This paper summarizes 15 key research areas on laser materials processing and 7 key research areas on laser micro-nano fabrication based on the statistic information from 6 ICALEO-International Congress on Applications of Lasers and Electro-Optics and 3 CNCLMP-China National Conference on Laser Materials Processing. Five hot research topics on laser materials processing and four hot topics on laser micro-nano fabrication have been concluded from the distribution of 1247 ICALEO papers and 231 CNCLMP papers in the key research areas. The research on laser materials processing in China has covered the main and leading research areas in the world. There show strong research interests and large number of papers in laser surface modification especially in laser cladding in China. More efforts and research work are needed to strengthen the research in novel laser development and laser micro-nano processing.

By research on the substitution of the traditional punching and trimming die with the laser cutting, substitution of the resistance spot welding in the general assembly of the car body with laser welding, and laser welding of multifarious thickness overlay of car,the characteristics of laser manufacturing technology in automobile industry are displayed. The roll matrix are fabricated by laser cladding. Compared the traditional roller technological process of sintering ,the short technological process of laser manufacturing not only increases productivity and shortens technological process，but also reduces the cost and saves the energy. This technology will have wide application in industrial process.

In carring gas/powder two phases flow from laser coaxial nozzle there are three main physical processings of energy, momentum and mass transferences, which directly affect the quality and accuracy of the parts by laser manufacturing. Comprehensive results reseached on momentum and mass transferences of the two phases flow have been reported: Physical model of the two phases flow from laser coaxial noozel is presented. A set of governing equations of mass and momentum conversation for each phase are established based on Euler theory for two-phase flow. FLUENT 6.0 software is developed to solve the momentum equation and continuity equations. DPIV (Digital Particle Image Velocimetry)with special image processing software is developed to measure concentration and velocity fields in the gas/powder stream. It is shown that there are good identical results between numerical simulation and DPIV measurement.

Laser-arc hybrid welding is a promising technology which can be widely used in industry and it attracts attention of the researchers worldwide. Combining two heat sources with different physical properties and energy transmission mechanisms together, laser-arc hybrid welding possesses the composite advantages of laser welding and arc welding. Some aspects on laser-arc hybrid welding such as the laser-arc interaction, droplet transfer characteristics, dynamic behaviors of the keyhole and the weld pool, hybrid welding processes and their applications are reviewed.

The lately developments of laser cutting technique of ceramic materials with hard and brittle properties in recent years are reviewed. According to the emphatic analysis of processing, the 4 kinds of laser damage-free cutting methods, including traditional optimized parameter method, laser multiple-pass cutting, laser cutting with controlled fracture by stress guiding method and aided laser cutting method, are summarized. Combined with the research experience of the authors, the present problems of laser cutting of ceramics with different kinds of thicknesses and dimensions are proposed and analyzed.

Nowadays, there is a great demand for rechargeable battery in the world, especially for the innocuousness and nonpollution ones. In process of manufacture, the automatic production line is used to ensure the productive tempo, the first-rate quality and consistency. And in the automatic production, the battery case, the electric terminal and the relief valve etc are welded by laser. So the battery laser auto welding technologies emerge as the times require. We make a summary of welding theories, research findings, techniques and the software and hardware design for the critical component in this article. We explain some questions that should be solved in the end, and give the developing direction for the future.

Laser cladding is a new type of technology to prepare nanostructured coatings. The present situation of domestic and foreign researches of laser cladding nanostructured coatings is reviewed, and the works of our group are also introduced. The main technologies to fabricate nanostructured coatings are introduced according to the different cladding samples, which can be divided into nano-particles and prefabricated nanostructured coatings. In terms of nano-particles, there are pure nano-particles, nanometer and micrometer composite particles, and reconstructed nano-particles etc. In terms of prefabricated nanostructured coatings, there are thermal-sprayed nanostructured coatings, nano-composite plating coatings, and sol-gel nanostructured coatings etc. The existent problems of the nanosturctured coatings prepared by laser cladding are presented. The development prospects of this preparation technology, such as in-situ synthesis of nanostructured coatings, laser cladding nanometer and micrometer composite particles, and numerical simulation of the laser cladding process are also discussed.

