Laser Surface Modification Research Articles

Improving the Properties of Gray Cast Iron by Laser Surface Modification.

Laser surface modification is a widely used technology to improve the properties of functional surfaces. In this study, the properties of gray cast iron are modified by laser surface modification, and the influence of laser quenching on the properties of cast iron in terms of frictional vibration and noise, friction and wear, internal structure, residual stress, hardness, and corrosion resistance is investigated. The experimental results show that, after high-power laser quenching, the frictional vibrations and noise of most gray cast iron specimens are decreased, but the coefficients of friction against a bearing steel counterface are increased and more stable. The surface and sub-surface hardness of all laser-quenched cast iron specimens is significantly increased. The residual stresses on the surface of the cast iron specimens are significantly increased and changed from tensile to compressive residual stresses. Experimental modal testing results show that the modal damping ratios of the laser-treated specimens are increased significantly, although their modal frequencies are not significantly changed. In addition, through the metallographic observation, XRD (X-ray diffraction) analysis, and TEM (transmission electron microscopy) observation, it is found that the microstructures of the cast iron specimen after high-power laser modification become fine-grained, and the pearlite and ferrite in the matrix become fine martensite, which leads to the improvement of the dynamical, tribological, and chemical properties of cast iron after laser modification.

Anomalously strong effects of plume contraction and material redeposition in nanosecond pulsed laser vaporization

Long-term dynamics of vapor plumes induced by irradiation of a copper target in argon background gas by nanosecond laser pulses is studied numerically based on a one-dimensional hybrid computational model. The model includes a thermal model of the irradiated target and a kinetic model of the gaseous plume flow. The latter is implemented in the form of the direct simulation Monte Carlo method. The simulations, performed at moderate laser fluences in the range from 1.5 to 4 Jcm−2 and background gas pressures between 0.01 and 1 bar, show that the long-term plume dynamics can be divided into three major stages: initial inertial expansion, plume contraction, and subsequent diffusive expansion. The simulations unexpectedly predict extremely strong effects of plume contraction, when the plume size can exhibit a two-fold reduction, and delayed material redeposition back to the irradiated surface, when ∼90% of vaporized material returns to the irradiated surface. Both plume contraction and delayed redeposition originate from the strong backward flow induced by the internal (secondary) shock wave that propagates from the mixing layer towards the irradiated surface. The major part of vaporized material condenses at the surface with a long time delay with respect to the laser pulse after the plume stopping and before the onset of diffusive expansion. As a result, only a marginal part of vapor, which can be as small as ∼5%, is retained in the plume by the beginning of the diffusive expansion. The obtained simulation results suggest that the plume contraction and delayed material redeposition are common phenomena for nanosecond laser vaporization and may affect the efficiency and quality of laser surface modification in the ablation regime as well.

Laser surface modification to improve the resistance of CMAS + molten salt coupling corrosion to thermal barrier coatings

In marine environment, thermal barrier coatings (TBCs) face coupling corrosion of calcium magnesium aluminum silicate (CMAS) and molten salt leading to premature failure. In this study, microstructure evolution of TBCs resulting from CMAS + NaVO3 (CN) coupling corrosion is investigated, and a corrosion protection method based on laser glazing is proposed. TBC degradation by the CN coupling corrosion is mainly due to the high penetration ability of the melt. Laser glazed TBCs have improved resistance to the coupling corrosion, however, the vertical cracks in the glazed layer provide paths for melt penetration. TBCs with double laser-glazed layer are designed, with vertical cracks in the glazed layer being bifurcated and staggered, which could largely suppress CN melt infiltration, and also exhibits excellent phase and microstructure stability in the coupling corrosion condition. This type of laser modified TBC is confirmed to be attractive against the coupling corrosion.

