Published papers

Previous simulations indicated that pure metals can be amorphized during diamond turning. However, no pure metal has been successfully amorphized during this procedure to date. Herein, a comprehensive study on the surface formation mechanism was performed by examining the surface finish and subsurface variation characteristics. Polycrystalline pure copper was selected as the working material. In this study, the amorphization phenomenon and lattice structure transformations (from face-centred cubic to hexagonal close-packed and monoclinic structures) of pure copper were observed. The amorphization and phase transformation inside the working material depended on the tool nose radius being large, the cutting edge being sharp, and the feed rate being low. By using a large-nose-radius (10 mm) diamond tool with a sharp cutting edge (10.3 nm) at a low feed rate (0.5 μm/rev), an ultrasmooth and ultrahard surface with a 0.61 nm roughness Sa and 5.0 GPa nanohardness was achieved. Molecular dynamics simulations revealed that the high shear strain was responsible for the amorphization and lattice structure transformation during pure copper diamond turning. The findings of this study were considered critical for generating an amorphous subsurface layer in a pure metal and for achieving a ultrasmooth and ultrahard surface using single-point diamond turning.

The delamination of copper lead frames from epoxy molding compounds (EMC) is a severe problem for microelectronic devices, as it leads to reduced heat dissipation or circuit breakage. The micro/nanoscale surface structuring of copper is a promising method to improve the copper–EMC interfacial adhesion. In this study, the generation of micro/nano hybrid structures on copper surfaces through femtosecond pulsed laser irradiation is proposed to improve interfacial adhesion. The micro/nano hybrid structures were realized by generating nanoscale laser-induced periodic surface structures (LIPSS) on microscale parallel grooves. Several types of hybrid surface structures were generated by changing the laser polarization direction, fluence, and scanning speed. At a specific aspect ratio of microgrooves, a latticed structure was generated on the sides of microgrooves by combining LIPSS formation and direct laser interference patterning. This study provides an efficient method for the micro/nanoscale hybrid surface structure formation for interfacial adhesion improvement between copper and EMC.

Reaction-bonded silicon carbide (RB-SiC) is an excellent engineering material with high hardness, stiffness, and resistance to chemical wear. However, its widespread use is hindered due to the properties mentioned above, making it difficult to machine functional surface structures through mechanical and chemical methods. This study investigated the fundamental characteristics of laser-induced periodic surface structures (LIPSSs) on RB-SiC via femtosecond pulsed laser irradiation at a wavelength of 1028 nm. Low-spatial-frequency LIPSS (LSFL) and high-spatial-frequency LIPSS (HSFL) formed on the surface along directions perpendicular to the laser polarization. SiC grains surrounded by a large amount of Si show a reduced threshold for LIPSS formation. By varying laser fluence and scanning speed, HSFL–LSFL hybrid structures were generated on the SiC grains. Transmission electron microscopy observations and Raman spectroscopy were carried out to understand the formation mechanism of the hybrid LIPSS. A possible mechanism based on the generation of multiple surface electromagnetic waves due to the nonlinear response of SiC was proposed to explain the hybrid structure formation. Furthermore, the direction of laser scanning with respect to laser polarization affects the uniformity of the generated LIPSS.

Graphene-coated silicon carbide (SiC@C) core–shell nanostructures have attracted attention in the fields of energy storage and nanoelectronics. In this study, multilayer graphene-coated silicon carbide (SiC) nanowires were obtained through the laser irradiation of a mixture target of graphite powder and silicon (Si) grinding sludge discharged from Si wafer manufacturing. Laser irradiation was performed using an ytterbium (Yb) fiber pulsed laser with a pulse width of 10 ms and a wavelength of 1070 nm with various defocus distances. The effect of laser defocusing on the morphology of the generated nanostructures was investigated. Results showed that nanowires were produced under the defocused conditions, and nanoparticles were observed at the on-focus position. The products obtained under all defocused conditions showed a core–shell structure, and the SiC nanowires were covered by graphene layers. The aspect ratio of the nanowires increased with the defocus distance. Observation of the laser-induced plume using a high-speed camera showed that when the laser was defocused, the plume propagation speed slowed down, and the shape of the plume changed to a swirling vortex. The nanowire formation was closely related to the propagation speed and shape variation of the plume. This successful production of SiC@C core–shell nanowires from Si waste opens up the possibility of the sustainable development of new materials for energy storage and nanoelectronics.

