Two Fe85Si15 amorphous alloy models were created based on molecular dynamics with different cooling rates of 1010 K/s (slower model) and 1012 K/s (faster model) and examined the effects of atomic structure on the mechanical properties and shear band (SB) propagation behavior, which determines the shear processing quality. Voronoi analysis of the short-range ordered structures (SRO) revealed that the slower model has more full icosahedral SROs than the faster model, and Young’s modulus and tensile strength were 11 % and 14 % higher than those of the faster model, respectively. Indentation calculations presuming crack propagation during shear processing were then performed on both models. Only in the case of the slower model, the icosahedral SRO in the SB changed to intermediate structures, increasing the distorted body-centered cubic (BCC) structure. The SB in the faster model spread out isotropically from the indenter, whereas that in the slower model propagated in the indent direction. These results indicate that intermediate and distorted BCC structures in the SB provide directionality to the SB propagation and suggest that the slower model, in which cracks propagate toward the shear direction of the material and break it in a straight line, may produce a higher-quality surface in shear processing.

Ultrafine bubbles (UFBs) are microbubbles with a diameter of 1 μm or less. In recent years, many reports have shown that grinding performance and machining accuracy can be improved by using coolant containing UFB (UFB coolant) as the coolant in the grinding process. However, the mechanism by which this effect occurs has not been clarified. Existing studies consider that UFB coolant has better wettability than normal coolant, which changes grinding performance. If the inclusion of UFB changes the liquid properties of the coolant, then grinding with UFB coolant should be effective for any work material. However, there are cases where the effect of UFB is not obtained. Therefore, wettability is not considered to be the main cause of the UFB effect. As a general characteristic of UFB, it is known that OH radicals are generated when UFB collapses, which is thought to promote oxidation of the mating material. This study examines and discusses the mechanism of UFB effect generation in grinding from the viewpoint of oxidation of the work material surface. In the case of UFB water, the oxidation state of the work material surface was found to differ depending on the gas type. The composition of the oxides formed also differed depending on the gas type. Furthermore, friction and wear tests simulating the grinding process were conducted, and it was found that the friction coefficient varied depending on the type of gas in the UFB coolant, suggesting that the oxidation of the work material surface by UFB affects the friction and wear properties, resulting in a change in grinding properties.

This study proposes a novel dental treatment method using powder jet deposition (PJD). PJD can be employed to fabricate hydroxyapatite (HA) films directly on human enamel by blasting fine HA particles. Acid resistance tests were performed on HA films fabricated with two blast angles (α = 60° and 90° with two samples each) and using human enamel (with one sample) to evaluate the usefulness of the HA films in acidic intraoral environments. All samples were dissolved in acid, and their volume gradually decreased over the test time tacid. Transmission electron microscopy images showed that the grain boundaries near the acid-exposed surface of the HA films were densely modified and prevented acid penetration, whereas the human enamel grains became finer owing to the acid–base reaction. Thus, the HA films lost lesser volume than the human enamel did, indicating higher acid resistance. However, one film fabricated at α = 60° partially peeled off during tacid = 6–9h. Analysis of the PJD phenomenon through smoothed particle hydrodynamics indicated that the tensile residual stresses promoting crack propagation and delamination increased as α became more acute, causing HA film peeling. Therefore, particles should be blasted in multiple directions to avoid stress bias.

Powder jet deposition (PJD) is a spray coating method and can perform under an environment of atmospheric pressure and room temperature. The deposition environment is advantageous for clinical use and the PJD process has been tried to apply to dental treatment by using fine particles of hydroxyapatite. However, its deposition rate is significantly low compared with other heating and/or vacuum processes. We, therefore, applied an atmospheric-pressure plasma jet (APPJ) to the PJD process to increase its deposition rate without changing the environment. The experimental results illustrate that the APPJ assistance provided the effect of increasing the deposition rate on the PJD process, while the effect of the APPJ irradiation time was saturated within 15 s. Additionally, the interval of the APPJ irradiation and the PJD process also had a significant effect on the deposition rate, i.e., the shorter the interval was, the larger the deposition rate got. These results are in accord with our assumption of the effect of the APPJ irradiation on increasing the PJD rate.

