Published papers

Precise control of surface microstructures is crucial for the functional design of advanced materials, particularly in applications such as superhydrophobic surfaces. However, current laser micro/nano fabrication techniques still face a persistent “easy-concave, hard-convex” challenge, where concave structures (e.g., microcraters and grooves) are readily produced but the fabrication of convex structures (e.g., micropillars, bulges) remains difficult. Consequently, the underlying mechanisms governing the functional difference between convex and concave structures are still not clear. In this study, both convex and concave microstructures were successfully fabricated on Ti6Al4V surfaces by optimizing the parameter window of nanosecond laser irradiation. The evolution of surface morphology under various laser parameters was systematically explored, and the formation mechanisms were clarified through the coupling effects of Marangoni convection and recoil pressure. Convex and concave arrays with varying hatch distances were fabricated and subjected to annealing treatment for comparatively studying their difference in wettability. After annealing, concave structures consistently exhibited superhydrophobicity, whereas convex structures demonstrated hydrophobicity or superhydrophobicity depending on the hatch distance. The mechanism underlying the difference in wettability was further revealed by analyzing the surface morphology and chemical composition. Furthermore, lossless liquid transportation was successfully realized by utilizing the adhesion difference between the convex and concave structures. This study not only offers a novel approach for constructing microstructures on titanium alloy surfaces but also provides new insights into the functional difference between convex and concave structures.

Garnet, the most widely used abrasive material in abrasive waterjet machining (AWJM), presents challenges in modelling its behaviour. Therefore, a finite element (FE) model was proposed to analyse the effect of using different material models and spatial distributions for garnet on the erosion behaviour of Al 7075-T6. Three popular material models were considered for garnet, including rigid, linear elastic, and tensile failure models, in addition to the Johnson-Holmquist (JH2) model. These four models were tested and compared for single and multiple particle impact under different waterjet pressures, abrasive mesh sizes, and impact angles. Furthermore, the effect of particle spatial distribution within the jet pass was examined. The model results demonstrated that using different material models for garnet significantly controls the erosion behaviour in AWJM. In addition, the radial distribution of the abrasive particles critically affected the erosion process and kerf geometry, while the axial distribution insignificantly influenced the erosion rate.

Electric discharge machining (EDM) is widely employed for machining hard, conductive materials. Tool rotation has emerged as an effective strategy to enhance debris flushing and improve stability during deep-hole EDM drilling. This study proposes a machine learning-based approach to evaluate the influence of tool rotation and predict the unstable machining conditions in EDM of ultrafine grained tungsten carbide. A structured analytical workflow, combining Taguchi–Grey optimization, regression analysis, and classification models, was designed to capture discharge dynamics across macro- and micro-timescales. Classification models trained on raw and processed electrical signal features achieved over 88% accuracy and 90% recall. SHAP analysis revealed that the relationship between key discharge events such as sparks and short circuits varied significantly across stable and unstable machining phases, underscoring the importance of phase-specific modeling. While correlation analysis showed weak global associations, phase-dependent SHAP values revealed opposing feature effects, allowing the context-informed interpretation of model behavior. Phase segmentation revealed that, compared to 1000 RPM, short circuits were reduced by about 40% during stable machining at 8000–9000 RPM. Conversely, during unstable phases, spark effectiveness dropped by nearly 45%, and secondary discharges increased throughout this range. These insights support the design of adaptive control strategies that adjust the rotation rate in response to detected phase changes, aiming to sustain machining stability. The findings support the development of dynamic control frameworks to improve EDM performance, particularly for mold fabrication using tungsten carbide.

In this research, a coating layer was formed on the tungsten carbide cobalt (WC-Co) substrate surface by using electrical discharge coating (EDC) with waste quarry dust powder suspension. The tribological test was carried out by using a micro pin-on-disc tribometer at a constant normal load (10N) and sliding speed (5 mm/s). The surface roughness, Vickers micro-hardness, coefficient of friction (CoF), wear weight loss, wear scar depth and wear track morphology of the coating layer were investigated and compared with the original surface of the WC-Co substrate in this study. The results indicated that under coating conditions of 5 A of peak current (Ip) and 300 μs of pulse on time (Ton), the Vickers micro-hardness increased by 28%, and the surface roughness, CoF, wear weight loss, and wear scar depth of coating layer reduced by 29%, 61%, 79%, 63%, respectively compared with the original WC-Co substrate. These results demonstrated that the coating layers produced by EDC with quarry dust waste powder suspension had good wear resistance, which could be beneficial to the cutting tool, mold and die industries.

