In order to improve the wear resistance of U71Mn steel and prolong the service life of rail, Stellite6 powder, TiC powder and Y2O3 powder were selected as cladding powder, and cobalt alloy cladding layer was prepared on the surface of U71Mn steel by laser cladding coaxial powder feeding technology. optical microscope, scanning electron microscope, X-ray diffractometer, microhardness instrument, ultra depth of field microscope and wear testing machine were used to analyze the macroscopic morphology, microstructure, phase composition, microhardness, wear morphology and friction and wear properties of the coating, respectively. Results show that the best single channel cladding layer can be obtained by adding 2% Y2O3 powder to 10% TiC-Cobalt-based powder. When the laser power is 1 200 W, the scanning speed is 5 mm/s, the powder feeding speed is 1.0 r/min and the lap rate is 40%, the most flat cladding layer can be obtained. The microstructure of the cladding layer is composed of equiaxed and columnar crystals. The cladding layer has good metallurgical bonding with the matrix. The cladding layer is mainly composed of TiC, Cr7C3, Cr23C6, γ-Co and Co3Ti. The hardness of the cladding layer is up to 572 HV, and the average hardness is about 1.8 times that of the matrix. The wear of the cladding layer is 3.83% of the wear of the substrate, and the wear resistance of the cobalt-based cladding layer is significantly improved.

Stellite6 Co-based coatings were prepared through the coaxial powder-feeding laser cladding technique. The laser cladding parameters were optimized by means of the combination of orthogonal test design, single pass cladding, single-layer multi-pass cladding and multi-layer multi-pass cladding. The microstructure of the cladded coatings was characterized through scanning electron microscope, optical microscope, X-ray diffractometer, while the microhardness and the tribological performance of the coatings were also investigated. Results show that the optimal laser cladding parameters were successfully obtained through comprehensively analyzing the dilution rate, forming coefficient and microhardness of the coating. Furthermore, homogeneous microstructure was developed inside the cladded coating, which was consisted of plane crystals near the fusion zone, dendrites in the central region and equiaxed grains in the top region. The laser-cladded Stellite6 coating was composed of fcc-Co, (Co,W)3 and Cr23C6 phases, and its average microhardness reached 457 HV. The wear-resistant property of the laser-cladded Stellite6 coating was found superior compared to the 316L base metal and the wear behavior of the coating was featured of abrasive wear.

In order to solve the failure problem caused by the impact of alternating loads on the surface of the oil drill pipe and obtain a higher quality wear-resistant coating, this paper adopts a high-speed laser cladding equipment, and JG-3 iron-based alloy is used as the cladding powder to coat the surface of 20CrMo steel for the preparation of alloy coatings. Taking laser power, scanning speed and powder feeding speed as optimization variables, and considering coating hardness and wear resistance as characterization variables, the optimal parameter group was obtained through orthogonal test range and variance analysis. Results show that in the range analysis, the order of the influence of process parameters on the microhardness and wear loss weight of the coating is as follows: scanning speed>powder feeding speed>laser power. In the variance analysis, the F values of microhardness and wear loss weight are both FB>FC>FA, indicating that the influence of various factors on the performance of high-speed laser cladding coatings is ranked as follows: scanning speed, powder feeding speed, laser power. This is consistent with the range analysis results. The optimal parameter combination obtained by orthogonal test is laser power 900 W, scanning speed 65 mm/s, powder feeding speed 4 r/min.

In order to study the influence of tungsten carbide (WC) dispersions on the mechanical properties of nickel-based alloy coatings, the composite coatings with different mass fractions of tungsten carbide (≤15%) were fabricated on 316L stainless steel substrate by laser cladding (LC) technique. The microstructures and mechanical properties, e.g. hardness and wear resistance, which are related to the composite coatings with different WC contents were characterized and analyzed by scanning electron microscopy (SEM) and tribology testings, respectively. Results show that the melting pool exhibits an obvious bimodal structures at the top of the overlaps where the fine equiaxed grains are on the top of the coarse columnar grains. Due to the gravity effect, the heavy WC particles is tend to aggregate at the bottom of melting pool, and the tendency of uneven dispersion of WC particles increases with the higher of WC concentrations. The hardness and wear resistance of WC/nickel-based composite coatings were also enhanced with the increments of WC additions. Hardness of 15% WC/nickel-based composite coatings increased about 11.4% with a large reduction in the friction coefficient by about 19.62% compared with the pure nickel claddings, and the abrasion morphology showed that the wear-resistance enhancements of hard particles in low content WC/nickel-based composite coatings was relatively weak. The improvement of the wear resistance of the composite is mainly attributed to the increase of overall hardness of composite coatings.

