Pulsed Laser Cleaning Research Articles

Laser cleaning for inorganic thermal control coatings on aluminum alloys: Microstructure evolution and mechanical properties of substrate

Thermal control coatings are crucial materials in spacecraft thermal protection systems. Investigating efficient, convenient, and environmentally friendly removal techniques for thermal control coatings is essential for their application and development. This study developed a new removal technology for thermal control coatings using nanosecond pulse laser cleaning technology. The removal effect of the thermal control coating was studied, and the microstructure evolution and mechanical properties of the substrate were analyzed. The results showed that the coating was completely removed at 5.73 and 7.00 J/cm2, while at 8.28 J/cm2, in addition to the coating, approximately 5±1.1 μm of the substrate was also removed. In the completely cleaned state, micro-melting occurred on the substrate surface, and nanostructures appeared. At 5.73 and 7.00 J/cm2, the thickness of the remelted layer is 4±0.9 μm and 5.5±0.6 μm, respectively. The grains in the remelted layer exhibit significant refinement, accompanied by the observation of numerous subgrain boundaries. Additionally, the substrate surface exhibits tensile residual stress after laser cleaning. Attributed to the influence of the remelted layer, the surface hardness and tensile properties of the substrate are slightly improved after laser cleaning compared to manual grinding.

Numerical Simulation and Experimental Study of Nanosecond Pulsed Laser Cleaning of Aluminum Alloy Surface Paint Layer

Numerical Simulation and Experimental Study of Nanosecond Pulsed Laser Cleaning of Aluminum Alloy Surface Paint Layer

Experimental study and mechanism analysis of a pulsed laser cleaning aluminum alloy process.

A pulse laser with a wavelength of 1064nm and a pulse width of 1µs was used to experiment on the coating of a 2024 aluminum alloy surface. The removal performance of the pulse laser cleaning coating was explored by a single factor analysis and orthogonally conditions, and the effects of the laser power, scanning speed, and pulse frequency on the quality of laser coating removal were summarized. The mechanisms of pulse laser cleaning the coating were studied. The results show that the three parameters of the laser power, scanning speed, and pulse frequency have different effects on the quality of laser coating removal. Among them, with the increase of the scanning speed and pulse frequency, the quality of laser cleaning first increases and then decreases, respectively. With the increase in laser power, the quality of laser cleaning increases. A good laser cleaning quality can be achieved at the laser power of 16.5W, a scanning speed of 600mm/s, and a pulse frequency of 30kHz. The laser cleaning coating involves a variety of mechanisms such as combustion, explosion, gasification, thermal vibration stripping, and laser plasma impact. The result can provide practical references for a better searching of the paint removal.

Removal mechanism of Hydroides fouling on high-strength steel in the marine environment during nanosecond pulsed laser cleaning

The surface of metal materials will be contaminated by marine organisms when serving in the marine environment, which seriously affects the service life of the materials, and must be cleaned regularly. The Hydroides fouling on the surface of 30Cr3 high-strength steel was taken as the object to be cleaned; the cleaning quality at different laser fluences was studied; the desorption behavior and the characteristics of spectral and acoustic signals during laser cleaning were analyzed; and the removal mechanism of Hydroides fouling on the surface of high-strength steel was summarized. The results show that the cleaning effect of nanosecond pulsed laser on Hydroides fouling increases with the increase of laser fluence, and the laser fluence of 9.95 J/cm2 can be used to clean the Hydroides fouling with the maximum diameter of 1.62 mm completely with little damage to the substrate. The removal mechanism of Hydroides fouling is the inverse bremsstrahlung mechanism. In the process of cleaning, the surface fouling is partially vaporized and ionized into high-temperature plasma under the action of pulsed laser. The laser energy is absorbed through inverse bremsstrahlung absorption to form shock waves to compress the surface, which leads to cracks on Hydroides fouling. When the surface compressive stress is released, the Hydroides fouling is removed from the surface, and the removal effect increases with the increase of laser fluence.

Femtosecond pulse laser cleaning of Makrana marble

We studied femtosecond pulse lasers for cleaning Makrana marble, used in the construction of Soami Bagh Samadh, Agra, India. We investigated laser irradiation at different wavelengths (1029 nm, 515 nm, and 343 nm) and found that ultraviolet radiation had the lowest ablation threshold at 0.23 J cm−2, followed by green at 0.34 J·cm−2, and infrared at 1.3 J·cm−2. Green irradiation was the most efficient, ablating marble at 0.9 mm3·(min W)–1 at 4 J·cm−2 compared to 0.73 mm3·(min W)–1 at 12 J·cm−2 for 343 and 1029 nm. We evaluated the wavelength’s effect on the stone. Infrared irradiation, having a higher ablation threshold, allowed for a broader range of laser fluence for the safe removal of contaminants, without risking inducing any chemical or morphological changes to the stone, and thus was selected for cleaning. We explored the cleaning effectiveness of infrared femtosecond laser pulses on a sculpted Makrana marble covered by environmental soiling. Optical and scanning electron microscopy, optical profilometry, Raman spectroscopy, and colorimetry demonstrated that satisfactory cleaning was achieved, with the removal of the unwanted layers without causing damage or chemical alteration to the marble structure. This study demonstrates the potential of femtosecond lasers for safe and effective heritage marble cleaning.

