Laser Surface Treatment Process Research Articles

Optimizing the Size of a Moving Annular Hollow Laser Heat Source

The physical phenomenon of the annular hollow laser surface treatment process is complex, and the internal mechanism involves multiple disciplines and fields. In addition to the general parameters of laser beams, such as laser power and scanning speed, an annular hollow laser beam exhibits unique physical characteristics, including hollow ratio and hollow area. The selection of the inner and outer annular radii of the laser plays a critical role in the study of metal surface heat treatment. From the point of view of heat transfer, the entransy dissipation theory is introduced in the metal surface treatment process with an annular hollow heat source. Firstly, using the principle of the extreme value of the entransy dissipation rate, under a constant heat flux boundary condition, the entransy dissipation rate is obtained through the temperature field distribution in the calculation area by numerical simulation. Secondly, the selection of the inner and outer ring radii of the annular laser is explored, and the average temperature difference of the heating surface is minimized to reduce the thermal stresses of the material. This paper seeks new insights into the geometric parameters of the inner and outer radii of the annular heat source.

Hydrophobic Surface Array Structure Based on Laser-Induced Graphene for Deicing and Anti-Icing Applications.

The exceptional performance of graphene has driven the advancement of its preparation techniques and applications. Laser-induced graphene (LIG), as a novel graphene preparation technique, has been applied in various fields. Graphene periodic structures created by the LIG technique exhibit superhydrophobic characteristics and can be used for deicing and anti-icing applications, which are significantly influenced by the laser parameters. The laser surface treatment process was simulated by a finite element software analysis (COMSOL Multiphysics) to optimize the scanning parameter range, and the linear array surface structure was subsequently fabricated by the LIG technique. The generation of graphene was confirmed by Raman spectroscopy and energy-dispersive X-ray spectroscopy. The periodic linear array structure was observed by scanning electron microscopy (SEM) and confocal laser imaging (CLSM). In addition, CLSM testings, contact angle measurements, and delayed icing experiments were systematically performed to investigate the effect of scanning speed on surface hydrophobicity. The results show that high-quality and uniform graphene can be achieved using the laser scanning speed of 125 mm/s. The periodic linear array structures can obviously increase the contact angle and suppress delayed icing. Furthermore, these structures have the enhanced ability of the electric heating deicing, which can reach 100 °C and 240 °C within 15 s and within 60 s under the DC voltage power supply ranging from 3 to 7 V, respectively. These results indicate that the LIG technique can be developed to provide an efficient, economical, and convenient approach for preparing graphene and that the hydrophobic surface array structure based on LIG has considerable potential for deicing and anti-icing applications.

Effect of double laser beam surface treatment on the surface morphological characteristics of Ti6Al4V at different heat source incidence angles

With the development of the high-end equipment manufacturing industry, the requirements for the surface performance of critical components are likewise increasing. To control the heat and mass transfer in the laser surface treatment process more efficiently and flexibly, the multiangle double laser surface treatment technology shows unique advantages. This study is focused on the experimental study of the laser surface treatment process for Ti6Al4V material. By changing the laser power and the incidence angle of the laser beam, the effects of single-laser beam surface treatment (SLST) and dual-laser beam surface treatment (DLST) on the surface morphology of the alloy were studied. The effects of laser treatment on the surface morphology, element distribution, roughness, surface chemical state, and surface structure of the alloy were emphatically analyzed. The mechanism of SLST and DLST at different incident angles of heat source and the effect of DLST on the formation of an oxide layer on the surface of the alloy were compared and analyzed. The results show that when the average power of the high-power nanosecond pulse width laser in DLST is 100 W and the incident angle is 135°, the surface oxygen content reaches the lowest, as low as 8.31%. The secondary effect of the laser makes the alloy surface remelt again, and then the best roughness after laser processing is obtained, with a roughness value of 2.801 μm. Finally, we obtain the optimal process for laser surface treatment and conclude that DLST can significantly optimize the surface state after a high-energy laser beam action.

