Structural Properties at Low Temperatures

Structural Properties at Low Temperatures It is most convenient to classify metals by their lattice symmetiy for low temperature mechanical properties considerations. The face-centered-cubic (fee) metals and their alloys are most often used in the construc tion of cryogenic equipment. Al, Cu Ni, their alloys, and the austenitic stainless steels of the 18-8 type are fee and do not exhibit an impact duc tile-to-brittle transition at low temperatures. As a general nile, the mechanical properties of these metals with the exception of 2024-T4 aluminum, improve as the temperature is reduced. Since annealing of these metals and alloys can affect both the ultimate and yield strengths, care must be exercised under these conditions. 

Both compounds are also unstable and undergo a structural distortion at low temperature with a marked change in their electrical properties. It is properly an electronic-Peierls transition, at 53 K, in the case of TTF TCNQ [2], and a spin-Peierls transition, at 381 K, in the case of RbTCNQ [67,69] (see the next section). 

R. Michael McClintock and Hugh P. Gibbons, Mechanical Properties of Structural Materials at Low Temperatures, National Bureau of Standards Monograph 13, U.S. Government Printing Office, Washington, D.C., 1960,180 pp. 

III. In some instances, recent data on relevant properties at low temperatures are available, as in the NBS-ARPA-Battelle Handbook [% but more are needed. In particular, data on low-temperature properties of materials for very large loadcarrying welded or bolted structures are not available. Radiation damage at 4 K and the effect of thermal cycling on irradiated metals and organics are other areas where little information is available. The same is true of composite materials, both as structural elements and as thermal and electrical insulators. Furthermore, since very large quantities of material will be necessary, and the structures will probably be subject to close public scrutiny, attention must be paid to heat and product-form... 

The Al-6Cu-Mn alloy differs from other aluminum alloys in that it has relatively good mechanical properties at low temperatures and, therefore, can be successfully used for low-temperature structures. Unlike the duralumin-type alloys, the Al-6Cu-Mn heat-treatable alloy contains more copper (5.8 to 6.8%) and no magnesium [ ]. It is similar to the USA alloy 2219. It has satisfactory weldability and mechanical properties over a wide range of temperatures from 20 K up to 523 K, making it suitable for welded vessels for liquefied gas transportation and storage. 

Tungsten carbide has a low resistance to oxidation. It is the result of low protective properties of tungsten oxides. Dissolution of oxygen in the carbide structure starts at low temperatures, and WO2 and WO3 form upon oxidation at 500°C and higher. The oxidation rate increases drastically at 800°C due to vaporization ofW03 [108]. 

Solids of hydrogen halides allow one to relate the observed trends in vibrational spectra to the differences in their pairwise additive and nonadditive effects. The different hydrogen halide crystals show fairly varying properties. At low temperatures HF, HCl, and HBr have the same type of crystal structure consisting of zig-zag... 

Mechanical Properties at Low Temperatures. Based on its fee crystal structure, Al and its alloys show neither a rapid increase in 3deld stress nor a rapid de-... 

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