Research on pulse laser cleaning and rust removal technology in power systems

In this paper, pulse laser cleaning and angle grinder polishing were used to clean the surface rust of carbon steel, and the cleaning effects of different cleaning methods for carbon steel surface rust were studied. The change of the micro-region morphology and element composition of the cleaned surface was analyzed. Comparative experiments were conducted on the corrosion resistance and paint anticorrosion ability of cleaned metal surfaces. Through comparison and analysis, the use of laser cleaning technology can improve the surface cleanliness and corrosion resistance of metals, reduce maintenance times, and extend service life. Laser cleaning machines with a power of 100 W or above can effectively perform precision cleaning and can be widely promoted in the field of power systems.

Pulsed laser cleaning of C contamination on a glass insulator surface.

When a pulsed laser cleans a glass insulator, the laser power, scanning speed, and repetition frequency affect the laser-cleaning effect. Herein, we considered glass insulators and their surface contaminations as objects, established a finite element model, analyzed the influence of these parameters on the temperature and stress fields, and explored the optimal cleaning parameters for glass insulator surface contamination. In addition, a laser test platform was constructed to verify the cleaning effect. The results indicated that the difference in the cleaning effect was negligible for lasers at repetition frequencies of 10-75kHz. When the power increased, the scanning speed decreased and the temperature of the fouled layer increased. When the power was 60-70W and the scanning speed was 240mm/s, the equivalent tensile stress did not exceed the tensile strength of the insulator. The ablation reaction can remove the fouling part, and the tensile stress can overcome the adhesion force generated between the dirt and glass insulator to achieve effective cleaning. Experiments confirmed that the surface dirt removal rate of glass insulators can be approximately 99% at 60-70W (laser power) and 240mm/s (scanning speed).

Effect of Laser Cleaning Parameters on Surface Filth Removal of Porcelain Insulator

To study the influence of the laser power, scanning speed, and cleaning water content on the laser cleaning effect and obtain the best cleaning parameters, this paper conducted a simulation analysis of the laser cleaning process and carried out a pulse laser cleaning of porcelain insulators experiment to verify. The results show that the cleaning rate gradually increases as the laser power increases from 20 W to 25 W. As the scanning speed increases from 1000 mm/s to 2500 mm/s, the laser overlapping rate gradually decreases, and the cleaning takes the lead in increasing and then decreasing. The appropriate cleaning water content is conducive to laser cleaning; when the water content is 0.115 g, the cleaning efficiency reaches the highest value of 98.20%. When the laser power is 25 W, and the scanning speed is 2000 mm/s, the cleaning efficiency can reach the highest value of 96.87%. This paper shows that the reasonable choice of cleaning parameters can effectively clean the insulator surface filth and obtain a better surface morphology.

Femtosecond pulse laser cleaning of biofilm and dirt: Preserving the Sydney Harbour Bridge

Femtosecond pulse laser cleaning of biofilm and dirt: Preserving the Sydney Harbour Bridge

Ultra-Short Pulse Laser Cleaning of Contaminated Pleistocene Bone: A Comprehensive Study on the Influence of Pulse Duration and Wavelength

The impact of wavelength and pulse duration in laser cleaning of hard blackish contaminants crust from archaeologically significant Pleistocene bone is investigated in this research. The objective is to determine the practical cleaning procedures and identify adequate laser parameters for cleaning archaeological bone from Sima de los Huesos (Spain) based on conservation and restoration perspectives. Bone surface cleaning was performed utilizing two Q-switched Nd:YAG lasers: sub-nanosecond pulsed lasers with emission wavelengths at 355 nm and 1064 nm, respectively, and a Yb:KGW femtosecond pulsed laser with an emission wavelength in the third harmonic at 343 nm. In all experiments, the laser beam scanning mode was applied to measure cleaning efficiency in removing contaminants and degradation products while assessing the underlying substrate surface damage. Several properties, including wavelength-dependent absorption, pulse repetition rate, and thermal properties of the material, are analyzed when evaluating the ability of these lasers to boost the cleaning efficiency of the deteriorated bone surface. Bone surface morphology and composition were studied and compared before and after laser irradiation, using Optical Microscopy, Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS) characterization methods. The results indicate that 238-femtosecond UV laser irradiation with 2.37 TWcm−2 is significantly safer and more efficient toward surface contaminant desorption than sub-nanosecond laser irradiation. The results herein presented suggest that these types of fs lasers may be considered for realistic laser conservation of valuable historic and archaeological museum artifacts.