Nd∶YAG laser beam butt-welding of invar36 alloy is carried out. The influence of the welding line′s surface, bead penetration and width to the laser parameter is investigated with plate-welding. The composition and hardness of the fusion zone is investigated with the butt-welding of the thickness of 2 mm. The result indicated that: laser power and pulse duration are the main factors which influence the weld bead penetration, weld width and heat affect zone (HAZ). There is a narrow selection range of the welding speed. The defocusing distance mainly affects the weld bead penetration and weld width. The composition of the welding-line has no obviously change, the hardness is appreciably lower than base body. The crystallographic orientation of the welding line had columnar crystals appeared and austenite growth.

The temperature field of laser-induced plasma in laser welding is hard to be obtained by the spectral analysis method. By using fast Fourier transform (FFT) and Hankel inversion algorithms, a data processing method based on Abel inversion for measuring temperature distribution of plasma is studied. Meanwhile the precision in the process of the dada is analyzed. The standard error e was about 3.23×10-2 at the number of dispersed points N of 41. The results show that the data process method can be very useful in the observation of the temperature filed of laser-induced plasma by using a multi-channel spectral analyzer. The temperature of plasma plume in the center area of laser beam appeared to be higher than the area near the laser beam.

Experiments of dual-beam CO2 laser welding aluminum alloys were conducted. The weld appearance, porosity content and joint strength with parallel and serial dual-beam laser welding were investigated. CCD and CMOS image sensors were respectively used to monitor the metal pool and plasma from both paraxial and coaxial directions. The results in above aspects of single-beam and dual-beam welding were simultaneously compared. The results indicate that dual-beam laser welding aluminum alloys can reduce the size and therefore increase the stability of plasma in comparison with single-beam laser welding, which usually results in better weld shaping. A comprehensive comparative analysis on the parallel and serial dual-beam welding shows that the former is more favorable in weld shaping, but it will decrease the penetration in some degree.

The structure of Mach shock disk (MSD) is analysed emphatically by constructing free jet model, adopting compressible liquid axial symmetric N-S equation and RNG k-ε model. Through the numerical simulation of free jet outer flow field under the outlet static pressure of 6.145×105 Pa, the paper describes the jet structures of different outlet Mach numbers, analyses the relation between MSD and outlet Mach number of nozzles. It reveals that the width of MSD presents convergent trend with the increasing of Mach number, and indicates that the outlet Mach number should be improved properly by ensuring disappearance of overexpanding waves under the working pressure. It is illuminated that the Mach number will be convergent to a fixed position with the increasing of outlet Mach number. The veracity of simulation results and the validity of conclusion analysis are proved by contrasting validating of flow field visualization to the solved model.

CO2 Laser welding of 5A02 and 5A06 aluminum alloys sheet with different thickness is performed with or without the addition of filler metal powder . The main factors affecting welding process stability and formability of weld are investigated. Meanwhile, based on the finite element analysis (FEA), temperature field and the stress-strain field of aluminum alloy with different thickness on laser welding are simulated. The residual stresses distribution and deformation features of tailored welded blanks (TWB) are analyzed. The results indicate that with the increasing of magnesium in aluminum alloys, the absorptivity is also improved, so a stable welding process can be obtained for a higher content of magnesium in aluminum alloys. The addition of the metal powder can enhance the energy coupling efficiency during laser welding of aluminum alloys sheet with different thickness, and the weld formation and process stability can be improved greatly. The simulated results indicate that temperature field distribution is unsymmetrical. The distributions of the stress-strain are also asymmetric. The distributions of pulling stress field in the thinner plate are larger than that in the thicker one and the deformations in thinner plate are more serious than that in thicker one.

A three-dimensional (3-D) thermal model based on the finite element theory is implemented to simulate the temperature field on laser transmission welding of polyvinylchloride (PVC) by means of software ANSYS. With the ANSYS parametric design language APDL, a moving Gaussian distributed heat source is applied, and the distribution of the temperature field is gained. Effect of process parameters, including laser power, scanning welding and spot diameter, on the welding result is investigated, and the calculated melting width is obtained. The results show that with increasing of scanning speed, the maximum temperature and the melt width decrease; with increasing of laser average power, the maximum temperature and the melt width increase; with increasing of spot diameter, the maximum temperature decreases and the melt width increases. Very good agreement is achieved between the calculated value and the measured value.

