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In this work, ultrasonic micro-forging treatment (UMFT) was introduced to achieve homogeneous microstructure, reduce defects and improve mechanical properties of GH3039 superalloy cladding layer processed by directed energy deposition (DED). The microstructure, defects and mechanical properties of the cladding layers treated by UMFT with different ultrasonic powers (UIPs) were investigated. Results revealed a gradient structure as equiaxed grains distributed at the top, a columnar-to-equiaxed transition (CET) region that mixed of columnar dendrites and equiaxed grains distributed at the middle and columnar dendrites at the bottom of the cladding layer was formed. After UMFT, the proportion of equiaxed grains was increased, the average size of equiaxed grains was refined to 10 μm from 16 μm, the orientation of grains was more uniform and the phases enriched of Al, Ti, C, Nb and Mo were precipitated. The grain refinement can be attributed to the fracture of columnar dendrites induced by the ultrasonic vibration during solidification. Besides, the porosity of the cladding layer was reduced after UMFT. The microhardness of the cladding layers exhibited a depth-dependent gradient at the top region. The microhardness of the top surface was the highest and showed an increasing trend with the increase of UIP. The microhardness of different grain morphologies exhibited no substantial difference. However, due to grain refinement and precipitation of strengthening phase induced by UMFT, the microhadness of some local locations were improved. These results indicated UMFT has a significant effect on improving the microstructure, defects and mechanical properties of the deposited cladding layer.

This work uses first-principles total energy calculations on the basis of density functional theory to predict the structural stability, mechanical and thermodynamic properties of Zn atom doped AlL...

A laminate and gradient structured (LGS) AZ31 magnesium alloy was produced via a combination of surface mechanical attrition treatment (SMAT) and accumulative roll-bonding (ARB) in an attempt to im...

A magnesium-based ‘supra-nanometre-sized dual-phase glass-crystal’ (SNDP-GC) coating had been fabricated on AZ31 alloy by magnetron sputtering. Surface mechanical attrition treatment (SMAT) was also introduced to form a gradient structure in order to reduce the hardness mismatch between Mg-based SNDP-GC coating and substrate. Microstructure, mechanical properties and corrosion behaviors of the as-received AZ31 (AR), AZ31 with Mg-based SNDP-GC coating (SC) and AZ31 after SMAT with Mg-based SNDP-GC coating (SSC) were investigated by optical microscope, scanning electron microscopy, transmission electron microscope, X-ray diffraction, Vickers hardness penetrator and electrochemical characterization. Results revealed the Mg-based SNDP-GC coating together with a gradient structure contributed to the improved microhardness. The decreased hardness mismatch between the coating and substrate prevented the delamination of the coating from the substrate. There is a decrease trend in Ecorr in sequence of AR, SC and SSC, while a rise in icorr in the same sequence. Corrosion uniformity was decreased in sequence of AR, SC and SSC, and corrosion cracks exhibited on corrosion products due to formation of galvanic cells and stress concentration. These results indicated the presence of gradient structure and Mg-based SNDP-GC coating led to better mechanical properties but worse corrosion resistance.

The effect of rolling temperature on AZ31 alloy with accumulative roll bonding (ARB) had been investigated. The results showed that dynamic recrystallization occurs and forming shear bands in the direction of shear stress, exhibit the shape that width decreases from the surface to the inside when ARB at 450 °C. Strength was increased result by strain hardening after ARB process, with compromise of elongation was attributable to the internal crack. Microhardness was enhanced after ARB, while decreasing with the increase rolling temperature. Because of the formation of shear band, microhardness of outer plate was lower than inner plate. Interface bonding strength was increased by improving ARB temperature. Interface bonding is a process in which dynamic recrystallization occurs on both sides of the interface, fine recrystallized grains constantly swallowed and replace the original grains until the interface is annihilated. Crack initiation in shear band and extends along the shear band.

Observing different types of pores in aluminum alloy from A356 high-pressure die casting by X-ray computerized tomography and scanning electron microscopy, we found that equivalent spherical diameters of pores obeyed the 3-parameter lognormal distribution rather than the 2-parameter one. Statistically, the sphericity of most round gas pores with smooth inner surfaces consisting of oxide films was > 0.58, while the sphericity of shrinkage pores with unfractured dendrites was

The pressure-dependence of mechanical, electronic and thermodynamic properties of metastable (L12 type) and stable (D023 type) Al3Zr precipitations in Al–Li alloys were investigated by employing the first-principle calculations. The calculated equilibrium parameters are in good agreement with experimental and previous calculation results available. Elastic properties including bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and universal anisotropic index are determined by Voigt–Reuss–Hill approximation. It is found that for both phases, external pressure can improve the mechanical stability, ductility and plasticity. The electronic structures are determined to reveal the bonding characteristics of both phases. In addition, both phonon method and Gibbs program have been proposed to predict thermodynamic properties of two phases. All of these results can help to have a better understanding of the physical and chemical properties of Al3Zr precipitations in Al–Li alloy. And can offer th...

For most current POI (point-of-interest) recommendation algorithms, only the common visited POIs among users are used to calculate the similarity among users. Due to the high sparsity of the data, the recommendation result of POI is inaccurate. Aiming at this problem this paper proposes a method to determine the similarity among users by combing the similarity that using Cosine similarity with the similarity among users by Jensen-Shannon divergence (JS divergence) after mining the user interest distribution with the Latent Dirichlet Allocation (LDA). At the same time combining POI’s commentary text information, rating information, geographical location information and friend relationship information in social networks, a multi-Factor personalized POI recommendation model Sc-Ge is proposed to improve the precision and recall rate of POI recommendation. Experiments are carried out on the comment dataset Yelp, and it is concluded that this model is better than other mainstream POI recommendation algorithms.

High-speed railway has achieved remarkable development in China, and safety monitoring of high-speed railway is becoming an important research. Fiber bragg grating (FBG) sensing technology is applied for monitoring and early warning system of high-speed railway track condition in this paper. The sensor network is built by putting FBG sensors on the high-speed rail tracks, which is necessary for real-time online monitoring of railway track temperature, displacement and strain. These different variables are collected, processed and analyzed by FBG demodulator. In addition, the railway track temperature prediction model are established based on relevance vector regression algorithm, which further improves the prediction accuracy and generalization performance. The system has been applied in the real-time online monitoring and early warning system of Guangzhou-Shenzhen-Hong Kong high-speed railway track condition. The system is running in good condition and playing an important role in early warning.