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Stainless steels have wide application in the field of micro manufacturing industry. The size effect occur in thin metal foils because of low number of grain. Martensitic phase transformation (MPT) occur after plastic deformation subjected to stainless steel thin metal foils. Beside that, free surface roughening occur in thin metal foils after plastic deformation. The surface roughening mechanism in stainless steel thin metal foils after plastic deformation such as uniaxial tensile test not yet clarified well. MPT and grain misorientation (GMO) have huge effect to surface roughening behavior in stainless steel thin metal foils. The effect of GMO and MPT to surface roughening in SUS 316 and 304 thin metal foils were studied through uniaxial tensile stress state, repeated five times in 6% strain level for one time strain and 30% strain for the total of strain level. After that, an Scanning Electron Microcope-Electron Backscatter Diffraction (SEM-EBSD) analysis applied to 304 and 316 thin metal foils. The result showed that in stainless steel thin metal foil, surface roughening increase proportional both in fine gain (grain size 1,5 μm) and in coarse grain (grain size 9,0μm). The surface roughening in coarse grain, increased higher than in fine grain. The grain strength in SUS 304 is more inhomogeneous compared to SUS 316 that shown by SEM-EBSD results and as a result, increasing ratio of the surface roughness (Ra) is higher in fine grain and coarse grain of SUS 304 compared to SUS 316. The inhomogeneity of the grain strength in SUS 304 thin metal foil is higher than SUS 316 thin metal foil as shown by SEM-EBSD result. Furthermore, the increased surface roughness in stainless steel 304 is higher than stainless steel 316 thin metal foil both in fine grain and coarse grain. Key words : Surface roughening, Martensitic phase transformation (MPT), Grain Misorientation.

The martensitic phase transformation (MPT) is one of the most important factors that enhances the surface roughening of stainless-steel thin metal foils (TMF), such as SUS 304, compared to others without MPT, even in the same plastic strain. However, the conventional roughening model does not take into account the influence of MPT. In this study, the authors proposed a new constitutive model to express the surface roughening by taking the influence of MPT into account. The volume fractions of MPT for TMF of SUS304 in various grain sizes are accounted for quantitatively after the tensile test at room temperature and an elevated temperature, and the effect of MPT on the surface roughening is evaluated in comparison to using TMF of SUS316, in which MPT does not occur during plastic deformation. Then, a constitutive model of the surface roughening based on the experimental results is successfully built.

An investigation into the effects, including the athermal effect, of a pulsed current on AZ31B magnesium alloy was carried out. Different peak current densities were applied at the same temperature under uniaxial tensile testing. The results indicate that the stress reduction caused by the increasing peak current density is independent of temperature. The strain hardening coefficient also shows a similar trend. The fracture strain shows the optimum value due to the current crowding effect.

The ionization region model (IRM) is applied to model a high power impulse magnetron sputtering discharge with a tungsten target. The IRM gives the temporal variation of the various species and the average electron energy, as well as internal discharge parameters such as the ionization probability and the back-attraction probability of the sputtered species. It is shown that an initial peak in the discharge current is due to argon ions bombarding the cathode target. After the initial peak, the W+ ions become the dominating ions and remain as such to the end of the pulse. We demonstrate how the contribution of the W+ ions to the total discharge current at the target surface increases with increased discharge voltage for peak discharge current densities J (D,peak) in the range 0.33-0.73 A cm(-2). For the sputtered tungsten the ionization probability increases, while the back-attraction probability decreases with increasing discharge voltage. Furthermore, we discuss the findings in terms of the generalized recycling model and compare to experimentally determined deposition rates and find good agreement. Funding Agencies|Icelandic Research Fund [196141]; Free State of Saxony; European Regional Development Fund [100336119]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]

