According to the requirements of full-penetration welding of marine pipe and field working conditions, a technical solution of double pass backing welding by laser-MAG hybrid welding of marine pipe was proposed. The groove assembly gap was filled by MAG welding, and then the full penetration bead was formed by laser-MAG hybrid welding. The results showed that the scheme has strong adaptability to working conditions, and can adapt to the welding under the condition of 3 mm gap and 2 mm misalignment. The front side of the weld is well formed, and the back side has uniform penetration. The mechanical properties of the welded joint were qualified and met the actual production requirements.

Absorber-free laser transmission welding of PVC (polyvinyl chloride) and PC (polycarbonate) was conducted by using a 1 710 nm semiconductor laser. The welding specimens with ideal welding effect was obtained through designing multiple comparative tests by taking laser power, welding speed, and defocus distance as three factors that affecting the welding results. The results show that the welding specimens has the flat surface, uniform weld seam without bubbles, and the largest breaking force when the laser power of 20 W, welding speed of 10 mm/s, and the defocus distance of -4 mm.

To improve the wear resistance of YT tool steel, TiB2/TiN coating was prepared by laser cladding on its surface, and the influences of power parameters on microstructure and wear resistance were studied by experimental tests. Results show that the TiB2/TiN coating forms a compact structure which means the coating is closely bonded with the substrate. As the power increases gradually, the coating thickness also increases. Many small convex structures are formed on the coating surface area, and boundary layer is clearly observed. The deposition rate of TiB2/TiN coating increases linearly with the increase of power, from 2.63 nm/min to 6.64 nm/min, and the hardness of the coating continues to increase. The nanocomposite structure is formed between the h-BN structure and nanocrystalline TiB2. Higher cohesion energy is formed at the grain boundary, which improves the strengthening effect of grain boundary significantly. As the power is increased, both the friction coefficient and wear rate of TiB2/TiN coating increases first and then decreases. When the power is 2.0 kW, the friction coefficient rises to 0.79 that results in maximum wear rate of 4.75×10-6 mm3/(N·mm). This study has a significant theoretical guidence for improving the wear resistance and service life of YT tools.

The laser cladding Cr3C2/Ni coating was prepared under the optimized process parameters, and the Cr3C2/Ni cladding layer was remelted with the same process parameters. The effects of remelting on the microstructure and properties of single pass and multi pass Cr3C2/Ni cladding layer were studied. The results show that the average hardness of Cr3C2/Ni single pass cladding layer decreases from 893.26 HV to 748.33 HV, which decreased by 16.23%, and columnar crystals with obvious growth direction appear in the middle of the single pass cladding layer. The average hardness of Cr3C2/Ni multi-pass cladding layer decreases from 844.75 HV to 819.92 HV by 2.93%. After remelting, the microstructure of multi-pass cladding layer is more uniform and fine, the wear resistance of cladding layer relative to GCr15 steel is reduced from 0.68 to 0.45, the adhesive wear is intensified, the bending strength of remelting cladding layer is improved and the plasticity is enhanced. While remelting improves the surface forming quality of Cr3C2/Ni multi-pass cladding layer, the microhardness remains high, the wear resistance decreases slightly, and the bending strength increases.

The safety of the nuclear power has become the main problem in the development, and the failure of structural materials caused by corrosion is one of the main reasons for the safety problems. In order to improve the corrosion resistance of 304 stainless steel, which is a candidate material for molten salt reactor, Hastelloy C276 coating and C276 coating with 1.0% (mass fraction) Y2O3 were cladded on the surface of 304 stainless steel by laser cladding technology. The microstructure, phase composition, hardness and resistance to FLiNaK molten salt were studied, respectively. Results show that the two cladding layers are well combined with the substrate. The microstructure of C276 cladding layer is composed of equiaxial, secondary dendrite, cellular, columnar and planar grains from top to bottom, and the average hardness is 297 HV. After Y element was added, the microstructure of the cladding layer does not change obviously, and the hardness of the cladding layer decreases slightly. After static corrosion at 700 ℃ for 20 h in FLiNaK molten salt, 304 stainless steel exhibits obvious intergranular corrosion and Cr element loss and the corrosion depth is 30 μm. The corrosion depth of C276 cladding layer is 16 μm and the corrosion depth is about 8 μm after Y addition. The corrosion resistance of the laser cladding C276 coating in the molten salt is greatly improved compared with that of the 304 substrate.

