International Journal of Modern Physics B

Aiming at the high-speed friction stir welding deformation and thickness reduction of 1 mm 6061-T6 aluminum alloy sheet, the characteristics of the axial pressure of the welding process and its influence on the joint structure and mechanical properties were analyzed in this paper. Experiments were performed to optimize process parameters. A fuzzy controller with axial pressure error and its change rate as input and welding speed as output had been designed to realize axial pressure control during friction stir welding. The welding axial pressure fluctuates slightly around the target value, and the system was stable with the controller. Besides, the microstructure of the corresponding weld nugget area was uniform, dense, and the transition area was uniform without obvious welding defects. The joint hardness distribution was stable with the classic “W” shape distribution. The mechanical properties of the joint were excellent, and the tensile strength reaches 195 MPa, which was about 70% of the base material (290 MPa).

Titanium alloy is widely applied in the pressure hull of the manned submersible for its good mechanical properties. The operations of the manned submersible include diving, cruising and ascent. The load spectrum of the pressure hull is a typical dwell-fatigue process. The dwell effect is known to induce a reduction in the fatigue life of titanium alloys at room-temperature. The dwell fatigue of the new titanium alloy is the key issue to ensure a safe submersible operation. In this paper, the dwell-fatigue behavior of a new titanium alloy for pressure hull is investigated. It is found that the accumulated strain at the final rupture increases with the increase of dwell time, and the total cycle decreases. The total cycle life of the specimen decreases, and the accumulated strain increases with increasing peak stress level. The introduction of the dwell time at the peak stress will significantly reduce the dwell-fatigue life and the mechanism is due to the accumulation of the plastic strain.

This work aims to discover the effects of ultrasonic vibration and heat pipe assistance during the friction stir welding (FSW) of AZ31 magnesium alloy. The microstructure and mechanical properties of FSWed AZ31 alloy were investigated. The ultrasonic vibration and heat pipe assistance can promote the dynamic recrystallization of AZ31 magnesium alloy during the FSW process, which reduces the inhomogeneous microstructure and the grains and weakens the texture intensity of the FSWed AZ31 alloy. The microstructure and texture of the joint are regulated by the ultrasonic vibration and heat pipe assistance, to enhance the tensile strength, elongation and microhardness.

This study develops the Ni–Fe–P–TiO₂ nanocomposite coatings via an electroless deposition process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the coating structures. Hardness and wear tests were conducted to measure the coating’s mechanical performance, and polarization curves were recorded to evaluate the corrosion behavior. The results show that the TiO₂ nanoparticles are incorporated into the coatings. The proper addition of TiO₂ refines the coating surface morphology without changing the coating phase constituents. The best mechanical and corrosion performance is obtained for the 0.5-g/L modified Ni–Fe–P–TiO₂ sample, owing to its compact surface feature and well-dispersed TiO₂ nanoparticles.

The thermal conductivity of single-crystal silicon was investigated by using Raman spectroscopy. The laser simultaneously acted as an excitation source and a heating source. The correlations between Raman spectra with both temperature and laser power for single-crystal silicon, which has a potential relationship with the thermal conductivity, were estimated. The results showed the localized compressive stress caused by laser heating would underestimate Raman peak shift. So, the temperature was determined based on the variation of linewidth. The predicted thermal conductivity of single-crystal silicon is 125 W/m ⋅ K, which is comparable to the theoretical value.

Post-weld heat treatment is a standard method to improve the performance of welded joints. Different heat treatment processes have different influences on the performance of welded joints. Therefore, it is of great significance to explore the impact of the heat treatment process on welded joints’ performance. This work applied three different heat treatment processes to the welded joints with three different properties. Then hardness test, impact test, tensile test, metallographic analysis and other means were used to evaluate the performance of welded joints after heat treatment. The following conclusions were drawn through the experiments: The change of phase compositions of the welded joints caused by the post-weld heat treatment was considered as the main reason for changes in mechanical properties of the welded joint. The difference in mechanical properties after different welding process and post-weld heat treatment combination was obtained, which has a guiding significance for practical production.

Supersonic atmospheric plasma spraying (SAPS) is a newly developed technique in preparing high-performance Cr₃C₂–NiCr coatings with a high deposition efficiency. In this work, the effect of post-heat treatment on carbide precipitation and corrosion property of the SAPS Cr₃C₂–NiCr coatings was investigated. The results suggested that heat treatment induced the precipitation of secondary carbide grains, and the size of these carbides increased with the increasing heat treatment temperature. In addition, the self-corrosion current density of the coatings thermally treated at 500^∘C was seven times smaller than that of the coating without heat treatment. The corrosion morphology showed that significant corrosion cracks were present on the as-sprayed coating. In contrast, the heat-treated coatings demonstrated small corrosion holes due to the formation of small corrosion galvanic cells between the precipitation of carbides and the substrate.

