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Papers - Yan, Jiwang

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Towards understanding the mechanism of vibration-assisted cutting of monocrystalline silicon by cyclic nanoindentation

Huang W., Yan J.

Journal of Materials Processing Technology (Journal of Materials Processing Technology) 311 2022.10

ISSN 09240136

Ultrasonic vibration cutting (UVC) is a promising technology that can promote the processing of hard-brittle materials in ductile mode. The feature of intermittent cutting in UVC is considered to promote the ductile responses of brittle materials. However, the effect of cyclic loading/impact on microscopic deformation behavior of the workpiece material in UVC is not clearly understood. This study used cyclic nanoindentation to reveal the UVC mechanism in monocrystalline silicon (Si). The surface morphology and subsurface microstructure of the residual indents were characterized and compared with those of the UVC-machined grooves. This work attempted to correlate the tool-workpiece contacts for cyclic nanoindentation and vibration cutting. Cyclic nanoindentation results show that cyclic loading promotes the extent of silicon amorphization and decreases the threshold for transitioning the β–Sn phase to the bc8 and r8 phases. As the number of indentation cycles increases, the subsurface microstructure changes from the amorphous phase to the bc8 and r8 phases. In UVC, both the critical cutting depth for brittle-to-ductile transition and the degree of amorphization in cutting chips increase in comparison to conventional cutting, which matches the trend of cyclic nanoindentation results. The findings inform the chip formation and subsurface deformation mechanisms of brittle materials during UVC.

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Microstructure and mechanical properties of SiC particle reinforced Zr-based metallic glass surface composite layers produced by laser alloying

Qian Y., Zhang D., Hong J., Zhang L., Jiang M., Huang H., Yan J.

Surface and Coatings Technology (Surface and Coatings Technology) 446 2022.09

ISSN 02578972

Metallic glasses (MGs) are a promising candidate for advanced structural applications due to their superior mechanical properties. Improving their surface mechanical properties would be of great importance for promoting their structural and functional applications. In this study, SiC particles were used as the reinforcement to improve the mechanical properties of Zr-based MG via laser surface alloying. The influences of the average laser power and overlap ratio between neighboring laser processing lines on the microstructure and mechanical properties of the laser-alloyed surface layer were investigated. The experimental results indicated that ZrC and SiC phases were successfully introduced into the MG matrix by laser surface alloying, and the content of these two hard ceramic phases was dependent on the laser processing parameters. The formed laser-alloyed surface layers exhibited a significant improvement in overall hardness compared with the as-cast specimen. At a relatively high overlap ratio of 70%, the average hardness of the MG matrix within the laser-alloyed surface layer reached 28.91 GPa, which was three times higher than that of the as-cast specimen (6.46 GPa). Furthermore, the microstructural characteristics and mechanical properties of the cross-sections of the laser-alloyed samples were characterized. The thickness of the laser-alloyed surface layer reached several tens of microns, and the SiC particles were uniformly dispersed in the whole laser-alloyed surface layer. This study confirms the feasibility for improving the mechanical properties of MGs by laser surface alloying, which is expected to broaden the application of MGs as structural and functional components under harsh severe conditions.

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Achieving Superhydrophobicity of Zr-Based Metallic Glass Surfaces with Tunable Adhesion by Nanosecond Laser Ablation and Annealing

Cui M., Huang H., Wang C., Zhang L., Yan J.