Effect of Nanosecond Pulsed Laser Cleaning Scanning Speed on Cleaning Quality of Oxide Films on TC4 Titanium Alloy Surface

Effect of Nanosecond Pulsed Laser Cleaning Scanning Speed on Cleaning Quality of Oxide Films on TC4 Titanium Alloy Surface

Microstructure and mechanical properties of laser welded hot-press-formed steel with varying thicknesses of Al–Si coatings cleaned by nanosecond pulsed laser

The Al–Si coatings are commonly used for hot-press-forming (HPF) steel to prevent oxidation in the automobile industry. However, due to the presence of Al–Si coating, undesirable intermetallic compounds are easily formed in the welds of HPF steel. In this work, an environment-friendly and effective nanosecond pulsed laser cleaning process was used to remove the Al–Si coating, and HPF steel with varying thicknesses of coatings was prepared for laser welding. The microstructure and mechanical properties of laser welded HPF steel with different thicknesses of coatings were further investigated. The results showed that there was a threshold of power to remove the Al–Si coatings in the laser cleaning process. The reduced thickness of coatings not only could improve the stability of the welding process due to the diminishing of metal vapor generated by coating ablation, but also decrease the content of the Fe–Al phase in the welded joint, which is detrimental to weld performance. The tensile strength and cupping test pass rate of weld joints gradually increased with the decreasing thickness of coatings to 5 μm. After that, the Al–Si coating almost had no effect on the mechanical properties of the laser weld joints. The laser weld joint with 5 μm-thick of Al–Si coating showed, a tensile strength of 1435.05 MPa, a microhardness of 488.38 HV and a pass rate of 100% for the cupping test.

A study of surface quality and mechanical strength in 5083 aluminum alloy plates using pulsed laser cleaning

A study of surface quality and mechanical strength in 5083 aluminum alloy plates using pulsed laser cleaning

Nanosecond pulsed laser cleaning of titanium alloy oxide films: Modeling and experiments

Nanosecond pulsed laser cleaning is an indispensable green technology. A three-dimensional (3-D) finite element model (FEM) was used to predict the surface temperature during laser cleaning. Then, the macroscopic morphology of the FEM that was obtained was verified using digital ultra-depth-of-field microscopy (OM). Finally, the variation in the surface morphology with the maximum power density (F), x-axis spot overlap ratio (Ux), and y-axis spot overlap ratio (Uy) was determined using field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The change in surface composition was analysed using X-ray photoelectron spectroscopy (XPS), and optical emission spectroscopy (OES) was used to monitor laser cleaning. Transmission electron microscopy (TEM) was used to analyse the surface secondary oxidation thickness. The original surface consisted of titanium oxides (Ti4+ and Ti3+) and organics. The Ti0 peak was enhanced, and the O content was reduced after laser cleaning. Therefore, the laser-cleaning effect was clear. The surface was smooth without cracks when the maximum power density and the spot overlap ratio were set to 31.85 MW/cm2 and 80 %, respectively. A dense and uniformity oxide film, 29 nm thickness, was formed on the surface of TA15 titanium alloy after laser cleaning. Changes in F, Ux, and Uy caused noticeable changes in the Ti I and Ti II peaks in the OES spectra, which were used to monitor laser cleaning.

Femtosecond pulse laser cleaning of spray paint from heritage stone surfaces.

We explore the use of femtosecond laser pulses to clean a variety of colors of spray paint from the Moruya granite, a stone with high heritage value that is widely used for monuments and sculptures in Sydney and New South Wales (Australia). The efficiency of the cleaning treatment and the effects on the stone substrate are evaluated using optical microscopy, optical profilometry, Raman spectroscopy, energy-dispersive X-ray spectroscopy, and colorimetry. We demonstrate that femtosecond laser cleans granite without damaging it and without discoloration when the laser fluence is set below the damage threshold of the stone.