To explore a new method to improve the glass cutting quality, the principle of glass laser cutting by thermal stress was introduced. The advantages and the disadvantages of cutting glass by single focused and un-focused CO2 laser beams were analyzed, respectively. A novel method of cutting glass by dual CO2 laser beams was proposed, where a focused CO2 laser was applied to pre-score a line on the glass surface and the other unfocused laser beam was applied to separate the substrate along the scoring line. The cutting qualities with single and dual laser beams were compared experimentally. The results show that cutting glass by dual laser beams is an ideal cutting method, which not only makes the cutting path in a straight line but also makes the cutting profile very smooth.

Based on geometric curvature method， the scanning path planning for laser bending of straight tube, AISI304L stainless steel, into a bent tube in a plane or three-dimension curvature was researched. To two dimensional(2D)laser bending tubes, the tube is divided into several segments according to the extreme point and inflection point of the desirable tube, taking the extreme point as the initial place of the path planning, using different scanning space for every subsection in order to identify the heating/scanning paths. In order to 3D laser bending of tubes using projection decomposition method, three-dimensional surface is decomposed into two two-dimensional curved surfaces, the scanning path planning and process parameters were thus acquired respectively. Through combining two groups’ data, the 3D heating/scanning path planning was obtained. Finally experimental verification is carried out by using a typical complex sinusoidal surface and helical coils of three-dimensional shape as the desirable shape on Nd∶YAG solid laser , scanning bending results show that in the paper scanning path planning method is effective and feasible.

In order to detect samples with convenience, high speed and low cost, we presented a fabrication method of microchip with embedded optical fibers. Polymethyl methacrylate (PMMA) microchip with embedded optical fibers of 35 μm diameter was fabricated using a 248 nm KrF excimer laser processing technique. The processing parameters of excimer laser and the embedding method of optical fibers were studied. The results show that the excimer laser processing is controllable, easy, reliable to realize automation. With the embedded optical fiber system, the mutual aim of the fibers and the aim between the fibers and channel core can be realized, thus resulting in the sensitive detection of optical signal, which is expected to have good applications in the portable blood cell counts and bio-sensors.

In laser forming, except for the desirable bending deformation, the undesirable deformation is also produced. The undesirable deformation can be ignored in the conventional laser forming, however, for the high precision workpiece, these inaccuracies influence not only the assembly accuracy, but also the operational life. To reduce the undesirable deformation of the forming workpiece and seek for the optimal process technology, the temperature distribution of laser forming and restraining force variation of the surrounding cold material on the heated area are analyzed， the undesirable deformation mechanism is disclosed， and two new scanning strategies are proposed. The results show that the metal plates have the different undesirable deformation under the different scanning strategies. In real industrial applications, the different scanning strategies should be chosen according to the different forming requirements.

Direct forming 2Cr13 parts were studied experimentally for explaining the performance of laser direct metal deposition (DMD) forming. The microstructure of single track cladding, multiple tracks overlapping cladding, and multi-layer deposition were observed. The mechanical properties of specimens, such as hardness, anti-abrasive, tensile and residual stress distribution, were tested. The experimental results showed that the typical patterns of single track had cellular dendritic, column dendritic, and equiaxed crystals. The patterns depended on the temperature gradient and the solidification rate of cladding. The overlapping zone of DMD specimen was different from that of powder preset cladding. The grains of multi-layer deposition specimen showed the characteristic of orientated growth which was influenced greatly by scanning path. Under different technological parameters, the average hardnesses of specimens changed from 300 HV0.2 to 550HV0.2. When the microstructure was thin dendritic crystal, the anti-abrasive property increased one time than that of 2Cr13 substrate which was quenched and tempered. The average tensile strength increased by 30%. The residual stresses were different at different positions, but all of them were small.