Skidding is a primary cause of rolling element bearing (REB) failure, which is influenced by operating conditions, lubricant properties, and bearing design. This paper presents an improved nonlinear dynamic model of REBs to analyze the impact of lubricant characteristics on REB skidding at different speed states. The model considers time-varying traction coefficient, cage flexibility, and cage pocket clearance. The selected tested lubricants include lithium grease (LGT2), compound calcium sulfonate (CCS) grease, and 4109 Chinese aviation oil. Simulation results show that CCS grease effectively reduces cage skidding, with the lowest load limits (300 N at 2000 RPM) under constant speed conditions and the highest stable limit (2932 RPM) during acceleration. LGT2 grease exhibits minimal sensitivity to acceleration and fluctuation speed parameters change.

Yttria-stabilized zirconia (YSZ) is an outstanding ceramic material with applications in dentistry, biomedical, and mechanical device, where a smooth and durable surface is required. This study employed ultrasonic vibration-assisted burnishing (UVB) to enhance the surface hardness of YSZ while simultaneously reducing its roughness. The surface topography formation, subsurface microstructure evolution, and surface hardness change of YSZ were investigated. It was found that a smooth surface with an average roughness (Ra) of 0.12 μm was achieved using UVB, representing 67.6 % reduction in surface roughness from the original sintered surface, which is attributed to the burnishing-to-cutting phenomenon during the processing. The UVB-induced compression and material densification prevented the formation of the monoclinic phase during the processing of YSZ. Grain refinement and crystal lattice distortion occurring in the subsurface layer led to an increase in surface hardness, reaching up to 19.7 % higher than that of the original sintered surface. Moreover, the UVB-processed surface demonstrated a high resistance to mechanical impacts, effectively inhibiting the tetragonal-to-monoclinic phase transformation in indentation testing. These findings demonstrate that UVB is an effective approach for enhancing the surface and subsurface properties of the material.

Introducing wear-resistant layers or constructing microtextures is normally employed to improve the wear resistance of materials. However, single role of the wear-resistant layer or microtexture still could not effectively address the wear issue of titanium alloys. In this study, a sinusoidal nitriding layer is directly fabricated on the Ti6Al4V surface by one-step laser irradiation. Chemical composition and microstructure analysis indicate that the nitriding layer contains TiN and α-Ti phases, and it is metallurgically bonded to the heat-affected zone. Friction wear tests show a 96.9 % reduction in wear rate with dry sliding and 99.6 % with oil lubrication, without exhibiting groove orientation dependence. The wear mechanism is discussed by scrutinizing the morphology of the wear scars and their corresponding cross-sections.

The fraction of materials that does not reach the target product in discrete manufacturing is very significant. Directing secondary material streams towards other manufacturing processes, possibly after intermediate pre-processing, offers opportunities for more energy and resource efficient recycling routes. This paper contributes to the exploration of such symbiotic recycling strategies by identifying relevant process mechanisms and by systematically scanning the manufacturing domain for relevant process combinations. Emerging and proven symbiotic combinations within the discrete manufacturing domain are reviewed, with proper attention for the quantification of the thus avoided environmental impact. A series of representative case studies illustrates the feasibility of applying industrial symbiosis principles in a discrete manufacturing context, with uniform data sheets providing detailed information on relevant research achievements.

Initiation and evolution of flow units and their correlation with mechanical behaviors of metallic glasses (MGs) are well known significant for understanding the rheological behavior of glassy substances. Here, the evolution of plastic deformation behavior of a typical Zr-based MG induced by ultrasonic vibration is investigated by means of nanoindentation, especially focusing on studying structural evolution through analysis of load-displacement curves. Furthermore, the micro-morphologies of residual indentations are characterized by using the scanning electron microscope (SEM) and atomic force microscope (AFM). Compared to quasi-static nanoindentation tests, a significant reduction in the hardness and elastic modulus of the MG by about 15 % and 30 %, respectively, is observed when subjected to ultrasonic vibration nanoindentation with an amplitude of 0.4 μm, accompanied by a pronounced indentation size effect. In addition, higher ultrasonic vibration amplitude induces larger indentation depth, more pronounced serrated flows in the load-displacement curves and more remarkable shear bands around the residual indentations, indicating ultrasonic vibration-promoted plastic flows in MG. This study provides an insight into the structural origin of plastic flows in MG systems under ultrasonic vibration, which will help to facilitate their application in the fields such as ultrasonic vibration assisted forming.