Tribological Behavior Analysis of the ISO 5832-1 Austenitic Stainless-Steel Treated by Optical Fiber Laser Used for Biomedical Applications

The present work analyzed the influence of an optical fiber laser surface treatment process on the tribological behavior of the ISO 5832-1 austenitic stainless-steel, basing on the wear volume and friction coefficient. Specimen of this biomaterial were treated by alternating the laser frequency, in order to find out a condition that improves its tribological resistance. Ball-cratering micro-abrasive wear tests were carried out with a test ball of AISI 316L stainless-steel, used as counter-body, and an abrasive slurry prepared with abrasive particles of black silicon carbide (SiC) and distilled water. The micro-abrasive wear tests results indicated that: i) the hardness of the ISO 5832-1 austenitic stainless-steel increased as a function of the laser frequency, decreasing, consequently, the wear volume, as predicted by Archard’s Law; ii) the friction coefficient did not present a proportional behavior with the increase of the optical fiber laser frequency; iii) the best condition to improve the wear resistance of the ISO 5832-1 austenitic stainless-steel was obtained adopting an optical fiber laser frequency of 350 kHz, being reported the lower wear volume.

Investigation on wear resistance of nodular cast iron by laser surface treatment

The surface of nodular cast iron was treated by laser melting and quenching with 5 kW CO2 laser. The corresponding effect on hardness, microstructure was studied. And a comparison between the tribological behaviour of the laser quenched and laser melted ductile cast iron was presented. The results show that the material hardness after laser surface treatment processes (LST) was significantly improved, and the hardness of the area treated by the laser melting is slightly higher than that of the laser quenching treatment. And LST enhanced the microstructure and the wear resistance of the nodular cast iron. The analysis shows that the wear resistance of the area after heat treatment was obviously improved compared with that of the substrate but the laser quenching has more obvious influence on the wear resistance than the laser melting.

Overview of Laser Absorptivity Measurement Techniques for Material Processing

During laser surface treatment, the beam absorption can vary considerably depending on the surface quality, temperature and environment. The metallic surfaces exhibit higher absorptivity when irradiated with a focused laser light. Investigation of the dynamic variation of absorptivity of metals during laser processing is a topic of interest for manufacturing community. This paper focuses on a brief review of absorptivity measurement methods adopted for industrial metals such as steel, titanium, aluminium and copper during laser surface treatment processes. It provides state of art in analytical, numerical and experimental techniques for measuring the absorptivity in order to design an efficient laser control systems.

Three-dimensional transient thermodynamic analysis of laser surface treatment for a fiber laminated plate with a coating layer

Based on the method of separation of variables and equivalent temperature method, three-dimensional transient temperature field for a fiber metal laminated (FML) plate with a coating layer (total structure is named as a CFML structure) during laser surface treatment process is firstly obtained. Subsequently, the three-dimensional transient thermodynamic governing equations for the CFML structure under such laser work condition are solved by applying the finite difference method and Newmark method in space domain and time domain, respectively. The aim of this research is to give the analytical solution of three-dimensional transient temperature field for CFML structure under laser surface treatment technology, understand the influence of number of fiber species, laser moving velocity, number of FML layers and selected coating layer’s heat conduction coefficient on the deflection, normal stress, shear stress and vibration frequency of the CFML structure. Besides, it could guide engineers designing the CFML structure to adapt to hostile laser surface treatment environment.

Application of the Finite Elements Method for computer simulation of properties of surface layers

Purpose: The work presents the application of the Finite Elements Method in a computer simulation whose aim is to determine the properties of PVD and CVD coatings on various substrates and to optimise parameters of a laser surface treatment process of surface layers of tool steels. Design/methodology/approach: The article discusses the application of the finite elements method for simulating the determination of stresses and microhardness of Ti+TiN, Ti+Ti(CN) and Ti+TiC coatings obtained in a magnetron PVD process on a substrate of sinter high-speed steel, of Ti/Ti(C,N)/CrN, Ti/Ti(C, N)/(Ti, Al)N, Ti/(Ti, Si)N/(Ti, Si)N, Cr/ CrN/CrN, Cr/CrN/TiN and Ti/DLC/DLC coatings obtained in a PVD and CVD process on magnesium alloys, of graded and monolayer coatings (Ti, Al)N, Ti(C,N) produced with the PVD arc technique on a substrate of sintered carbides, cermets and oxide tool ceramics and tool steel remelted and alloyed with a high-performance diode laser (HPDL). Modeling of stresses was performed with the help of finite element method in ANSYS and MARC environment, and the experimental values of stresses were determined based on the sin2Ψ. Findings: The models presented satisfy the assumed criteria, and they can be applied for the determination of properties of surface layers and optimisation of PVD and CVD processes and laser alloying and remelting. The results of a computer simulation correlate with experimental results. The models developed allow to largely eliminate costly, timeconsuming and specialist experiments which have to be done during investigations for the benefit of computer simulations. Research limitations/implications: To be able to assess the possibility of application of surface layers, a computer simulation of other properties of coatings has to be additionally carried out, and a strength analysis has to be made of other coatings coated onto various substrate materials. Originality/value: value Computer simulation and modelling is an interdisciplinary field necessary for the development of science and technology, enabling to perform direct visualisation of properties, which cannot be identified in experimental observations. The purpose of computer simulation and modelling is to improve the ability to predict results and to optimise solutions.

