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This contribution presents a comprehensive analysis of the low temperature deformation behavior of CoCrFeMnNi on the basis of quasistatic tensile tests at temperatures ranging from room temperature down to 4.2 K. Different deformation phenomena occur in the high-entropy alloy in this temperature range. These include (i) serrated plastic flow at certain cryogenic temperatures (4.2 K/8 K), (ii) deformation twinning (4.2 K/8 and 77 K), and (iii) dislocation slip (active from 4.2 K up to room temperature). The importance of deformation twinning for a stable work-hardening rate over an extended stress range as well as strain range has been addressed through the use of comprehensive orientation imaging microscopy studies. The proposed appearance of ε-martensite as well as a previously uninvestigated route of analysis, essentially a quantitative time-dependent, strain-dependent, and stress-dependent evaluation of the serrated plastic flow in CoCrFeMnNi is provided.

The effects of variable cryogenic temperature on the mechanical and electromechanical properties are implemented for REBCO coated conductor (CC) tapes. A versatile facility was used to provide the successive cooling environment from room temperature (about 293 K) to 5 K with a cryogenic-type extensometer for the strain measurement of the tested samples. At different cryogenic temperatures, the mechanical parameters were measured during the REBCO CC tapes being stretched. The cryogenic temperature dependence of mechanical behavior, including elastic limit, offset yield strength and equivalent elastic modulus of the REBCO CC tapes with two different substrates were captured at different cryogenic levels. In addition, the tensile strain dependence of the critical current ( I c ) of REBCO CC tapes with two different substrates at variable cryogenic temperatures was investigated, and the relations between I c degradation and mechanical properties were revealed. The experimental results show that all the investigated mechanical parameters exhibit a temperature dependence. A uniaxial strain dependence of I c is found under all the test temperatures, and the irreversible strains are between elastic limit and offset yield strains regardless of temperature for both two kinds of test specimens.

In the present work, the effects of carbon-based nanofillers (0.5 wt%), i.e., graphene nanoplatelets (GNPs), carbon nanofibers (CNFs), and carbon nanotubes (CNTs), on the cryogenic temperature (77 K) mechanical properties of carbon fiber reinforced polymers (CFRPs) were investigated. The study utilized an ex situ conditioning method for cryogenic tests. The nanofillers were mixed with the epoxy matrix by a solvent-free fluidized bed mixing technique (FBM), while unidirectional carbon fibers were impregnated with the resulting nanocomposites to manufacture CFRP samples. Optical microscopy was employed to analyze the dispersion of the carbon-based fillers within the matrix, revealing a homogeneous distribution in nanocomposites containing GNPs and CNFs. Fracture toughness tests confirmed the homogeneity of the GNP-loaded systems, showing an improvement in the stress intensity factor (KC) by 13.2% and 14.7% compared to the unmodified matrix at RT (25 °C) and 77 K, respectively; moreover, flexural tests demonstrated a general increase in flexural strength with the presence of carbon-based nanofillers at both temperature levels (RT and 77 K). Additionally, interlaminar shear strength (ILSS) tests were performed and analyzed using the same ex situ conditioning method.

Fabric composites are widely employed in self-lubricating bearing liners as solid lubrication materials. Although the tribological behaviors of fabric composites have been extensively studied, the cryogenic tribological properties and mechanisms have been scarcely reported and are largely unclear to instruct material design for aerospace and other high-tech applications. Herein, the tribological properties of polytetrafluoroethylene (PTFE)-based hybrid-fabric composites were investigated at cryogenic and ambient temperatures in the form of pin-on-disk friction under heavy loads. The results suggest that the friction coefficients of the hybrid-fabric composites obviously increase with a decrease in wear when the temperature drops from 25 to −150 °C. Moreover, thermoplastic polyetherimide (PEI), as an adhesive for fabric composites, has better cryogenic lubrication performance than thermosetting phenol formaldehyde (PF) resin, which can be attributed to the flexible chemical structure of PEI. The excellent lubrication performance of hybrid-fabric composites is attributed to the transfer film formed by PTFE fibers on the surface of fabrics.

In this work, the transport properties of charge carriers in β-Ga⁢2O⁢3 were investigated, along with intrinsic physical mechanisms such as lattice vibrations, impurity scattering, and interfacial effects. The high-field behavior of carrier mobility was characterized using vacuum deposition techniques for the fabrication of electrodes with ohmic contacts, and the Hall effect measurement system was employed to test the temperature-dependent mobility of Sn-doped n-type (100) and (001) β-Ga⁢2O⁢3 samples at a cryogenic temperature. A predictive model for β-Ga⁢2O⁢3 mobility was developed by examining the effects of the temperature on the scattering mechanisms based on a theoretical transport model. The experimental results for β-Ga⁢2O⁢3 mobility, which varied with the temperature and doping concentration, showed good agreement with the theoretical model within the temperature range of 15–300 K. The maximum discrepancy between the predictive model and the experimental data was less than 5%. This study provides valuable theoretical insights for the design and simulation of β-Ga⁢2O⁢3 devices.