Fe-based metallic glasses (MGs) have attracted much attention because of their cheap raw materials, outstanding soft magnetic properties and superior catalytic activity. Meanwhile, the fabrication of micro/nano-structures on its surface could further improve its functional properties. In this study, it was attempted to fabricate micro/nano-structures on a Fe-based MG (Fe52Cr13Mo12C15B6Er2, in at. %) surface by nanosecond pulsed laser irradiation technology. The surface characteristics and microstructural evolution of Fe-based MG were investigated. The experimental results showed that under different laser fluences, the laser-irradiated areas exhibited distinguished microstructures, i.e., nanoparticles, the network nanostructures or a combination of these two microstructures. Furthermore, oxygen and erbium were enriched inside the network nanostructures. By analyzing the microstructural evolution, formation mechanisms of the nanoparticles and the network nanostructures were discussed. The nanoparticles were actually caused by laser-induced element enrichment (i.e. amorphous erbium oxide) and the mismatch of its wettability with the substrate; the formation of the network nanostructures was attributed to the diffusion and connection of nanoparticles under the combined influence of recoil pressure and surface topography.

Increasing the hardness and wear resistance of metallic glasses (MGs) is beneficial to prolong their service life in highly aggressive environments. For the purpose of achieving surface hardening, in this work, laser surface alloying technology was employed to modify Zr-based MG with silicon powder as the pre-placed powder. The experimental results showed that the laser alloyed layer with thickness of several tens of micrometers was generated on the MG substrate. The surface hardness of the laser alloyed layers ranged from 11.34 to 17.97 GPa, which was significantly higher than that of the as-cast MG surface (6.36 GPa). Furthermore, the scratch resistance of the laser alloyed layer was improved compared to the as-cast sample. The chemical composition analysis indicated that the laser alloyed layer was mainly composed of in-situ formed ZrSi2 phase and residual Si, and these hard phases were responsible for the high hardness of the laser alloyed layer.

Ultrasonic vibration cutting is a potential method for ductile machining of brittle materials. Although there are some research works trying to answer why the ultrasonic vibration promotes ductile machining of brittle materials, most of them are based on geometrical and kinematic analysis. In this study, plunge-cutting experiments under the conventional and vibration-assisted cutting conditions were conducted on single crystalline silicon and the results were compared to those of multi-cyclic nanoindentation tests. The surface morphology and subsurface microstructure of both machined grooves and residual indents were characterized. Results of plunge-cutting experiments show that with ultrasonic vibration cutting, the critical depth of cut for ductile-to-brittle transition and the amorphous phase in cutting chips are increased compared with conventional cutting. Results of multi-cyclic nanoindentation tests show that the indentation-induced amorphous layer increased as the cyclic number increased, which is consistent with the cutting results. The findings from this study may help understand the removal mechanism of brittle materials during ultrasonic vibration cutting.

The tool wear is severe and the machined surface quality is low in dry cutting of cobalt-based superalloy. The traditional coolant is harmful to the environment and not in line with sustainable development. The liquid nitrogen (LN2) clean cutting of cobalt-based superalloy GH605 using AlTiN coated tools is proposed in this work. The tool wear mechanism and the machined surface integrity are investigated. The results show that, with the decrease of LN2 injection temperature, the sharp wear stage of the tool can be delayed. The injection temperature directly affects the tool life. Compared with dry cutting, the tool life is increased by 42.5% at LN2 injection of −190 °C. Under the lower liquid nitrogen condition, the coating peeling is reduced on the rake face. The decrease of LN2 injection temperature can effectively reduce the damaged area of the flank face and inhibit the oxidation wear. The injection temperature between −30 °C and −150 °C can significantly reduce the surface roughness. The minimum surface roughness value at the injection temperature of −90 °C is 0.486 μm, which is 39.4% lower than that at dry cutting condition. When the LN2 injection temperature is below −90 °C, the thickness of the white layer is less than half of that in dry cutting condition. The hardness of the machined surface is enhanced and the residual stress is reduced at injection temperature below −150 °C. This work demonstrates the possibility of improving the machinability of cobalt-based superalloy by optimizing the LN2 injection temperature.