Dual-Phase-Lag Heat Conduction in Finite Slabs With Arbitrary Time-Dependent Boundary Heat Flux

Applying a constant or transient heat flux on a plane slab is a common technique in microelectronics technology and material processing, including laser patterning, micromachining, and laser surface treatment processes. Although Fourier's law is typically very precise for evaluating temperatures in solids, a number of experimental observations suggest the existence of non-Fourier transient conduction in these applications. Since the dual-phase-lag (DPL) model of heat conduction can be compatible with the hypothesis of local equilibrium thermodynamics (as shown here), the effects of temperature gradient relaxation time on the non-Fourier hyperbolic conduction in a finite slab subjected to an arbitrary time-dependent surface heat flux is examined by this model. The combination of diffusion- and wave-like features in heat conduction process is properly monitored by the DPL model for two types of heat flow regimes, namely, gradient precedence and flux precedence. The results indicate considerable deviations between the predictions of these regimes.

Machinability Study of Laser Surface Treated 15-5 PH Stainless Steel

In this work, 15-5 PH stainless steel which is one of the hard to machine materials has been selected to investigate the machinability characteristics under dry cutting condition with the aid of laser surface treatment process. Turning experiments were performed on the laser surface treated 15-5 PH samples with TiAlN coated tungsten carbide inserts. Machinability of both as received and laser surface treated samples were evaluated in terms of microstructure, microhardness, tangential cutting force, surface roughness, chip morphology and tool wear. Experimental consequences revealed that laser surface treated sample exhibits a remarkable effect on microstructure and microhardness. From the parametric analysis, it is found that machining of laser surface treated samples are beneficial in terms of reducing cutting force and are effective in prolonging tool life when compared with that of as received samples.

Evolution of the microstructure, mechanical properties, and high-order modal characteristics of AISI 1045 steel subjected to a simulative environment of surface grinding burn

The thermal damage of AISI 1045 steel induced by laser surface treatment (LST), which is used to simulate the surface grinding burn, was comprehensively studied in this paper. By experimental investigation, a deep analysis was performed on the microstructure, hardness, and residual stress of the AISI 1045 steel specimens subjected to the LST process. Furthermore, the high-order modal characteristics of the AISI 1045 steel specimen were studied based on the high-frequency vibrator system. The experimental results reveal that the phase transformation-induced microstructure change, which can be reflected by hardness value, can be regarded as essential of the laser-induced thermal damage. The large tensile residual stress is another inevitable product that resulted from the LST process, which can be used to define the degree of surface grinding burn and belongs to the nondestructive classification technology for surface grinding burn by comparing with the microstructure-based classification technology. Moreover, the strain mode is more sensitive to the thermal damage of the specimen than the displacement mode and the resonant frequency, and the significant strain mode change of the specimen before and after the LST process will occur at higher vibration frequency. The findings confirm that the degree of surface grinding burn can be classified by using the X-ray diffraction (XRD) method, and the thermal damage in surface grinding process can be detected by using both the XRD method and the high-order strain mode method.

Influence of picosecond laser irradiation on nickel-based superalloy surface microstructure

The investigation presented in this paper was carried out on the nickel-based superalloy, Nimonic 263, a material widely used at elevated temperatures and pressures. The samples were exposed to a Nd3+:YAG pulsed laser, at a wavelength of 1064 nm and a pulse duration of 170 ps, and the estimated threshold damage was 2 mJ. Different pulse energies and numbers of pulses were applied in air and helium-enriched atmospheres. Spots obtained by the laser interaction with the material were observed by optical and scanning electron microscopes and analyzed by energy-dispersive spectroscopy. Vickers microhardness tests were performed. In this paper, the changes that had occurred at the sample surface microstructure as a result of laser–material interaction are discussed with the aim of contributing to the determination of optimal laser parameters in the laser surface treatment process.