In order to solve the Achilles’ heel of recast layer and heat affected zone produced during laser machining, a new processing of neutral salt solution assisted laser machining (SALM) is put forward, which can remove recast layer and heat affected zone (HAZ) on-line by using the effect of salt solution on the thermal chemical reaction and continuing cooling effect of materials. Based on the properties of laser attenuation in neutral salt solution, the experimental system was designed, and a drilling experiment on a 0.5mm thickness stainless steel sheet was done. It is confirmed that the principle of SALM is right and the processing is feasible by comparing the results of the SALM with laser beam machining (LBM) in air. The drilling experiment results show that the quality of removing recast layer and HAZ are better with the increase of solution concentration and flow velocity, and the thickness of recast layer is reduced by 80%, the dimension of HAZ is reduced by more than 90% during SALM in NaCl solution with concentration of 20% and flow velocity of 5 m/s.

A kind of binary optical elements is introduced to implement the transformation of laser beam for high power laser processing. The even sampling Pixellated Dammann grating is adopted to perform the Guassian beam transformation in order to obtain the given output spots. The principle and implementation of the beam transformation technology of pixellated Dammann grating is described with examples of the linear, even, annulus and uneven array. Results show that the output spots have high diffractive efficiency and uniformity. The application of the even and uneven array spot in the laser surface modification is investigated, showing the improvement of the hardness and the wear resistance of the sample surface, and the uniformity of the modified surface.

A home made high-power laser processing system for industry application is reported. The symmetrical parallel plane four-rod series resonator CW Nd∶ YAG laser with krypton lamp-pumped has been developed, the output power is more than 2100 W with beam parameter product of 24 mm·mrad. The total electro-optics efficiency of system with lamp pumped YAG crystal is as high as 3.5 %. The output laser is transmission with 600 μm core diameter fiber. The key factors, such as high-power laser output, high efficiency fiber coupling and controlling system of adaptive processing at the premise that the high-power laser processing system guarantees the beam quality, are analyzed. It is conclusion that the laser processing machine is a stability, fastness, operating convenience system. The system can connect with moving components, such as robot and machine, and meet the processing requirements of industry application.

The design principle and experiment result of a novel kind of wide-band shaping parabolic mirror for high power laser processing are introduced. According to the geometrical optics, the focusing spot of this parabolic mirror is studied by ray tracking. It is demonstrated that after being focused by this parabolic mirror, the original circular laser beam could be shaped into the narrow strip with uniform distribution of light intensity. The laser hardening is carried out for 45# steel using crosscurrent CO2 laser and the parabolic mirror, the laser hardening band size and hardened depth are tested, then the hardened layer shape and microstructure in the hardened layer are observed and analyzed. The results show that the micro hardness is 3.5～4 times as high as the unquenched area which reaches 540～580 HV0.3, when the laser output power is 3 kW, the length of the strip spot is 12 mm and the scanning speed is 15 mm/s . The hardened depth is approximately 1 mm, the single quenching width is larger than 10 mm , and the hardened layer is well-distributed.

Ta2 O5 single crystals have been grown by the laser heated pedestal growth (LHPG) technique up to several centimeters length with diameter of 1.1 mm. The crystal, characterized by X-ray diffraction, dielectric measurement, and thermal expansion analysis, has Htri -Ta2 O5 symmetry. Dielectric permittivity, loss tangent along [001] and [110] direction were investigated over the temperature range from －180 °C to 100 °C. Large dielectric anisotropy in Ta2 O5 single crystal was observed. At room temperature, the dielectric permittivities (1 MHz) along ［001］ and ［110］ are 33.2 and 231.9, respectively. The reason of dielectric enhancement in Ta2 O5 crystal grown by LHPG was also discussed.

Material processing is based on the philosophy of either removing material or adding material. Traditional machining technologies gradually remove material from top to down. Selective laser sintering (SLS) composes the powder material bottom up layer by layer. A novel method to sinter powder by the investigation of laser interaction with powder is developed. This fabrication technology combines material removing and adding together named laser vaporizing sintering (LVS) technology. This technology removes the material with laser vaporizing and meanwhile the powder around laser beam is molten and sintered to form structure by laser. It shows great potential advantages to fabricate thin or micro parts in the future.