With the development of bypass-coupling technique, the process window of twin-wire indirect arc welding has been effectively broadened, but the process stability is required to be further improved. In this paper, the influence of arc voltage on the stability of welding process was investigated through process experiments. It was found that the direct arc and indirect arc were alternately ignited. Under the condition of the output voltage at 32 V, the ratio of the indirect arc current to overall welding current was the largest. The weld was well formed with the output voltage above 32 V. Considering both the deposition efficiency and process stability, the desirable output voltage was 32 V.

Amorphous Ni–W–P coatings were prepared by electroless plating and annealed at 250${}^{\circ }$C for different times to obtain different microstructures. The local atomic structure of these amorphous coatings was analyzed by calculating the atomic pair distribution function from the XRD patterns. The type of crystals in coatings was obtained from the TEM image and corresponding selected area diffraction (SAED) pattern. The proportion of microscopic particles in the matrix was roughly estimated from the first DSC exothermic peak area. Corrosion resistance in 0.5-M sulfuric acid solution was investigated via electrochemical techniques. Experimental results showed that all annealed coatings still held amorphous structure, albeit the microstructure had been changed. The correlation radius and the atomic number of clusters had increased, especially when the annealed time extended to 12 h and 20 h. The number of microscopic particles in the amorphous matrix also increased with rise in heat treatment time. The type of crystals in these amorphous matrices increased from Ni/Ni (W) to Ni/Ni (W), Ni₁₂P₅ and Ni₅P₄. The decreasing corrosion resistance was in agreement with the increasing number of microscopic particles and higher-order clusters in annealed Ni–W–P coatings. These microscopic particles could form micro-galvanic cells in corrosion solution. The higher-order clusters increased the composition difference in the amorphous matrix, and this also promoted to form micro-galvanic cells in solution.

We report the fatigue fracture in a mounting bracket, which is attached to a front bumper. We conducted the macro- and micro-scale fracture morphology analyses and base materials characterization. We used a bracket made of QSTE 420 TM high-strength steel and did not find any metallurgical defects. Three cracks were formed on the bracket, and the cracks were initiated from the outer edges of the screws. From the scanning electron microscopy (SEM) images, we observed ratchet marks among the three cracks at their initiation positions with a similar distance between each other. We also observed fatigue striation in the propagation zones. We deduce from the macro- and micro-scale analyses that the three cracks were initiated and then expanded spontaneously with a similar growth rate. The stress concentration, assembly operation and joining effects cause the bidirectional bending fatigue fracture in the three locations. Optimized tightening forces and new gaskets are recommended to extend the fatigue life of the mounting bracket.

Al/Mg/Al composite plates were fabricated by hot pressed sintering (HPS) and hot rolling. The main purpose of this study is to understand the effect of rolling on the microstructure, interface and mechanical properties of HPS Al/Mg/Al composite plates. Rolling can increase the compactness of the microstructure by improving the distribution of internal voids and promote the diffusion of interfacial elements, forming a transition layer consisting of phases $\beta$-Al₃Mg₂ and $\gamma$-Al${}_{12}$Mg${}_{17}$, which improves the strength, plasticity, interfacial bonding strength and interfacial deformation compatibility of the HPS Al/Mg/Al composite plates. The bending strength, tensile strength and elongation of HPS Al/Mg/Al composite plates after rolling are 520 MPa, 300 MPa and 17%, respectively. The fracture mode changes from brittle intergranular fracture to ductile dimple.

In this work, we aimed to evaluate the influence of working pressure on the structure and magnetic properties of the iron film. Iron films were deposited on Si (100) substrates by direct current (DC) magnetron sputtering at different working pressures. The X-ray diffraction (XRD) results indicated that all iron films were polycrystalline BCC structures with the obvious (110) orientation. When the working pressure increased, the (110) peak became weaker and wider, indicating that the crystallinity and the particle size decreased. Particle size gradually decreased, easily seen from the surface morphology. The (100) peak shifted toward the smaller angle with the increase of working pressure, displaying the production of compressive strain. The increase of the working pressure raised the density of defects, which was the origin of the strain. It was the main reason that the Hc dramatically increased. The atomic force microscope (AFM) results exhibited that low working pressure was conducive to obtaining uniform and smooth surface morphology. This is why the iron film at low working pressure can achieve better magnetic properties. The iron film deposited at 0.6 Pa had the largest saturation magnetization (Ms) and squareness ratio (Mr/Ms), the smallest coercivity (Hc), reaching 1573 emu/cm³, 0.86, 102 Oe, respectively.