Induced multiple heterogeneities and related plastic improvement by laser surface treatment in CuZr-based bulk metallic glass

Microstructure and mechanical properties of Cu46.5Zr47.5Al5Co1 bulk metallic glass (BMG) irritated by laser surface treatment (LST) were investigated. A surface-multilayer glassy composite structure with micron- and nano-scale CuZr (B2) particles was synthesized. The forming mechanism of the unique structure was studied by analyzing the thermal behaviors of glassy matrix and simulating the LST process using finite volume method. Plasticity of the treated rods is enhanced about five times because of the induced multiplication of shear bands and martensitic transformation of B2 precipitates. The LST method is powerful for tailoring BMG composites with controllable position and morphology of second phase.

Suppression of the development of pores during laser-induced surface dispersion of TiC into aluminium, by means of a static magnetic field

A static magnetic field having the strength of B=0.6 T has been used as an additional process parameter in order to suppress the establishment of pores while dispersing TiC particles in surface layers of aluminium alloys using a laser. The migration of hydrogen towards regions of high temperatures within the melting pool can lead to the creation of gas bubbles, therefore yielding pores after resolidification in the processed layer. This mechanism (known for instance in welding technologies of aluminium) could be suppressed by Lorentz-forces induced by an externally applied magnetic field. It could be shown experimentally that magnetic fields could assist laser surface treatment processes beneficially if higher beam powers were coupled in. This may be interesting if, for instance, thicker dispersed layers should be achieved.

Metal Rapid Prototype Fabrication Using Selective Laser Cladding Technology

Non-metallic rapid prototyping has been successfully applied in several industries, but a metal rapid prototype is required for functional prototypes and tooling applications. A metal rapid prototype fabricated using selective laser cladding is presented in this paper. Laser cladding is one type of laser surface treatment process. During this process an alloy is fused onto the surface of a substrate. Laser cladding devices, i.e. powder feeder, CNC workstation table, laser shutter, and shielding gas controller, were integrated to make automatically any cladding profile possible. The metal prototype was then fabricated layer by layer. This is called the selective laser cladding system (SLC). The fabrication of the metal rapid prototype using SLC technology is described and the detailed design and construction of the SLC is presented in this paper.

A displacement-based reference frame formulation for steady-state thermo-elasto-plastic material processes

A reference frame formulation for steady state thermo-elasto-plastic processes is presented. The displacement and history dependent response fields appear as the primary variables in this mixed formulation. Unlike displacement based Lagrangian formulations, our formulation does not require a transient analysis to simulate a steady state process and yields results that are free of numerical oscillations and which require considerably less computational effort. And unlike velocity based Eulerian methods, our formulation does not require free surface corrections or streamline integration algorithms. A laser surface treatment process is simulated and our results are in agreement with those obtained from a computationally intensive transient Lagrangian analysis.

Surface treatment of thermoplastic composites with an excimer laser

A high-power excimer laser (KrF, 248 nm) was used to treat the adherend surfaces of a glass-fibre-reinforced poly(butyl terephthalate) composite for the purpose of improving adhesion quality. Two joint geometries, the lap joint and the butt joint, were investigated. It was found that, with optimum process parameters, excimer laser can be used to etch away the polymer matrix selectively and leave the fibres undamaged. The surface morophology of the laser-treated surfaces was investigated. A large improvement in lap-joint and butt-joint strengths was achieved for laser-treated surfaces compared with untreated, chemical cleaned and abraded ones. The improvement was mainly attributed to the fibres that were protruding from the matrix after the laser surface treatment process.

Coating by laser surface treatment

The application of optical engineering in industrial processing is gaining greater acceptance. The range of surface treatment processes available goes all the way from transformation hardening, annealing, shock hardening and bending (as processes which do not involve melting) to processes which involve melting such as surface melting, surface alloying, surface cladding and those processes which involve some form of photochemistry such as laser chemical vapour deposition, laser physical vapour deposition and stereolithography. One of these processes, laser cladding, has been recently extended at University of Liverpool to provide a technique of rapid alloy scanning whereby variable composition laser clad tracks can be laid down by the laser thus giving the whole range of compositions in the alloy system in a single sample. Evaluation of specimens of this type can be carried out by a range of micro testing techniques including corrosion testing procedures. Laser surface treatment processes available for the production of corrosion resistant surfaces are reviewed. These include surface melting, surface alloying and surface cladding procedures. Consideration is then given to the new variable composition laser melt track technique with particular reference to the rapid prototyping of corrosion resistant alloys.