WCp/Ti-6Al-4V graded metal matrix composites (MMC) layer was produced by the laser melt injection (LMI) process and the formation mechanism of the graded layer was studied. The results show that the initial speed of the particle (v0), the minimum velocity of injected particles necessary for penetrating through the melt surface (vmin) and the viscosity of the melt pool (η) play key roles in the distribution of the WC particle. With big density, the WC particle has high kinetic energy during the laser melt injection process, and therefore the viscosity of the melt pool is not a critical factor anymore. The solidification front of the solid-liquid interface of the melt pool is the most sensitive factor that determines the formation of the graded layer when the WC particle is used as injection particle. Meanwhile, the total amount of WC particle at different depth of the MMC layer is dominated by the length of the solidification front in this depth. The injection location plays an important role in the distribution of WC particles. When the WC particles are injected into the extended part of melt pool, the depth of this region is low ,and the WC particles meet the solidification front at higher position. In that case, most WC particles are trapped at the top part of the melt pool and therefore a WCp/Ti-6Al-4V graded metal matrix composites layer is formed.

The VC-VB-B4C complex particulate reinforced Ni-based composite coating has been successfully synthesized in situ by prior pasting laser cladding on steel A3. The microstructural and metallographic analyses were carried out by a scanning electron microscopy, energy-dispersive spectroscopy(EDS) and X-ray diffractometer(XRD). The microhardness and wear resistance of the coatings were also tested. The results indicate that the composite coating is bonded metallurgically to the substrate. The microstructure in the bottom of coating consists mainly of oriented dendrites of γ(Ni). The microstructure locating in the center and upper zones contain a large number of VC-VB-B4C complex particles and acicular Cr3C2 phases distributed uniformly in the matrix of γ(Ni) solid solution. The VC-VB-B4C particulate reinforced composite coating gives a high average hardness of HV0.31350 and better wear resistance. The wear mass loss of the composite is just one third of that of the pure Ni60 coating. This could be attributed to the presence of the high content of in-situ synthesized VC-VB-B4C complex particulates and their well distribution in the composite coatings.

It is great that the influence of laser beam intensity distribution and its shape on laser hardened layer performance. Rectangle facula or wide-band facula are applied widely. But laser beam of uniform intensity distribution can not always generate uniform hardened layer. At present, using general laser heat treatment beam optimum equipment, the distribution shape of laser hardened layer was crescent. Based on the analysis of research on beam optimum system for laser heat treatment in the world, two different methods on laser beam optimum are present in order to improve distribution uniformity of hardened layer. Laser scanning ring facula and linear facula are analyzed in the new methods. The mathematic models of laser beam optimum are built and their temperature field distributions are simulated. The distribution uniformity of the hardened layer is improved.

Laser shock peening (LSP) is a non-traditional anti-fatigue manufactureing technology based on mechanical effect of laser shock wave.Up to now, research on LSP mostly focuses on mechanism and experiment, whereas experimental method is hard to achieve comprehensive understanding on the correlative influence of various parameters to the effect of LSP. A numerical analysis method on typical LSP process is introduced, FEA code ABAQUS and MSC.Fatigue are used as platforms, laser shock loading module is programmed to solve the interface problem of data transfer. Taking 2024-T3 aluminum alloy samples for example, propagations of laser shock wave, size and distribution of compressive residual stress as well as the fatigue properties are studied by numerical analysis technique, and the fatigue life with LSP is predicted. The relationship between laser shock wave pressure, residual stress and fatigue life is established by digital analysis method. Visualization of LSP process and evaluation of peening effect could be achieved.

NiCrBSiC laser clad coatings are fabricated on TC4 substrate using CW-CO2 laser. The influence of processing parameter on the microstructure and dilution rate of the coatings is examined. Under the same power density and irradiation time, the depth of substrate fusion is deeper, the dilution rate of the coatings is higher and the reinforcing phases are mainly TiB2 and TiC when the laser beam diameter is lager (D=6 mm). The depth of substrate fusion is shallower, the dilution rate of the coatings is lower and the reinforcing phases are mainly CrB and small amount of M23(CB)6 and TiC when the laser beam diameter is smaller (D=3 mm).

In order to find out the broken critical-position of coating interface, a theoretical analysis is made on the thermal field generated when the coating is scratched by infrared laser. The examined results of real-time temperature of coating being scratched by laser are analyzed. It is indicated that the change of surface temperature of the coating presents a two-phase process, which corresponds with the results of theoretical analysis. The turning point of temperature is just the critical position where the coating breaks off from substrate. The laser power is calculated to be about 31.92 W at the critical position. The result directly reflects the adhesion strength between coating and substrate.