Powder jet machining is a blast machining process in which micrometer-order particles are projected onto a workpiece at near-supersonic speeds, to remove the workpiece (abrasive jet machining (AJM)) or to deposit the particles (powder jet deposition (PJD)). We report a novel dental treatment method for powder jet machining using hydroxyapatite, which is the main component of teeth, as deposited particles. The surfaces and interdental spaces of human teeth are not only flat, but also have complex groove structures. However, PJD and AJM exhibit impact-angle-dependent machining phases. Therefore, it is necessary to investigate the effect of the particle impact angle on machining, before dental treatment. Furthermore, because machining interacts not only with the particle impact angle but also with the particle impact velocity, a comprehensive investigation of the effects of the machining parameters is required, for delineating the phase-transition conditions. Accordingly, in this study, we conducted machining experiments using hydroxyapatite particles (particle diameter, 2.16 μm) and four different blasting angles of 30°, 45°, 60°, and 90°, to infer the machining amount. Machining efficiency was evaluated based on the amount of machining. The impact angles and velocities of the particles were calculated using computational fluid dynamics (CFD). Three-dimensional process mapping was performed using the machining amount, particle impact angle, and particle impact velocity, obtained from the experiments and CFD calculations. The results showed that PJD crossed to AJM at the impact angle of approximately 60°. Moreover, PJD exhibited high processing efficiency for impact angles above 60° and impact velocities in the 280–310 m/s range. In contrast, AJM exhibited high processing efficiency for impact angles below approximately 35° and impact velocities above 310 m/s.

We propose a novel blanking method to improve the machinability of amorphous alloys by taking advantage of changes in mechanical properties during local heating. The local heating is achieved through an ultrashort pulsed laser with a low thermal effect, allowing us to control the size and structure of heat-affected zones by adjusting laser power, pulse width, and shot numbers. This method hence causes phase transformation only in the blanking area. Namely, heat storage effects increased with a prolonged ablation process, and crystallization was observed at a repetition rate of 200 kHz or more. A fully crystallized microstructure, which formed at elevated temperatures, was seen at the center of the laser irradiation, while, as the distance from the irradiation point increased, small crystallites are found to disperse in the amorphous matrix. In addition, a thin crystalline phase appeared on the surface layer of the crystallized region. In general, the locally heated area was embrittled by the aforementioned structural changes, and consequently, the blanking resistance decreased with an increase in the crystallized area. Yet, it was found that laser irradiation which did not bring about crystallization also led to a decrease in the blanking resistance, showing that thermal effects below the crystallization temperature are still effective in reducing the blanking resistance. Additionally, the blanked cross-section of the locally heated specimen showed good surface quality without defects such as a large shear droop, which often occurs when punching amorphous alloys.

The high saturation magnetic flux density, low coercivity, and high permeability of iron-based amorphous alloys make them excellent magnetic core materials for electrical devices. Their local embrittlement and high fracture strength, however, make them difficult to machine. To overcome these difficulties, we have developed a new machining method with optimized heat treatment to improve the machinability of amorphous alloys. We conducted a series of blanking tests on melt-spun and post-annealed Fe-Si-B-Cr amorphous alloys with as-quenched, relaxed, partially or fully crystallized, and grain-grown microstructures. SEM examinations of the fractured surfaces of the blanked specimens and TEM observations revealed that the blanking resistance and overall machining performance correlated with these microstructures. The as-quenched sample showed the largest blanking resistance, and the fracture surface exhibited a drooped top edge, vertical marks, and the formation of horizontal voids, suggesting that plastic deformation occurred. For the samples annealed up to 763 K, the blanking resistance decreased and fractographic examination indicated that the blanking occurred in a brittle manner. Annealing at higher temperatures (773-873 K) increased the blanking resistance and changed the fracture morphology, exhibiting intragranular and intergranular fractures of crystalline precipitates. After complete crystallization, several burrs appeared at the bottom of the sample. Annealing at 1073 K led to a further decrease in blanking resistance related to the intergranular fracture of large grains. The plastic deformation of the sheet deteriorated the blanking quality. Based on these findings, the optimum microstructure and posttreatment of the amorphous alloy for ideal blanking performance are proposed.