Removal mechanism of liquid-assisted nanosecond pulsed laser cleaning TA15 titanium alloy oxide film

Liquid-assisted pulsed laser cleaning is achieved by coating kerosene on titanium alloy oxide film, and the surface was processed to form micro- and nanostructured amorphous-nanocrystalline phases oxidized layer after laser cleaning. The surface morphology is acquired by changing the laser fluence (F) and spot overlap ratio (Ux = Uy) with field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The surface composition change was analyzed by X-ray photoelectron spectroscopy (XPS). The transmission electron microscopy (TEM) was used to analyze the sample section. The surface quality is optimal when the laser fluence is between 5.095 J/cm2 and 6.37 J/cm2 at the spot ratio of 70%. The ridge structure appears on surface when the laser fluence exceeds 7.644 J/cm2. The original oxide film consisted of titanium oxides (Ti4+ and Ti3+) and C-containing contaminants. Ti0 peak appears on the surface at 6.37 J/cm2 and TiC might be formed on the surface for new peak (281.6 eV). The martensitic heat-affected layer was formed about 2.33 um at 6.37 J/cm2, and surface oxide layer is only about 12 nm. The removal mechanisms of liquid-assisted laser cleaning titanium alloy oxide film are laser-induced shock wave, laser ablation and phase blasting at difference fluence. Liquid-assisted laser cleaning technology can provide an effective surface cleaning and material processing process.

High-quality micro-shape fabrication of monocrystalline diamond by nanosecond pulsed laser and acid cleaning

The flat plane of small surface roughness below 0.1 µm average roughness was obtained for monocrystalline diamond by nanosecond pulsed laser irradiation of 1060 nm and post-process acid cleaning, at a laser fluence around the material removal threshold value. The glossy and flat plane at the bottom of the micro-groove was parallel to the top surface of the specimen, although the round beam of Gaussian mode was irradiated in the direction perpendicular to the top surface of specimen. The square beam of top-hat mode produced a shallower micro-groove with a wider, flatter bottom compared with the round beam in Gaussian mode. The creation method of the flat plane with small surface roughness was discussed in the arrangement strategy of linear micro-grooving by the square beam of top-hat mode. Normal side-by-side repetition of linear micro-grooving did not create a flat plane with constant depth. Therefore, a two-step scanning method was proposed in order to overcome the problem in the normal side-by-side repetition of liner micro-grooving. Non-removal areas were partly retained between the processing lines in the first step, and the laser scanning was conducted on the retained area in the second step. The newly proposed two-step scanning method was practical and useful to create a widely flat plane with small surface roughness, and the two-step scanning method provided superior control over the micro-groove depth. This proposed method can reduce the surface roughness in addition to the shape creation of monocrystalline diamond, and it can be used as a high-quality micro-shape fabrication method of monocrystalline diamond.

Pulsed laser cleaning (PLC) applied to samples in cultural heritage field

The pulsed laser cleaning (PLC) technique employing different laser wavelengths, with a ns pulse duration, is presented. Such a technique can be applied to the preservation of cultural heritage artworks on different materials, like metals, ceramics and glasses to clean the surfaces of debris accumulated over the years, to remove the oxidation layers, the dust, the organic materials and other unwanted layers, restoring their original composition and shape. PLC should be preceded by surface analyses to control the state of the surface before and during the cleaning process, which has to be carefully controlled, in order to stop the cleaning before to damage the underlying original surface. PLC examples, applied to metals, terracotta and glazy ceramics, are presented and discussed using IR, visible and UV pulsed laser irradiations at low intensity.

Removal mechanisms of nanosecond pulsed laser cleaning of blue and red polyurethane paint

Removal mechanisms of nanosecond pulsed laser cleaning of blue and red polyurethane paint

Numerical and experimental analysis for morphology evolution of 6061 aluminum alloy during nanosecond pulsed laser cleaning

Laser cleaning technology has become an important method for surface cleaning of aluminum alloy oxide film . However, the heat and mass transfer mechanism during the laser cleaning process is still unclear, which hinders the precise control of surface morphology . In this work, a 3D heat transfer and flow coupling model of laser cleaning for aluminum alloy oxide film was established, and the dynamic evolution behavior of surface morphology with different average laser power ( P L ) was analyzed. The simulation morphology was agree with experimental results. There is no splashing for P L as 20 W, while a large amount of splash is generated as P L increased to 40 and 60 W. The morphology evolution is mainly attributed to the combined effects of recoil pressure, surface tension and gravity. The maximum flow velocity ( v ) is only 5 m/s for P L as 20 W, while v can reach 150 m/s for P L as 40 and 60 W. With increasing P L , the depth of molten pool reached 4.5, 5 and 8 μm for 20, 40 and 60 W, respectively. The strong heat effect caused by high P L can not only enhance the melting phenomenon, but also enhance the force effect, which plays an important role in the morphology evolution. • A 3D heat transfer and fluid flow coupling model for laser cleaning was developed. • Simulation results were in good agreement with the experimental results. • Transient distribution and evolution of temperature and flow field was analyzed. • Evolution mechanism of aluminum alloy surface morphology was expounded.