ConclusionsIn this study, the Ni60A/WC composite coatings with different contents of CNTs are successfully prepared on the surface of 45 steel by laser cladding. The results show that the five coatings are composed of Ni-Cr-Fe solid solution and hard phases such as WC, W2C, Cr3C2, Cr7C3, Cr23C6, and B4C. Adding an appropriate amount of CNTs promotes the uniform distribution of hard phase, refines the microstructure of cladding layer, and greatly improves the microhardness of cladding layer. When 0.5% mass fraction CNTs are added, the microhardness reaches 1100 HV, the friction coefficient decreases to 0.3, and the wear volume decreases to 1.24×10-4 mm3, indicating CNTs have excellent self-lubricating properties and Ni-based composite coatings with excellent properties can be prepared by adding an appropriate amount of CNTs.

ConclusionsFor the high-speed and high-precision fabrication of complex three-dimensional micro-nano structures, a dual-beam laser direct writing lithography system based on the PPI technology is designed and developed. To meet different requirements, the system may operate in different modes at user options, including piezoelectric platform scanning mode, galvanometer scanning mode, and composite processing mode. By the accurate control of laser power and scanning speed, polymerized line-arrays attached on substrate surfaces with 64 nm linewidth and a group of suspended lines with 30 nm linewidth are obtained in the experiments. The maximum fabricating speed of our system reaches 50 mm/s. It is suitable for the efficient manufacturing of a variety of planar and three-dimensional micro-nano structures, and it provides a powerful scientific research tool for many research fields of micro-nano optics, micro-nano electronics, biology, and other disciplines.

ConclusionsIn this paper, porous micron sliver bump arrays composed of nano-Ag particles are deposited on DBC substrates by the PLD technique to replace the traditional solder bumps, and they are applied to the connection between Si chips and DBC substrates. The results show that, by adopting stainless steel mask, Ag bump arrays with feature sizes of 500 μm and 300 μm can be deposited with a height of 60 μm and morphology of circular truncated cone, and the top diameters of two kinds of bumps are 330 μm and 100 μm, respectively. Under the thermo-compression bonding parameter of 250 ℃-2 MPa-10 min, metallurgical connections form at the upper and lower interfaces of Ag bumps with the metallized layer. The Ag bumps are transfered into a porous network structure, in which the porosity of the edge area is about 42% and that of the central area is 22%. The shear strengths of chip-DBC joints with 500 μm and 300 μm feature size Ag bump arrays are 14 MPa and 12 MPa, respectively. The joint fracture mainly occurs at the interface between the sintered Ag bumps and the chip or DBC substrate. This paper proves that it is feasible to replace the traditional solder bumps with porous micron silver bumps in the integrated circuit chip package, but it is still necessary to improve the morphology of bumps from the aspects of mask materials and PLD technology.

ConclusionsIn this paper, an S-130 MSS is successfully produced by SLM. For SLM as-deposited samples, the phase analysis reveals a large amount of martensite and a small amount of retained austenite, and the microstructure is characterized by the cellular dendrite structures and a large number of martensite laths. After the two kinds of heat treatments, the formation of reverted austenite increases the content of austenite, and a large number of nanosized precipitates are uniformly dispersed in the martensite laths. Meanwhile, the lamellar retained/reverted austenite is distributed among the martensite laths. Compared with those of the SLM as-deposited samples, the microhardness and tensile strength are significantly improved and the elongation is not reduced after two kinds of heat treatments. Moreover, in comparison to that after five-step heat treatment, the sample after three-step heat treatment possesses a high content of austenite and slenderer martensite laths as well as finer precipitate, which contributes to high microhardness and tensile strength under the condition of ensuring elongation. The optimized heat-treatment regime for the SLM as-deposited S-130 MSS is three-step heat treatment (solution+ cryogenic cooling+ aging).

