ADVANCES IN CRYOGENIC ENGINEERING
824(2006); http://dx.doi.org/10.1063/1.2192327View Description Hide Description
Shape memory alloys possess the ability to return to a preset shape by undergoing a solid state phase transformation at a particular temperature. This work reports on the development and testing of a low temperature thermal conduction switch that incorporates a NiTiFe shape memory element for actuation. The switch was developed to provide a variable conductive pathway between liquid methane and liquid oxygen dewars in order to passively regulate the temperature of methane. The shape memory element in the switch undergoes a rhombohedral or R‐phase transformation that is associated with a small hysteresis (typically 1–2 degrees C) and offers the advantage of precision control over a set temperature range. For the NiTiFe alloy used, its thermomechanical processing, subsequent characterization using dilatometry, differential scanning calorimetry and implementation in the conduction switch configuration are addressed.
Effect of Thermal Cycling on Martensitic Transformation Characteristics of (Ni47Ti44)100−xNbx Shape Memory Alloys824(2006); http://dx.doi.org/10.1063/1.2192328View Description Hide Description
(Ni 47Ti44)100−x Nb x (x=3, 9, 15, 20, 30at.%) shape memory alloys are prepared and their transformation temperatures and transformation latent heats under conditions of various thermal cycling times are systematically investigated by differential scanning calorimeter (DSC). It is found that the martensitic transformation behavior in the experimented alloys are strong influenced by the Nb‐content and thermal cycling times. The results showed that the transformation temperatures of experimented alloys decreased with increase of the cycling number, and the lower the Nb‐content in the (Ni 47Ti44)100−x Nb x alloy, the more the Ms temperature decreased. With increasing of the thermal cycling times, the martensitic transformation latent heats ( Δ H B2→B19′ ) and the reverse transformation latent heats (Δ H B19′→B2) of (Ni 47Ti44)100−x Nb x alloys all linearly decrease, but the decrease amplitude is not high.
824(2006); http://dx.doi.org/10.1063/1.2192329View Description Hide Description
The low temperature heat capacity of (Er1−xHox)In3 alloys have been measured from ∼3.5 to 350 K. The alloys are found to order antiferromagnetically between 4.45 K (ErIn3) and 8.0 K (HoIn3). The alloys, especially for 0 ⩽ x < 0.7, have large volumetric heat capacities at the magnetic ordering temperature (as large as 1.5 J/cm3K), and thus may be useful regenerator materials for cooling down to 4 K. The concentration dependence of the lattice constant, the magnetic ordering temperature, and the maximum value of the heat capacity are anomalous between x = 0.25 and x = 0.75 and do not follow a linear dependence between the two end members ErIn3 and HoIn3.
824(2006); http://dx.doi.org/10.1063/1.2192330View Description Hide Description
This paper deals with recent developments of extensometers working in cryogenic environments down to 4 K capable to transfer accurate, high resolution, and reproducible signals for a variety of engineering measurement tasks such as tensile, fracture, compression, fatigue, flexural, and component tests. Based on strain gauge technology it was possible to manufacture extensometers with resolutions lower than 20 nm. The extensometers foreseen for uniaxial tensile tasks were designed as a twin extensometer system firmly attached onto the specimen and providing for bending during loading by averaging the signals either via software or by special electrical wiring. In particular, for structural component tests, different types of extensometer designs were represented. With the production of a new series of small, low weight, worldwide first twin extensometer system of ∼ 0.5 g mass it was possible to resolve the local strains of fragile Nb 3Sn wires. Besides the measurement of distances, it was possible to develop ultra sensitive load cells (resolution < 0.01 N) using a similar technique working inside a cryostat capable of avoiding the loads resulting from the friction between the 4 K rig and the machine actuator. In addition, modern laser technology based on an averaging extensometer system is presented for future generation high sensitivity transducer systems to be used in materials testing.
Linear Thermal Expansion Measurements of Single Crystal Silicon for Validation of Interferometer Based Cryogenic Dilatometer824(2006); http://dx.doi.org/10.1063/1.2192331View Description Hide Description
Linear thermal expansion measurements were performed for high‐purity P‐type single crystal silicon over a temperature range of 30K to 310K to validate the accuracy of JPL’s interferometer‐based Cryogenic Dilatometer Facility. This system was developed to better characterize thermophysical properties of precision engineering materials at cryogenic temperatures for space‐based optical systems. An accurate measurement of these properties is critical for the success of missions such as the James Webb Space Telescope and the Terrestrial Planet Finder Coronagraph where picometer‐level instabilities and thermal deformations impact performance. Results from these single crystal silicon measurements show a mean system repeatability of 4 ppb/K in the coefficient of thermal expansion (CTE) from 35K to 305K. Comparison with NIST/CODATA recommended values shows agreement of better than 2 ppb/K from 30K to 80K, better than 11 ppb/K from 80K to 165K, and better than 2 ppb/K from 165K to 305K.