Mg alloy has become promising materials for industrial structural and transport applications due to their attractive properties such as low density,high specific strength, good electrical and thermal condivity. The poor wear property is the major concern when it is subjected to motion in automotive or other engine components.To improve its wear property , many different surface engineering methods have been developed. Laser surface cladding technology is a very promising one among these methods.Nano-Al2O3 particles are dispersed on the ZM5 surface by laser surface engineering to improve its wear resistance property. Laser processing is carried out with a 500 W pulsed Nd∶YAG laser by melting preplaced nano-Al2O3 particles on the surface of ZM5. Following laser processing, a detailed microstructural analysis of the surface modified layer is carried out. The microhardness of the surface layer is measured as a function of laser parameters and wear resistance property was evaluated in details. Microhardness of the surface layer is significantly improved to as high as 350 HV as compared to 100 HV of the substrate compared to the as-received specimen, the wear resistance property of the laser surface modified samples is considerably improved.

Titanium matrix composite coatings were fabricated on Ti-6Al-4V substrate by laser cladding using powder mixtures of Ti+Cr3 C2 and Ti+TiB2 , respectively. The chemical compositions and microstructures of the coatings were analyzed using scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). Microhardness was measured by a microhardness tester. The results showed that Cr3 C2 particles were dissolved and deposited to form dendritic TiC in the upper section and spherical grain TiC in the bottom of Cr3 C2 +Ti coating. Most of TiB2 was dissolved in the molten pool by laser irradiation, then formed TiB with fine needles and coarse needles in the TiB2 +Ti coating. A few quasi-melted TiB2 particles with irregular shape at the bottom of the coating were observed. The average microhardnesses were approximately HV850—HV1000, HV800—HV1050 in the Cr3 C2 +Ti and TiB2 +Ti coating, respectively, which were 2～3 times higher than that of Ti-6Al-4V substrate.

The experiment research on damage in K9 glass induced by pulsed CO2 laser is carried out, which has a pulse width of 10 μs. The theoretical model of K9 glass irradiated by pulsed CO2 laser is developed and a numerical simulation is performed to calculate temperature and stress distributions in K9 glass sample irradiated by pulsed CO2 laser using finite element method. The simulation and experimental results indicate that the damage-threshold of K9 glass irradiated by single pulse is 6.533J/cm2, and the effect of laser irradiation on samples can be affected considerably by the change of laser energy density. The damage mechanism of K9 glass induced by pulsed CO2 laser are melting damage and compress stress damage in irradiated zone, and the damage mechanism of K9 glass induced by pulsed CO2 laser is circular tensile stress damage in the periphery of irradiated zone when the laser energy is high. The model prediction agrees well with the experiment data.

Wear-resistant coatings were fabricated by laser cladding with direct injection of the Ni-Cr-B-Si powder. Laser cladding was conducted with a Rofin-Sinar CW025 YAG laser. Laser cladding coatings were characterized by scanning electron microscopy (SEM, LEO1450), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). The results show that there is a good metallurgical bonding between the coating and the C86300 bronze substrate without pores and cracks. The laser cladding Ni-Cr-B-Si alloy coating was mainly γ-Ni, Cr7C3, Ni2B, Ni3B together with lesser proportions of CrB2 and Cr3Si. The basic elements (Cr, Fe, Ni, Cu and Zn) content from the bronze substrate to the coatings vary regularly. Near the interface, the main elements are gradient distributed.

To strengthen the wear resistance of AISI321 stainless steel, the TiC carbide-reinforced composite coating was produced by laser surface alloying. The microstructure, microhardness, and wear resistance of the composite coatings were investigated using optical microscopy, X-ray diffraction (XRD) meter, scanning electron microscopy (SEM), microhardness tester, and sliding wear tester. The results show that the composite coating is metallurgically bonded to the substrate and the microstructure is fine and uniform. The hardness of the composite coating is up to 400 HV, which is 2.5 times that of the substrate. Under room temperature and oil lubrication condition, the sliding wear tests indicate the friction coefficient and weight loss of the composite coating are smaller than those of substrate. The worn surface of the composite coatings is much smoother than that of the substrate, without grooves and crater. The wear resistance of the material has been greatly improved by laser surface alloying.