ConclusionsIn this paper, we present a phase-interface-based heat source model and analyze the temperature and flow fields of a 3 mm steel plate during laser perforation based on the thermal fluid-solid coupling effect. The model truly reflects the dynamic process of temperature and flow fields, and the calculation results can effectively explain the influence of laser heat source and auxiliary gas on laser perforation. The simulation results show that, in the early stage of laser perforation, under the influence of auxiliary gas and heat source, the keyhole has a stronger blowing ability, fewer deposits on both sides, and slightly vibrates in the horizontal direction. With the increase in keyhole depth, the keyhole shape tends to be stable, the keyhole center is reduced under gas thermal convection, and the auxiliary gas' blowing ability is weakened, increasing the amount of molten matter at the bottom of the keyhole. The confirmatory experiment results show that the amount of molten matter increases with an increase in the hole depth, which is consistent with the simulation results. The phase interface-based heat source model can simulate the interaction between the temperature and flow fields in laser perforation efficiently and can reflect heat accumulation during laser perforation. It provides a theoretical basis for laser perforation.

ConclusionsWe propose a method to rapidly prepare LIG-based sensors on wood using laser. The integrated pressure and temperature sensor is prepared and its performance is tested. The optimal sample is obtained by using a fiber laser with a wavelength of 1070 nm, a laser pulse frequency of 10 kHz, a laser power of 10 W, the vacuum chamber pressure of 100 Pa, a defocus distance of 4 mm, a scanning speed of 100 mm·s-1, and marking time of 14. Its sheet resistance is 8 Ω·sq-1. The structure and forming mechanism of laser-induced graphene are obtained by SEM, Raman spectroscopy, and infrared spectra. The porous carbon pressure sensor and temperature sensor are fabricated. The sensitivity of the pressure sensor can reach 86.53. The hysteresis error is 0.06%. The non-linear error is 15%. The repeatability error is 0.31%. The response time and recovery time are both 1 s. The temperature coefficient of resistance of the temperature sensor is -0.101%. The sensing mechanisms of the LIG-based porous carbon pressure sensor and the temperature sensor are analyzed. Finally the integrated pressure and temperature sensor is made. The above LIG-based sensors have excellent sensing performances and are degradable. They have obvious commercial advantages and research prospects in current non-degradable electronic products that pollute the environment and have important applications in wooden construction and furniture.

ConclusionsLaser-arc hybrid welding is carried out in the groove, when the laser-arc distance is 2 mm, the arc and laser-plasma are strongly coupled. From the beginning of the welding process to the end of the welding process, the arc and laser-plasma are inextricably linked. The plasma brightness is high, the spatter is increasing, and the weld pool is violently fluctuating; the results show that weld penetration is high but weld surface forming is poor. The laser and arc plasma are periodically coupled when the laser-arc distance is 4 mm. With the increase of the filling height at the bottom of the groove, the laser and the arc are not in the same horizontal plane, the distance between the laser and arc increases, and the arc and laser-plasma are separated; When the liquid at the bottom accumulates to a certain height, it flows to the laser action area due to gravity and surface tension; the liquid level tends to be horizontal, and the laser-arc distance decreases; the laser and the arc begin to couple, and the molten pool is joined together; the weld surface is well-formed, and the weld depth is slightly reduced. When the laser-arc distance exceeds 6 mm, there is no coupling between the laser and the arc in the groove. During laser-arc hybrid welding in the groove, the liquid level of the whole weld pool is inclined due to the accumulation of liquid in the weld pool. The range of the best coupling distance of laser and arc is narrow (~4 mm), and the weld penetration is high and the surface forming is good.

ConclusionsIn this study, laser etching using a laser energy density of 0.7 J/cm2 resulted in a grating structure with an appropriate height and total side area on the Ag/FTO/AZO film surface, which could effectively improve the anti-reflection ability of the film. Furthermore, the additional laser annealing effect produced during laser etching promoted grain growth in the film, reduced crystal defects, and resulted in less light and carrier scattering loss and higher carrier mobility. Therefore, the film's optical transmittance and electrical conductivity were enhanced. The resulting film received the highest figure-of-merit (2.80×10-2 Ω-1), indicating that its overall quality was superior to that of the original AZO film (2.58×10-2 Ω-1).