Fe-based amorphous alloys, which exhibit excellent soft magnetic properties, are difficult to machine, owing to their high strength, toughness, and hardness resulting from their unique structures. The authors proposed a novel blanking method that improves the machinability by crystallizing only the local regions involved in machining, thereby reducing the local strength and toughness. Because the micro-region mechanical properties of amorphous alloys vary greatly depending on the precipitated crystal species and volume fraction, it is necessary to nondestructively investigate the type of microstructure achieved by local heat treatment to determine the appropriate blanking conditions. However, an appropriate method for investigating crystals precipitated locally in an amorphous matrix is yet to be established. In this study, we used the 2D X-ray diffraction method to investigate the local crystallization of an Fe-based amorphous alloy ribbon after local heat treatment using an ultrashort pulsed laser. Furthermore, the 2D method was used to investigate the residual stresses in the fully crystallized amorphous alloy ribbons, and the results were compared using the sin2(") method. The 2D method detected the slightly precipitated crystals in a local area with a radius of about 40 mu m in the amorphous matrix. The integrated intensity of the diffraction peaks can be used to predict the internal structure after local heat treatment. Furthermore, the 2D method could measure residual stress with smaller error than the sin2(") method. The core-shell crystals precipitated by heat treatment exhibited a compressive residual stress of-82 MPa to-67 MPa in the core Fe3B crystals and tensile residual stress of 39-60 MPa in the shell alpha-Fe crystals, approximately. The residual stress values of the precipitated crystals depended on the direction of rotation of the quenching roll used in the production of the amorphous alloy ribbons.

Low-temperature degradation (LTD) is a progressive degradation following tetragonal-to-monoclinic transformation in a water environment, and it represents a problem for the long-term integrity of zirconia implants. However, there is little documentation on the low-temperature degradation characteristics of zirconia with surface treatment. We investigated the LTD properties of such systems to assess the influence of surface treatment using nanosecond (thermal) and picosecond (less thermal) pulsed lasers, as well as an additional annealing process. The nanosecond and picosecond pulsed lasers generated periodic structures on the surfaces of tetragonal zirconia polycrystals stabilized with 3 mol% yttria (Y-TZP). Cross-sectional observations using scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) revealed the characteristics of the microstructure and the heat effects. Both laser treatments resulted in heat-damaged layers. Moreover, the nanosecond laser induced grain growth on the outermost surface. However, annealing after nanosecond laser treatment resulted in a porous structure below the surface. X-ray diffraction analysis detected monoclinic crystals on the surfaces treated with the nanosecond and picosecond pulsed lasers after the LTD acceleration test. Cross-sectional observations revealed the propagation of the monoclinic-transformed layer. We concluded that the thermal shock from the lasers deteriorates the LTD resistance of the materials, and the use of additional annealing hinders LTD propagation. Stress relaxation and the microstructures produced by annealing may contribute to maintaining toward LTD resistance.

This study aims to induce a laser-induced periodic surface structure (LIPSS) on different coatings using a pico-second laser. An energy dispersive X-ray (EDX) spectroscopy analysis was performed, and wettability and friction tests were performed. Additionally, the surface electric field intensity (EFI) distribution was analyzed using the finite element method (FEM) to study LIPSS generation on different coating morphologies. The EDX results demonstrated that the LIPSS induced on the TiN coatings did not destroy them; however, the TiCN coatings were oxidized in the LIPSS fabrication process. The numerical simulation results indicated that the surface EFI and depth of the surface roughness were significantly linear, and the EFI was significantly related to the refractive index and extinction coefficient of the coating material. The wettability and friction test results implied that the LIPSS on different coatings could exhibit super hydrophilicity and played a role in friction reduction.

The UltraSonic Machining (USM) process is simulated by using Smoothed Particle Hydrodynamics (SPH) numerical simulation method. The influences of abrasive shape on material removal and abrasive wear are investigated. According to the simulation results, the abrasive shape has a strong influence on USM process. Using the abrasive with round shape is helpful to improve the machining efficiency. Experiments were also conducted to verify the SPH model. The experimental results agreed well with the simulation results.