Formation of A Hardened Surface Layer Under Complex Laser Action on the Cutting Edge of Parts Made of Structural Carbon Steels

The purpose of the work was to study the effect of laser modification of the cutting edge on changes in the structure and mechanical properties of the surface layer of parts made of hot–rolled structural carbon steels of grades 20, 35, 45 using a fiber laser.Methods. Structural carbon steels of grades 20, 35, 45 were selected as the objects of the study. To study the effect of laser modification on changes in the structure and mechanical properties of machine parts using laser cutting, special samples were made in the form of plates with a thickness of 2 mm (st20 and st45) and 4 mm (st35). After gas laser cutting, laser modification of the Q-switch cutting edge was performed with a fiber pulsed laser.Results. The regularities of changes in the structure of the zone of gas-laser thermal exposure after laser treatment (cutting, modification) are revealed. It has been established that repeated laser treatment (laser modification) of the cutting edge does not lead to a change in the structural components and microhardness in the zone of gas-laser thermal effects obtained after laser cutting. It has been established that the nature of the microhardness change is the same for all the studied steel grades: the highest values are reached near the surface of gas-laser treatment and are, for example, for steel grade 35 470-560 HV, which is 3,2-3,9 times greater than the initial microhardness (145 HV). Thus, a hardened layer with increased wear resistance is formed on the surface of the part after laser treatment. It is shown that the use of laser surface modification as an additional operation in the manufacture of parts by laser cutting makes it possible to improve the quality (roughness) of the surface layer. At the same time, the greatest effect of reducing roughness is given by laser modification in three passes along the X-Y plane.Conclusion. The results obtained can be used in the creation of resource-saving material processing processes.

Hot corrosion behavior of CYSZ thermal barrier coating with optimized laser surface modification

The current study aims to investigate the influence of laser surface modification on the hot corrosion, fracture toughness, and hardness resistance of atmospheric plasma sprayed Ceria-Yttria Stabilized Zirconia (CYSZ) thermal barrier coating. Throughout the laser surface modification process, a variety of laser processing parameters are used to obtain the finest surface properties and optimum laser parameters. In this study, the whole coating surface is modified using the optimal parameters. The results show that 52.9 W laser power at a 220 mm laser distance and a 60 mm/s scanning speed were found as the optimum laser glazing parameters. A hot corrosion test is performed in a box furnace for 20 h at 1050 °C. Scanning electron microscopy (SEM) images show denser surfaces in laser-glazed coatings when compared to air-spraying coatings. A dense microstructure combined with the top coat is created in the coating cross-section, and a smooth microstructure with a coaxial fracture network is produced on the surface. The laser-glazed layer has superior mechanical characteristics to the as-sprayed coating, including hardness and fracture toughness. This layer also restricts the damaging monoclinic-tetragonal phase change for CYSZ TBC, blocking the infiltration of molten salt. The hot corrosion behavior of TBCs is improved by the inclusion of a dense laser-glazed layer.

Superhydrophobic aluminum surfaces with nano-micro hierarchical composite structures: A novel and sustainable approach to corrosion protection

The unique properties of aluminum (Al) and its alloys make Al one of the most versatile, economical, and widely-used materials in various industries. However, the corrosion and leaching of Al can cause significant issues for the lifetimes of mechanical structures and machine components as well as environment and health problems. In the present study, a simple, eco-friendly, and rapid fabrication of superhydrophobic Al surfaces was introduced. The superhydrophobic Al surfaces with hierarchical composite structures combining microstructures prepared by laser texturing, the new formation of pseudo-boehmite nanostructures prepared by boiling water treatment, and low surface energy prepared by silicone oil heat treatment showed excellent corrosion resistance. The mechanism for wettability change and anti-corrosion were analyzed. The influence of laser parameters and surface modification procedures on the wettability and corrosion resistance of Al surfaces was also analyzed systematically through a series of surface characterization techniques, potentiodynamic polarization tests, and electrochemical impedance spectroscopy tests. The corrosion protection efficiency of the fabricated superhydrophobic Al surface has reached up to 99.40 % as compared with an untreated flat surface. Furthermore, the fabricated superhydrophobic surfaces show good stability even after prolonged exposure to air, fresh water, seawater, and high temperature environments. The performance of the non-wetting surfaces is demonstrated through self-cleaning, water jetting, and water droplet bouncing phenomena. This research provides a novel and sustainable approach for superhydrophobic metal surfaces and improved corrosion resistance for potential practical applications.