ACS Applied Materials and Interfaces (ACS Applied Materials and Interfaces) 14 ( 34 ) 39567 - 39576 2022.08

ISSN 19448244

Tuning the surface wettability and adhesion of metallic glasses (MGs) is a promising approach to enrich their engineering applications. In this study, using nanosecond laser ablation in air, hierarchical micro/nanostructures were directly fabricated on a Zr-based MG surface. Following subsequent annealing, the surface exhibited superhydrophobicity (maximum contact angle: 166°, minimum sliding angle: 2°). Furthermore, the superhydrophobic surface could be tuned from low to high surface adhesion force by controlling the laser-ablated spot interval. By analyzing the laser-ablated structures and surface chemical compositions, the superhydrophobicity was related to the formation of hierarchical micro/nanostructures and the absorption of organic compounds with low surface free energy in air, and the change in surface adhesion force was attributed to the difference in surface roughness. The experimental results showed that the superhydrophobic surface with low adhesion force could be used in self-cleaning applications, while the superhydrophobic surfaces with different adhesion forces could be used in no-loss liquid transportation. This study provides an efficient and low-cost way to fabricate superhydrophobic MG surfaces with tunable adhesion, which will broaden the functional applications of MGs.

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Visualization of indentation induced sub-surface shear bands of Zr-based metallic glass by nanosecond pulse laser irradiation

Cui M., Huang H., Wang C., Qian Y., Zhang L., Zhang Z., Yan J.

Vacuum (Vacuum) 202 2022.08

ISSN 0042207X

Characterizing the shear band of metallic glasses (MGs) is meaningful to understand its plastic deformation mechanism. However, the direct method for detecting the internal shear bands of deformed MGs with large field of view is still lacking. Inspired by the fact that surface defects have the enhanced absorption of laser energy, this study attempted to visualize the indentation induced sub-surface shear bands of Zr-based MG by nanosecond pulse laser irradiation in argon. The principle was first verified by laser irradiation of the surface scratch, and then implemented on the visualization of sub-surface shear bands. The experimental results demonstrated that the indentation induced sub-surface shear bands were successfully visualized by nanosecond pulse laser irradiation, and meanwhile, the laser irradiated surface maintained the amorphous characteristic. This study may open a new window for exploring the shear band characteristics of MGs upon external loads.

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Direct Observation of Discharge Phenomena in Vibration-Assisted Micro EDM of Array Structures

Esser G., Yan J.

Micromachines (Micromachines) 13 ( 8 ) 2022.08

The batch mode electrical discharge machining (EDM) method has been developed to improve the throughput and accuracy in fabricating array structures, but the process suffers from insufficient debris removal caused by the complex electrode geometry. Tool vibration has been used to improve flushing conditions, but to date the underlying mechanism of the tool vibration on the micro EDM of array structures remains unclear. This study aimed to investigate the effect of tool vibration on the machining process by direct observation of the discharge phenomena in the discharge gap by using a high-speed camera. Micro EDM experiments using 9 and 25 array electrodes were performed, and the effect of tool vibration on the discharge uniformity and tool wear was evaluated. It was found that tool vibration improved the uniformity of the discharge distribution, increased the machining efficiency, and suppressed the tool wear. The discharges occurred in periodic intervals, and the intensity increased with the amplitude of tool vibration. The results of this study indicate that the vibration parameters determine the discharge period duration and intensity to achieve optimum stability and efficiency of the machining process.

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A novel method for fabricating micro-dimple arrays with good surface quality on metallic glass substrate by combining laser irradiation and mechanical polishing under wax sealing

Huang H., Qian Y., Zhang L., Jiang M., Yan J.

Journal of Manufacturing Processes (Journal of Manufacturing Processes) 79 911 - 923 2022.07

ISSN 15266125

Surface micro-patterning is an emerging technique to endow a wide range of materials with specific functions, such as superhydrophobicity and anti-reflection, but it is still technically challenging and inordinately expensive via existing manufacturing approaches. Compared with crystalline metals, metallic glasses (MGs) are talented with some unique mechanical and chemical properties due to their isotropic internal structure. Here, a novel two-step method, involving nanosecond pulsed laser irradiation and mechanical polishing, was proposed to fabricate micro-dimple arrays with good surface quality on the MG substrate. In the first step, multi-pulse laser irradiation experiments were performed to study the correlation between the peak laser power intensity and the feature sizes of the micro-dimple (i.e. the depth and diameter of the micro-dimple as well as the height of the pile-up), and then various micro-dimple arrays were fabricated on the MG substrate by adjusting the peak laser power intensity and the interval between adjacent laser shots. Subsequently, aiming at improving the surface quality, the micro-dimple arrays were mechanically polished under wax sealing. The experimental results indicated that after polishing, the pile-ups around the micro-dimples were completely removed, and at the same time, the surface quality of their inner walls was improved. Furthermore, based on experimental results, the possible material removal mechanism during polishing was discussed. This study provides a convenient method to fabricate micro-dimple arrays with good surface quality on the MG substrate, which would be one of the potential alternatives for large-area, low-cost micro/nano-manufacturing.