824(2006); http://dx.doi.org/10.1063/1.2192332View Description Hide Description
Nano crystalline Bi0.85Sb0.15 powders were prepared by mechanical alloying. The powders were pressed into pellets and then pressed to form bulk samples under high pressure of 6 GPa at different pressing temperature and time. The X‐ray diffraction shows that there are no secondary phases. Electrical conductivity, Seebeck coefficient and thermal conductivity were measured in the temperature range of 80–300 K. The thermoelectric properties were compared with those of single crystals presented in previous studies by other authors. The electrical conductivity and thermal conductivity are lower than that of single crystal. The absolute Seebeck coefficient has a maximum value of 173 μV/K at about 150 K. The largest figure‐of‐merit 3.46 × 10−3 K−1 is about 50 % higher than that of single crystal at 200 K.
824(2006); http://dx.doi.org/10.1063/1.2192333View Description Hide Description
The CMR manganites are one of the most interesting and widely noticed objects in the physical and materials sciences based on their possible application on CMR properties and sensor technology at low‐temperature, strong correlation characteristic, ordering of spin/charge/orbital including lattice degree of freedom. In this paper, a Kondo‐like transport was observed in the term of a metal‐semiconductor transition at low temperature in this ferromagnetic metallic phase system. The experiments show that this kind of Kondo‐like behavior can be tuned with an applied magnetic field and depends strongly on the content of a spin glass phase, which can be explained by the scattering of spin disorder or/and antiferromagnetic cluster in a micro‐scale. In undoped sample, the M‐SC transition would mean the existence of intrinsic spin disorder with magnetic inhomogeneities and gives a direct evidence of Kondo effect in ferromagnetic metallic manganites. It was also proved that Kondo‐like abnormity appears not only in the metal containing small amounts of magnetic impurities but also in ferromagnetic conducting compound containing the spin disorder clusters, which would possibly be one of general characteristics for the strong correlation manganites.
Measurement of the Emissivity of Clean and Contaminated Silver Plated Copper Surfaces at Cryogenic Temperatures824(2006); http://dx.doi.org/10.1063/1.2192334View Description Hide Description
An experiment has been designed, fabricated, and conducted to measure emissivity of clean and contaminated metallic surfaces at temperatures between 25 K and 35 K. Samples of silver‐plated copper with a total surface area of 0.25 m2 are secured to the coldhead of a single stage cryocooler and enclosed within an effective black thermal shield, which has an effective emissivity of 0.95 and temperatures between 275 K and 280 K. From error analysis, a sample with an emissivity of 0.020 had an experimental error between +/− 0.001 and +/− 0.002. From measurement of the radiation heat transfer, the emissivity at 30 K was 45% of the emissivity that was measured at 300 K for a set of silver‐plated copper samples. In addition, 110 μg of water vapor was sufficient to increase the emissivity of the silver‐plated copper between 50% and 200%.
824(2006); http://dx.doi.org/10.1063/1.2192335View Description Hide Description
Low‐density alloys include aluminum alloys, titanium alloys and magnesium alloys. Aluminum alloys and titanium alloys have been widely investigated and used as structural materials for cryogenic applications because of their light weight and good low‐temperature mechanical properties.
For aerospace applications, persistent efforts are being devoted to reducing weight and improving performance. Magnesium alloys are the lightest structural alloys among those mentioned above. Therefore, it is necessary to pay attention to magnesium alloys and to investigate their behaviors at cryogenic temperatures. In this paper, we have investigated the mechanical properties and microstructures of some magnesium alloys at cryogenic temperatures. Experimental results on both titanium and magnesium alloys are taken into account in considering these materials for space application.
824(2006); http://dx.doi.org/10.1063/1.2192336View Description Hide Description
Cryogenic treatment and its variables have been described. Results of eight engineering tests carried out on cryotreated parts have been presented. Cryogenic treatment of metal parts enhances useful properties which in turn, improves various strengths. Our tests viz. Abrasion, Torsion, Fatigue, Tensile, Shear, Hardness and Impact on Mild steel, Cast Iron, Brass and Copper show that the cryogenic treatment improved useful properties of mild steel parts appreciably but did not show promise with brass and copper parts.