Hot corrosion and CMAS degradation of laser-glazed YSZ coating with optimum parameter

The purpose of this research is to look into the effect of laser surface modification on the hot corrosion and hot corrosion + calcium–magnesium aluminosilicate (CMAS) resistance of YSZ thermal barrier coating. Metco AMDRY 997 (Ni–22Cr–10Al–Y) powder was coated as a bond coat on the AISI 304L stainless steel substrate using a high-velocity oxy-fuel spray technique. As a ceramic top layer, 204 NS YSZ (ZrO2·8Y2O3) particles were plasma sprayed on the bond coat. Following that, the entire coating surface was treated with a 20-kHz pulsed CO2 laser to increase the coatings’ surface performance. A corrosion test was carried out in a box furnace for 20 h at 1050 °C. SEM images of laser-glazed coatings revealed denser surfaces than those of air-spraying coatings. The laser-modified coating is more resistant to hot corrosion than unmodified coatings. The X-ray diffraction analysis revealed that the reaction between yttria (Y2O3) and V2O5 resulted in the formation of YVO4 crystals as a corrosion product. According to energy dispersive spectroscopy results, laser-glazed coatings reduced molten salt diffusion from surface to bond coat. As a result, laser-glazed coatings demonstrated improved hot corrosion resistance and decreased corrosion products on the bond coat zone. After the hot corrosion test, the laser-treated composite had a 55% lower thermally grown oxide layer than untreated APS YSZ. The optimum laser parameter was used as 77.7 W laser power, 120 mm/s scanning speed, and 215 mm laser distance.

Interface stress calculation and failure behavior of TBCs on the surface of aluminum alloy with anodic oxidation

Aluminum protective coatings have poor performance due to the significant difference in coefficient of thermal expansion (CTE) between the substrate and the coating. In this study, porous anodic aluminum layer, which have high bonding, well matching and grew in situ on the substrate of aluminum alloy (4032) using anodic oxidation, and then thermal barrier coatings were produced on the surface by laser surface modification and atmospheric plasma spraying (APS). The aim of this way is to improve the interface thermal shock resistance (TSR) of the coatings. The results showed that the coatings with anodic aluminum layer (highest group average of 444 cycles) have a much higher number of thermal shock cycles than metallic bond coatings. Furthermore, the failure analysis suggested that the bonding stability of the coatings is influenced by the surface state, surface mosaic structure, as well as such as CTE and surface roughness. Eventually, a double-layer mismatch stress model was developed to characterize the residual stresses caused by deformation mismatch in the coatings. After performing calculations，from a force perspective τa≈10τb, and from a work perspective Wfa≈3.34Wfb.

Effect of cryogenic laser surface modification on the microstructure evolution and corrosion resistance of accident-tolerant FeCrAl alloys

Accident-tolerant FeCrAl alloys require a thinner cladding wall than zirconium cladding to overcome the extra neutron loss, thus requiring enhanced corrosion resistance. Surface treatment was used in this study to address this issue via cryogenic laser surface modification. A finite element model based on heat-transfer theory was raised to reveal the temperature field change during cryogenic laser treatment. The relationship between the laser processing parameters and surface morphology was studied with various characterizations to better understand the process mechanism and verify the correctness of the model. Hydrothermal corrosion test was proceeded in an autoclave at 290 °C and 7.5 MPa for 150 h to examine the enhancing corrosion resistance. STEM observations were used to study the microstructure evolution by cryogenic laser processing and corrosion. Electrochemical tests were performed to analyze the relationship between processing parameters and corrosion resistance before and after corrosion. The oxide film thickness and corrosion rate of the cryogenic laser-modified sample were 66 % and 80 % smaller than the as-received sample. The enhanced corrosion resistance was attributed to the microcrystalline layer and the thin duplex passive film that formed during the cryogenic laser process.