Laser coloration is an emerging technique for surface functionalization of metallic glasses (MGs). Understanding the influence of laser parameters on surface color of MGs will accelerate their commercialization. Herein, surface coloration was conducted on a Ti-based MG, and the hue–saturation–intensity (HSI) color space was employed to evaluate color variation. Various colors were achieved by varying the average power and scanning speed in an ambient atmosphere. The results indicated that the overlap rate and number of repetitive scans had a negligible effect on the color and significantly changed the microscopic morphology. The irradiated surfaces were yellowish and colorless in nitrogen and argon atmospheres. Furthermore, the effect of morphology on the surface color and the mechanism of surface coloration were examined. This study demonstrates that nanosecond laser irradiation is an effective method for achieving surface coloration of MGs, which is expected to enrich the surface functionality of MG products.

Characterizing grains is the most common method in materials science research, but the existing techniques for grain characterization are generally expensive and time-consuming. In this study, nanosecond pulse laser irradiation with low laser fluence is attempted to visualize the grains of two typical high-entropy alloys (HEAs) with different crystal structures and elemental compositions. The effects of laser parameters and gas atmospheres on the laser visualization of grains are comparatively investigated. Under specific laser irradiation conditions, the grains of these two HEAs could be well visualized by producing different surface nanostructures. By experiments and analysis, the underlying mechanisms of laser visualization of grains under different conditions are elucidated, and the role of O element on the promotion of the visualization of grain boundaries is confirmed. This study provides a simple and efficient method to visualize the grains of HEAs, and on the other hand, enhances the understanding of nanosecond laser-HEA interaction.

The inherent hard-brittle nature of RB-SiC composite poses significant challenges for efficient machining, hindering its application and promotion. Laser processing is a non-contact treatment technique that can effectively modify the mechanical properties of the material surface, thereby altering its removability. Accordingly, the change in surface characteristics of RB-SiC composite induced by nanosecond laser irradiation was investigated. It was found that laser irradiation could effectively soften the RB-SiC composite (with a maximum reduction in hardness by 40.7%), and the softening degree was strongly dependent on the laser parameters. The chemical composition analysis showed that the SiC content was decreased while the Si content was increased after laser irradiation, which was mainly responsible for the hardness reduction of RB-SiC composite. In addition, compared to the original RB-SiC composite, the laser-irradiated samples exhibited enhanced weight loss during the polishing process. This work gives a feasible route to improve the removability of RB-SiC composite.

Laser shock peening (LSP) is an ideal surface modification technique which has been extensively applied to improve the room-temperature plasticity of metallic glasses (MGs) by generating extra-deep compressive residual stress region and increasing the free volume content. Nevertheless, after LSP treatment, the surface quality and hardness of MGs are usually impaired simultaneously, which hinders their applications as structural and functional materials. In the current study, an attempt was made to achieve simultaneous flattening and hardening of LSP treated (LSPed) Zr-based MG by nanosecond laser irradiation in a flowing nitrogen atmosphere. The effects of laser power level on the macro- and micro-morphology, chemical composition, surface hardness, and surface roughness (Sa) of the laser-irradiated LSPed MG were comprehensively investigated. It was found that the minor surface defects of the LSPed MGs could be effectively reduced by nanosecond laser irradiation under appropriate laser irradiation parameters, and accordingly, the surface quality was improved (with a maximum reduction in surface roughness (Sa) by 86.3%). Furthermore, the nanoindentation test results indicated that nanosecond laser irradiation at a relatively high laser power of 15.6 W resulted in an impressive improvement (173.9%) in surface hardness of the LSPed MG, which could be attributed to the introduction of hard nitrided phases mainly consisting of Zr3N4. This study provides an insightful understanding of the microstructure changes and surface characteristics of the LSPed MGs after nanosecond laser irradiation in a flowing nitrogen atmosphere, which paves the way for improving the applicability of MGs as structural and functional materials.