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Nanometric cutting: Mechanisms, practices and future perspectives

Fang F., Lai M., Wang J., Luo X., Yan J., Yan Y.

International Journal of Machine Tools and Manufacture (International Journal of Machine Tools and Manufacture) 178 2022.07

ISSN 08906955

Nanometric cutting removes material at nanoscale and generates high-quality surfaces with a nanometric finish. In past decades, it has thrived as a mainstream manufacturing technology to produce critical components to advance scientific discovery and promote innovation in various fields, such as astronomy, aerospace, microelectronics, optics and photonics, biology and quantum technology. Therefore, it is timely to develop a review article capturing such developments and establishing directions for future advancement. This article systematically reviews the fundamental issues such as cutting model, material deformation mechanism and tool wear in nanometric cutting. It also presents the working principles of innovative ion implantation-assisted, laser-assisted and ultrasonic vibration-assisted nanometric cutting methods to overcome the challenges of machining difficult-to-cut materials. Practical techniques for the generation of high-quality complex or structured surfaces are also discussed. Finally, challenges and future perspectives of nanometric cutting, as well as the evolution towards atomic and close-to-atomic scale manufacturing, are outlined.

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Micro Electrical Discharge Machining of Ultrafine Particle Type Tungsten Carbide Using Dielectrics Mixed with Various Powders

Sai Dutta Gattu and Jiwang Yan

Micromachines ({MDPI} {AG}) 13 ( 7 ) 998 2022.06

Electrical discharge machining (EDM) is widely used to machine hard materials, such as tungsten carbide; however, the machining rate and surface quality are low. In this research, the effects of mixing electrically conductive carbon nanofiber (CnF), semiconductive silicon (Si) powder, and insulative alumina powder (Al2O3) at different concentrations in a dielectric fluid were studied by observing single discharge craters and hole machining performance in the EDM of ultrafine particle type tungsten carbide. Craters obtained using carbon nanofiber and alumina were much smaller than in oil-only conditions. In contrast, The results show that adding CnF significantly improved the material removal rate under all conditions. Si and Al2O3 powders only improved the machining performance at a high discharge energy of 110 V. Furthermore, improvement in surface roughness was observed prominently at high voltages for all the powders. Among the three powders, alumina was found to improve the surface roughness the most.

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Crack Propagation Behavior of Fused Silica during Cyclic Indentation under Incremental Loads

Kosai K., Zhao Y., Yan J.

Applied Sciences (Applied Sciences (Switzerland)) 12 ( 13 ) 2022.06

Fused silica is an important optical material with important applications, where the surface must be precisely machined without subsurface damage. In this study, multi-cyclic indentations under incremental loads were performed on fused silica using two kinds of indenters to clarify the mechanisms of crack generation and propagation induced by precision grinding. It was found that incremental loading cyclic nanoindentation induced various patterns of subsurface cracking and surface spalling. Four kinds of surface spalling were identified at different locations around an indent, the temporal formation mechanisms of which were clarified by microscopic observation and topographical measurement. Load–displacement curve analysis demonstrated that incremental propagation of lateral cracks during early indentation cycles caused large-scale brittle fractures during later cycles. Compared with a Berkovich indenter, a cube-corner indenter caused more significant brittle fractures and surface spalling. The findings in this study will deepen the understanding of subsurface damaging mechanism of fused silica and other brittle solids caused by cyclic tool-workpiece interactions in grinding and other mechanical machining processes.