824(2006); http://dx.doi.org/10.1063/1.2192337View Description Hide Description
It has been shown by Shibata et al. that serrated deformation behavior of metals at cryogenic temperatures can be simulated generally very well by computer calculation. At the CEC‐ICMC 2003, however, they reported that there are several differences between the deformation behavior of 304L steel obtained by the calculation and by actual tensile tests. For instance, the degree of load drops in the calculated serration of 304L steel is smaller than that of 316L steel in liquid helium, while the degree of load drops in the actual serration of 304L steel is larger than that of 316L steel. Shibata et al. suggested that this confliction was attributed to martensitic transformation, which is induced by much amount in practice during deformation of 304L steel but had not been considered in the calculation. In the present paper, heat, strain and strengthening generated by the transformation are considered in the calculation and their effects on the serration are examined. As a result, it was shown that the transformation strain decreases strain‐hardening rate and transformation heat increases the degree of the load drops and temperature rises in the serration. Transformation strengthening increases strain hardening rate increases. If only martensite nucleated in Stage 3 is assumed to strengthen the steel, calculations reveal overall stress‐strain curves approximately similar to ones actually observed.
Result of International Round Robin Test on Young’s Modulus Measurement of 304L and 316L Steels at Cryogenic Temperatures824(2006); http://dx.doi.org/10.1063/1.2192338View Description Hide Description
Ogata et al. reported in 1996 results of international Round Robin tests on mechanical property measurement of several metals at cryogenic temperatures. Following the report, the standard deviation of Young’s modulus of 316L steel is much larger than those of yield and tensile strengths, that is, 4.6 % of the mean value for Young’s modulus, while 1.4 % and 1.6 % of the mean values for yield and for tensile strengths, respectively. Therefore, an international Round Robin test on Young’s modulus of two austenitic stainless steels at cryogenic temperatures under the participation often institutes from four nations has been initiated within these two years. As a result, the ratios of standard deviation to the mean values are 4.2 % for 304L and 3.6 % for 316L. Such a drop in the standard deviation is attributable to the decrease in the number of institute owing to the application of single extensometer or direct strain gage technique.
824(2006); http://dx.doi.org/10.1063/1.2192339View Description Hide Description
This paper reports a study to relate microstructure to cryogenic mechanical properties of a 316L plate and its weldments. Both the tensile and fracture toughness test values at 4 K are governed by microstructure that is influenced by the thermo‐mechanical treatment of the materials. The mechanical properties are better when the loading direction is parallel to the rolling directions. 77 K Charpy impact values show much stronger dependence on the orientations than 4 K fracture toughness and tensile test values. This indicates that the anisotropy in microstructure results in much higher anisotropy in fracture mechanisms in dynamic mode than in static mode. Therefore, care has to be taken when one relates the 77 K Charpy impact strength to 4 K fracture toughness. Stress relieve in weldment enhances the fracture toughness and yield strength, but reduces the strain‐hardening rate and ultimate tensile strength.
Effect of an Aging Heat Treatment on the 4 K Fracture and Fatigue Properties of 316LN and Haynes 242824(2006); http://dx.doi.org/10.1063/1.2192340View Description Hide Description
Since the introduction of the cable‐in‐conduit conductor (CICC) concept, a variety of alloys have been proposed for fabricating the jacket. The jacket provides primary containment of the liquid helium coolant and is typically also the primary structural component for the magnet coils. These functions create requirements for strength, toughness, fatigue crack resistance, and fabricability. When the CICC uses Nb3Sn superconductor, the conduit alloy must retain good mechanical properties after exposure to the superconductor’s reaction heat treatment. Here we present data from cryogenic fracture toughness and fatigue crack growth rate tests on 316LN and a Cr‐Mo‐Ni base super‐alloy (Haynes 242) at 4 K before and after the exposure to the heat treatment. These alloys are presently being considered as candidates for use in the next‐generation series connected hybrid magnet for the NHMFL. Both of the alloys are found to have adequate fatigue and fracture properties for the CICC application while the superalloy has distinctly better elastic properties of modulus and thermal expansion.
Effect of Heat Treatment on Low Temperature Toughness of Reduced Pressure Electron Beam Weld Metal of Type 316L Stainless Steel824(2006); http://dx.doi.org/10.1063/1.2192341View Description Hide Description
Austenitic stainless steels are considered to be the candidate materials for liquid hydrogen vessels and the related equipments, and those welding parts that require high toughness at cryogenic temperature. The authors have found that the weld metal of Type 316L stainless steel processed by reduced pressure electron beam (RPEB) welding has high toughness at cryogenic temperature, which is considered to be due to the single‐pass welding process without reheating effect accompanied by multi‐pass welding process.
