Materials at Low Temperatures
Research in Europe during the late 1800s led to the liquefaction of first oxygen (1877), followed by nitrogen (1883), hydrogen (1891), and, finally, helium (1908). These fluids provided scientists the opportunity to conduct research at low temperatures on subjects as basic and diverse as magnetic transitions and deformation twinning. In 1911 Onnes discovered the phenomena of superconductivity, which stimulated the fundamental studies of solid materials. For many years materials at low temperatures were found mainly in the research laboratory. In recent years, research in this field has responded to needs for materials to be used in practical systems at low temperatures.
As refrigeration techniques improved and liquid air, nitrogen, and oxygen became readily available, suitable materials were needed for storage Dewars, industrial processing equipment, and refrigerators. The need to transport and store large quantities of liquefied natural gas (LNG) led to the development and use of tough iron-nickel and aluminum alloys that are less expensive than the austenitic stainless steels traditionally used for small liquid-nitrogen Dewars. The safety and long service lifetime demanded of these large containers required an increased understanding of materials properties at low temperatures.
The space program, utilizing liquid oxygen and hydrogen fuels, led to the development and use of high-strength, lightweight materials, such as colddrawn stainless steels and precipitation-hardened aluminum alloys, and the first use of nonmetallic composites.
The development of stabilized, practical superconductors generated a need for large, strong structures for the very high magnetic field superconducting magnets and other superconducting applications. The development of structural alloys to contain liquid helium and to withstand the large forces from superconducting magnetic fields is currently underway. In this complex application, the requirements are high strength, adequate toughness, good weldability, and minimum costs; strengthened austenitic steels are the leading candidate. Significant developments in insulating nonmetallics, structural composites, and the superconductors themselves are also the results of persistent research.
Design and test procedures for materials at low temperatures have improved along with the materials themselves. Because material properties change dramatically with temperature, new parameters take on added importance. There are many examples: The development of fracture mechanics has led to new test procedures and the opportunity for a quantitative design assessment of structural lifetime. Measurements of fracture toughness and fatigue crack growth rates are now indispensable for most cryogenic applications. Balancing the thermal expansion of components eliminates residual thermal stresses. The composite materials engineer can actually design a material to meet his needs by combining properties of constituents.
The thirteen contributors to this book formed the nucleus of the materials group of the Cryogenics Division of the National Bureau of Standards (NBS). The Division was formed in 1952 as part of the expansion of NBS to their new Boulder (Colorado) Laboratories, and our group was composed of specialists in physical and mechanical properties of solids at low temperatures. We primarily served emerging low-temperature technologies requiring cryogenic materials, such as space, LNG storage and transportation, magnetohydrodynamic energy conversion, fusion, high-energy physics, and other aspects of applied superconductivity. We evolved into the largest materials research group in the free world devoted to low-temperature research.
We have now dispersed into several disciplines, but most of our lowtemperature research capabilities and interests remain. While these are still strong, we thought it appropriate to summarize our data and experience in this book. We hope our contributions will establish a firm basis for the understanding of materials behavior and property measurement to use for design and material selection at low temperatures.
We acknowledge the support and encouragement of Dave Sutter of the Office of High-Energy Physics, Department of Energy, and of Carl Henning, Dick Foley, Ed Dalder, and Don Beard of the Office of Fusion Energy, Department of Energy. Marilyn Stieg was indispensable in assisting us in editing. Expert typing was performed by Vickie Grove, Carole Montgomery, JoAnne Wilken, and Deb Wilson. We greatly appreciate the intensive reviews of specific chapters by our colleagues.
ALAN F. CLARK