ConclusionsThe morphology of the sample’s upper surface is primarily related to the melting width, and there is slight powder sticking, spheroidization, and splashing in some areas; the morphology of the up-skin and vertical surfaces is greatly affected by the powder sticking and spheroidization, which is related to the width of the melt channel, Furthermore, the hatch distance, powder diameter, and forming angle are directly related. The powder adheres more on the up-skin surface than the vertical surface regardless of the process parameters, and most of the powder does not melt, which decreases the surface quality of the oblique side. The liquid phase area of the molten pool increases with the increase in the line energy density. Hence, the melt width is directly proportional to the laser power and line energy density and inversely proportional to the scanning speed. The larger the melt width, the smaller the upper surface roughness; as the line energy density increases, the energy accumulation effect increases the surface temperature of the molded part. Moreover, the temperature rise on the up-skin and vertical surfaces cause the powder spheroidization and sticking phenomenon in the contact area and the powder pile substantially grows in size, thereby increasing the surface roughness value of the SLM molded part. The predicted value of theoretical roughness and the actual measured value are basically the same under different process parameters. Additionally, the prediction error of the upper, vertical, and up-skin surfaces are less than 20%, 30%, and 15%, respectively, which can be used to predict the surface roughness of 316L stainless steel SLM molded metal powder parts under different process parameters.

ConclusionsThis paper has proposed a method to realise weld path identification. Before welding, the area of the weld center is automatically extracted from the image of the weld. Based on the kernel correlation filter algorithm, the area of the weld center can be located in real-time during welding. To reduce noise contamination of the weld target template, the template is updated based on the response map’s peak sidelobe ratio. Specifically, the peak sidelobe ratio is compared with the set threshold to determine template update. A Kalman filtering model of the position of the weld center is established to get the optimal estimation of the weld center and the state amplification method is adopted to process the colored observation noises. The experimental results show that the proposed method can accurately and stably identify the center position of the butted weld and the lapped weld, and the identification errors can be controlled within 0.137 and 0.105 mm, respectively, meeting the requirements of identifying the weld path with high accuracy.

ConclusionsIn this study, TiO2 nanotube layers were prepared by anodic oxidation on the Ti6Al4V laser shock peening surface. Under simulated body fluid conditions, the surface properties, microstructure, and friction and wear properties were studied. The results showed that the surface of Ti6Al4V had plastic deformation after laser shock peening, and grain refinement improved the surface’s microhardness and wear resistance. The length of TiO2 nanotubes prepared by laser shock peening increased, the wall of TiO2 nanotubes became thicker, the microhardness of the surface decreased, and the surface roughness increased. The TiO2 nanotube layer’s adhesion to the laser shock peening surface increased by 17.7% compared to the substrate. The higher hydrophilicity of the TiO2 nanotube layer improved lubrication, which contributed to a decrease in wear mass and friction coefficient. The wear mechanism was a combination of abrasive wear, fatigue wear, and adhesive wear.

ConclusionsThis study combines laser flattening, laser imprinting, and laser welding technologies, which have the potential to reduce the impact of the skin effect. Firstly, the surface of copper foil is flattened, the effect of flattening parameters on the flattening effect is investigated, and the flattening mechanism is revealed. Then, the nanostructure is then created using the nanomold on the surface of the flattened annealed copper foil. Finally, laser welding is used to connect the flattened and annealed imprinted copper foil and LCP. Microtension experiments are used to test the bonding strength of the copper foil and LCP treated under various conditions. The sample’s surface morphologies are examined using an atomic force microscope, optical microscope, and a scanning electron microscope, and the mechanisms of flattening, imprinting, and welding are discovered.

ConclusionsA three-phase solidification model based on the volume-averaged method with considerations of non-equilibrium dynamic solute redistribution coefficient and constant solute redistribution coefficient is established. The morphologies of the temperature field and flow field are the same when compared to the simulation results of the two solidification models, as is the variation trend of solute field concentration. However, the dynamic solute redistribution coefficient solidification model predicts the solute distribution in the deposition layer with less error and is closer to the experimental data. In the laser cladding process, the solidification rate of the molten pool varies with the change in the solute redistribution coefficient, which leads to the instability of the solute distribution process and obvious element segregation. Our findings indicate that the dynamic solute redistribution coefficient has a significant impact on solute distribution in the deposition layer. To more accurately predict the solute distribution in the deposition layer, the change in the solute redistribution coefficient should be considered in the laser cladding process simulation.