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Microstructures and mechanical properties of Zr-based metallic glass ablated by nanosecond pulsed laser in various gas atmospheres

Y Qian, M Jiang, Z Zhang, H Huang, J Hong, J Yan

Journal of Alloys and Compounds, 163717 (Journal of Alloys and Compounds) 901 2022.04

ISSN 09258388

The surface with micro-convex prepared by laser ablation is beneficial to improving the functional properties of metallic glasses (MGs). However, accompanied by the formation of micro-convex, surface hardness of the ablated area generally decreases due to the softening effect caused by laser thermal shock. Previous studies have shown that the mechanical properties of laser-ablated MG surface are significantly different when using different gas atmospheres. In this study, a comparative investigation was performed to analyze the influence of gas atmosphere (i.e. argon, nitrogen, and air) on the formation of micro-convex as well as its surface characteristics and mechanical properties. Experimental results showed that the atmosphere type did not affect the formation of micro-convex, but significantly affected the surface morphology and element composition of the laser-ablated area. The element analysis and Raman spectral measurements indicated that laser ablation in nitrogen or air atmosphere resulted in local nitridation or oxidation. The results of nanoindentation tests demonstrated that laser ablation in nitrogen or air atmosphere also resulted in surface hardness inhomogeneity, i.e., softening and hardening effects coexist in the ablated area, which could be attributed to the combined influence of laser thermal shock, the introduction of secondary phase as well as laser ablation induced loose structure.

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Tool Path Generation and Optimization for Freeform Surface Diamond Turning Based on an Independently Controlled Fast Tool Servo

Y Sato, J Yan

International Journal of Extreme Manufacturing (International Journal of Extreme Manufacturing) 4 ( 2 ) 025102 2022.03

ISSN 26318644

Diamond turning based on a fast tool servo (FTS) is widely used in freeform optics fabrication due to its high accuracy and machining efficiency. As a new trend, recently developed high-frequency and long-stroke FTS units are independently driven by a separate control system from the machine tool controller. However, the tool path generation strategy for the independently controlled FTS is far from complete. This study aims to establish methods for optimizing tool path for the independent control FTS to reduce form errors in a single step of machining. Different from the conventional integrated FTS control system, where control points are distributed in a spiral pattern, in this study, the tool path for the independent FTS controller is generated by the ring method and the mesh method, respectively. The machined surface profile is predicted by simulation and the parameters for the control point generation are optimized by minimizing the deviation between the predicted and the designed surfaces. To demonstrate the feasibility of the proposed tool path generation strategies, cutting tests of a two-dimensional sinewave and a micro-lens array were conducted and the results were compared. As a result, after tool path optimization, the peak-to-valley form error of the machined surface was reduced from 429 nm to 56 nm for the two-dimensional sinewave by using the ring method, and from 191 nm to 103 nm for the micro-lens array by using the mesh method, respectively.

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Generation of Si@ C/SiC@ C core–shell nanoparticles by laser irradiation of silicon grinding waste

K Minami, K Kobinata, J Yan

Nano Select (Wiley) 3 ( 7 ) 1192 - 1200 2022.03

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Flexible fabrication of fresnel micro-lens array by off-spindle-axis diamond turning and precision glass molding