In this study, powder compacts produced by mixed elemental Fe, Mn, Al and C powders without ball milling were sintered at 640^∘C and 1200^∘C, respectively. The results revealed that intermetallic phases belonging to Fe₂Al₅ and Al₈Mn₅ appeared after pre-sintered at 640^∘C. When the temperature increased to 1200^∘C, only α-Fe phase existed. The total porosities of the sintered samples were ∼60 vol.% at 640^∘C and ∼70 vol.% at 1200^∘C, and the peak compressive strength of the 1200^∘C-sintered samples was ∼1.6 MPa at the strain of ∼11%.

In this work, two types of models for a closed-cell Al foam with 80% porosity were established by Digimat and ABAQUS. The compression characteristics of the Al foam-filled stainless steel tube structure with both Al foam models were simulated and compared in combination with experiments. The results showed that Al foam-filled tubes presented higher peak compressive force compared with unfilled stainless steel tube. Compared with the crushable Al Foam model established by ABAQUS, the Digimat model could intuitively observe the plastic deformation in the cells of the Al foam-filled structure. However, the simulated results derived from Digimat software were slightly different from the experimental result. In general, the crushable-foam model embedded in ABAQUS can better match the experimental results from a macro perspective.

In this study, Carbon–Carbon (C–C) composite joints were prepared using BNi-1a paste filler metal as the intermediate layer in a vacuum brazing method. The interfacial structures and compositions of the joints were analyzed using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The results show that element interdiffusion and chemical reactions occurred in the joining zone, and various compounds were formed, including Cr₃C₂, Ni₃₁Si₁₂, Ni(_s.s), MB and MC ((M = Cr, Fe, Ni). The optimum joining parameters were determined to be the brazing at the temperature of 1120^∘C for 60 min, which produced the joint with the maximum shear strength of 24.13 MPa. The joint shear strength and fracture morphology demonstrate that bonding temperature and retention time have a significant effect on the strength of C–C composites.

Porous Ni–Ti alloys were fabricated by reactive synthesis of Ni and Ti elemental powders. The corrosion behavior of porous Ni–Ti alloys was explored by electrochemical methods and weight change measurements at 298 K in seawater. The polarization curves and electrochemical impedance spectroscopy data show that porous Ni–Ti (6.5:3.5) alloys provide the best corrosion resistance. The values of corrosion current density and corrosion rate are 1.6944 × 10⁻⁴ mA/cm² and 1.9929 mm/a, respectively. The corrosion behavior and corrosion mechanism of porous Ni–Ti alloys are also discussed.

In this paper, we investigated the influence of cooling rates on electrical properties and positive temperature coefficient of resistance (PTCR) effect of (Ba_1.22−xSm_x)TiO₃ + 0.007 mol SiO₂ (BTS) ceramics, which were fired at 1200^∘C for 30 min in a reducing atmosphere and then reoxidized at 700–800^∘C for 1 h. The results showed that the room-temperature (RT) resistivity and the resistance jump of the chip-type BTS ceramics increased with an increase in the cooling rate. Furthermore, the RT resistivity of the BTS specimens gradually decreased at first and then increased with increasing donor-doping concentration. In addition, the influence of cooling rates on the microstructure of ceramics was also investigated.

The graphite nanoparticles (GNPs) were prepared on the surface of monocrystalline Si by laser irradiation under different laser energy densities (3.3–8.33 kJ/cm²). The effects of laser energy density on structure and surface morphology were systematically investigated. The results show that the morphology of GNPs remained polycrystalline structure under laser irradiation with an energy density of 2.22 kJ/cm². When the laser energy density was 2.78 kJ/cm², the GNPs can induce the preset GNPs to transform into amorphous graphite nanofibers. The GNPs under the laser density of 3.33 kJ/cm² showed a more amorphous structure. With the further increase of the laser energy density to 5.55 kJ/cm², the main phase composition turned to SiC and Si.