ConclusionsAiming at the problem that the optimized processing parameters of LMD are extremely complicated to obtain, an effective method is proposed by constructing a dimensionless processing diagram in this paper. A group of dimensionless processing parameters applicable to LMD has been defined, and a dimensionless processing diagram has been constructed on the basis of parameter data available in the literature. The practicability of the dimensionless processing diagram has been proved experimentally for the LMD of Ti6Al4V. The optical micrographs show that the prior-β columnar grain morphologies of the as-deposited samples are a function of E0*. A high value of E0* leads to a relatively low cooling rate and coarse columnar grain. The cooling rate of the melt pool dictates the grain size formed in a deposited layer with a lower cooling rate, resulting in a coarse microstructure. By the experimental design of orthogonal array and ANOVA, the significance of processing parameters related to the microhardness of the LMD Ti6Al4V is q>v>h. The lack of fusion voids and gas pores is strongly affected by E0*, and these defects, in turn, affect the mechanical property. The ductility of the as-built samples is compromised at a lower value of E0*; however, owing to irregular lack of fusion voids, despite having comparable tensile strength with those samples at a higher value of E0*, the yield strength, ultimate strength, and elongation reach a maximum value of 890 MPa, 963 MPa, and 13.4%, respectively, at E0*=3.74, which exceed the forgings standard and is close to those fabricated by additive manufacturing reported in the literature. High-performance parts are obtained because of the dimensionless processing diagram constructed in this paper, which effectively narrows the processing window.

ConclusionsIn this study, a laser-MIG hybrid welding monitoring system was designed based on the LabVIEW environment and the accuracy of the monitoring system was verified via experiments. The conclusions are as follows:1) The designed monitoring system was capable of monitoring plasma signals and had three functions: saving plasma signals in TDMS format, saving process parameters, and playback of data.2) Binarization processing, morphological filters, HUBER linear fitting, and path-tracing-based bifurcation removal algorithms were used to locate the wire and workpiece successfully. Thus, we calculated the distance of laser transmission through the hybrid plasma.3) The monitoring system extracted DLTP values from the plasma images and output them. Compared with the DLTP value obtained via the image analysis software, the accuracy of the DLTP value calculated by the system reached about 96.5%.

ConclusionsThe composite coating had a good metallurgical combination with the substrate. The matrix of the coating showed a compact TixAly phase with short rod structure, and a large number of TiC1-xNx phase dendrites mainly distributed on the matrix. During the melting process, Al atoms diffused into the TiC1-xNx phase dendrites, resulting in the formation of a layer of MAX phase at the dendrites' edges. TiC and Ti2AlC in the composite coating were gradually replaced by TiN and Ti2AlN as the AlN/TiC content ratio in the mixed powder increased. The solid solution TiC1-xNx changed from solid solution N in TiC to solid solution C in TiN, that is, from TiC0.7N0.3 to TiC0.3N0.7,and finally to TiC0.2N0.8. The coating's hardness was increased to 2.04 times of the TC4 matrix by forming a fine and dense structure and a dispersed reinforcing phase with the proper powder ratio. The Ti-Al-(C, N) composite coating is expected to improve the surface properties of titanium alloy, allowing it to adapt to more difficult working conditions.

ConclusionsTo alleviate the stress shielding effect caused by the implantation of the traditional femoral stem, the TPMS structure with better affinity for the biological cell is selected as the porous structure of the femoral stem. The TPMS structure sample can be formed better through SLM technology. The compression test results show that the mechanical properties of the three common TPMS porous structures can meet the requirements on the use of femoral stems within the constraints of bone growth and SLM equipment manufacturing. Compared with the G and D structures, the P structure shows greater comprehensive advantage in manufacturability and ability to adjust. It is a porous structure more suitable for the design of the femoral stem. The results of finite element analysis show that the peak stress of the P structure femoral stem does not exceed the yield strength of porous materials under common daily active loads, which proves that the application of P structure in the femoral stem can meet the needs of daily activities. Moreover, after the introduction of P structure in the femoral stem, the stress distribution of the corresponding femur is significantly improved, which can effectively alleviate the stress shielding effect. Among these, the P structure with a porosity of 75% is the best, which can reduce the stress shielding rate by 41.83 percentage points. This is beneficial in improving the long-term stability and service life of the prosthesis after implantation.