Efficient metal-ion-irradiation during film growth with the concurrent reduction of gas-ion-irradiation is realized for high power impulse magnetron sputtering by the use of a synchronized, but delayed, pulsed substrate bias. In this way, the growth of stress-free, single phase alpha -W thin films is demonstrated without additional substrate heating or post-annealing. By synchronizing the pulsed substrate bias to the metal-ion rich portion of the discharge, tungsten films with a 110 oriented crystal texture are obtained as compared to the 111 orientation obtained using a continuous substrate bias. At the same time, a reduction of Ar incorporation in the films are observed, resulting in the decrease of compressive film stress from sigma =1.80-1.43GPa when switching from continuous to synchronized bias. This trend is further enhanced by the increase of the synchronized bias voltage, whereby a much lower compressive stress sigma =0.71GPa is obtained at U-s=200V. In addition, switching the inert gas from Ar to Kr has led to fully relaxed, low tensile stress (0.03GPa) tungsten films with no measurable concentration of trapped gas atoms. Room-temperature electrical resistivity is correlated with the microstructural properties, showing lower resistivities for higher U-s and having the lowest resistivity (14.2 mu Omega cm) for the Kr sputtered tungsten films. These results illustrate the clear benefit of utilizing selective metal-ion-irradiation during film growth as an effective pathway to minimize the compressive stress induced by high-energetic gas ions/neutrals during low temperature growth of high melting temperature materials. Funding Agencies|Swedish Research CouncilSwedish Research CouncilEuropean Commission [VR 2018-04139]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; Japan Society for the Promotion of Science (JSPS)Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Japan Society for the Promotion of Science [17KK0136]

Electricity-assisted metal forming, especially using pulsed-current, was demonstrated to promote a drop in flow stress and improving formability. To investigate the effect of pulsed-current on stress relaxation, a uniaxial tensile test was conducted with different pulsed-current parameters by changing its pulse-width and frequency. Short pulse-width was used in the range of microseconds, while the frequency was arranged under 1 kHz. Different level of temperature was used to consider the effect from joule heating. Stress relaxation in the tensile test was repeated at constant strain interval at 3% strain. This research presents an analysis of stress relaxation influenced by the time-dependent parameter of short pulsed-current.

Conventional high power ultrasonic vibration has been widely used to improve manufacturing processes like surface treatment and metal forming. Ultrasonic vibration affects material properties, leading to a flow stress reduction, which is called ultrasonic volume effect. The volume effect contains multi-mechanisms such as stress superposition due to oscillatory stress, acoustic softening by easier dislocation motion and dynamic impact leading to extra surface plastic deformation. However, most researches ignored the stress superposition for the convenience of measurement, and few studies considered ultrasonic dynamic impact since the relatively low ultrasonic energy in macro scale. The purpose of this study is to investigate the characteristics and mechanisms of different ultrasonic volume effects in micro-forming. A 60 kHz longitudinal ultrasonic-assisted compression test system was developed and a series of ultrasonic-assisted compression tests at different amplitudes on commercially pure aluminum A1100 in micro-scale were carried out combining the surface analysis by SEM, EDX and micro-hardness test. Three different ultrasonic volume effects, stress superposition, acoustic softening and dynamic impact, were confirmed in the ultrasonic-assisted compression tests. In order to quantitatively predict stress superposition, a hybrid model for stress superposition is developed considering the elastic deformation of experimental apparatus in practice, the evolution of the modeling results fitted well with the experimental results. With low ultrasonic amplitude, stress superposition and acoustic softening occurred because vibrated punch contacted with the specimen all the time during compression. However, with higher amplitude, due to the extra surface plastic deformation by larger ultrasonic energy, forming stress was further reduced by the ultrasonic dynamic impact. A possible method to distinguish the effects of dynamic impact and acoustic softening is to analyze the waveform of the oscillatory stress in the process. In the case of ultrasonic dynamic impact effect, a higher amount of oxidation was observed on the specimen surface, which could be the result of local heating by surface plastic deformation and surface friction when the vibrated punch detached from the specimen. The findings of this study provide an instructive understanding of the underlying mechanisms of volume effects in ultrasonic-assisted micro-forming.

Vertically aligned carbon nanotubes (VACNTs or CNTs) were synthetized by thermal chemical vapor deposition method on the Si/SiO2 substrates, using Al/Fe as catalyst. In the present study, the influence of the annealing duration and synthesis time on the length, grow rate and quality of the VACNTs according to 9 different regimes was investigated. The outcomes of the study was observed using scanning electron microscope, atomic force microscopy and Raman spectroscopy analysis was utilized in order to evaluate the quality of the obtained nanotubes. Results have shown that the length of the VACNTs increases with the rise of annealing time, however only to a certain degree, after which the deterioration of the nanotubes occurs and the reduction of their length is noticeable.