Influence of Laser Treatment Medium on the Surface Topography Characteristics of Laser Surface-Modified Resorbable Mg3Zn Alloy and Mg3Zn1HA Nanocomposite

In this study, a Mg3Zn alloy and a Mg3Zn1HA nanocomposite were fabricated through disintegrated melt deposition, followed by the hot extrusion process. The specimens were subjected to fiber laser surface modification in air and demineralized water (DM) medium to determine the influence of the laser treatment medium on the microstructure, microhardness, grain size, and surface topography. During the laser treatment, the samples under the water medium produced a lower surface roughness when compared with the air medium. The atomic force microscope (AFM) surface topography scan showed the presence of surface modifications caused by the presence of nanohydroxyapatite (nHA) in the matrix, resulting in a 367.4% and 632.4% increase in the surface roughness (Ra) in the Mg3Zn1HA nanocomposite when compared with the Mg3Zn alloy in water and air media, respectively.

Mpact of laser surface modification on polycrystalline silicon photovoltaic cell by means of CO2 laser

In this research, we investigate the effect of laser texturing on the photo-electrical properties of the polycrystalline silicon solar cell. Laser surface texturing technique was used to achieve the texturing results, which based on the interaction between pulsed CO2 laser (10.6μm) and polycrystalline silicon used for solar cells. Four of photovoltaic solar cells have been textured in two dimensions in different ranges (1 cm x 1cm and 2 cm x 2 cm) with different line spacing. Solar cells with laser-modified surface were characterized by SEM as well as photo-electrically before and after texturing process. The obtained results showed that laser surface texturing with small grooves spacing, results in increasing of the melted silicon surface area which enhance the silicon electrical properties. Furthermore, it increases the optical path length inside the solar cell which enhances light trapping.

Laser Surface Modification of Vermicular Cast Iron to Resist Erosion

Laser Surface Modification of Vermicular Cast Iron to Resist Erosion

Real-Time Cutting Temperature Measurement in Turning of AISI 1045 Steel through an Embedded Thermocouple—A Comparative Study with Infrared Thermography

During machining processes, a high temperature is generated in the cutting zone due to deformation of the material and friction of the chip along the surface of the tool. This high temperature has a detrimental effect on the cutting tool, and for this reason, it is of the utmost importance to assess the cutting temperature in real time during these processes. Despite all the advances and investigation in this field, accurately measuring the cutting temperature remains a great challenge. In this sense, this work intends to contribute to solving this problem by experimentally evaluating the potential of the developed approach for embedding thermocouples into the rake face of cutting tools for measuring cutting temperature in real time during dry turning of AISI 1045 steel for different cutting parameters and comparing the obtained results with infrared thermography measurements at the exact same point. A well-defined, smooth micro-groove with good surface quality was produced by laser surface modification. Then a laser-welded K-type thermocouple was fixated in the micro-groove with a MgO ceramic adhesive, ensuring protection from wear and chips, which allowed the creation of WC-Co cutting inserts with the ability to measure cutting tool temperature with a maximum error of 0.96%. Results showed that, despite yielding the same trend, the tool temperature measured by the IR thermographic camera was always lower than the temperature measured by the K-type embedded thermocouple. The proposed embedded thermocouple method proved to be a reliable, precise, accurate, and cost-effective approach for real-time temperature measurement capable of providing useful information for cutting parameter optimization, thus allowing increased productivity and tool life.

Ultrashort Laser Texturing of Superelastic NiTi: Effect of Laser Power and Scanning Speed on Surface Morphology, Composition and Wettability

