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Niobium carbide (NbC) is often used as a reinforcing phase to improve the mechanical properties of composite coatings, but its low thermal conductivity makes the flow of molten pool poor, and the cladding layer is prone to defects such as non-fusion and slag inclusion. Therefore, in this paper, Ni60–NbC composite coatings with different NbC content were prepared by laser cladding technology, and the 10 vol% graphene-20 vol% NbC-70 vol% Ni60 composite coatings were prepared under the optimal NbC component. The effects of the addition of NbC and graphene on the microstructure and microhardness of the coating were systematically discussed. The results show that the microhardness of 20 vol% NbC composite coating is increased from 680.1 HV to 882.9 HV compared with Ni60 coating without NbC.The composite coating with both NbC and graphene has a microhardness of up to 1048HV, which is 18% higher than the composite coating with only 20 vol% NbC. The mechanism is that the addition of graphene promotes the formation of chromium carbide (Cr23C6, Cr7C3) and increases the fluidity of the molten pool, which causes small niobium carbide particles to dissolve and recondense to form large particles. Large niobium carbide particles and chromium carbide jointly inhibit the excessive growth of other grains. This study provides a new idea for laser cladding of nickel-based composite coatings.

The joining of zirconium alloys is an important issue in the field of nuclear energy since zirconium alloys are often used as nuclear fuel cladding tube. The article reviews the research progress on the diffusion bonding, brazing and resistance welding of zirconium alloys. The main focus of this work is on the process parameters, interfacial microstructure and mechanical properties of joint. For diffusion bonding, the process parameters including temperature and interlayer have significant influence on the properties of joint. The range of temperature and the selection of interlayer was reviewed and the influence of them on interfacial microstructure and properties of joints was also discussed. For brazing, the influence of brazing filler, temperature and holding time on the properties of joint was summarized. For resistance welding, the main process parameters include welding current and contact resistance. Numerical simulation method was often used to describe the influence of process parameters on microstructure during welding end plug with cladding tube. Some suggestions for the further research direction on the welding and joining of zirconium alloys were also proposed.

Membrane separation technology plays a vital role in natural gas processing due to its cost-effectiveness, excellent efficiency and low energy consumption. In this study, we demonstrate the superior permeability and selection capability of the graphene kirigami (GK) membrane for natural gas purification via molecular dynamics insights. The results indicate that the separation rate of the GK membrane can reach up to 4.1 × 106 GPU (gas permeance unit) with nearly 100% selectivity of the permeating gases mixture (H2S, CO2 and N2) over the non-permeating gas (CH4). Furthermore, the Monte Carlo simulation reveals that the unique geometry of the GK structure introduces a funnel-shaped adsorption channel to guide specific molecules’ separation and enhance the efficiency of the membrane. Compared with the nano-porous graphene (NPG) membrane, the gas separation rate of the GK membrane can be increased by more than four times. Moreover, the GK membrane does not require the modification of functional groups in natural gas purification, which provides great convenience for future applications in practical projects. The considerable potential of the GK membrane underpinned by the findings of this study will attract broad interest in the field of separation and purification.

In this paper, CrCoNi medium-entropy alloy coatings were prepared by laser cladding process, and ultrasonic impact treatment (UIT) with different impact amplitudes (0 μm, 10 μm, 15 μm, 20 μm) was performed on the coating surface to systematically study the microstructure and properties of the coatings. The results showed that the surface deformation of the coatings became more and more severe with the increase of ultrasonic impact amplitude. After the UIT treatment, the impact layer with obvious plastic deformation appeared on the top of the coating, and the depth of the impact layer gradually increased with the increase of the amplitude, and the influence range of the impact layer could be roughly judged according to the increase of the small-angle grain boundary on the top, which was about 200–400 μm at the amplitude of 20 μm. The grain size was 64.067 μm at an amplitude of 20 μm, which was about 34% of the original size. The microhardness of the coating was found to increase with the impact amplitude, and when the impact amplitude reached 20 μm, the microhardness of the coating reached 374.1 HV0.2, which was 122% higher than that of the unimpacted coating. Also, the wear resistance of the Cr–Co–Ni coating increased with the increase of impact amplitude, and the wear weight loss of the coating increased by 85.71% compared to the untreated specimen at an impact amplitude of 20 μm.