L Zhang, YY Allen, J Yan

Precision Engineering (Elsevier {BV}) 74 186 - 194 2022.03

Research paper (scientific journal), Joint Work, Accepted, ISSN 01416359

Fresnel micro-lens arrays with close-to-wavelength features have significant advantages in minimization of optical systems. However, in the fabrication of a Fresnel micro-lens array by conventional diamond turning, the discontinuous features of the surface profile cause interference between the tool flank face and the finished surface. In this manuscript, a novel off-spindle-axis diamond turning method is proposed to fabricate Fresnel micro-lens array mold insert and a toolpath generation algorithm is developed. The generation of each lenslet is treated as an independent turning operation, and the whole fabrication of a Fresnel micro-lens array is completed by a succession of repetitive turning operations. With this approach, the interference between the tool and the finished surface is avoided, and the form accuracy and surface integrity are improved for each lenslet. Then, the Fresnel micro-lens array mold insert is further utilized in precision glass molding to replicate the micro-lens structures onto transparent polymer substrates. The experimental results indicate that both the diamond-turned and molded Fresnel micro-lens arrays are achieved with homogeneous quality. As an application, a compact imaging system based on the molded Fresnel micro-lens array is demonstrated. The proposed machining method in this study can be employed in the fabrication of Fresnel micro-lens arrays and other micro-optics with discontinuous profiles with high accuracy and machining efficiency.

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Development of High-Sensitivity Electrically Conductive Composite Elements by Press Molding of Polymer and Carbon Nanofibers

S Aikawa, Y Zhao, J Yan

Micromachines 13 (2), 170 ({MDPI} {AG}) 13 ( 2 ) 170 2022.01

Research paper (scientific journal), Joint Work, Accepted

Carbon nanofibers (CNFs) have various excellent properties, such as high tensile strength, electric conductivity and current density resistance, and thus have great application potential in electrical sensor development. In this research, electrically conductive composite elements using CNFs sandwiched by thermoplastic olefin (TPO) substrates were developed by press molding. The metal mold used for press molding was processed by a femtosecond laser to generate laser-induced periodic surface structures (LIPSS) on the mold surface. The aggregate of CNFs was then flexibly fixed by the LIPSSs imprinted on the TPO substrate surface to produce a wavy conductive path of CNFs. The developed composite elements exhibited a sharp increase in electrical resistance as strain increased. A high gauge factor of over 47 was achieved, which demonstrates high sensitivity against strain when the composite element is used as a strain gauge. Scanning electron microscope observation revealed that the TPO filled the spaces in the aggregate of CNFs after press molding, and the conductive path was extended by the tensile strain. The strain-induced dynamic changes of contact states of CNFs and CNFs networks are discussed based on the electrical performance measurement and cross-sectional observation of the elements. This research provides a new approach to the production of flexible and high sensitivity strain sensors.

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Nitrogen assisted formation of large-area ripples on Ti6Al4V surface by nanosecond pulse laser irradiation

C Wang, H Huang, Y Qian, Z Zhang, W Huang, J Yan

Precision Engineering (Elsevier {BV}) 73 244 - 256 2022.01

ISSN 0141-6359

Ti6Al4V is one of the most widely used titanium alloys due to its excellent mechanical, physical, and chemical properties. Laser surface texturing is a promising method to endow new functions of material surfaces; however, direct generation of laser-induced periodic surface structure (LIPSS) on the Ti6Al4V surface by nanosecond laser is rarely reported. In this study, by nanosecond laser irradiation in nitrogen atmosphere, the ripples (a typical LIPSS) were directly fabricated on the Ti6Al4V surface. By single-line laser scanning, the effects of laser irradiation parameters including the laser power and repetition frequency on the formation and evolution of the ripples were systematically investigated, followed by optimizing the laser irradiation parameters to achieve the large-area regular and clear ripples with relatively good surface quality as well. Furthermore, by performing contrast experiments in argon atmosphere, the role of nitrogen atmosphere on the formation of ripples was confirmed. Accordingly, formation mechanism of the ripples was discussed. Finally, the effects of the formed ripples on the surface color and wettability were preliminarily characterized to demonstrate the potential applications of surface ripples. This paper provides a nitrogen assisted method to fabricate large-area ripples on the Ti6Al4V surface by nanosecond laser irradiation.