Laser nitriding is an effective modification technique to improve the comprehensive mechanical properties of metallic glasses (MGs). However, numerous micro-defects, such as pores and humps, usually appear on the laser-nitriding-treated (LNed) MG surface, and therefore additional post-treatment is required. Herein, laser shock processing was implemented to flatten the LNed MG and as well modify its surface mechanical property. The dependence of the laser shock flattening process on the laser energy density was investigated. The results revealed that the surface micro-defects on the LNed MG were significantly reduced after laser shock flattening, and accordingly, the surface roughness (Sa) was decreased, with a maximum reduction of 61.87% (from 0.48 to 0.183 μm) achieved at a relatively high laser energy density of 178.3 J/cm2. Furthermore, nanoindentation measurements indicated that although the surface hardness of the LNed MG was decreased after laser shock flattening, it was still higher than that of the as-cast MG.

The single-roll cooling method excels in producing metallic glass ribbons (MGRs), offering rapid cooling rates and exceptional thickness consistency. Nevertheless, a large number of defects including micro-pits and micro-gaps usually appear on the surface of MGRs after the roll forming process, significantly impacting their service life and performance. Laser gas nitriding is a cutting-edge surface modification technology that has been extensively used to improve the comprehensive performance of various metal components. Herein, an attempt was made to simultaneously improve the surface quality and mechanical properties of Zr41.2Ti13.8Cu12.5Ni10Be22.5 MGRs by nanosecond pulsed laser irradiation in a flowing nitrogen atmosphere. The effects of laser irradiation parameters on the surface characteristics of the laser gas nitrided regions were systematically investigated. The experimental results showed that the surface quality of MGRs after laser gas nitriding was enhanced, accompanied by a simultaneous improvement in hardness and scratch resistance. This study underscores laser gas nitriding as a potent strategy to augment the comprehensive surface characteristics of MGRs. This enhancement is poised to significantly extend their service life and reinforce their reliability when utilized as structural and functional materials in sectors such as machinery, national defense, and aerospace.

Understanding the processes and mechanisms of laser-matter interaction is fundamental to the treatment of materials by using laser-based methods, but it is quite challenging because the response of matter to laser irradiation is influenced by many factors, especially the intrinsic properties of the matter. In this study, the influence of crystallinity on micro-nano structure response of Zr-based alloys (Zr41.2Ti13.8Cu12.5Ni10Be22.5) treated by nanosecond laser is investigated. The microscopic topographies and geometrical dimensions of the laser-induced micro-nano structures formed on the surface of Zr-based alloys with different crystallinity have been explored and compared. The experimental results indicate that the microstructural transformation between micro-concave and micro-convex is observed for both amorphous and crystallized Zr-based alloys, i.e., independent of the arrangement of the internal atomic structure. The geometrical dimensions of the laser-induced micro-nano structures and the critical peak laser power intensity required for the microstructural transformation are different, which can be attributed to the difference in thermal conductivity. Inspired by laser-induced micro-convex, a point-by-point laser patterning technique has been proposed for highly efficient and flexible preparation of micro-nano patterns. Importantly, this patterning technique exhibits ultra-high processing efficiency with a material accumulation rate of more than 1012 μm3/s. This work paves an avenue for understanding the laser-matter interaction and is expected to facilitate the advanced functional applications of Zr-based alloys in many fields.

In our era, smart clothes for personal health monitoring in home care is a promising and innovative approach. These clothes are integrated with sensors and electronic devices that could follow vital signs, levels of activities, and other health metrics. Therefore, in this paper, the design of such smart clothes and their potential applications are presented to realize the novel concept in the healthcare service. Using various sensors, it is expected to obtain the health parameters or habitual activities of patients, while this cloth still maintains personal comfortability. Then, data is collected and transmitted via wireless communication to host server. Owing to this design, several algorithms could be deployed to predict any abnormal health status. Additionally, this approach could reduce the burden care from medical staff or nurses who are in the over-work circumstance. From this achievement, the potential applications of smart clothes on healthcare and the future research directions could be outlined clearly in the related fields.