The precise control of the growth nanostructured thin films at low temperature is critical for the continued development of microelectronic enabled devices. In this study, nanocomposite Ni-Si-N thin films were deposited at low temperature by reactive high-power impulse magnetron sputtering. A composite Ni-Si target (15 at.% Si) in combination with a Ar/N2 plasma were used to deposit films onto Si(0 0 1) substrates, without any additional substrate heating or any post-annealing. The films microstructure changes from a polycrystalline to nanocomposite structure when the nitrogen content exceeds 16 at.%. X-ray diffraction and (scanning) transmission electron microscopy analyses reveal that the microstructure consists of nanocrystals, NixSi (x > 1) 7–8 nm in size, embedded in an amorphous SiNx matrix. It is proposed that this nanostructure is formed at low temperatures due to the repeated-nucleation of NixSi nanocrystals, the growth of which is restricted by the formation of the SiNx phase. X-ray photoelectron spectroscopy revealed the trace presence of a ternary solid solution mainly induced by the diffusion of Ni into the SiNx matrix. Four-probe electrical measurements reveal all the deposited films are electrically conducting.

Conventional ultrasonic-assisted forming in macro scale has been studied widely for decades. However, ultrasonic dynamic impact effect, more likely to occur in micro scale, has never been studied thoroughly. The purpose of this study is to investigate the material deformation behavior under ultrasonic vibration in micro scale considering the dynamic impact effect. In this study, based on the newly developed 60 kHz ultrasonic vibrator, compression tests with ultrasonic assistance were carried out on pure aluminum specimens with varying amplitudes. The effects of ultrasonic vibration on the force reduction, the improvement of surface finishing, and the variation of the contour shape of deformed specimens were analyzed and discussed. The results confirm that the ultrasonic dynamic impact and acoustic softening are two different mechanisms by ultrasonic vibration and the critical condition for ultrasonic dynamic impact effect is whether the vibrated punch is able to detach from the specimen or not in process. The deformation caused by ultrasonic dynamic impact effect is accumulated by the repeated impact step by step. Ultrasonic dynamic impact effect produces much more surface plastic deformation near both ends of specimens, which causes the significant contact surface expansion and can reduce the apparent force and surface roughness more effectively than acoustic softening and stress superposition. In addition, to confirm the proposed mechanism, the micro-structural evolution of specimens was investigated by using electron backscatter diffraction (EBSD). It is found that both acoustic softening and ultrasonic dynamic impact effect can produce severe plastic deformation, resulting in much finer grains. However, with ultrasonic dynamic impact effect, the low-angle grain boundaries on the top side (severer deformation zone) are even less than those on the center, which suggests the more significant grain boundary rotation and/or extremely local heating. The ratio of amplitude to specimen height is identified as an influencing index for occurrence of ultrasonic dynamic impact effect for the same material, confirming the promising prospect of ultrasonic vibration in micro forming. The findings in this study can help to provide a basis to understand the underlying mechanisms of ultrasonic-assisted micro forming and a guideline for designing the process in next step.

For high sensitivity and rapid reaction of enzyme-linked immunosorbent assay (ELISA), the film-stack reaction field with micro-pillars array was designed and developed. The film-stack reaction field was fabricated by a nanoimprint process and an automatic punch-press process. The films with different gaps between micro-pillars (5, 10 and 50 μm) were prepared. These reaction fields were evaluated by IgA ELISA using 96-well microtitre plates and the computational simulation analysis of the fluid flow and the particle trajectory. Compared with ELISA using only the microtitre plate, higher detection sensitivity and shorter incubation time were achieved using the film-stack reaction field due to the increased surface area and the circulating flow through the space between films in a well by the rotation of the film-stack reaction field. Furthermore, in the ELISA results obtained using the film-stack reaction fields, the fluorescence intensities in 10-μm and 50-μm pillar gaps were the minimum and maximum values, respectively. This trend was due to the flow rate between micro-pillars, and the number and the diffusion distance of supplied biomolecules to the inertial space in the film-stack reaction field. In simulation results, the trend of the number of adsorbed biomolecule particles with different gaps between micro-pillars was in agreement with the trend in the ELISA results. Hence, these simulation analyses were validated in the quantitative evaluation of this reaction field and could be applied in the design of this reaction field as an effective design tool.

