Titanium alloys have become the material of choice for marine parts manufacturing due to their high specific strength and excellent resistance to seawater corrosion. However, it is still challenging for a single titanium alloy to meet the comprehensive specifications of a structural component. In this study, we have applied a molecular dynamics approach to simulate the aging phase transformation, K-TIG welding process, and mechanical properties of the TC4-TA17 (Ti6Al4V-Ti4Al2V) alloy. The results show that during the aging phase transformation process, changes in the structure of the titanium alloys are mainly manifested in the precipitation of a new phase from the sub-stable β-phase, and after the state stabilization, the α-phase content reaches 45%. Moreover, during the melting and diffusion process of TC4-TA17, aluminum atoms near the interface diffuse, followed by titanium atoms, while relatively few vanadium atoms are involved in the diffusion. Finally, the results of tensile simulations of the TC4-TA17 alloy after welding showed that stress values can reach up to 9.07 GPa and that the mechanical properties of the alloy in the weld zone are better than those of the single alloys under the same conditions. This study will provide theoretical support for the optimization of process parameters for TC4-TA17 alloy welding.

In this paper, Tungsten Inert Gas Welding (TIG) and single-sided welding and double-sided forming have been used to weld the 7A05-T6/5A06-O dissimilar aluminum alloy circular welded joint of a ring-stiffened closed cylindrical sandwich shell. Microstructural characterization and mechanical properties of welded joints were investigated by use of scanning electron microscopy (SEM), backscatter electron diffraction (EBSD) and transmission electron microscopy (TEM), respectively. Hardness distribution and tensile properties of the welded joints were examined. The results showed the failure of the welded joints produced in the fusion zone (FZ). The tensile strength and yield strength of the welded joints were, respectively, 78.87% and 97.24% of the 5A06-O base metal (BM), and the elongation reached 84.29% of 7A05-T6 base metal. Welding high heat input led to the coarse grain size in the fusion zone, and the long-term similar quenching effect can lead to the full dissolution of the strengthening zone of the fusion zone resulting in the reductions of strength and hardness. Around 7A05 heat-affected zone (HAZ), there is an obvious hardening zone and softening zone, the solid solution precipitates into the Rayleigh brilliant η′ (MgZn₂) phase, which results in natural aging strengthening, thus obtaining high hardness. η′ (MgZn₂) enhanced phase dissolved fully and the dislocation density decreased rapidly in the HAZ region resulted in a softening zone with a lower hardness at about (10–18) mm from the center of the weld center.

In recent years, many scholars have paid attention to wear-resistant coatings for shield machine cutterheads due to their very high consumption rates. Among these coatings, nickel-based tungsten carbide (Ni-based WC) is one of the best, showing both corrosion resistance and wear resistance. However, to further improve the wear resistance of such coatings, there are still numerous issues that need to be resolved. Herein, a new method, distinct from conventional methods, is presented. Specifically, the brittle phase W₂C is not widely regarded as the main wear-resistant phase, but we were surprised to find that careful adjustment of its rigid structure can yield satisfactory results. Experimental results and first-principles simulations have indicated that the friction coefficient and weight loss of a coating with a suitable distribution of W₂C are only half of those of a traditional Ni-based WC coating (about five times higher than those of the substrate), which can mainly be attributed to the excellent thermal expansion coefficient and hardness of the W₂C phase. As we expected, the surface morphology of the material after wear revealed that the suitable W₂C layer has a well-defined friction morphology. We hope to provide new ideas for the study of Ni-based WC coatings in shield machine cutterheads.

Gold nanoparticles (AuNPs) have attracted wide attention in the field of catalysis because of their excellent stability and electrical properties. Herein, an accurate vacancy formation energy model based on nanothermodynamics theory is developed, the intrinsic correlation between vacancy formation energy and CO oxidation activity is investigated in detail, and the relationship between vacancy formation energy and activity-influencing factors such as particle size, temperature, and crystal surface is analyzed. The results show an excellent linear relationship between vacancy formation energy and CO oxidation activity, with an accuracy of up to 95%. In addition, the vacancy formation energy also corresponds well to the influencing factors of size, temperature, and crystal surface, and its correspondence is particularly accurate when the size is below 20 nm and the temperature is below 500 K. It can serve as a normalized expression of the three influencing factors. Moreover, the present research reveals that the essence of the vacancy formation energy descriptor is the chemical bond energy, and gives its correspondence with the coordination number, diffusion activation energy, and adsorption energy (with a decrease in vacancy formation energy, the adsorption effect of AuNPs is stronger), further demonstrating the feasibility and accuracy of the vacancy formation energy as a descriptor. This research not only overcomes the problem that traditional single-influence descriptors are difficult to apply in complex environments but also has considerable potential for defect modulation.

Fatigue tests subjected to constant amplitude under the environments of dry air were performed on 5A06-O aluminum alloy, 7A05-T6 aluminum alloy and 5A06-O/7A05-T6 dissimilar aluminum alloy ring welded joints in a new type sandwich high-pressure shell, and the fatigue behaviors were analyzed and compared based on the experimental data, and the mechanisms of welding defect impacts on fatigue properties of the welded joints were deduced from fractographic analysis. It is showed that welding defect has a detrimental influence on fatigue properties of the welded joints. The lower stress level caused the more obvious decrease of fatigue life of the welded joints. Fatigue cracks of aluminum alloys base metal usually initiated at the surface defects such as two-phase particles and inclusions, however, welding defect of welded joints were more likely to cause stress concentration and lead to the early initiation of fatigue cracks, which is dominated in decreasing of fatigue life of the welded joints.