In order to clarify the effect of cell size on the axial load capacity and compression properties of hexagonal thin-walled honeycomb structures, hexagonal 18Ni300 thin-walled honeycomb samples of 10 mm in diameter, 15 mm in height and 0.1 mm in thickness with different cell size of 1.75 mm, 2.25 mm, 2.75 mm and 5 mm filled were fabricated by selective laser melting. Static axial compression tests of the samples were performed, and load capacity and specific energy absorption performance of the samples were analyzed. Results show that the samples with cell size above 2.25 mm are compressed by stacking during compression, and the load capacity per unit volume and specific energy absorption increase as the cell size decrease. However, for the sample with cell size of 1.75 mm, it is damaged by outward tearing mode during axial compression with significant decrease of load capacity per unit volume and specific energy absorption.

The microstructure of cross sections (i.e. X-Y and X-Z), which are perpendicular to and parallel to the rolling or build-up directions for the hot rolled or selective laser melting (SLM) built 316L stainless steel blocks, respectively, was characterized by means of optical microscopy (OM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). Results show that the 316L stainless steel prepared by the two methods mainly consists of austenitic phases. In comparison to the rolled 316L stainless steel, the SLM built 316L stainless steel has much more low angle grain boundaries and sub-grain boundaries, as well as higher dislocation density. It could be observed that the SLM-316L stainless steel shows a preferred texture parallel to (110) direction in X-Y plane and (001) direction in X-Z plane. The deviation of grain orientation from the (001) direction on the X-Y plane may be related to the complex heat flow during the laser remelting process. Texture is available in the (001) direction in the X-Z plane, and the texture index is the largest at (001), which is related that the crystals grow parallel to the build-up direction. Moreover, the heat dissipation is the heat fastest along the (001) direction during the SLM process; therefore, grains grow preferentially along (001) in shape of strips.

To improve the walking energy efficiency and dynamic balance performance, the innovative lightweight design of robot calf was proposed with the help of topological optimization technology, and the calf assembly structure was redesigned as an integrated structure, reducing the parts from 11 to 1. Besides, with the help of laser powder bed fusion technology, AlSi10Mg was selected as printing material to carry out the additive manufacturing process research. Using Altair Inspire software to carry out laser powder bed fusion process simulation, and the optimized laser process parameters window was obtained, line energy density was 90~210 J/m. On this basis, the finished product was printed, finally realizing the goal of calf weight reduction up to 63.8%.

The hybrid of laser additive and subtractive manufacturing technolog, which involves selective laser melting (SLM) and femtosecond laser subtractive manufacturing, has been considered as an effective process to achieve near-net-net forming of complex and fine structures. In the SLM process, due to the movement of the molten pool and the overlap of the molten channel, the surface of the SLM formed part has a certain periodic structure, which has a great influence on the subsequent femtosecond laser subtractive manufacturing. In this study, the surface structure of the SLMed Ti-6Al-4V workpiece was measured first, and the femtosecond laser subtractive manufacturing experiment was designed. Through experiments and a two-dimensional numerical model, the evolution of the surface morphology in the process of femtosecond laser subtractive manufacturing is studied, and the surface roughness value is predicted. The simulation results are very close to the experimental results, and the error is only 7.63%. In addition, the model is used to study the surface movement speed and processing depth of the positive/negative defocus position: both the surface movement speed and processing depth of the negative defocus position are greater than the positive defocus position, revealing the mechanism of surface roughness reduction during the femtosecond laser subtraction process.

Welding of aluminum/steel dissimilar materials was carried out by continuous fiber laser. The microstructure, element distribution, precipitated phases and failure mechanism of the joint were carefully investigated. Results show that island, block and layered Fe-Al compounds are formed at the interface during the solidification process of weld. They have high hardness and brittleness, leading to low plastic toughness of the material itself. The formation of cracks in welds mainly depends on the continuous or concentrated distribution of brittle Fe-Al compounds at interface, which reduces deformation capacity of materials themselves. The fracture mode of the joint belonges to brittle fracture, and the failure of the joint is caused by Fe-Al brittle compounds at the interface.