The surface of Q235 steel were prepared Fe-based laser cladding layers with different powder feeding rates. Microstructure morphology was studied by OM, SEM and EDS. The results show that with the increase of powder feeding rate, the carbide in the heat affected zone aggregates into blocks and the corrosion resistance decreases. The cladding layer is composed of planar crystals, coarse columnar crystals, columnar dendrites, dendrites, and equiaxed crystal. With the increase of powder feeding rate, in the bottom layer, the area of coarse columnar crystals decreases and the shape changes into columnar dendritic crystal and dendritic crystal. In the middle layer, the microstructure is refined and changes to equiaxed crystal rapidly. In the top layer, equiaxed crystal size decreases sharply. The dendrites are composed of Ni-enriched austenite, and intercrystal is composed of skeleton-like eutectic which is composed of carbides, ferrite, and martensite rich in Cr and Mo. The data for the microstructure morphology change principle of the laser cladding layer will be added.

In order to improve the service life of materials, the influence mechanism of lap ratio on the performance of multi-channel laser cladding layer was investigated, and the key problem restricting the wide application of laser cladding technology in the industrial field-cladding area was solved. In this paper, based on SYSWELD software platform and 3D Gaussian heat source distribution model, three lap coatings of NiCrCoAlY alloy were prepared by laser cladding on the surface of TC4 titanium alloy. The effects of different lap rates on the temperature field and thermal cycle characteristics of the three lap coatings were discussed. Combined with experiments, the optimum bonding ratio of laser cladding NiCrCoAlY coating on TC4 titanium alloy was obtained. Results show that the optimal parameter is the lap rate of 30%. With the increase of lap ratio, the area of secondary melting and phase transformation of the first two cladding layers increases, and the cladding layer surface is uneven and prone to crack.

In this paper, selective laser melting thermal stress of 316L stainless steel materials was studied, and real-time stress monitoring platform was established. The change discipline of thermal stress, correlation between temperature and thermal stress, change discipline of scanning thermal stress of SLM finished single-layer multi-channel and multi-layer single-channel were discussed, and the change of thermal stress under varied craft parameters was further studied. Results show that in the process of selective laser melting, the change of thermal stress includes four stages: press, pull, offsetting of press and pull, balance of pull and press, and the final residual stress is pull stress; the change altitude of thermal stress is negatively correlated with scanning speed, and positively correlated with laser power. However, slow scanning speed led to remelting in the process of melting and made residual stress released.

In the experiment, 316L stainless steel component was manufactured by fiber laser-arc hybrid additive manufacturing. The influence of welding current on the stability of laser-arc hybrid additive manufacturing process was studied by high-speed camera, and the process parameters with the highest welding stability were selected for the stacking experiment. Experimental results show that when the current is 210 A and the laser power is 1 500 W, the welding stability is the best, and the porosity is the key factor affecting the mechanical properties of the sample. The tensile strength and elongation of the multilayer stacking sample prepared are 569.9 MPa and 16.8%, respectively.

In this paper, the principle, advantages and disadvantages of laser cutting and abrasive water jet cutting are briefly described, and then a method of water jet assisted laser composite machining is mentioned. The water jet continuously impacts the surface of the workpiece to reduce the surface temperature and wash away the slag, reducing the thermal damage of laser processing. However, this machining method has higher requirements on the working position of laser and water jet. Most of the current experimental systems are independent laser and water jet at a certain angle, which makes it extremely difficult for them to maintain stable working position during the processing. According to this problem, in this paper, an integrated laser/water jet cutting head is designed that can work coaxially with the laser and water jet channels, and it uses the principle of thermal shock fracture to complete the cutting of materials, so as to obtain higher cutting accuracy. Finally, ANSYS software is used to simulate and analyze the temperature field in the machining process to verify the reliability of the machining system.

Aiming at the problems of long optimization time, large empty distance and low optimization performance in the current zoom laser cutting path optimization method, this paper studies the zoom laser cutting path optimization based on machine vision. In this method, the parameters of laser cutting path are obtained according to the principle of machine vision. The relevant paths are traversed through computer technology. According to the path constraints and objective optimization function, the path optimization model is established, and then the model is solved based on the improved ant colony algorithm to obtain the best zoom laser cutting path and realize the path optimization. Experimental results show that when using this method to optimize the zoom laser cutting path, the optimization accuracy is higher than 95%, and the optimization time is kept at about 3.5s with the increase of test times. Therefore, this method has low optimization time, small idle travel and high optimization performance.

