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• The sound welded joint was obtained with Ni interlayer for 316L/Cu dissimilar laser welding joint. • No welding defects and spherical particles were formed in the fusion zone. • The average tensile strength of dissimilar welded joint is 408 MPa at 77 K. To improve the quality of welded joints between copper and 316L stainless steel, laser welding with Ni interlayer was carried out. A sound welded joint was obtained and the microstructures as well as mechanical properties were investigated. Results indicate that no welding defects or spherical particles were formed in the fusion zone. The microstructures in the fusion zone were characterized as dendritic grains, and no macroscopic segregation was observed. The welded joint failed at copper base material with an average tensile strength of 408 MPa at 77 K, and ductile fracture mode with dimples on the fracture surface were presented. Moreover, the addition of Ni interlayer prevents formation of welding defects and spherical particles and improves mechanical properties of the joint. [ABSTRACT FROM AUTHOR]

• Mechanical properties of 316LN stainless steel with cryogenic pre-strain were studied at different temperatures (RT, 77 K and 4.2 K). • The pre-strained samples stretched at cryogenic temperature obtain higher mechanical strength. • The samples stretched at 77 K possess higher elongation and hardness than RT and 4.2 K, the mechanism was explained. • The results are attributed to the changes in dislocation density and martensite transformation due to temperature and cryogenic pre-strain. The 316LN stainless steel (SS) used for TF conduits in the ITER must undergo a series of pre-deformation during the fabrication. In order to investigate the variation of mechanical properties of 316LN SS with different temperature and cryogenic pre-strain, the cryogenic pre-strained samples with 0%, 15%, 25%, and 35% pre-strain were prepared and stretched at room temperature (RT), 77 K and 4.2 K, respectively. The yield strength (YS), ultimate tensile strength (UTS), elongation and microhardness of the samples were measured. Besides, the Scanning Electronic Microscopy (SEM) and Transmission Electronic Microscopy (TEM) were applied to observe the microstructure of 316LN SS. The magnetic measurements for the samples were carried out to investigate the volume percent of phase transformation. The results indicate that the YS, UTS and microhardness of 316LN SS are improved by means of cryogenic pre-strain and the decrease of elongation of pre-strained samples is different at different temperatures. All 316LN samples show the ductile fracture. The dislocation of samples promotes by cryogenic pre-strain and hinders by cryogenic temperatures. The martensitic transformation occurs after all pre-strained samples were stretched. The volume percent of α' martensite is minimal at RT and increases dramatically at cryogenic temperatures (77 K and 4.2 K). The combination of dislocation density and martensitic transformation results in changes in the 316LN SS mechanical properties. [ABSTRACT FROM AUTHOR]

• The epoxy resin has a low viscosity and long pot life. • At 77 K, the epoxy resin offers high tensile strength and modulus. • The superconducting magnet exhibits high shear and compressive strength at 77 K. Superconducting magnet is a key component in magnetic resonance imaging (MRI). In general, vacuum pressure impregnation (VPI) technology is used for insulating system of the superconducting magnet. Performance of the superconducting magnets is affected by the adhesion strength between superconducting wires and resins at cryogenic temperature. In this study, experimental superconducting coil was prepared by modified bisphenol-A type epoxy resin and the VPI technology. Tensile, shear, and compressive properties of the samples cut from the superconducting coil were measured at both room temperature (RT) and liquid nitrogen temperature (77 K), and the bonding properties between the superconducting wire and the resin were discussed. The results show that the resin exhibits low viscosity, long pot life and higher mechanical strength, and it is suitable for impregnating superconducting magnets by VPI technology. Moreover, the shear and compressive strength of the impregnated superconducting magnet at 77 K are significantly higher than that at room temperature, with the increase of 132% in radial compressive strength, 170% in axial compressive strength, 63% in radial shear strength and 70% in axial shear strength, respectively. This study provides references for the design of insulation for superconducting magnet system and the manufacture of insulating materials for MRI superconducting magnets. [ABSTRACT FROM AUTHOR]

Laser welding of modified 316LN steel with a thickness of 20 mm was conducted using a YLS-20000 fiber laser. The microstructure of the weld joint was characterized and tensile and fracture toughness tests were carried out. The microstructure evolution of the fracture specimens was studied systematically to elucidate the fracture mechanism. The weld was composed of the single austenite phase and was characterized by cellular and columnar grains, and the grain size became coarser with a weak orientation. The R m values of the laser welded joints were almost equal to that of the base metal both at RT and 4.2 K, and the fracture surfaces were featured by ductile fracture with quantities of dimples and microvoids. The fracture toughness of the weldments decreased to ˜84% of that of the parent metal at 4.2 K. Enhancement of the fracture toughness was attributed predominantly to the presence of twins and to the fine grain size, and the reduction was caused by the partially stress-induced phase transformation of the austenite to martensite. The synergistic effects of these factors result in a favorable improvement in the fracture toughness of the weldment. [ABSTRACT FROM AUTHOR]