The CrMnFeCoNi alloy with a stable single face-centered cubic (FCC) phase, representing a typical class of high-entropy alloys (HEAs), has garnered considerable attention owing to their exceptional mechanical properties. However, the inherent low hardness has impeded their utilization in structural or contact components. This study attempted to improve the surface hardness of CrMnFeCoNi HEA via grain refinement realized by nanosecond pulse laser irradiation. The effects of laser parameters on the surface microstructures, chemical composition, and mechanical properties were investigated, and the mechanism for grain refinement was analyzed. The experimental results showed that the hardness of the laser-irradiated surface was significantly improved without altering the chemical composition. This study provides a simple but effective method to refine the grain of HEAs and improve their surface hardness.

Creating a smooth surface finish with nanometer-scale roughness on SiC is extremely difficult due to its hard, brittle properties and crystal anisotropy. In this study, nanoscratching tests were performed on single-crystal 4H-SiC along various crystal directions by using a sharp Berkovich tip (radius ~150 nm) and a blunt spherical tip (radius ~1 μm), respectively, to reveal the effects of tool geometry on its surface integrity. Results indicate that, under the same load conditions, the Berkovich face-forward tip produced the greatest penetration depth, followed by the Berkovich edge-forward tip and the spherical tip. The extent of surface and subsurface damage caused by the three tips follows the same trend as the penetration depth. Phase transformation did not occur in the scratched surface with the three tips, while it was occurred in the chips generated with Berkovich face-forward tip. The critical load for surface crack formation was larger when scratching along <01−10> directions compared to scratching along <11−20> directions, independent of tool geometry. Microcrack-like defects may form in the subsurface even the surface is free of damage. The microcracks were caused by {01−11} pyramidal and slip and by {11−22} pyramidal slip when scratching along <11−20> and <01−10> directions, respectively.

Micro dome arrays are applied as moulds to injection/press moulding to produce micro lens arrays. Fast tool servo (FTS) based diamond turning is a promising technique for manufacturing such micro dome arrays with high accuracy and machining efficiency. In this study, cutting of micro dome array (MDA) on copper with FTS was performed to evaluate the dynamics behaviour of the tool servo and its effects on surface topography. Results show that local surface speed dramatically affects the servo dynamics behaviour. When the local surface speed is higher than a critical value, overcutting and wavy patterns could be formed on the cut-in area of the domes and exit area, which is caused by the servo response and its limitation. By capturing and analysing the position signal and correlating it with the surface topography of the generated dome surface and considering its limitations, an effective strategy for optimizing micro dome array machining parameters was proposed. MDA cutting tests with optimized cutting conditions achieved a significantly improved form accuracy. This study will guide the optimal use of FTS systems in machining micro structured surfaces.

Yttria-stabilized zirconia (YSZ) ceramic is a widely used material in mechanical and biomedical engineering, such as machine parts and dental implants. For most applications, surface conditioning methods are required to produce smooth and reinforced surfaces with compressive residual stress. This paper investigates the processing characteristics of YSZ under ultrasonic vibration-assisted burnishing (UVB) enhanced by flexible stage and tool rotation techniques, respectively. For the use of flexible stage-enhanced UVB, the fluctuation of burnishing force was greatly reduced. As results, a smooth surface with a roughness of 164 nm Ra was obtained, which shows 39.7% surface roughness reduction from the original surface, and 9.4% surface roughness reduction from the surface burnished with conventional UVB. The burnished surface yielded strong residual compressive stresses of 401 MPa in the burnishing direction and 695 MPa in the step-feed direction. For the use of tool rotation-enhanced UVB, tool rotation-induced arc-shaped surface textures were formed on the burnished surface, and the textures became more distinct and denser as the rotation speed increased. The surface roughness was reduced by 58.9% from the original surface with the tool rotation-enhanced UVB. Stress-induced phase transformation of YSZ was identified in all burnished surfaces. This study demonstrates the feasibility of one-step manufacturing of a smooth surface with high residual compressive stress, which expands the applications of YSZ.

