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High-energy continuous wave (CW) laser ablation can cause severe damage to structural materials in an extremely short time, which generates considerable concern in terms of material safety. For the purpose of reducing or even eliminating such laser-induced damage, a novel composite coating consisting of a boron-modified phenolic formaldehyde resin incorporating ZrC and SiC has been designed and prepared. The experimental results reveal that ZrC and SiC are rapidly oxidized to ZrO 2 and SiO 2 respectively, leading to the formation of a white ceramic layer consisting of ZrO 2 particles and melted SiO 2. After ablation at 1000 W/cm2 for 50 s, elemental analysis indicates that no Si can be found in the central ablation zone because of gasification. A relatively compact ZrO 2 layer is formed through the sintering of adjacent ZrO 2 particles, which effectively improves the reflectivity of the coating from 7.3% (before ablation) to 63.5% (after ablation). The high reflectivity greatly reduces the absorption of laser energy. In addition, no obvious ablation defects are observed in the composite coating. The excellent anti-laser ablation performance of the coating makes it a promising system for protecting a material against the effects of long-term CW laser ablation. [ABSTRACT FROM AUTHOR]

Faced with the challenge of ultra–high–temperature ablation problems, multi-synergy and efficient energy dissipation method is a feasible solution. A structure-modified silica-graphite composite with multiple copper layers was prepared by hot-pressing. The ablation behaviors and mechanisms were analyzed in detail. During the laser ablation, the designed composite exhibits excellent ablation resistance with a multi-synergy effects strategy. As ablation time increases, the ablation mechanisms change from reflection and horizontal thermal diffusion to reaction and horizontal thermal diffusion and vertical heat insulation. Moreover, the gap generated by the reaction volume contraction can further insulate against heat transfer in the vertical direction. The rate of increase of back-surface temperature can be further reduced. This multi-synergy effects strategy and designed structure accompanied with appropriate materials can greatly enhance the ablation resistance ability of the composite. [ABSTRACT FROM AUTHOR]

Graphite and SiO 2 composite was prepared by hot-pressing at 1300 °C for 3 h under a uniaxial load of 20 MPa. The ablation behavior of graphite and SiO 2 composite by high-intensity continuous laser was investigated. The X-ray diffraction, scanning electron microscopy, 3D-super-depth-digital microscopy, Raman spectroscopy and reflectivity were used to characterize the sample. The results show that under low laser power (500 W/cm 2 ), and no obvious damage appears, while just the irradiation area changes from grey to white and the reflectivity increases. With the laser power increasing, some heat-absorbing chemical reactions between graphite and SiO 2 occurred on the surface, and SiC was produced, which can increase the energy consumption of the surface and thus reduce the absorbed laser energy of the interior. Moreover, at the center of irradiation area, the formation of columnar structure graphite is beneficial to obstruct laser energy conduction from surface to interior material. [ABSTRACT FROM AUTHOR]

High-energy continuous-wave (CW) lasers can cause severe damage to traditionally structured materials within several seconds because of the formation of an extremely high temperature field. To prevent laser damage, zirconium carbide (ZrC)-modified short-carbon-fiber-reinforced phenolic-resin matrix composites have been successfully prepared. The micro-morphologies and elemental distributions of the composites were investigated and phase detection was performed to study their laser-ablation behavior. The results reveal that the ZrC particles are oxidized rapidly, forming ZrO 2 , during laser ablation. Owing to binding of the short carbon fibers and sintering of neighboring ZrO 2 particles, a compact ZrO 2 layer was obtained. Owing to the formed ZrO 2 layer, the reflectivity increased from 8.0% to 52.5% following irradiation at 500 W/cm2 for 180 s. This greatly mitigates the absorption of the laser energy. In addition, no distinct ablation pits were observed. This indicates that the composites exhibit excellent anti-laser ablation performance, and could be potentially applied as protective shields for materials exposed to high-energy CW lasers. [ABSTRACT FROM AUTHOR]

Abstract Laser is becoming increasing threat to materials due to its high energy that can induce thermal damage, especially high energy continuous-wave (CW) laser. In this case, laser protection has attracted more and more concerns. Nanocomposite coatings that consist of nano-copper filler with phenolic resin matrix have been designed and successfully prepared to meet the requirement of anti-laser ablation. The anti-laser ablation ability of the nanocomposite coatings is evaluated through the temperature of the back-surface substrate. Results show that the transpiration cooling effect of nano-copper particles do improve the anti-laser ablation property of the coating. The residual char with porous structure which is the pyrolysis result of phenolic resin plays a key role as a barrier to prevent laser from irradiating inside of the coating. The amorphous carbon gradually transforms to graphitic structure during CW laser irradiation. The latter has better stability at high temperature, improving anti-laser ablation. The micro-morphologies and element content analysis indicate that the evaporation of nano-copper particles occurs layer by layer until the total pyrolysis of phenolic resin located in the vertical direction of the coating. All the analyses show that this nanocomposite coating has excellent performance as a protective shield to anti-laser damage. [ABSTRACT FROM AUTHOR]

