Nb-based alloys

There is hardly any published data on tensile creep on these systems. Compressive creep rates for the Mo-base materials exhibited minimum creep rates of 1 x 10 9/s at 1200°C / 100 MPa and 1 x 10"8/s at 1300°C / 100 MPa. For Nb-based alloys the minimum creep rates are 5 x 10"8/s at 1200°C /100 MPa and 10 7/s at 1300°C / 100 MPa. Much work is needed in determining tensile creep mechanisms and damage in both these systems. 

B. V. Cockeram and R. A. Rapp, Boron-modified and germanium-doped silicide diffusion coatings for Ti-Al-Nb, Nb-Ti-Al, Nb-Cr and Nb-base alloys. In Processing and Design Issues in High Temperature Materials, eds. N. S. Stoloff and R. H. Jones, Warrendale, PA, Mining, Metallurgy and Meterials Society, 1996, p. 391. 

Figure 3.1-165 summarizes values of Rpo.2 of the most common Nb-based alloys at elevated temperatures. AU of these alloys are hardened primarily by solid solution strengthening however, small amounts of precipitates are present. 

Similar improvements in the resistance to embrittlement and high values of hydrogen permeabihty have been reported for the Nb-W-Mo alloy membranes whose permeation tests are reported in Fig. 4.9. Finally, an alloy of V with W 5 mol% has also been studied. This alloy exhibited better mechanical properties (strength, ductility) than the Nb-based alloy, as well as excellent hydrogen permeabihty without hydrogen embrittlement. Figure 4.10 provides the results of the permeation test of this V-W alloy. 

The cold-rolling technique has been applied to synthesize new types of dense metal membranes made of Nb-based alloys. In particular, Luo et al. verified that an Nb-Ti-Ni alloy consisting only of the primary phase and the eutectic phase exhibited high hydrogen permeability and good resistance to hydrogen embrittlement. ... 

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. 

The full substitution of Zr by Nb is important since the oxygen reactivity of Nb is lower than that of Zr or Hf, and because the amorphous precursors of some Fe-Nb-B based alloys can be prepared under ambient atmosphere [70], making NANOPERM mass producible. 

Apart from its technical performance the material is based on the inexpensive raw materials iron and silicon. The amorphous precursor material for the Fe-Si-B-Nb-Cu alloys, furthermore, is easily accessible by rapid solidification from the melt - a well established technique for large scale production of amorphous metals. 

The EPR technique has been used for other alloys as well, including cast (36) and wrought (37,38) duplex stainless, as well as Ni-base alloys (39). Lee (38) used DL-EPR testing to determine the minimum amount of Ti and/or Nb required to render Type 430 SS immune from intergranular attack. In some cases, the details of the experimental method (i.e., solution temperature, KCNS and H2S04 concentrations, scan range) must be modified to differentiate best the levels of sensitization of interest. For example, Scully and Kelly doubled the... 

The focal point of this work is to extend the Nb-Ti-Ni membrane development work with a direct replacement of Nb with V. Characterization of the resulting microstracture and measurement of the permeabihty of the novel V-based alloy is reported. 

In conclusion, we note that deposition of submono- and monolayers of adatoms is the most controllable and reliably predictable method of obtaining metallic nanodimension compositions. At least two or three kinds of adatoms can be deposited in a strictly layer-by-layer fashion on single-crystal substrates [217], and mixed adlayers can also be obtained. The combined deposition of adatoms and phase deposits of metals [217] is even more promising. Among the metals, HTSC components such as lead, thallium, bismuth, and copper rank among the most thoroughly studied adatomic systems. Electrodeposition methods are also applied to the technological preparation of conventional superconductors based on Nb-Sn alloys [218]. 

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. 

In 1979, White [3.2] observed that, by milling elemental Nb and Sn powders, the distinct X-ray diffraction peaks of the elements disappeared and typical diffuse peaks of an amorphous pattern showed up. But these samples did not show the superconducting transition temperature of vapor-quenched amorphous Nb-Sn alloys. In 1983, Koch et al. reported on the Preparation of amorphous Ni60Nb40 by mechanical alloying [3.3]. After the detection of amorphization by solid-state reaction in evaporated multilayer films by Schwarz and Johnson [3.4] (see also Chap. 2), Schwarz et al. [3.5] proposed after investigating glass formation in Ni-Ti alloys, that amorphization by mechanical alloying is also based on the solid-state reaction process. Within the last couple... 

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