R. P. Reed

Advances in cryogenic engineering materials

Preface. Editorial. Best Paper Awards. 1999 International Cryogenics Materials Conference Board of Directors. A: Structural and Cryocooler Materials. Mechanical Properties: Austenitic Alloys & Steels. Mechanical Properties: Non-Ferrous Alloys. Mechanical Properties: Structural Composites. Mechanical Properties: Polymers. Mechanical Properties: Ceramics. Physical Properties: Metals, Polymers, Ceramics, & Composites. Magnetic Materials. Testing Methods. B: Superconductors. High Temperature Superconductors: Processing. High Temperature Superconductors: Properties. High Temperature Superconductors: Applications. High Temperature Superconductors: Coated Conductors. Low Temperature Superconductors: NbTi. Low Temperature Superconductors: A-15 Compounds. Low Temperature Superconductors: Ac Losses, Stability, & Current Distribution. Low Temperature Superconducting Cables. Indexes. Author Index. Materials Index. Subject Index.

Materials at low temperatures

The aim of this volume is to establish a firm basis for the understanding of materials behavior and property measurement to use for design and materials selection at low temperatures. The fourteen chapters of this book were written and edited by members of the materials group of the Cryogenics Division of the National Bureau of Standards. Each chapter concludes with a lengthy list of references with the full bibliographic citations. A detailed subject index is included. Contents abridged: Elastic properties. Electrical properties. Magnetic properties. Fracture mechanics. Martensitic phase transformation. Composites. Temperature, strain, and magnetic fields measurements.

Nitrogen in austenitic stainless steels

Nitrogen alloyed in austenitic stainless steels improves austenite stability, mechanical properties and corrosion resistance. Steels supersaturated with nitrogen (“super-nitrogen steels”) have been investigated, which rival the latest ferritic steels in strength but have potentially greater toughness.

Stacking fault energies of fcc Fe--Ni alloys by x-ray diffraction line profile analysis

The stacking fault energies of the fee alloy series Fe-28 Ni to pure Ni were investigated using X-ray diffraction line profile analysis. A minimum stacking fault energy of about 70 mJ/m2 occurs at the approximate composition of Fe-40 pct Ni. From this point, the lower nickel alloys rapidly increase to a very high stacking fault energy, estimated to be 200 mJ/m2, while the energies of the high Ni alloys rise linearly to the Ni value of 214 mJ/m2. Anomalous reductions of the lattice parameter after cold work were found for the low nickel alloys; this was interpreted as evidence for Fe3Ni ordering and corrections to the stacking fault energy were made.

Fracture and strength properties of selected austenitic stainless steels at cryogenic temperatures

Abstract Austenitic stainless steels have an excellent combination of mechanical and physical properties for load-bearing structures of large superconducting magnets for plasma containment in magnetic fusion experiments. To assess their relative suitability fracture toughness, fatigue crack growth, and tensile properties data for five austenitic steels at 295, 76, and 4 K have been obtained. The steels were AISI 304, 316, 304LN, and 316LN, and an Fe-21cr-12Ni-5Mn alloy with a higher nitrogen content than the other four grades. The two principal findings were the systematic variation of yield strength with nitrogen content and a systematic inverse correlation between fracture toughness and yield strength. Data from previous studies are reviewed which confirm the trends of the present data.

Mechanical, thermal, and electrical properties of selected polymers

Abstract An extensive compilation has been completed on the mechanical, thermal, and electrical properties of six commercially available polymers. These data are discussed and summarized here as a function of temperature, radiation, and frequency. A brief description and characterization of each polymer is included.

Properties of candidate ITER vacuum impregnation insulation systems

Composite insulation systems to be used in the International Thermonuclear Experimental Reactor (ITER) must meet demanding design requirements, including combined shear and compressive stresses, performance at cryogenic temperatures, and continued mechanical and electrical performance after exposure to high levels of neutron and gamma radiation. Several polymeric insulation systems that are reinforced with boron-free glass fabric and are suitable for the vacuum-pressure impregnation (VPI) method of fabrication were screened at 76 K using the short-beam-shear (SBS) test, with the leading candidates then tested in combined shear/compression at cryogenic temperatures. The shear/compression specimens were comprised of two, 12.7.mm diameter, stainless steel chips bonded together by the composite insulation, allowing characterization of its adhesive and cohesive properties. Using the shear/compression test at different ratios of shear to compression, a shear/compression failure envelope for each insulation system can be determined. Production variables of the shear/compression specimens, including molding techniques, were also investigated. The effects of desizing (4 h at 400°C) and heat treating (50 h at 700°C) the glass fabric to simulate the heat treatment of Nb3Sn superconductor, prior to vacuum impregnation, were also examined.

Low temperature thermal properties of composite insulation systems

The thermal contraction and thermal conductivity of candidate composite insulation systems for the International Thermonuclear Experimental Reactor toroidal field coils were measured from 295 to 4 K. Matrix materials consisted of a diglycidyl ether of bisphenol-A epoxy suitable for vacuum impregnation, a tetrafunctional epoxy suitable for pre-impregnation, a polyimide system produced by a high-pressure laminating process, and a bismaleimide system. These matrix materials were combined with S-2 glass fabric and various barrier systems, such as ceramic and organic coatings, polyimide film and mica/glass. Thermal contraction was measured by the strain gauge method in which strain gauges are attached directly to the specimen. The thermal contraction in the through-thickness direction was different at 4 K for each resin system and changed slightly with the addition of electrical barriers. The thermal conductivity of the materials, with and without the electrical barriers, was similar at 4 K, but more distinctive at higher temperatures. The systems with the ceramic coatings exhibited the highest thermal conductivities at all temperatures.

Shear/compressive properties of candidate ITER insulation systems at low temperatures

Abstract Shear/compression tests were performed at 76 and 4 K on candidate composite insulation systems for the International Thermonuclear Experimental Reactor (ITER) toroidal field coils. The insulation systems tested consisted of vacuum-pressure impregnated, pre-impregnated, and high-pressure laminate systems that included electrical barriers such as polyimide film or mica/glass. Sandwich-style specimens, in which the composite insulation is bonded to two AISI 316 stainless steel chips, were used. Two specimens were loaded at an angle, which resulted in combined shear and compressive stresses, and tested simultaneously. Various shear/compression ratios were achieved by using different test fixtures, each at a different angle (15 °, 45 °, 75 ° and 84 °) from the vertical direction. The shear strengths of specimens loaded at 15 ° to 75 ° increased with increasing compressive stress; these specimens experienced shear failures. For specimens loaded at 84 °, the compressive stress increased and the shear strength decreased; the failure modes of these specimens were more compressive than shear. The effects of electrical barriers on shear/compressive properties are also reported.

Inorganic and Hybrid Insulation Materials for ITER

Insulation systems are a critical component in superconducting fusion magnet systems, such as the International Thermonuclear Experimental Reactor (ITER). Past cryogenic magnet systems have often relied on organic composite (e.g., glass/epoxy) materials for insulation. Concerns regarding reliability, radiation resistance, and electrical properties of organic systems have prompted the search for alternate materials, particularly hybrids which incorporate an inorganic barrier. Fabricability, mechanical, and electrical performance of various inorganic and hybrid materials are investigated. Materials include mica based sheets, plasma-sprayed and porcelain-enamel ceramic coatings, polyimide films and coatings, reinforced cement, and polymer conversion ceramic prepregs. Radiation resistance of selected candidate material systems will be evaluated in subsequent investigations.