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The preparation of a single crystal superalloy surface overlay welding coating to improve its high-temperature mechanical properties is of great significance for prolonging the service life of blades. This work selected two types of welding wire alloys, CoCrMo and CoCrW, to prepare coatings on the surface of a single crystal superalloy. A comparative study was conducted on their mechanical properties, such as tension, compression, fatigue, durability, and wear at a high temperature of 900 ℃, aiming to reveal the high-temperature mechanical properties of the two types of welding coatings. Results showed that the average high-temperature tensile strength of the CoCrMo welded specimen was smaller than that of the CoCrW welded specimen; the average high-temperature duration of CoCrMo welded specimens at 150 MPa was lower than the average duration of CoCrW welded specimens; the high-temperature fatigue life of CoCrMo welded specimens at 220 MPa was 7.186 × 105; and the average high-temperature wear rate of CoCrMo sample was 3.64 × 10−6 mm3·N−1·m−1. The CoCrW alloy was more wear resistant than CoCrMo. The hardness of CoCrMo welded joints gradually increased from the substrate to the heat-affected zone and then to the fusion zone, and was much higher in the fusion zone than in the CoCrW alloy. [ABSTRACT FROM AUTHOR]

In order to study the evolution characteristics of the pore structure of medium and high rank coals, the low-temperature nitrogen adsorption method and the FHH fractal theory model were used to explore the regularity of pore structure characteristics and fractal characteristics of different rank coals. The results show that as the coal rank increases, the BET specific surface area of the coal increases first and then decreases, the BJH pore volume gradually decreases. As for the coal pore size distribution, the number of micro-pores decreases first and then increases, and the number of small and mesopores increases first and then decreases; the value of the FHH fractal dimension D1 can quantify the roughness of the coal surface, which increases with the increase of coal rank. The change of D1 value of the gas-fat coal and lean coal is small, and anthracite stage increases more, the range is 2.256 2 to 2.461 3; the D2 value can quantify the complexity of the pore structure of coal. The D2 value decreases first and then increases with the increase of coal rank, ranging from 2.459 1 to 2.806 5.

Lubrication and cooling are two important issues in the current industrial field. The former is of great significance to the energy consumption caused by friction, which is directly related to the service reliability and life of the components in the mechanical field. The latter is very important for the management and application of the final generation of thermal energy in the process of energy conversion.Combination of them exists widely in fields such as aerospace, automobile machinery, etc.Addition of nano-materials into working fluid can not only significantly improve the thermal conductivity of heat transfer fluids, but also achieve anti-wear and lubrication of mechanical parts, showing excellent mechanical and thermal comprehensive properties. Nanofluids are a good working medium for both aspects.In this paper, in view of the hotspot of graphene nanofluids, the theoretical basis and method of dispersion of graphene nanofluids were reviewed, and the factors affecting the suspension stability of graphene nanofluids were investigated.The thermal conductivity mechanism, the influencing factors and the current progress of graphene nanofluids were analyzed. The main reasons for the non-large-scale application of nanofluids were analyzed. The progress of graphene as an additive in the field of lubrication was reviewed. Finally, the application design of graphene nanofluid synergistically enhanced heat transfer and antifriction lubrication was proposed. In the current spacecraft and other applications, due to the lack of extensive research on the thermal mechanical coupling performance of graphene nanofluids and the stability of spacecraft and long-term operational reliability, future research should be based on the current aerospace heat transfer medium and focus on the targeted design of nanoparticles.The research on dynamic flow heat transfer performance and loop life based on space environment should be carried out, which will lay a theoretical foundation and provide technical support for the future application of nanofluids in the spacecrafts.

Remaining useful life (RUL) prediction for bearing is a significant part of the maintenance of urban rail transit trains. Bearing RUL is closely linked to the reliability and safety of train running, but the current prediction accuracy makes it difficult to meet the requirements of high reliability operation. Aiming at the problem, a prediction model based on an improved long short-term memory (ILSTM) network is proposed. Firstly, the variational mode decomposition is used to process the signal, the intrinsic mode function with stronger representation ability is determined according to energy entropy and the degradation feature data is constructed combined with the time domain characteristics. Then, to improve learning ability, a rectified linear unit (ReLU) is applied to activate a fully connected layer lying after the long short-term memory (LSTM) network, and the hidden state outputs of the layer are weighted by attention mechanism. The Harris Hawks optimization algorithm is introduced to adaptively set the hyperparameters to improve the performance of the LSTM. Finally, the ILSTM is applied to predict bearing RUL. Through experimental cases, the better performance in bearing RUL prediction and the effectiveness of each improving measures of the model are validated, and its superiority of hyperparameters setting is demonstrated. [ABSTRACT FROM AUTHOR]

Casting Al6.5Cu2Ni0.3Ti0.5Zr0.25V alloy is applied to aircraft engine components, but the casting defects are difficult to avoid. In this research, the local defects of casting heat‐resistant Al6.5Cu2Ni0.3Ti0.5Zr0.25V alloy parts are repaired by the arc‐directed energy deposition method. To examine the mechanism of the microstructure in the repaired zone of the heat treatment condition on the high‐temperature characteristics, the microstructure evolution of the repaired zone before and after heat treatment is analyzed. The results indicate that stratification exists in the sedimentary layer, however, the overall grain distribution is relatively uniform. After heat treatment, the microstructure of the repaired zone is changed, Cu element distribution becomes uniform and dendrite segregation disappears; simultaneously, the grain in the repaired zone mainly exists as high angle grain boundaries, which improves the fracture resistance ability of the material. At 350 °C, the average tensile strength, yield strength and elongation are 120.0 MPa, 98.6 MPa and 12.9%, respectively, the tensile strength reaches 94.1% of the matrix. Dimples abound on the fracture's exterior, and the fracture form of the repaired zone is microporous aggregate fracture. δ‐Al3CuNi and γ‐Al7Cu4Ni enhance the grain boundary strength, and θ′‐Al2Cu diffuses from the α‐Al matrix during aging, which is the main reason for the excellent high‐temperature performance of the repaired zone. [ABSTRACT FROM AUTHOR]

Background: The reliance on a solitary linear reference genome has imposed a significant constraint on our comprehensive understanding of genetic variation in animals. This constraint is particularly pronounced for non-reference sequences (NRSs), which have not been extensively studied. Results: In this study, we constructed a pig pangenome graph using 21 pig assemblies and identified 23,831 NRSs with a total length of 105 Mb. Our findings revealed that NRSs were more prevalent in breeds exhibiting greater genetic divergence from the reference genome. Furthermore, we observed that NRSs were rarely found within coding sequences, while NRS insertions were enriched in immune-related Gene Ontology terms. Notably, our investigation also unveiled a close association between novel genes and the immune capacity of pigs. We observed substantial differences in terms of frequencies of NRSs between Eastern and Western pigs, and the heat-resistant pigs exhibited a substantial number of NRS insertions in an 11.6 Mb interval on chromosome X. Additionally, we discovered a 665 bp insertion in the fourth intron of the TNFRSF19 gene that may be associated with the ability of heat tolerance in Southern Chinese pigs. Conclusions: Our findings demonstrate the potential of a graph genome approach to reveal important functional features of NRSs in pig populations. [ABSTRACT FROM AUTHOR]