Among metallic biomaterials, near-equiatomic NiTi is one of the most promising intermetallic system applicable for biomedical applications, thanks to its high biocompatibility and unique superelasticity (or pseudoelasticity), offering a complete recoverable strain up to 8%. In the prospective uses for bio-devices, the surface processing of NiTi medical components plays a fundamental role for guaranteeing both a Ti oxide passivizing layer for avoiding Ni ion release into the human body and surface morphology for controlling the cell proliferation. Mechanical polishing, thermal, chemical or electro-chemical treatments are typically performed for surface modifications. Recently, laser texturing has been successfully applied for different materials, included NiTi shape memory alloys, and also for tuning the surface properties, such as wettability. In the present work, ultrashort laser surface modification was carried out, through the use of a femtosecond laser, for the surface texturing of commercial superelastic NiTi plates. The main goal is to investigate the correlation among morphology, chemical composition and wettability with the principal process parameters, such as average power and scanning velocity in high power ultrashort laser texturing. Laser patterned surfaces were characterized by means of scanning electron microscopy, 3D-profilometry, XPS analysis and wetting measurements. After the laser treatments, both surface morphology and Ni/Ti ratio were largely modified from the initial surface, depending on the adopted process parameters. The wettability of the laser textured surfaces can be also varied with respect to the initial surface, due to the roughness values and grooves induced by the laser beam scans. The laser texturing process induced a combination between micro and nano structures, depending on the input energy. In details, the surfaces were tuned to lower roughness values (from 0.4 μm to 0.3 μm) with a laser power of 1 W, while it was increased up to 0.65 μm with a laser power of 13 W. The laser surface modification promoted a change of the contact angle from 70° of the untreated condition up to 135° to the surface laser treated with a power of 13 W.

Nanosecond pulsed laser surface modification of yttria doped zirconia for Solid Oxide Fuel Cell applications: Damage and microstructural changes

An effective strategy to reduce the cathode polarization in a Solid Oxide Fuel Cell (SOFC) is to enlarge the cathode-electrolyte interface, corrugating the electrolyte surface of zirconia doped with 8 mol% of yttria (8YSZ) by pulsed-laser machining. However, laser-material interaction using a nanosecond pulsed laser can involve thermal effects on the surface. The objective of this work was to analyze the microstructural and phase changes, and the collateral damage caused by laser machining on the 8YSZ electrolyte surface of the SOFCs, and compare it with the 3% molar in yttria (3Y-TZP). Several patterns consisting in parallel tracks below 10 µm depth were investigated. The results evidenced a heat affected zone (HAZ) limited to ⁓1–2 µm with microcracking and directional recrystallization, which was larger in 8YSZ than in 3Y-TZP. However, the mechanical response near the HAZ and chemical composition at the machined surface was not significantly changed.

Synthesizing Ti–Ni Alloy Composite Coating on Ti–6Al–4V Surface from Laser Surface Modification

In this work, a Ni-alloy Deloro-22 was laser-deposited on a Ti–6Al–4V bar substrate with multiple sets of laser processing parameters. The purpose was to apply laser surface modification to synthesize different combinations of ductile TiNi and hard Ti2Ni intermetallic phases on the surface of Ti–6Al–4V in order to obtain adjustable surface properties. Scanning electron microscopy, energy dispersion spectroscopy, and X-ray diffraction were applied to reveal the deposited surface microstructure and phase. The effect of processing parameters on the resultant compositions of TiNi and Ti2Ni was discussed. The hardness of the deposition was evaluated, and comparisons with the Ti–6Al–4V bulk part were carried out. They showed a significant improvement in surface hardness on Ti–6Al–4V alloys after laser processing, and the hardness could be flexibly adjusted by using this laser-assisted surface modification technique.

Femtosecond laser surface modification of 4H-SiC improves machinability

The high brittleness and hardness are harmful to the machinability of silicon carbide (SiC). To improve machinability, femtosecond laser (fs laser) surface modification was conducted. The results of scratching test for modification surface showed the fluctuation of tangential force and coefficient of friction (COF) and the decrease of energy of acoustic emission peak. COF under various axial loads tends to be 0.2. The scratching profile has a conformal shape and deeper depth. Experiments elucidate that machinability is improved by fs laser surface modification due to surface decomposition and laser-induced periodic surface structures. Although fs laser processing was treated as cold processing to some extent, the heat-related phenomena were non-negligible in SiC processing. To reveal the dynamic multi-scale mechanism during fs laser modification, the multi-physics finite element model and the molecular dynamics simulations coupled with a two-temperature model were applied. Multi-scale simulation results revealed that the recoil flow has a high speed of >1.2 m/s and the peak temperature exceeds 8000 K, causing the spatter and heat affect zone. The high electronic temperature gradient is generated during irradiating, causing the subsurface void generation. Consequently, fs laser surface modification can improve machinability, but the heat effect and subsurface void should be cautioned.