Abstract Composite coatings consisting of flake graphite and SiO 2 fillers in a hyperbranched polycarbosilane (HBPCS) matrix were designed and prepared to meet the requirements of laser protection. The laser ablation behavior of the composite coatings were investigated. Control experiments were designed to study the performance of SiO 2 during laser irradiation. The results show that the introduction of SiO 2 changes the anti-laser protective mechanism and can improve the anti-laser property of the coating. High power laser irradiation results in pyrolysis of HBPCS and the formation of SiC particles. Chemical reactions between SiO 2 , graphite, and SiC play an important role in consuming energy, and provide an excellent cooling effect to the substrate, leading to decreased temperature. SiC particles formed on the surface of the laser ablation area act as a shield to prevent the laser from irradiating deeper layers of the coating. Due to the cooling effect and thermal stability of SiC, the proposed coating shows a good anti-laser property. [ABSTRACT FROM AUTHOR]

High-energy continuous-wave (CW) laser has been considered as a significant technology in recent decades. Such laser can destroy conventional materials in an extremely short time, necessitating their protection. In this study, zirconium carbide (ZrC) and silicon carbide (SiC) particle-modified short silicon carbide fiber-reinforced phenolic resin matrix composites (SiC/BPF-ZS) with significant anti-laser performance were designed and prepared. Our results showed that the ceramic particles and SiC fibers rapidly oxidized, leading to the formation of a ceramic coating composed of ZrO 2 and SiO 2. Owing to the formation of the ceramic coating, the reflectivity of the composites improved significantly from 15.8% to 73.2% after ablation at 500 W/cm2 for 30 s. Additionally, the SiC fibers played an important role in the formation of a high-reflectivity coating during laser ablation. Contrast experiments indicated that SiC fibers lead to better performance than the carbon fibers. The high reflectivity and low mass ablation rate are demonstrated to be the key factors improving the anti-laser ablation performance of the SiC/BPF-ZS composites. [ABSTRACT FROM AUTHOR]

Despite many years of use of boron-modified phenolic resin (BPF) in the aerospace and auto industry, it is still unknown if such resin can be used in extreme environments, especially under exposure to high energy continuous-wave (CW) laser that can totally destroy many traditional materials in several seconds. Compression molded BPF plates are tested with high energy CW laser to study the laser ablation behavior. Results reveal that the laser parameters including irradiation time and laser power density have a great effect on the ablation morphology and mass ablation rate. BPF keeps decomposing into residual char due to the high temperature caused by laser. The graphite structure of residual char is gradually improved during laser irradiation, resulting in improved thermal stability of residual char. In addition, the micro-morphologies reveal that the residual char possess porous structure which leads to the thermal insulation property and minimizes the ablation damage propagating into the BPF bulk. Both the improved thermal stability and the thermal insulation property of the residual char can mitigate the ablation damage caused by the high energy CW laser. Unlabelled Image • Laser ablation behavior of boron-modified phenolic resin was first proposed. • The degree of graphitization of the formed residual char was demonstrated to keep increasing during laser ablation. • The porous structure of residual char is proved to be the key factor leading to the thermal insulation property. • The reason why boron-modified phenolic resin owns excellent laser ablation resistance is clearly proposed. [ABSTRACT FROM AUTHOR]

The laser-matter interaction contains complex thermophysical and thermochemical responses. The variation of energy and composition happen in thermophysical and thermochemical process will totally change the interaction behaviors. In order to obtain an accurate mechanism and promote the understanding of laser-matter interaction, all thermophysical and thermochemical responses, especially the thermochemical part, should be considered and investigated. In this study, a coupled heat-matter diffusion model based on thermodynamic chemical equilibrium finite-element method and thermochemical ablation theory was established. The materials with complex reaction enthalpy change in high temperature environment were chosen to validate the model. The results show that this model is accurate, as the maximum error of back-surface temperature response is just 4.0% between experimental and calculation values. The detailed variations of composition, temperature and optical reflection were obtained and analyzed, which is in good agreement with the experiment. This coupled heat-matter diffusion model including all thermophysical and thermochemical response has the great potential in nearly all laser-matter interaction involved application. [ABSTRACT FROM AUTHOR]

Abstract: Ultra high temperature ceramics (UHTCs) based composite ZrB2/20vol.% Cu was prepared by spark plasma sintering (SPS) at 1650C° for 3min. The ablation behavior of composite irradiated for 2–20s by 20MW/m2 high-intensity continuous laser was investigated. The phase and microstructure evolution of ZrB2/20vol.% Cu during ablation was demonstrated by XRD and SEM, respectively. The results reveal that no macroscopic damage but only one ablated layer with 40μm in thickness is observed even after being ablated for 20s. It implies that ZrB2/20vol.% Cu composite exhibits good ablation resistance against high-intensity continuous laser. The continuous Cu in composite evaporates preferentially, which impacts on the following ablation behavior. The generated ZrO2 at the spot center shows different forms such as closely packed nano-ZrO2, micron ZrO2 or melting ZrO2 for different ablation time. The melting ZrO2 is helpful to promote the ablation resistance of ZrB2/20vol.% Cu. [Copyright &y& Elsevier]