A fundamental study of the mechanisms of generation of the laser-induced periodic surface structure (LIPSS) includes electromagnetic deposition theories and matter reorganization theories. The proposed two-dimensional finite element model incorporates frequency-domain electric field analysis and the two-temperature model (TTM) to simulate the growth process of LIPPS in multi-pulse picosecond laser irradiation. The proposed simulation proceeds as follows: the electric field intensity (EFI) distribution is calculated by referring to the material surface morphology and determines heat distribution by the electromagnetic heating (EMH); the heat distribution is introduced into the TTM to calculate the electron and lattice temperatures; by comparing the lattice and the vaporization temperature, material ablation is determined to obtain a new surface topography and single-pulse simulation completes; and by introducing the new surface topography recursively, multi-pulse laser irradiation can be simulated. In the calculation of a picosecond laser with a wavelength of 1064 nm, pulse duration of 20 ps and different laser fluences for the irradiation of the Ti6Al4V alloy surface, this method could simulate the ripple-like distributed EFI, and a surface morphology similar to that of LIPSS grew after several pulses. The results were in agreement with the observed experimental results. The proposed assumption is a novel approach for the explanation of the LIPSS generation mechanism.

In biomedical engineering, laser-induced periodic surface structures (LIPSSs) have been extensively applied where laser irradiation of selective laser-melted (SLMed) samples to generate LIPSS-covered free-form samples is a promising technique. Using this technique, nanopillars around a spheroidal particle that was not molten during the SLM process have been formed, indicating that nanopillars can be induced around spheroidal particles on a material surface. This study investigates the mechanism of LIPSS and nanopillar formation on SLMed and uneven surfaces experimentally and through finite-difference time-domain simulation. A 50 Hz picosecond laser with 1064 nm fixed wavelengt, 20 ps pulse duration, 0.5 J/cm2 laser fluence, and 400 mu m/s scanning speed was employed to irradiate Ti6Al4V alloy samples with 100 mu s exposure time. The results show that induced nanopillars form a concentric area around a single particle with curvature radius approximately twice the particle radius. The simulated electric field intensity is ripple-like distributed for particle size beyond 5 mu m, with approximately 1 mu m periodic length and is close to the laser wavelength. This matches the experimental results from scanning electron microscopy for 800-00 nm LIPSS periodic length, indicating that desired nanostructures can be generated by appropriately designing the surface topography before laser irradiation.

Anti-reflection, light diffusion, diffraction, the major optical functions used in cameras, led displays and other devices. Highly-ordered micro-structures on surfaces are commonly used to obtain those functions, and development of fabrication method of those in large scale, high efficiency, high precision became an important issue due to increase of optical devices demand. In this paper a new method to fabricate highly-ordered micro patterns on glass was performed by scratching the half-reacted silica-glass-precursor coating, and fabrication mechanism was discussed. As silica-glass-precursor perhydropolysilazane (PHPS) solution was spin-coated on glass substrate to obtain coating with thickness around 0.6 μm, and heat-cured at 80–250 ℃ to consolidate surface of coating with variety of reaction distribution in coating. In the scratch test a stylus was oscillated at 45 Hz and drawn at 5–25 μm/s as load increased. Highly-ordered-periodic-structures with pitch around 1 mm were obtained by scratching, with a 50 mm-apex-radius stylus, the coating which was cured at 100 ℃ for 12 h. By degreasing scratch draw sped pattern pitch was decreased under 1 μm. Simulation has been conducted in order to estimate reaction rate distribution in the coating. From the simulation results it was found that there are two layers in the coating, reacted layer beneath coating surface and unreacted layer near PHPS-substrate boundary. It was considered that reacted layer on surface reduces friction so that film does not break off while scratching while unreacted layer enable deformation of coating.