ConclusionsIn this study, a Fe-Ni-Cr composite coating was applied to the surface of gray cast iron using the laser cladding method. Its phase and microstructure were investigated, as well as sliding friction and wear tests were performed at room-temperature and high-temperature. The specific conclusions were as follows: the main phases of the coating are γ-(Fe, Ni), Fe5C2,F3C, and Cr7C3. F3C had an excellent bonding property and was the main component of the transition zone between the coating and the substrate, resulting in a good metallurgical bonding between the coating and the substrate. Due to the undercooling degree, the microstructure of the coating from the heat-affected zone to the top of the coating gradually changed from columnar crystals to cellular crystals, dendrites, and equiaxed crystals, which had the effect of fine-grain strengthening and improving the coating’s hardness and wear resistance. At room temperature, the substrate’s wear mechanism was primarily abrasive wear, while at high temperatures, it was oxidation and adhesion wear. The wear mechanisms of the coating and substrate materials at room temperature were mainly abrasive wear. The thermal oxidation reaction became more severe as the test temperature rose, and the composite oxide film formed on the coating’s surface and alleviated adhesive wear and abrasive wear, which was one of the reasons for the coating’s ability to reduce friction coefficient and wear loss.

ConclusionsTo realize the multifocus stealth dicing of silicon wafers, an axial multifocus algorithm with a large numerical aperture is proposed. The number of on-axis foci, energy, and the interval between the foci can all be adjusted by changing the Fourier series coefficients. For the multifocus light field with equal energy, the simulation results show that the energy utilization rate is over 90% and the light intensity uniformity is over 90%. The phase diagram is loaded onto the spatial light modulator to simultaneously generate three focuses inside the silicon wafer. The 250 μm thick silicon wafer is successfully diced at a time by selecting the corresponding laser parameters and the movement speed of the displacement table. Because spherical aberration increases with machining depth, developing a multifocus laser dicing method for simultaneous aberration correction is essential in future work.

ConclusionsThe streamline layering technique is proposed in this study to tackle the ternary blade laser cladding formation trajectory problem. The main base surface is evenly spaced along the radial direction to obtain arc slices perpendicular to the radial direction, which are then evenly spaced along the scanning direction to obtain the segmentation unit. The streamlined layering technique is proposed in this study to solve the problem of ternary blade structural parts layering, bending, and inclination, and to accomplish the accumulation of ternary blade forming parts. The inspection results of the formed parts are as follows: the surface of the ternary blade-formed parts is smooth, and the average surface roughness value is less than 4.065 μm, which effectively reduces the step effect; it achieves a good metallurgical combination with the irregular base surface, and the average thickness of the formed parts is 5.97 mm. The relative errors of thickness and torsion angle are from -1.4% to 1.03% and -4.67%, respectively. The forming accuracy is high. The heat accumulation at the laser molten pool is evident as the height of the formed part increases. Further, the microhardness reduces as the microstructure increases; the microhardness of the formed part ranges from 348.3 to 360.4 HV, and the metallographic structure is uniformly dense with no evident holes or cracks.

ConclusionsAluminum alloy profiles based on laser-MIG hybrid welding were studied for high-speed trains, and the influence of different heat source angles on the welding characteristics, including appearance, pores and melt flowing, was investigated. Results show that the weld depth decreases with an increase in the angle between the laser and the welding direction. When the laser source angle is increased from 82.5° to 110°, the penetration depth and weld width decrease by 50% and 25%, respectively. Moreover, increasing the heat source angle is conducive for reducing the weld pores. When the laser source angle is increased from 82.5° to 97.5°, the weld porosity decreases from 3% to 0%. Moreover, the droplet transfer mode was observed under different heat source angles and the length of the molten pool was promoted by increasing the angle between the laser and the welding direction. Fluent simulation results suggested that the heat source angle has significant effects on energy propagation. With an increase in the angle between the laser and the welding direction, the propagation of energy in the depth direction will decrease. The heating range increases with increasing arc angle, which is beneficial for prolonging the solidification time of molten pools and the eliminating weld pores.