To improve its comprehensive properties, the W6Mo5Cr4VZ (MZ) high speed steel tool surface was nitrided by high power semiconductor laser. The differences of nitriding pool and surface microstructure undergone pure nitrogen and nitrogen-argon mixture gas were compared. The changes of the phase composition, microstructure and hardness of nitriding layer under different nitriding processes were analyzed. Results show that dendrites become fewer in the AlN nitride layer by increasing the ratio of argon, and the original large dendrites are gradually transformed into shorter equiaaxial crystal structures. AlN and Al are formed at the depth of 150~300 μm, and Al is the main phase at the depth of 450~600 μm. When the ratio of nitrogen and argon is between 3∶1 and 1∶3, the surface hardness reaches 900~1 000 HV, and the hardness of nitriding layer decreases slowly. As the proportion of argon increases gradually, the proportion of nitrogen decreases and less AlN dendrites are formed. With the ratio of argon rising, the nitrogen content in the molten pool decreases and the degree of undercooling increases, which makes the primary and secondary crystal axes longer, and reduces the radius of curvature at the dendrite tip. This study is helpful to improve the microstructure of laser nitriding layer of MZ tool, which can be extended to other materials with high surface requirements.

In order to explore the influence of the four process parameters of picosecond laser′s single pulse energy, scan times, scan speed, laser repetition frequency on the hydrophobic properties of 2024 aluminum alloy surface, a picosecond laser processing experimental platform was built and a response surface with 4 factors and 3 levels was designed test, the Design-Expert12 software was used to optimize the process parameters to obtain the best combination of process parameters, and verified the accuracy of the regression equation through experiments. According to the results of response surface analysis, the interaction between single pulse energy and scan times, scan times and scan speed, and scan times and laser repetition frequency has significant interaction effects on the surface contact angle. Taking the surface contact angle as the evaluation index, the order of the influence factors of each process parameter on the surface contact angle is: single pulse energy >scanning times>scanning speed>laser repetition frequency. Taking the maximum surface contact angle as the goal, the obtained process parameter combination is: single pulse energy14 μJ, scanning times 7 times, scanning speed 650 mm/s, laser repetition frequency2.2×106 Hz.The predicted surface contact angle is 147.5°, the actual surface contact angle of the test is 150.3°, and the error between the actual value and the predicted value is 1.9%.The test results show that after the picosecond laser process parameters are optimized by the response surface method, the established surface contact angle model has a good predictive ability, the microstructure etching on the surface of aluminum alloy through optimized process parameters can significantly improve its surface hydrophobicity.

6061 aluminum alloy with nickel-based self-melting alloy was alloyed by using YAG laser alloying method. The effects of process parameters on microstructure, composition, mechanical properties, and precipitates were investigated. The process of heat flow on the evolution of nitride precipitates in the alloyed zone were also investigated. Results show that the alloying zone increases wider and deeper as the current increase and the scanning speed decrease. From the alloyed surface to the substrate, the precipitated phase first appears as Al3N, followed by Al3Ni2 and AlNi until the AlNi is present of junction of the alloyed zone and the substrate. The hardness value gradually increases with depth and then decreases steeply to be close to the hardness of substrate. The hardness of the alloyed zone is up to 539 HV, which can be 6 times the hardness of the substrate.

Aiming at the problems of large measurement error and low measurement accuracy of handheld laser methane telemetry instrument in the current market, a telemetry simulation system of CH4 integral concentration based on tunable diode laser absorption spectroscopy (TDLAS) is established, and the calibration experiment and related measurement analysis of handheld laser methane telemetry instrument are carried out according to the simulation results. Through the CH4 integrated concentration telemetry simulation system, the simulation experiments of two calibration methods, namely, the absorption peak-peak value fitting calibration method and the absorption peak integral area fitting calibration method, were carried out. Through the simulation measurement and analysis of the experimental data of two calibration methods for the same group of integral concentration, the results show that the linear correlation between the integral concentration and the integral area of the absorption peak is 0.999 99, which is higher than the linear correlation between the integral concentration and the peak value of the absorption peak 0.999 88. At the same time, the measurement error range of the absorption peak integral area calibration method is -0.26%~0.86%, which is far less than the measurement error range of the absorption peak peak-value fitting calibration method -1.22%~1.16%. According to the simulation results, the calibration experiment and related measurement analysis of the telemetry instrument are carried out by using the absorption peak integral area fitting calibration method. Results show that the average error of the calibration method is 4.35%, and the error range is -2.89%~7.20%, which is 5.65% smaller than the error range (±10%) of the existing telemetry instrument in the market. Results show that the absorption peak integral area fitting calibration method can significantly improve the detection accuracy of the telemetry instrument and reduce the measurement error range.