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The effects of simultaneous laser nitriding and texturing on surface hardness and tribological properties of Ti6Al4V

C Wang, J Hong, M Cui, H Huang, L Zhang, J Yan

Surface and Coatings Technology, 128358 (Surface and Coatings Technology) 437 2022

ISSN 02578972

The low hardness and poor tribological properties of titanium and its alloys significantly hinder their practical engineering applications, so surface nitriding or texturing is widely employed to improve the surface performances. However, previous studies mainly used the single method (surface nitriding or texturing), and simultaneous nitriding and texturing are rarely reported. Therefore, their combined effects on the surface mechanical and tribological properties are rarely investigated as well. In this study, by nanosecond pulse laser irradiation in nitrogen atmosphere, simultaneous nitriding and texturing of the Ti6Al4V surface were achieved. The effects of laser parameters including laser power, laser overlap rate, and number of scanning cycles, on the surface hardness and tribological properties of laser irradiated surfaces were comparatively studied. The experimental results showed that after simultaneous laser nitriding and texturing, the surface hardness of Ti6Al4V surface was increased by 50%~95%, and the coefficient of friction (COF) was reduced by 70%~80%. Furthermore, the laser processed surfaces obtained under various irradiation parameters presented quite different scratching characteristics, and the corresponding deformation mechanisms during scratching were analyzed. This study provides a simple and effective method by simultaneous laser nitriding and texturing for improving the surface properties of Ti6Al4V, which would be meaningful for its practical engineering applications.

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Generation of micro/nano hybrid surface structures on copper by femtosecond pulsed laser irradiation

Nakajima A., Omiya M., Yan J.

Nanomanufacturing and Metrology (Nanomanufacturing and Metrology) 5 ( 3 ) 274 - 282 2022

ISSN 2520811X

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.

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Exploratory investigation of chip formation and surface integrity in ultra-high-speed gear hobbing

Ueda Y., Sakurai N., Takagi T., Ishizu K., Yan J.

CIRP Annals (CIRP Annals) 71 ( 1 ) 89 - 92 2022

ISSN 00078506

Gear hobbing is widely employed to manufacture automotive gears, where the productivity depends on the cutting speed. Currently, gear hobbing is performed at ∼300 m/min using high-speed steel hob cutters. In this study, ultra-high-speed gear hobbing was attempted using a large-diameter cemented carbide hob cutter on a gear grinder. This enabled a cutting speed up to 2450 m/min. Many interesting phenomena were acquired in this speed range. Chips were severely oxidized, whereas the gear surface was not affected. Compressive residual stress was generated at the gear surfaces with low surface roughness and high hardness, while the wear of hob cutter was insignificant.

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Dynamic modeling and in-process parametric compensation for fabricating micro straight thin walls by micromilling

Li Yang, Cheng Xiang, Zheng Guangming, Yan Jiwang, Liu Huanbao, Li Xuewei

JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T (Journal of Materials Research and Technology) 18 2480 - 2493 2022

ISSN 2238-7854

A comprehensive dynamic model is introduced try to further reduce dimensional errors of micromilled micro straight thin walls based on an in-process cutting parameter compensation device. First, a mathematical model is established to predict the dynamic elastic deformation of the thin walls in the micromilling process. Next, the radial deformation and the runout of the cutter are modeled. Then, the comprehensive in-process parametric compensation model and strategy are established. Finally, a real-time in-process cutting force measurement and cutting parameter compensation device is applied to the micromilling system and thin wall fabrication experiments have been conducted. It shows that the comprehensive dimensional error model and iterative compensation method are effective, and the dimension and shape precision of the micro straight thin wall has been obviously improved after the compensation of the radial cutting depth. The average relative errors have been reduced from 6.86% to 1.10%∼1.70%. The in-process compensation method introduced in this study is efficient and convenient as long as compensation strategies are integrated in the controlling unit for a specific micromilling process.

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Ultrasonic Vibration-Assisted Grinding of Carbon-Based Difficult-to-Cut Materials

Yan J.

Seimitsu Kogaku Kaishi/Journal of the Japan Society for Precision Engineering (Seimitsu Kogaku Kaishi/Journal of the Japan Society for Precision Engineering) 88 ( 7 ) 541 - 545 2022

ISSN 09120289

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