Improvement of Laser Shock Peening Depth Through Regulation of Surface Optical Absorption

Abstract

Higher depths at the millimeter scale (1-2 mm), along with greater magnitudes, have been reported after the NLSP of Ti6Al4V titanium alloy, [2,10] 2024, [11] 6061, [12] and 7075 [13] aluminum alloys. Elaborated laser systems with large power densities are currently required to increase the peak pressure to enable a high input of energy (slightly over 10 GW cm -2 ) during the interaction between the incident laser and metals. [14] The critical power density threshold for the confinement layer breakdown is validated to limit the possible peak pressure. [15][16][17] Changing the wavelength of the incident laser from 1064 to 532 nm decreases the breakdown threshold of the confining water layers from 10 to 6 GW cm -2 , and the maximum peak pressure from ≈5.5 to 4.5 GPa. [18,19] Compressive residual stresses can also be generated deep below the peened surface by multiple or overlapping laser pulses. [20,21] The reduced attenuation of the shock wave indicates an increased depth for the plastic-deformed layer during subsequent peening, while the affected depths usually reach saturated border values within three to five impacts. [22,23] Additionally, femtosecond laser shock peening is applied to induce a shallower affected depth and a limited compressive layer owing to the high instantaneous power density. [24] It is necessary to increase the surface optical absorption and associated energy conversion at higher affected depths in NLSP. The surface optical absorption property determines the thermal energy fraction, [25,26] with a value of ≈0.2 utilized in investigations. [27,28] In this case, optical absorption is defined by the surface morphology of the metal rather than its intrinsic absorptance. [29] Various absorption mechanisms with different optical behaviors are found in the structures induced using lithographic and chemical techniques. [30,31] These essentially originate from selective absorption responses such as the surface plasmon resonance, magnetic-polariton, geometric optical response, and metamaterial resonances. [29,[32][33][34] A nanoscale structure and laser-induced periodic surface structure can enhance the absorption of laser energy by the reconstruction of surface electromagnetic distributions. [35] The absorption of light is enhanced on structured surfaces by multiple reflections based on the angular dependence of Fresnel absorption. [35] The absorption spectrum of femtosecond laser treated surfaces increased sharply over a wide range of wavelengths of incident Laser shock peening is conducted to enhance the mechanical properties of metals. Efficient optical absorption of metal surface is desirable to increase the laser shock peening depth. In this work, a method is proposed to regulate the absorption behavior by surface colorizing to increase the affected depth and magnitude of nanosecond laser shock peening (NLSP). Colorized samples are fabricated with high absorption of 400-1500 nm, which is 89% higher than that of un-colorized samples. This regulated optical response is attributed to the multi-ref...

Nanoengineered Carbon‐Based Interfaces for Advanced Energy and Photonics Applications: A Recent Progress and Innovations

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“…[140,141] As a characteristic example, we can mention the prominent role played by Ψ functions in determining key properties of metamaterials through the associated morphological parameters. [136,137] Hierarchical carbon-based metamaterials have been recently demonstrated to generate white light via photoluminescence from a single structure, without the use of red-green-blue emitters. [142] The former were created by applying an advanced technology resulting from a simple yet effective combination of oxygen plasma with a high-temperature treatment; when used individually or in combination, these technologies have previously been demonstrated to be promising technology for the synthesis and modification of nanomaterials and their systems.…”

Magnetic Field‐Assisted Laser Shock Peening of Ti6Al4V Alloy

“…In order to overcome this problem, integrated laser shock peening technologies are studied, such are warm laser shock peening, [ 12 ] cryogenic laser shock peening, [ 13 ] electropulse‐assisted laser shock peening, [ 14 ] ultrasonic‐assisted laser shock peening, [ 15 ] and combined pulses laser shock peening. [ 16 ] External field excitation provides the potential driving capability for dislocation motion, multiplication, and annihilation. The coupling effect of assisted field and laser shock peening is evidenced to realize the mechanical property improvement of metallic materials.…”

Laser Shock Peening of Ti6Al4V Alloy with Combined Nanosecond and Femtosecond Laser Pulses

“…The application of confinement layers dominates the increase in sufficient shock wave pressure to deform the target materials plastically [20,21]. In contrast, femtosecond laser shock peening (FLSP) can be conducted directly under air conditions, which provides different engineering potentials [22][23][24]. In FLSP processing, milli-Joule-scale energy input (even micro-Joule-scale energy input [25,26]) is adopted, which is three orders of magnitude lower than that used in NLSP [20,22,23].…”

“…The adding effects of multi-cycles NLSP on the affected depths usually reach saturated values within 3-5 impacts [30]. LSP with combined nanosecond and femtosecond laser pulses (F-NLSP) offers a different way to increase the affected depth by the improvement of light absorption on target samples [24]. Totally, LSPs with femtosecond or nanosecond laser pulses are investigated under different conditions to clarify the material-laser interaction, microstructural evolution, and material property improvements.…”