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Owing to superior physio-chemical characteristics, titanium alloys are widely adopted in numerous fields such as medical, aerospace, and military applications. However, titanium alloys have poor machinability due to its low thermal conductivity which results in high temperature during machining. Numerous lubrication and cooling techniques have already been employed to reduce the harmful environmental footprints and temperature elevation and to improve the machining of titanium alloys. In this current work, an attempt has been made to evaluate the effectiveness of two cooling and lubrication techniques namely cryogenic cooling and hybrid nanoadditive–based minimum quantity lubrication (MQL). The key objective of this experimental research is to compare the influence of cryogenic CO 2 and hybrid nanofluid–based MQL techniques for turning Ti–6Al–4V. The used hybrid nanofluid is alumina (Al 2 O 3 ) with multi-walled carbon nanotubes (MWCNTs) dispersed in vegetable oil. Taguchi-based L9 orthogonal-array was used for the design of the experiment. The design variables were cutting speed, feed rate, and cooling technique. Results showed that the hybrid nanoadditives reduced the average surface roughness by 8.72%, cutting force by 11.8%, and increased the tool life by 23% in comparison with the cryogenic cooling. Nevertheless, the cryogenic technique showed a reduction of 11.2% in cutting temperature compared to the MQL-hybrid nanofluids at low and high levels of cutting speed and feed rate. In this regard, a milestone has been achieved by implementing two different sustainable cooling/lubrication techniques.

Ni-based superalloy GH4169 is widely demanded in the aerospace industry because of its excellent properties. However, the cutting of GH4169 at normal temperature has many challenges, such as tool wear, machining accuracy, and production efficiency. Cryogenic cutting has been an advanced method in assisting material removal machining. This paper focused on the cryogenic cutting performance of GH4169 at different initial temperatures, namely, 20 °C, −30 °C, −80 °C, and –130 °C. Firstly, the cryogenic mechanical properties of GH4169 were obtained by the Hopkinson pressure bar test at speed of 12 m/s and 18 m/s. The obtained data was used to analyze the cryogenic cutting performance of GH4169 at evaluated temperatures. The single factor milling experiments of GH4169 were carried out at room temperature and evaluated cryogenic levels, and the cutting performance in terms of cutting chips, cutting forces, and tool wear was investigated. The results showed that cryogenic cooling at −130 °C could increase the shear yield strength of the GH4169 by around 19.80% and the length of the cutting chip decreased monotonically by 53.45% compared with the length at room temperature. However, the cutting forces were not monotonically decreased. The cutting forces increased with the decrease of temperature when the initial temperature varied from 20 to −80 °C. However, when the initial temperature further dropped to –130 °C, the cutting forces were reduced by 30.60% for Fx , 24.02% for Fy , and 16.15% for Fz , respectively. Similarly, tool wear at the rake face and flank face is the most severe at –80 °C and the least at –130 °C. The average wear bandwidth at room temperature is 92.06 μm and decreases to 83.358 μm at –130 °C, which is reduced by 9.45%.

Owing to poor thermal conductivity, heat dissipation, and high chemical reactivity toward most of the tool materials, temperature elevation in the machining of titanium alloy leads to poor surface quality. Based on analyzing the variation laws of the milling forces under cryogenic cooling, the present investigation concerns the surface integrity (surface roughness, micro-hardness, microstructures, and residual stresses) in cryogenic milling of Ti-6Al-4 V alloy under the application of liquid nitrogen (LN 2 ) as a cooling mode. Findings have indicated a dramatic increase in milling forces, and decreasing surface roughness was observed under variation of jet temperature (20~−196 °C). Besides an increase in cutting speed from 60 to 120 m/min, a linear increase in cutting forces, surface roughness, micro-hardness, and residual compressive stress was observed. The minimum micro-hardness decreased at cutting speed of 90 m/min and up to 30 μm in depth. A holistic comparison between obtained results under cryogenic milling and previously studied results under dry milling at same cutting conditions depicted higher micro-hardness and higher compressive residual stress under cryogenic LN 2 on the machined surface. However, the residual stress under LN 2 cooling conditions tends to decrease relatively slower compared to dry milling. Also, there are no significant differences in grain refinement and twisting under dry and cryogenic LN 2 machining. The research work proves the effectiveness of cryogenic milling in improving the surface integrity of the Ti-6Al-4 V alloy.

In this study, the effect of both cryogenic and dry machining of AZ31 magnesium alloy on temperature and surface roughness was examined. Cryogenic machining experiments were conducted by applying liquid nitrogen at the cutting zone. The cutting parameters (cutting speed, depth of cut, and feed rate) were varied, and their effect on the results was identified. It was found that the cryogenic machining was able to reduce the maximum temperature at the machined surface to about 60% as compared with dry machining. A finite element model was developed to predict the temperature distribution at the machined surface. The simulated results showed good agreement with the experimental data. After analyzing the temperature distribution, the model also suggested that the cryogenic-assisted machining removes heat at a faster rate as to that of the dry machining. An arithmetic model using the response surface method was also developed to predict the maximum temperature at the surface during cryogenic and dry machining. The analysis pointed out that the maximum temperature was greatly affected by the cutting speed followed by feed rate and depth of cut. Cryogenic machining leads to better surface finish with up to 56% reduction in surface roughness compared with dry machining.