Laser nanopatterning is an effective strategy to manipulate the surface properties of materials. One of the glaring restrictions is that the fabrication of long-range ordered nanostructures typically relies on ultrafast lasers, especially femtosecond lasers, while the insurmountable thermal effects associated with the longer pulse durations of nanosecond lasers are deeply considered to be the nemesis of this scenario. Herein, for the first time, a nanosecond laser-based nanopatterning technique for fabricating highly ordered nanodot arrays on the monocrystalline silicon surface through a remarkably straightforward process is proposed. The mechanism involves Marangoni flow-assisted low-threshold oxidation of monocrystalline silicon induced by nanosecond laser, along with a domino-like growth process of nanodots driven by optical near-field enhancement. Finite-difference-time-domain (FDTD) simulations provide insight into the underlying origin of nanosecond laser-induced nanodot arrays. The prepared large-area nanodot arrays demonstrate a range of functionalities, including the manipulation of light reflection and diffraction, structural color, and surface-enhanced Raman scattering (SERS). The present study challenges the established view that the pronounced thermal effects associated with the long pulse durations of nanosecond lasers are incompatible with high-precision nanopatterning, which opens new avenues for research into laser-matter interactions.

Carbon fiber reinforced plastic (CFRP) has found extensive applications in aerospace, automotive, and biomedical fields owing to its exceptional mechanical properties. Nanosecond pulsed laser processing offers a promising avenue for treating CFRP laminates; however, the inevitable thermal damage during processing may significantly degrade the surface integrity. An in-depth analysis of the correlation between ablation characteristics of CFRP and laser processing conditions is essential for understanding the complex heat transfer and ablation mechanisms during laser processing of CFRP and is a prerequisite for improved control of thermal damage. This study examines the thermal transfer and ablation behavior of CFRP subjected to nanosecond laser ablation, focusing on how laser scanning direction and processing parameters influence the surface characteristics of the laser-ablated regions. The results indicate that the width of the heat-affected zone (HAZ) increases with increasing laser power, decreasing scanning speed, and decreasing scanning pitch. Moreover, the scanning direction plays a crucial role in determining the HAZ characteristics and material removal rate. Processing CFRP along the 0° direction relative to the carbon fiber orientation yields higher efficiency and less thermal damage compared to the 90° direction. Chemical composition analysis reveals that laser ablation induces a structural transformation in carbon fibers, shifting from sp2 graphite-like lattice orbitals to sp3 hybird orbitals. Numerical simulations further elucidate the heat transfer and ablation mechanisms under various experimental conditions. This study contributes to a deeper understanding of the laser-CFRP interaction, facilitating the development of high-integrity CFRP surfaces and broadening their practical applications across multiple industries.

Fused silica has garnered significant attention in various industrial applications. The creation of surface micro/nanostructures on fused silica can impart specialized functional properties, such as extreme wettability, ultra-high transmittance, and excellent antimicrobial characteristics. Nonetheless, existing technologies for achieving surface micro/nanopatterning of fused silica, including wire electrical discharge machining, chemical etching, and electrochemical deposition, generally suffer from long processing cycles and high energy consumption, which are inconsistent with the development concept of the low-carbon economy. In this study, a novel approach termed micro-convex structure-assisted laser-induced backside dry etching (MCSALIBDE) is proposed for high-efficiency fabrication of micro-groove array on fused silica surfaces. The synergistic effect of enhanced heat conduction and plasma explosion in a confined space facilitates material ablation. The impact of processing parameters including scanning pitch and peak laser power intensity on the morphological and topographical features of the MCSALIBDE-processed fused silica surfaces is studied. Notably, the micro-groove structures with a depth-to-width ratio of 1.19 is fabricated. Furthermore, the wetting behaviors of the MCSALIBDE-processed fused silica surfaces before and after annealing treatment are studied. Experimental findings reveal that the MCSALIBDE-processed fused silica surfaces exhibit enhanced hydrophilicity compared to the untreated one. After annealing treatment, a transformation from hydrophilicity to superhydrophobicity is observed. The superhydrophobic surfaces produced under different laser parameters exhibit distinct adhesion and droplet bouncing behaviors. This work offers an in-depth understanding of the high-efficiency fabrication of micro/nanostructures on fused silica surfaces and as well the modulation of their wetting characteristics, heralding innovations in surface engineering for diverse applications.