In this work, the effect of heat treatment on low temperature toughness of the RPEB weld metal of Type 316L was investigated by Charpy impact test at 77K. The absorbed energy decreased with higher temperature and longer holding time of heat treatment. The remarkable drop in the absorbed energy was found with heat treatment at 1073K for 2 hours, which is as low as that of conventional multi‐pass weld metal such as tungsten inert gas welding. The observations of fracture surface and microstructure revealed that the decrease in the absorbed energy with heat treatment resulted from the precipitation of intermetallic compounds near delta‐ferrite phase.
Tensile Properties, Ferrite Contents, and Specimen Heating of Stainless Steels in Cryogenic Gas Tests824(2006); http://dx.doi.org/10.1063/1.2192342View Description Hide Description
We performed tensile tests at cryogenic temperatures below 77 K and in helium gas environment for SUS 304L and SUS 316L in order to obtain basic data of mechanical properties of the materials for liquid hydrogen tank service. We evaluate tensile curves, tensile properties, ferrite contents, mode of deformation and/or fracture, and specimen heating during the testing at 4 to 77 K. For both SUS 304L and 316L, tensile strength shows a small peak around 10 K, and specimen heating decreases above 30 K. The volume fraction of α‐phase increases continuously up to 70 % with plastic strain, at approximately 15 % plastic strain for 304L and up to 35 % for 316L. There was almost no clear influence of testing temperature on strain‐induced martensitic transformation at the cryogenic temperatures.
824(2006); http://dx.doi.org/10.1063/1.2192343View Description Hide Description
Mechanical low temperature investigations were carried out to determine the cryogenic mechanical properties of newly developed Fe‐Cr‐Mn alloys with contents of chromium between 5 % and 10 % and manganese between 30 % and 40 % under the Project G‐811, Russia. The final products were forged, rolled, and solution heat treated to obtain appropriate plate sizes necessary for the mechanical measurements. The tensile properties of these alloys determined between 4 K and 7 K show for certain alloy combination high elongation values at fracture of greater than 50 % with considerable high yield strengths around 900 MPa. The measured fracture toughness values with small scale compact tension specimens using elastic plastic J‐tests show KIC data between 100 MPa√m and 220 MPa√m according to the alloy combination. Fatigue crack growth rate (FCGR) measurements of these alloys result also in some alloy combination case, high resistance against crack propagation with measured Paris coefficients of m ∼ 5 and C ∼ 8.5 E‐13 mm/cycle. Thermal expansion of these alloys has been also determined resulting in values between 1600 μm/m and 1700 μm/m expansion from 5 K to 290 K.
824(2006); http://dx.doi.org/10.1063/1.2192344View Description Hide Description
The National Compact Stellerator Experiment (NCSX) is the first of a new class of stellarators. The modular superconducting coils in the NCSX have complex geometry that are manufactured on cast stainless steel (modified CF8M) winding forms. Although CF8M castings have been used before at cryogenic temperature there is limited data available for their mechanical properties at low temperatures. The fatigue life behavior of the cast material is vital thus a test program to generate data on representative material has been conducted. Fatigue test specimens have been obtained from key locations within prototype winding forms to determine the 77 K fatigue crack growth rate. The testing has successfully developed a representative database that ensures confident design. The measured crack growth rates are analyzed in terms of the Paris law parameters and the crack growth properties are related to the materials microstructure.
Effect of Specimen Diameter on Tensile Properties of Austenitic Stainless Steels in Liquid Hydrogen and Gaseous Helium at 20K824(2006); http://dx.doi.org/10.1063/1.2192345View Description Hide Description
Tensile tests using round bar type specimens of 3, 5 and 7 mm in diameter were conducted at 20K in liquid hydrogen and also in gaseous helium at the same temperature for three major austenitic stainless steels, JIS SUS304L, 316L and 316LN, extensively used for cryogenic applications including liquid hydrogen transportation and storage vessels. Stress‐strain curves were considerably different between circumstances and also specimen diameter, resulting in differences of strength and ductility. In liquid hydrogen, serrated deformation appeared after considerable work hardening and more active in specimens with larger diameter. Meanwhile serrated deformation was observed from the early stage of plastic deformation in gaseous helium at 20 K and serration was more frequent in specimens with smaller diameter. The serrated deformation behaviors were numerically simulated for 304L steel with taking thermal properties such as thermal conductivity, specific heat, heat transfer from specimens to cryogenic media into account, and some agreement with the experiments was obtained.