The laser-MIG welding process of medium-thick plate aluminum alloy is simulated by ANSYS, and the distribution of temperature field, residual stress and welding deformation in the laser-MIG composite welding process are obtained. Results show that the temperature field presents an elliptical distribution with the weld as the central axis, and the temperature field is high in the middle and low around the workpiece. Because the equivalent stress of the workpiece is increasing with the welding, during the welding process, a high stress zone of > 300 MPa appears on both sides of the workpiece. With the cooling of the workpiece, the stress concentration of the rigid fixed surface on both sides of the workpiece begins to disappear, and the high stress area disappears after the workpiece is cooled. After the workpiece is completely cooled, the high stress zone is mainly distributed around the welding seam, with the maximum value up to 175 MPa. The stress distribution on both sides of the workpiece is relatively uniform, in the range of 125-130 MPa. After welding, the total deformation of the workpiece presents an elliptical distribution with the weld as the central axis. The maximum deformation on both sides of the weld can reach 0.19, and the weld deformation is 0.09.

Research on laser scanner welding technology of three-layer lapped steel structure of car body was carried out in this paper by 6 kW laser. The influences of defocusing distance, welding speed, welding power on weld width, weld depth, bonding layer width and typical defects were clarified. The process window was established and well-formed welding joints were obtained. On this basis, the tensile strength of the joints were further analyzed and compared with those of the resistance spot welding joint. Results indicate that the maximum tensile strength of the laser scanner welding joints is 12.64 kN, for the triple-layers lap steel structure of the body, which is 1.98~2.47 times of the maximum tensile strength of the resistance spot welding joint, having a significant advantage.

In this paper, the 1 066 nm fiber laser wafer identification system is used to carry out the research of wafer identification process. The duty ratio and pulse width are respectively changed by the control variable method to mark SEMI T7 code on the wafer. The Dot morphology is observed by the digital microscopic system, and the code reader is used for reading test. Results show that there was a wide process window for 1 066 nm laser identification wafer, and the Dot morphology was smooth and spatter free in the duty ratio range of 10%~22%. The pulse width has a great influence on the Dot morphology, but it has little influence on the read time after the hardware and software processing and optimization of the reader. Within the duty ratio of 10%~22% and pulse width of 100~300 ns, no splash, uniform identification can be obtained, which meets the SEMI identification requirements.

In order to study the influence of general F-Theta lens on telecentric F-Theta lens on wafer marking process, a wafer laser marking system using 1 066 nm acousto-optic Q-switched pulse fiber laser as light source and general F-Theta lens and telecentric F-Theta lens respectively is built. Dot matrix marking is carried out on the wafer surface with the same process parameters, and the ablation threshold, defocus effect and ablation plan of wafers under two F-Theta lenses are studied. Moreover, the three-dimensional morphology of wafer identification area is analyzed by white light interferometer. It is found that general F-Theta lens and telecentric F-Theta lens have little effect on the ablation threshold of wafers. In terms of defocusing effect, the ablation aperture of ordinary F-Theta lens decreases gradually with the increase of defocusing amount, while the ablation aperture of telecentric F-Theta lens first increases and then decreases with the increase of defocusing amount. In terms of the mark quality in the marking range, the mark quality of the two in the center of the marking range is basically the same, the farther away from the center, the telocentric lens does not show better mark morphology.

In this paper, nanosecond pulsed laser-induced 304 stainless steel surface is used to conduct coloring experiments, and the mechanism of nanosecond laser-induced stainless steel surface coloring is analyzed. Firstly, the laser directly processes the surface of stainless steel samples to study the effect of processing area on the coloring uniformity. Small areas are colored at different distances from the center of the mark, and the effect of the distance from the center of the mark on the coloring effect of the sample is explored. Finally, the laser is used for cyclic marking, and the multi-axis CNC platform reciprocates to improve the coloring effect. Results show that the processing area of the sample can affect the coloring effect of the stainless steel surface, and reducing the processing area of the sample can make the color more uniform. With the increase of the distance from the center of the mark, the coloring stability of the surface of the sample becomes worse. By introducing a multi-axis CNC platform to assist laser coloring can effectively improve the stability of stainless steel surface coloring and reduce the color difference value.