In this study, the change in the strength of B-rich Fe-based amorphous alloy was investigated as a function of its microstructure controlled by the annealing at temperatures from 713 to 873 K. The strength was measured by using a micro-tensile test in a focused ion beam apparatus, and its machinability was tested by a blanking test. It was found that the static strength and machinability of the alloy varied drastically depending on its microtexture. In the micro-tensile test, the as-received sample exhibited ductile fracture with a tensile strength of about 1200 MPa, concurring with the bulk material. During the annealing up to 773 K, fine Fe3B crystals stared to precipitate sparsely in the matrix, and alpha-Fe crystals grew around Fe3B the crystals. Due to this microstructural change, the tensile strength dropped down to about 300 MPa, the fracture mode changed from ductile to brittle, and the toughness of the alloy decreased significantly. However, when the annealing temperature exceeded 773 K, the microtexture changed to clear polycrystalline, and thus, large plastic deformation reappeared, and the tensile strength returned to about 900 MPa. The blanking test revealed that the annealing reduced the blanking resistance significantly, in particular, in the sample annealed at 763 K. High-quality machining traces without burrs and shear droops were obtained from this sample. From the viewpoint of machinability, it was concluded that the microstructure with the fine precipitates dispersed in the amorphous matrix was most appropriate for this amorphous alloy.

With the recent increase in the size and image quality of optical equipment, there is a strong demand for higher precision aspherical lenses. Generally, an aspherical glass lens or its mold is formed by grinding and then finished by polishing. Since the shape accuracy deteriorates in this polishing process, it is necessary to keep the polishing amount small. Therefore, it is desirable to optimize the grinding conditions and reduce the grinding surface roughness. In this paper, to optimize the grinding conditions of axisymmetric aspherical surface, maximum height roughness of axisymmetric aspherical ground surface is analyzed theoretically utilizing the statistical grinding theory. From the view point of relationship between the grain cutting direction and workpiece feed direction, grinding can be classified into parallel grinding and cross grinding. And it is found that the parallel grinding is suited to axisymmetric aspherical grinding.

As the fatigue strength of metallic components may be affected by residual stress variation at small length scales, an evaluation method for studying residual stress at sub-mm scale is needed. The sin2ψ method using X-ray diffraction (XRD) is a common method to measure residual stress. However, this method has a lower limit on length scale. In the present study, a method using at a 2D XRD detector with ω-oscillation is proposed, and the measured residual stress obtained by the 2D method is compared to results obtained from the sin2ψ method and the slitting method. The results show that the 2D method can evaluate residual stress in areas with a diameter of 0.2 mm or less in a stainless steel with average grain size of 7 μm. The 2D method was further applied to assess residual stress in the stainless steel after treatment by laser cavitation peening (LCP). The diameter of the laser spot used for LCP was about 0.5 mm, and the stainless steel was treated with evenly spaced laser spots at 4 pulses/mm2. The 2D method revealed fluctuations of LCP-induced residual stress at sub-mm scale that are consistent with fluctuations in the height of the peened surface.

We have systematically prepared diverse microstructures by annealing B-rich Fe–Si–B–Cr amorphous sheets to obtain the optimum mechanical property and cutting machinability of the alloy. Thermal, structural, and mechanical analyses showed that the early reaction sequence of the amorphous alloy upon annealing is characterized by structural relaxation, heterogeneous nucleation of the α-Fe(Si) phase at the surface, and homogeneous nucleation of metastable Fe3B core, which is enclosed by the α-Fe shell. The development of the core–shell structure, approximately 200 nm, is governed by the repeated partitioning out of Si and B from the Fe3B and α-Fe phases, respectively. The hardness and specific cutting resistance force (SCRF) were found maximum for the alloy annealed to 873 K, which is filled with the aforementioned core–shell crystalline phases. On the other hand, the best cutting performance with minimum burrs and chips, and the lowest SCRF, was realized for the alloy annealed at 763 K, which exhibits a heterogeneous microstructure, where the core–shell units are finely dispersed in the amorphous matrix.

The goal of this study was to investigate a study for the efficient generation of pillar-like nanostructure (nanopillar) on a material surface over a large area. In this research, a vertical cross-scanning (VCS) strategy using two linearly-polarized lasers with different laser conditions was proposed for the generation of nanopillars on a mirror-polished surface on a large scale. It found that the laser fluence and scanning speed of the second laser scanning should be controlled within a specific range to generate the nanopillars. Additionally, the distance between scan lines, which is defined as hatch distance, h, of the second scan, is also a non-negligible factor to induce nanopillars to cover the entire surface. This work demonstrated that the VCS method is a feasible strategy for the fabrication of nanopillars on the entire mirror-polished surface of Ti6Al4V alloy by linearly-polarized picosecond laser conveniently and efficiently.