EH36 offshore engineering steels with varied yttrium-based rare earth content were prepared by trials in industrial production. The effects of yttrium-based rare earth on the inclusions and cryogenic temperature impact properties of EH36 offshore engineering steel were investigated by scanning electron microscopy, automatic statistics of inclusions, thermodynamic analysis and fracture morphology analysis. Yttrium-based rare earth could refine the inclusions and modify irregular Al2O3 and MnS inclusions into small, spherical, regular rare earth inclusions. The optimal impact properties were found in EH36 steel with 0.020 wt.% yttrium-based rare earth. Compared with 0RE steel, the RE-inclusions were within 3 μm (91.95% of total inclusions) in diameter and were spherical or quasi-spherical when dispersed in 200RE steel. Meanwhile, the cryogenic temperature impact properties significantly increased: 200RE steel impact properties were increased by 245.1% at −80 °C.

High-manganese steel (high-Mn) is valuable for its excellent mechanical properties in cryogenic environments, making it essential to understand its deformation behavior at extremely low temperatures. The deformation behavior of high-Mn steels at extremely low temperatures depends on the stacking fault energy (SFE) that can lead to the formation of deformation twins or transform to ε-martensite or α′-martensite as the temperature decreases. In this study, submerged arc welding (SAW) was applied to fabricate thick pipes for cryogenic industry applications, but it may cause problems such as an uneven distribution of manganese (Mn) and a large weldment. To address these issues, post-weld heat treatment (PWHT) is performed to achieve a homogeneous microstructure, enhance mechanical properties, and reduce residual stress. It was found that the difference in Mn content between the dendrite and interdendritic regions was reduced after PWHT, and the SFE was calculated. At cryogenic temperatures, the SFE decreased below 20 mJ/m2, indicating the martensitic transformation region. Furthermore, an examination of the deformation behavior of welded high-Mn steels was conducted. This study revealed that the tensile deformed, as-welded specimens exhibited ε and α′-martensite transformations at cryogenic temperatures. However, the heat-treated specimens did not undergo α′-martensite transformations. Moreover, regardless of whether the specimens were subjected to Charpy impact deformation before or after heat treatment, ε and α′-martensite transformations did not occur.

Investigations by electron backscatter diffraction (EBSD) and X-ray diffraction with the use of synchrotron radiation, as well as parallel extended finite element (XFEM) simulations, reveal the evolution of the 316L stainless steel microstructure in the vicinity of a macro-crack developing at the temperature of liquid helium (4.2 K). The fracture propagation induces a dynamic, highly localized phase transformation of face-centred cubic austenite into α’ martensite with a body-centred cubic structure. Synchrotron studies show that the texture of the primary phase controls the transition process. The austenite grains, tending to the stable Brass orientation, generate three mechanisms of the phase transformation. EBSD studies reveal that the secondary phase particles match the ordered austenitic matrix. Hence, interphase boundaries with the Pitsch disorientation are most often formed and α’ martensite undergoes intensive twinning. The XFEM simulations, based on the experimentally determined kinetics of the phase transformation and on the relevant constitutive relationships, reveal that the macro-crack propagates mainly in the martensitic phase. Synchrotron and EBSD studies confirm the almost 100% content of the secondary phase at the fracture surface. Moreover, they indicate that the boundaries formed then are largely random. As a result, the primary beneficial role of martensite as reinforcing particles is eliminated.

Alloy 21-6-9 is an austenitic stainless steel with high strength, thermal stability at high temperatures, and retained toughness at cryogenic temperatures. This type of steel has been used for aerospace applications for decades, using traditional manufacturing processes. However, limited research has been conducted on this alloy manufactured using laser powder-bed fusion (LPBF). Therefore, in this work, a design of experiment (DOE) was performed to obtain optimized process parameters with regard to low porosity. Once the optimized parameters were established, horizontal and vertical blanks were built to investigate the mechanical properties and potential anisotropic behavior. As this alloy is exposed to elevated temperatures in industrial applications, the effect of elevated temperatures (room temperature and 750 °C) on the tensile properties was investigated. In this work, it was shown that alloy 21-6-9 could be built successfully using LPBF, with good properties and a density of 99.7%, having an ultimate tensile strength of 825 MPa, with an elongation of 41%, and without any significant anisotropic behavior.

In this work, the physical characterization of LiGdxY1−xF4 (x = 0.05, 0.3, 0.7, and 1.0) and LiGdF4:Eu3+ microparticles was performed. The distribution coefficient of LiGdxY1−xF4 (x = 0.05) was determined for the first time (0.84). Based on kinetic characterization data, the LiGdF4 sample was chosen for further Eu3+ doping (0.1 and 1.0 at.%). For the LiGdF4:Eu3+ sample, Eu3+ emission was clearly observed under the excitation of Gd3+. This fact indicates an effective energy transfer from Gd3+ to Eu3+. The temperature-dependent spectral characterization of the LiGdF4:Eu3+ (1.0%) sample revealed that in the 30–250 K temperature range, a broad emission peak is evidenced. Its intensity sharply increases with the temperature decrease. We made a suggestion that this phenomenon is related to the irradiation-induced defects. The integrated luminescence intensity ratio of this broad peak and the Eu3+ emission were taken as temperature-dependent parameters. The sensitivity values are very competitive, and the first maximum occurs at 174 K (3.18%/K). The kinetic characteristics of both Gd3+ and Eu3+ did not demonstrate a notable temperature dependence. The LiGdF4:Eu3+ sample showed the possibility of being used as an optical temperature sensor, operating in the cryogenic temperature range.