The purpose of this study is to investigate the specific method of laser ultrasonic nondestructive testing technology applied to the detection of arc surface defects commonly found in industrial production. To verify the influence of different dimensional parameters of defects on the reflected and transmitted surface waves, a finite element model for the detection of arc-shaped surface defects was established based on the ultrasound excitation mechanism by thermoelastic effect. Meanwhile, the empirical mode decomposition method was used to process the signal data to extract the reflected and transmitted waves of defects and superimpose the signal components of corresponding characteristic frequencies. Results reveal the changing laws of the relevant ultrasonic characteristic parameters. Based on this, two prediction models for the depth of arc surface defects are established. By comparison and analysis, the maximum error between the defect depth calculated by using the transmission wave parameter model, and the actual defect depth is only 0.6%. Therefore, the proposed defect depth prediction model provides a feasible solution for the on-site detection of arc surface defects with high accuracy.

Laser Doppler velocimetry technology has the advantages of non-contact,wear-free and high precision. It is widely used in high-precision velocity, acceleration and length measurement in industry, navigation, aerospace and other fields. Dual beam laser Doppler velocimetry has the characteristics of simple structure and strong anti-interference. In order to improve the measurement accuracy of dual beam laser Doppler velocimetry, this paper introduces a double beam laser Doppler system for measuring the linear velocity of circular rotation. When the linear velocity of the target is 1 596.6 mm/s, the theoretical value of laser Doppler difference frequency signal is 0.975 MHz. The measurement angle is 0°, and the difference frequency signal observed in the experiment is 1.013 MHz, with an error of about 3.8%. Furthermore, by changing the different angular positions of the observer, the measured Doppler frequency shift and 0° frequency shift error are within 0.8%. Results show that the measurement system can measure the Doppler frequency shift signal of moving objects and change the observer angle of dual beam laser Doppler velocimetry without affecting the measurement results. This experiment provides a useful reference for the development of this kind of sensor.

Gaussian doped fiber source has high stability, which can effectively reduce the phase error of FOG and improve the measurement accuracy of FOG. Based on the theoretical analysis of the classical structure of the doped fiber light source, a two-stage single-pump structure is proposed, which is composed of the double-way forward structure and the one-way backward structure, and the optical path structure simulation is carried out to determine the optimal optical path parameter range. The stability of pump output wavelength and power directly affects the power stability and average wavelength stability of the light source. Therefore, a constant current driving scheme and a constant temperature control scheme are designed for the current-driven pumped laser. Experimental results show that the power variation rate of the doped fiber light source is 8.27%, and the average wavelength stability is 1.7×10-6 K-1 in the temperature range of -45 ℃ to 65 ℃.

Er-doped Al2O3 films were prepared using the magnetron-sputtering method, and the films were thermal-annealed. We measured the refractive index and X-ray diffraction patterns of the films, and it was found that the films were amorphous at annealing temperatures up to 600 ℃, and the refractive index was 1.67 at 1.5 μm. We investigated the correlation between the photoluminescence intensity and Er-doping content, and the optimal deposition conditions for the films were obtained. We simulated the mode field distribution and achieved the structural parameter of the waveguide where the interaction between light and Er-doped layer is the maximum. We further optimized the fabrication conditions and achieved Er-doped Al2O3 waveguide with smooth side wall and low optical loss. The 2 μm-wide waveguide has an optical loss at 1.6 dB/cm at 1.31 μm. Compared with the alumina ridge waveguide with a loss of 3.8 dB/cm prepared by the ultrafast laser ablation method, the loss is greatly reduced, showing the potentials of the Er-doped Al2O3 waveguide used as on-chip optical amplifiers.

Objective: the effect of low-level laser on Canine distal movement was evaluated to evaluate the efficiency of low-level laser on accelerating orthodontic tooth movement. Methods: this meta-analysis follows the PRISMA statement. We searched PubMed, Cochrane Library, Embase, CNKI, VIP, and WanFang, and the search was conducted between January 2000 and December 2021. We pooled all randomized controlled trials and conducted a meta-analysis using Revman 5.3 and STATE. Results: a total of 224 samples were included in 7 studies. The results of meta-analysis show that: compared with the control group, the low-level Laser group within 7 days after treatment (WMD = 0.360, 95% CI = 0.330-0.389, P < 0.05) ; Within 28 days (WMD = 0.353, 95% CI = 0.141-0.566, P < 0.05) , within 60 days (WMD = 0.301, 95% CI = 0.101-0.502, P < 0.05) , within 90 days (WMD = 0.414, 95% CI = 0.179-0.650, P< 0.05) , the canine movement distance increased significantly. Conclusion: as an auxiliary means of orthodontic treatment, Low-level laser can effectively accelerate orthodontic tooth movement.