Evaluating the Effect of Laser Surface Modification on the Corrosion Behavior of Ni-P-SiC Electroless Coating Deposited on Al356 Alloy

Regarding their higher wear/corrosion resistance than conventional coatings, nickelphosphorus based composite coatings can reduce components’ costs and degradation. This study employed laser surface modification of Ni-P-SiC electroless coatings deposited on Al356 substrate, followed by investigating their microstructural changes and corrosion behavior. The results showed that increasing the laser power increases surface defects and causes substrate diffusion to the coating, which significantly reduces the corrosion resistance of the coating. In contrast, low-power laser operations can improve the corrosion resistance of Ni-P-SiC composite coatings by creating stable nickel phosphide phases, more uniform element distribution, and enhanced SiC particle-substrate coherence. All these factors increase the wear and corrosion resistance simultaneously.

Surface Enhancement of Magnesium Implants for Long Term Applications

Mg is a biodegradable metal that possesses excellent biocompatibility, bioactivity, nontoxic degradation products, and unique mechanical properties. These characteristics make it an attractive element to be used as implant material in physiological environments because it biodegrades and has excellent biocompatibility and bioactivity. In addition, an excess of magnesium ions does not result in cellular toxicity in the human body, where it is often getting rid along with urine. The most significant disadvantage of magnesium is its uncontrolled quick corrosion rate, which can cause rapid loss in mechanical qualities. As a consequence, this might cause the implant to fail before the tissue has completely healed.The purpose of this research is to improve the surface features of the implant, as well as to control the rate at which magnesium corrodes and, as a result, the concentration of magnesium ions that are released into the surrounding environment. This will be accomplished by coating the implant surface with a composite biodegradable polymer (Polycaprolactone PCL) matrix reinforced with MgO Nano-particles which will act as a protective layer to increase the corrosion resistance of magnesium implants. In addition, a laser surface modification procedure was implemented in order to improve the surface's qualities and make certain that there is a strong adhesion between the coating and the surface of the substrate. In order to increase the surface roughness of the specimen, (Nd: YAG) laser device was utilized to create pulses on the surface of the specimen.

Effect of laser surface modification on the structure and mechanical properties of Al–8%Ca, Al–10%La, Al–10%Ce, and Al–6%Ni eutectic aluminum alloys

Additive manufacturing, which includes a set of technologies for manufacturing complex-shaped products with the required set of properties, is currently widely developed. Most additive technologies are associated with the manufacture of the product by melting and fusion of metal powder particles due to laser irradiation. Al–Ca, Al–Ce, Al–La, and Al–Ni eutectic aluminum alloys featuring excellent casting properties are supposedly promising for use in additive technologies. However, there is very little information on the effect of laser processing on such eutectic structures in the literature. In this regard, the paper investigated the effect of laser irradiation on the structure and mechanical properties of samples made of eutectic compositions, namely Al–8%Ca, Al–10%La, Al–10%Ce, and Al–6%Ni. This was achieved by continuous laser modification of their surfaces. The hardening level was evaluated by measuring the microhardness of the modified surface. The mechanisms of sample fracture under tensile testing were established. It was shown that the distribution of the second component in the structure of modified sample surfaces of all the four alloys becomes more uniform compared to the base metal structure. In the Al–8%Ca alloy, the greatest hardening effect was observed, which, however, contributes to embrittlement under tensile stress. However, the modified Al–8%Ca alloy is of interest because of its increased hardness and possibly increased wear resistance. On the contrary, laser modification of the Al–10%Ce, Al–10%La, and Al–6%Ni alloy sample surfaces provides a lower hardening effect, but increases their tensile strength with the formation of a ductile or mixed ductile-brittle fracture. The results obtained confirm the prospects of using the Al–Ca, Al–Ce, Al–La, and Al–Ni alloys in additive manufacturing.