High-strength galvanized steel has the advantages of high strength, lightweight and high reliability. However, there are many defects in the forming process, especially the springback, which seriously affects the forming quality. To improve the forming quality of high-strength galvanized steel in rolling forming, a three-dimensional finite element analysis model of a hat-shaped section roll forming process was built by software ABAQUS. The hat-shaped section with a single-layer flange was simulated with three different base-level roll forming methods. The base-level roll forming method was used to simulate and experiment the hat-shaped section with double-layer flanges. This paper provided a method to precisely control the springback angle of high-strength galvanized steel and improved its forming quality.

A Sr-incorporated Na–Ti–O nano-network with a lateral pore size of 20–300 nm was developed on titanium (Ti) substrate using one-step alkali etching in a mixed solution of NaOH and Sr(OH)₂. The pore size of coating increases with Sr content, implying the proper amount of Sr in the electrolyte accelerates nanowire aggregation. The Sr(OH)₂ particle precipitation has no significant effect on the coating morphology. Moreover, biological experiments suggest the prepared coating exhibits good cytocompatibility, and the amount of Sr under 0.7 at.% has no noticeable promoting effect on the cytocompatibility.

A two-step cyclic closed-die forging (CCDF), with the first step to enhance the formability and the second step to refine the matrix grain, was implemented on a solution-treated SiC/AZ91D nanocomposites. Results show that the initial coarse grain is refined from ∼105 μm to ∼27 μm after the implementation of CCDF at 400^∘C, and further refined to ∼6.8 μm after another 6-pass of CCDF at 300^∘C. Mg₁₇Al₁₂ precipitates are gradually crushed with the progress of CCDF and eventually evolve into small particles uniformly distributed within the matrix. SiC clusters are effectively dispersed into smaller clusters or single particle. Yield stress (YS) and ultimate tensile strength (UTS) of the SiC/AZ91D nanocomposites increase after 1 pass of CCDF at 300^∘C, while the elongation to fracture decreases. With the progress of CCDF, YS, UTS and elongation to fracture exhibit a continual increase, reaching their maximum values of 196 MPa, 371 MPa and 9.2% after 6 passes of CCDF.

Surfaces of polycrystalline Al samples were treated by using electropolishing, etching or mechanical polishing methods. Surface morphologies, laser-induced damage thresholds (LIDTs) and ejected particle numbers of different samples were analyzed and compared. Results showed that several different surface morphologies of Al were prepared. A new surface electropolishing technique was developed and an improvement of 95% of LIDT of Al was obtained by using this method. Ejected particle numbers of different samples were monitored and compared to investigate their damage-resistant properties. The particle numbers ejected from the electropolished sample are much smaller than those of etched or mechanically polished samples under Q-switched 355-nm Nd:YAG laser irradiation at 6.8 ns pulses.

Particulate contaminants are common damage precursors on optics in the daily operation of high laser power systems. In this paper, the damage behaviors of silica particles attached to the front and back surfaces of fused silica optics under the irradiation of a 355 nm laser were studied. Results showed that silica particles on the front surface tend to splash severely under high fluence, while the particle on the back surface forms a large laser-induced shallow pit (LSP)-like pit on the substrate. Different damage morphologies were observed, and damage mechanisms were also proposed.

This study presents the tensile properties of glass fiber-reinforced polymer (GFRP) composites under dynamic loadings. The dynamic tensile tests were performed via a high-speed servo-hydraulic testing machine with a velocity ranging from 1 m/s to 15 m/s, corresponding to a strain rate range between 4.9 s⁻¹ and 93.7 s⁻¹. The effects of the strain rate on the tensile strength and dynamic increase factor (DIF) were considered. The results showed that the tensile strength and DIF of GFRP increased with the strain rate. The failure pattern of GFRP was discussed via a group of high-speed camera images. The results of this research can provide useful information for future construction, e.g., protective structures under extreme impacts.

To clarify the anti-adhesive properties of the textured tool, two types of micro-grooved textures were fabricated on the tool rake face. The cutting tests were conducted on aluminum alloys under no lubrication condition. Experimental results showed that the cutting force, tool–chip friction coefficient, and surface wear of the P_1 textured tool decreased. However, noticeable disadvantages were observed in samples with other textures. Detailed research indicated that the chip material (Al alloy) was easy to squeeze into and clog in the micro-grooved texture, due to low hardness and high ductility. In contrast, the cutting force, tool–chip interfacial friction, and wear of steel samples with T_1, T_2, and P_2 textures were all greater than that of the nontextured tool. The difference observed in these various textures signifies the importance of the small geometric size of the surface texture in the P_1 texture. Thus, an improvement of tool anti-adhesion with aluminum alloy material was obtained under dry cutting conditions.

