.2] has attained commercial importance. The only important tungsten-base solid-solution alloy today is tungsten-rhenium. 

Superalloys are produced via master alloys. In case of nickel-based alloys they include NiW and more complex nickel-based alloys containing Cr, Ta, and Mo. Some examples are given in Table 8.5. All raw materials have to be of high purity. Melting (performed in induction furnaces), casting and cooling takes place in vacuum. Master alloys are supplied in small lumps or as powder. 

They also contain low amounts of other metals such as Al, V Nb, Ta, Mn, Zr and/ or Sn. The only pure metals used for medical devices are Ti and Ta. The only binary alloys applied for biomaterials are Ti-base alloys, for example, Ti30Nb, Ti30Ta Ti(n)Mn, and memory super alloys NiTi (Bradley 1994 Breme 1994 Breme and Wadewitz 1989). 

The oxidation resistance of TiAl alloys can be improved by special pre-oxidation treatments (Suzuki etal., 1991). Alternatively, it can be improved by alloying with Nb, Ta, and W which, however, reduces the ductility whereas V, Cr, and Mn, which are used for increasing ductility, reduce the oxidation resistance (Kim, 1989). Ti Al-based alloys with high contents of Nb have been studied recently with respect to the conditions for protective scale formation, and indeed protective oxidation has been found at 1400°C for an Al content of 50 at.% (Brady et al., 1993). In view of the oxidation problems of the titanium alu-minides a coating has been proposed for providing sufficient oxidation protection, and various approaches have been studied (Nishiyama etal., 1990 Taniguchi etal., 1991 b Yoshiharaet al., 1991 Wuand Lin, 1993). 

JA Charles. The coming ages of copper and copper-based alloys and iron A metallurgical sequence. In TA Wartime, JD Muhle, eds. The Coming of the Age of Iron. New Haven, CT Yale University Press, 1980. 

As discussed before, hard metal-like composites can be prepared by pressureless sintering of ternary borides with Fe, Ni, or Co melts. Materials with x-phase (M21M2 Bg, where = Fe, Ni, or Co, and M = Zr, Hf, Nb, Ta, or W with M as the matrix phase) have not been developed for technical use but Ni-based alloys with x are in applications as wear- and corrosion-resistant coatings on steels [355]. The x phase is also used for the improvement of the creep resistance of Ni-based superalloys. 

Metals are utilized for applications requiring high strength and/or endurance, such as structural components of heart valves, endovascular stents, and stent-graft combinations. Commonly used alloys include austenitic stainless steels (SS), cobalt-chrome (Co-Cr) alloys including molybdenum-based alloys, tantalum (Ta), and titanium (Ti) and its alloys. Elgiloy, a cobalt-nickel-chrome-iron... 

Table HI lists the neutron absoiption cross sections for many of the metals described above, as well as their cross section relative to the typical reactor material, zirconium. Materials with a very large cross section relative to zirconium would result in a reduction in the thermal utilization factor f and hence a reduction in Nff. Consequently, Ta, W, V, Mo and Ni based alloys would be impractical choices for a reactor core. From this literature survey, it appears that Fecralloy would provide the greatest promise as a containment material for liquid lead. In addition Tantiron may be an alternate choice. More extensive studies on the applicability of inhibitors such as Ti should be undertaken to determine their affect on the corrosion resistance of these materials. 

Pd/Au, Pd/Cu, and Pd/Ag alloy membranes have been the most extensively studied among aU of the Pd-based binary alloy membranes. Other Pd-based binary alloy membranes that have also been studied for H2 separation include Pd/Y, Pd/Ru, Pd/Ni, Pd/ Ee, and Pd/Ce. There are many ternary or even higher levels of Pd-based alloy membranes that are smdied for H2 separation, such as Pd/In/Ru, Pd/Au/Ag, Pd/Cu/Ni, Pd/ Ag/Ru, Pd/Cu/Y, and Pd/Cu/Ta. It has been reported that a Pd/In/Ru ternary alloy membrane can withstand thermal cycles in a gas mixmre containing up to 1.5% H2S. 

It has already been conhrmed that similarly treated titanium-based alloys such as, Ti—6A1—4V, Ti—6A1—2Nb—Ta, and Ti—15Mo—5Zr—3A1 also form... 

As stated in the introduction, Ta coating may be used as substrate in the preparation of DSA oxygen electrodes it consists of a thin and porous layer of Iridium oxide, which acts as catalyst, obtained by thermal oxidation of an iridium compound on a valve metal. The lifetime of the anode in water electrolysis in extreme conditions of polarization (anodic current = 50 A/m ), acid concentration (30% m/m) and temperature (T = 80°C) is sensitive to the corrosion resistance of the valve metal This is shown on table I [24], which standardized life time (lifetime reported for the mass surface density of the catalyst Ir02) for some varieties of titanium base alloys and a tantalum coating as substrate ... 

Peters TA, Kaleta T, Stange M, Bredesen R. Development of thin binary and ternary Pd-based alloy membranes for use in hydrogen production. J Membr Sci 2011 383 124-34. 

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