Due to the excessive wear, the failure of U-shaped rings has become the main cause of wire breaking and dropping. Laser quenching is a green strengthening technology that can effectively improve the wear resistance of U-shaped rings. COMSOL Multiphysics is used to establish a simulation prediction model of temperature field and microstructure field for laser quenching U-shaped rings in this study. This model is used to investigate the influence of laser irradiation time on the distribution of temperature field and quenching field during the laser quenching U-shaped rings process. The model is verified by experimental comparison, and the simulation prediction results fit well with the experimental results. The simulation prediction results show that the temperature fields in the cross and longitudinal sections of the U-shaped rings′ center are crescent-shaped and diffuse into the inner U-ring with the increase of irradiation time. The surface layer of U-shaped rings after quenching is the fine quenched martensite structure. With the increase of depth, the microstructure in the heat affected zone is quenched martensite and a small amount of ferrite. The maximum temperature of U-shaped rings, the bottom depth and the surface area of the laser hardened zone are positively correlated with laser irradiation time. When the laser irradiation time is 7 s, the maximum temperature reaches 1 434 °C, the bottom depth reaches 3.12 mm, and the surface area reaches 817 mm2 covering 92.21 % of the upper surface area of the bending section of the U-shaped rings, which can effectively improve the wear resistance of U-shaped rings. Under the conditions of 5 000 W laser power and 24 mm×18 mm laser spot size, the laser quenching time window of U-shaped rings is 3~7 s.

The millisecond laser and ultrafast laser were used to process gas film holes on the superalloy with thermal barrier coatings (TBC). The thermal cycle test was carried out on the hole-making sample. The effects of two pulsed lasers on the morphology of the thermal barrier coating and the hole wall of the metal matrix were compared and studied. The changes of the micro-hole morphology before and after thermal cycling were analyzed. The results showed that: When millisecond laser was used to make holes on the superalloy sample with thermal barrier coating, the ceramic coating at the edge of the holes would lose lumps, the bonding layer and metal matrix would produce recast layer. When using picosecond laser to make holes, there was no obvious change of the structure either near or away from the hole edge, and there was no recast layer or microcrack formation in the ceramic coating, bonding layer and metal matrix. After the hole-making sample was thermally cycled 450 times, there was no obvious change in the structure of the ceramic coating around the hole. The bonding layer at the edge of the hole and the organization far away from the edge of the hole changed significantly. The thickness of the recast layer of metal matrix at the edge of the hole produced by millisecond laser increased, and the metal matrix layer at the edge of the hole produced by picosecond laser also had a diffusion area which was different from the structure away from the edge of the hole. After millisecond laser hole-making sample was thermal cycled, the TGO layer between the hole edge bonding layer and the ceramic coating appeared micro-cracks. However, there was no micro-crack between the bonding layer and the ceramic coating at the edge of the hole produced by picosecond laser after thermal cycling.

In order to solve the problem of poor imaging quality of traditional imaging to target objects in complex environment background, Based on the characteristic that the polarization information of reflected light wave is different due to the difference of external texture and characteristics of different objects, In this paper, polarization imaging and image mean are combined to obtain the polarization information of the target and the background, and the mean of the degree of polarization image is processed, so as to enhance the target contour and significantly improve the contrast of the target. In the experiment, the polarizer that can rotate along the main optical axis is added to the CCD lens, and the polarization image of the target under different polarization angles under the complex background is obtained. The algorithm based on Stokes parameter is used to process the polarization image of the target. Finally, the polarization image is averaged and analyzed. After the low contrast target is processed, the results show that in the original polarization image, the contrast of target a is improved by 4.1 times, target b by 3.6 times, target c by 3.5 times, and target d by 4.3 times. The boundary and texture information of each object is greatly enhanced, and its contour can be clearly distinguished.