A new type of titanium alloy for the pressure shell of a manned deep-sea submersible is studied. The fatigue performance and the fracture toughness of the titanium alloy are obtained under R = 0.03, 0.3, and 0.5. The curves of fatigue crack growth rate under three load ratios are predicted based on the existing fatigue crack growth rate prediction model. The results show that the fatigue crack growth threshold decreases with the increase of the load ratio, and the fatigue crack growth rate increases with the increase of the load ratio. The fatigue crack growth prediction model can accurately predict the fatigue crack growth rate of titanium alloy under different load ratios.

In this paper, the Ni–Fe–P–TiO₂ coatings with different TiO₂ sol addition have been prepared by a sol-enhanced electroplating process. The microstructures and elemental compositions of prepared coatings were systematically characterized. The coating performance including mechanical properties and corrosion resistance were investigated. The results show that the proper addition of 10 mL/L TiO₂ sol slightly refines the surface morphology, while a much higher 50 mL/L TiO₂ sol addition causes a relatively nonuniform surface. The much-improved mechanical and corrosion performance is achieved by adding 10 mL/L TiO₂ sol, due to the strengthening effect by the well-dispersed nanoparticles and the compact, uniform surface structure. The wear tests confirm that abrasive wear dominates in the sample modified by 10 mL/L TiO₂ sol, while adhesion is the primary type for other samples.

3C-SiC nanowires were synthesized using Si, SiO₂, and active carbon as raw materials at different reaction temperatures without additional metal catalysts. The influence of reaction temperature on the phase assemblage and morphologies of the products were investigated by XRD and SEM. The experimental results indicate that a suitable reaction temperature is essential for the final products. When the reaction temperature was not high enough (1400 and 1450^∘C), the raw materials were not reacted completely, and a small amount of targeted nanowires were formed. When reaction temperature increased to 1500^∘C, the nanowires were mainly composed of 3C-SiC phase, and they were straight, curved, and needle-shaped. The straight nanowires ranged from several to tens of microns, but the diameters were not uniform. The vapor-solid mechanism dominantly governed the formation of SiC nanowires.

Ni–P–TiO₂ composite coatings were deposited on brass substrates using a sol-enhanced electrodeposition method. The cyclic voltammetry tests were used to study the effect of TiO₂ sol on Ni–P deposition. The surface morphologies of Ni–P–TiO₂ deposits were observed, and their elemental analysis was also conducted. The systematic tests were performed to characterize the mechanical and corrosion behavior of as-prepared coatings. The voltammetric studies showed that the addition of TiO₂ sol at 12.5 mL/L slightly promoted the Ni–P electrodeposition, while the excessive addition at 50 mL/L reduced it. The results showed that the in-situ generated TiO₂ nanoparticles ( ∼15 nm diameter) could be highly dispersed in the electrolytic bath. The addition of TiO₂ sol at 12.5 mL/L slightly promoted the Ni–P electrodeposition, while the excessive addition at 50 mL/L caused the opposite.

In this paper, in order to obtain a larger amplitude–frequency width, a T-shaped vibration energy harvester device with 1:2 internal resonance buckling was investigated and designed in a parametric study way, whose natural frequency can be adjusted by changing the geometric parameters and buckling load exerted on the T-shaped piezoelectric beam. The effects of different model lengths and widths on the output voltage of the energy harvester were studied systematically. By comparing the difference between the variation trend of displacement value and output voltage value of harvester model, it can be concluded that internal resonance can broaden the frequency band of vibration energy collection of buckling T-shaped piezoelectric beam. Additionally, when the internal resonance ratio is 1:2, the amplitude width and voltage output value can be effectively increased. The results show that when the buckling T-shaped piezoelectric beam resonates at a ratio of 1:2, the vibration energy collection frequency band of the buckling T-shaped piezoelectric beam can also be broadened.

In this paper, hierarchical surface structures were developed to achieve the superhydrophobicity on AZ31 magnesium alloys. The uniform nodular microstructure was constructed by laser processing, and the subsequent cobalt electrodeposition fabricated a nanostructured needle-like morphology onto the surface nodules. The superhydrophobic surfaces prepared under varied electrodeposition current densities were characterized. When applying 7 mA/cm² current density, the sample revealed the best superhydrophobic performance. The chemical stability of superhydrophobic samples was tested, which confirmed excellent superhydrophobicity was hardly affected by the corrosion environment. The results showed the samples still possessed the hydrophobic ability after tests. The developed fabrication method combines the advantages of laser processing and electrodeposition, which serves as a fast and cost-effective pathway to manufacture superhydrophobic surfaces.