Yttria-stabilized zirconia (YSZ) is a fine ceramics material that has been applied to dental implants and mechanical components. As YSZ is a hard, brittle, and chemically stable material, that undergoes phase transformation during mechanical loading, it is difficult to fabricate nanostructures using mechanical processing methods. In this study, a surface structuring method using a femtosecond pulsed laser was proposed, which is effective in suppressing the mechanical loading-induced phase transformation. As the material properties of YSZ vary with the concentration of yttria dopant, polycrystalline zirconia samples with different yttria concentrations (2, 3, 5, and 8 mol%) were used to investigate the effect of yttria concentrations on laser processing characteristics for nanostructuring. At all concentrations, nanopore generation in the surface grain was achieved by laser irradiation near the ablation threshold. In addition, there was no significant change in the crystal structure before and after laser irradiation, and no damage to the bulk occurred. At 2 mol%, intergranular cracks were generated around the pores. By increasing the dopant level to 5 mol%, the lens effect of the crystal grains became stronger due to enhanced grain growth, and the diameter and number of pores increased. In addition, pores formed preferentially on smaller grains at 5 mol%. However, for YSZ with 8 mol%, the pore formation phenomenon was different from that in the lower dopant level, as the area near the grain boundary was preferentially ablated, and microcracks formation and exfoliation of the surface also occurred. These results contribute to a deeper understanding of the laser ablation characteristics of zirconia with different dopant levels and to the development of surface structuring methods for fine ceramics materials.

The application of biodegradable cutting fluids in metal cutting processes has raised interest among multidisciplinary researchers. Vegetable oils with long and polar fatty acid chains provide thick lubricant coatings that interact strongly with metallic surfaces, making them ideal biodegradable cutting fluids. In this review, the viscosity, oxidation performance, and machining performance of several vegetable oils, including palm, coconut, neem, and jatropha oils, were analysed and compared with conventional cutting fluids. The associated challenges in this field are discussed, and future research directions presented. Through this review, vegetable oils with particle additives, like alumina, silicon dioxide, molybdenum disulfide, and hexagonal boron nitride, were identified to be capable of improving the machining performance. The particles’ mending, polishing, and rolling effects are effective mechanisms for improving machining performance. Furthermore, chemical modification processes, such as transesterification and epoxidation, improve the anti-oxidation ability of vegetable oils by altering the carboxyl group (esterification/transesterification) or the fatty acid chain (epoxidation). Consequently, vegetable oils with particle additives and chemical modification surpass conventional cutting fluids in metal cutting operations and contribute to sustainable manufacturing technologies.

The failure modes of a nanographite-on-silicon system and the effects of the coating on the load-induced phase transformation of the silicon substrate were investigated using a series of nanoscratching tests with a spherical diamond indenter. The critical normal load for the failure of the nanographite coating was determined based on the thickness of the coating. When the load increased beyond the critical point, cracks, press spallation, and lift spallation were observed, and the silicon substrate underwent a phase transformation from the original crystalline phase to a mixture of amorphous, Si-III and Si-XII phases. For a thin coating, the silicon substrate was free of phase transformation owing to the coating protection. These findings provide guidance for glass molding and other applications.

Wire electrical discharge machining (WEDM) is highly suitable for processing the hard-brittle materials like metallic glasses (MGs). However, the electro-thermal energy conversion involved in the WEDM process inevitably introduces some surface defects including bulges, discharge craters, and recast materials on the WEDMed MG surface, which significantly impedes its practical application. Here, an emerging automated polishing technology, laser polishing (LP), was performed in the nitrogen-rich environment to simultaneously improve the surface quality and hardness of the WEDMed Zr-based MG surface. The detailed effects of LP parameters on the surface roughness and morphology were systematically investigated. The morphology evolution and temperature distribution of the molten pool during LP were analyzed by simulation analysis. The experimental results indicated that after single LP of four representative WEDMed Zr-based MG surfaces using the optimized laser parameters, the surface roughness (Sa) was remarkably reduced from 1.27, 2.10, 3.49, and 4.58 μm to 0.09, 0.14, 0.17, and 0.21 μm, respectively, accompanied by an increase in surface hardness from 6.30 GPa to 7.39, 7.67, 8.51 and 8.99 GPa. This study demonstrated that LP could effectively achieve simultaneous enhancement of the quality and hardness of WEDMed MG surfaces, which would contribute to expanding the application prospects of MGs.

Titanium and its alloys are widely used in aerospace and biomedical fields but suffer from poor tribological properties. Surface coating and texturing have proven to be effective ways for improving tribological properties. However, integrating these methods may introduce complexity and increased costs. In this study, laser nitriding and surface texturing were simultaneously achieved on Ti6Al4V surface via a nanosecond pulse laser. The tribological properties of textured surfaces under lubricated conditions were investigated, and the wear mechanism was discussed. Experimental results showed significant improvements in the tribological properties, including a smaller and stable coefficient of friction (COF) and a remarkable 99.3 % reduction in wear rate. This study provides valuable insights for improving the tribological properties of titanium alloys, benefiting industrial and biomedical applications.