Liquid hydrogen is the main fuel of large-scale low-temperature heavy-duty rockets, and has become the key direction of energy development in China in recent years. As an important application carrier in the large-scale storage and transportation of liquid hydrogen, liquid hydrogen cryogenic storage and transportation containers are the key equipment related to the national defense security of China’s aerospace and energy fields. Due to the low temperature of liquid hydrogen (20 K), special requirements have been put forward for the selection of materials for storage and transportation containers including the adaptability of materials in a liquid hydrogen environment, hydrogen embrittlement characteristics, mechanical properties, and thermophysical properties of liquid hydrogen temperature, which can all affect the safe and reliable design of storage and transportation containers. Therefore, it is of great practical significance to systematically master the types and properties of cryogenic materials for the development of liquid hydrogen storage and transportation containers. With the wide application of liquid hydrogen in different occasions, the requirements for storage and transportation container materials are not the same. In this paper, the types and applications of cryogenic materials commonly used in liquid hydrogen storage and transportation containers are reviewed. The effects of low-temperature on the mechanical properties of different materials are introduced. The research progress of cryogenic materials and low-temperature performance data of materials is introduced. The shortcomings in the research and application of cryogenic materials for liquid hydrogen storage and transportation containers are summarized to provide guidance for the future development of container materials. Among them, stainless steel is the most widely used cryogenic material for liquid hydrogen storage and transportation vessel, but different grades of stainless steel also have different applications, which usually need to be comprehensively considered in combination with its low temperature performance, corrosion resistance, welding performance, and other aspects. However, with the increasing demand for space liquid hydrogen storage and transportation, the research on high specific strength cryogenic materials such as aluminum alloy, titanium alloy, or composite materials is also developing. Aluminum alloy liquid hydrogen storage and transportation containers are widely used in the space field, while composite materials have significant advantages in being lightweight. Hydrogen permeation is the key bottleneck of composite storage and transportation containers. At present, there are still many technical problems that have not been solved.

Fracturing of rocks subjected to cryogenic treatment significantly impacts the stability and permeability of underground storage facilities for liquefied natural gas (LNG). However, existing fracturing damage models lack coverage across the entire spectrum of practical engineering conditions, spanning potential temperature ranges from room temperature to − 160 °C and saturation levels from 0 to 100%. Addressing this gap, this study utilizes cracked sandstone disks to investigate the fracture toughness of sandstone following cryogenic treatment to − 160 °C using the Brazilian splitting test. In the experimental setup, treatment temperatures are specified at 15, − 40, − 80, − 120, and − 160 °C, while saturations range from 0 to 100%. The experimental findings reveal that ultralow temperatures reduce the fracture toughness of saturated sandstone by approximately 30%, whereas for dry sandstone, this reduction is approximately 7.4%. This suggests a significant influence of different pore saturations on fracture toughness. A damage model, based on the Boltzmann function, is established to incorporate the effects of both temperature and saturation. This model accurately predicts the damage variable concerning treatment temperature and saturation. Generally, as temperature decreases, the damage variable also decreases, exhibiting two stages: rapid decrease followed by gradual decrease. The transition temperature, marking the division between these stages, tends to be lower in sandstone with higher saturation levels. The experimental results are further discussed within the context of the mineral compositions present in the sandstone, elucidating the thermal–mechanical mechanisms at play. Although the current damage model is specific to sandstone, the methodological approach is generalizable to generic rock types. The damage model’s adaptability allows for testing fitting parameters for specific rock types or adjusting the relevant thermal coefficients. These findings and the developed model offer valuable insights for the reliable analysis of stability and permeability in LNG storage facilities or similar geologic engineering projects.HighlightsThe Mode-I fracture toughness of sandstone under variable saturation conditions subjected to cryogenic temperatures of − 160 °C is investigated.Saturated sandstone experiences more than four times the amount of damage compared to dry sandstone under ultralow temperatures.A damage model is developed to incorporate the influences of both temperature and saturation.

To address the issue of slow temperature adjustment in cryogenic balance, which severely affects the efficiency of wind tunnel tests, this study investigates the temperature control system for cryogenic balance. Considering the wide temperature range and deep cooling requirements of cryogenic wind tunnels, a comprehensive design of the temperature cryogenic was developed. Based on MCGS and PLC, the first domestically developed cryogenic balance temperature control system was implemented. After installation, equipment testing and wind tunnel experiments were conducted. The experimental results indicate that the newly developed system achieves stable temperature control from room temperature to 110 K, which operates reliably, conserves energy, and significantly improves the economic efficiency of cryogenic wind tunnel tests. Furthermore, an analysis of the relationships between balance temperature range, system pressure, and wind tunnel temperature on the system’s thermal performance during tests provides valuable insights for precise control in future applications.

In this paper, the effect of deep cryogenic treatment on the corrosion resistance of 42CrMo low alloy steel is investigated and compared with conventional heat-treated counterparts. The low-temperature treatments of the cryogenic process are −120 °C, −160 °C, and −190 °C, respectively. Electrochemical corrosion tests show that the self-corrosion current density of −120 °C, −160 °C and −190 deep-cooled specimens is reduced by 38%, 20% and 30% respectively compared to the usual heat-treated specimens. Scanning electron microscope analysis shows that the precipitation of fine carbides on the surface of the samples treated at −120 °C has improved their corrosion resistance. Electrochemical impedance spectroscopy also shows that the samples treated with −120 °C cryogenic treatment have the smallest corrosion tendency. At a −160 °C deep-cooling process, the precipitated carbide aggregation limits the corrosion resistance of the material. The corrosion resistance of the samples in the −190 °C process group is between the two. The simulation results also express a similar trend to the electrochemical corrosion results.