A uniaxial tensile test was developed to investigate material deformation behavior under DC pulsed current load. Duty cycle was kept low to provide wide gap between peak current density and average current density. With average current density preserved at low value, the Joule heating effect can be minimized thus keeping temperature low. Tensile tests were carried out by changing peak current density value while keeping temperature near 40 ˚C. That approach can further distinguish effect of Joule Heating. In this research, it was observed that the effect of peak current density was not present.

A novel ultrasonic vibration-assisted piercing system was developed. To clarify the effect of ultrasonic vibration on fine-grained stainless steel SUS304 foils, experiments were conducted under different amplitudes (0, 2.3 and 3.2 µm) and grain sizes (9.0 and 1.5 µm). With this method, as the amplitudes of ultrasonic vibration increased, the shearing load tended to decrease. Furthermore, the results of load reductions with applying ultrasonic vibration indicated that maximum load reductions at grain sizes of 9.0 and 1.5 µm were 13.3 and 60%, respectively. The effect of ultrasonic vibration on fine-grained materials was experimentally demonstrated.

The local chemical composition of (Ti, Al)N thin films grown on the inner-walls of holes by high-power impulse magnetron sputtering (HiPIMS) was analyzed in detail to investigate the transport behavior of ionized and neutral species into small holes. HiPIMS deposition was performed at the floating substrate potential and at − 50 and − 150 V with a fixed pulse length of 100 μs and a frequency of 333 Hz. The deposition rate on the inner-walls decreased with increasing substrate bias at all hole depth. From the obtained local chemical compositions of (Ti, Al)N films on inner-walls, it was found that the content of the metal elements, Ti and Al, decreases with increasing depth. In addition, the rate of decrease of the Ti content with increasing depth on the inner-walls is greater than that of the Al content. This tendency becomes increasingly significant with increasing substrate bias voltage. These bias dependencies are discussed by considering the degree of thermalization for ionized species from the viewpoint of the difference in the mass number between Ti, Al, and the gas species.

To contribute to process design of microforming at elevated temperatures, the effect of grain size on mechanical behavior of pure titanium foils was studied. Uniaxial tensile tests and microbending tests were performed at different temperatures of 298, 433, 573, and 723 K and at different strain rates of 10 −3 , 10 −2 , and 10 −1 s −1 . Pure titanium (Ti) foils with various grain sizes of 2.7–42.4 µm were used. As results, flow stress of Ti foils with a larger grain size showed stronger dependency on the temperature and strain rate conditions. In particular, both the reduction rate of the yield stress and that of the ultimate tensile strength relative to that at 298 K increased with increasing grain size at higher strain rates of 10 −2 and 10 −1 s −1 . However, only at a higher temperature and at a lower strain rate of 10 −3 s −1 , the flow stress increased for the foils with larger grain sizes. This is attributed to the dynamic strain aging, which is known as hardening behavior due to the diffusion of additional inclusion under higher temperatures. Furthermore, in microbending tests, the reduction rate of springback angle by increasing temperature also increased with increasing grain size. This is attributed to the increased reduction of strain gradient of the foils with a larger grain size. To clarify the mechanism of grain size effect on the mechanical behavior of pure Ti foils deformed at high strain rates, a composite constitutive model involving statistically stored dislocations (SSDs) and geometrically necessary dislocations (GNDs) was built with the capability of being employed at elevated temperatures. The effect of strain gradient on the material behavior was discussed in terms of its relationship with the density of GNDs.

Background The quantitative evaluation of the biomolecules transport with multi-physics in nano/micro scale is demanded in order to optimize the design of microfluidics device for the biomolecules detection with high detection sensitivity and rapid diagnosis. Objective This paper aimed to investigate the effectivity of the computational simulation using the numerical model of the biomolecules transport with multi-physics near a microchannel surface on the development of biomolecules-detection devices. Methods The biomolecules transport with fluid drag force, electric double layer (EDL) force, and van der Waals force was modeled by Newtonian Equation of motion. The model validity was verified in the influence of ion strength and flow velocity on biomolecules distribution near the surface compared with experimental results of previous studies. The influence of acting forces on its distribution near the surface was investigated by the simulation. Results The trend of its distribution to ion strength and flow velocity was agreement with the experimental result by the combination of all acting forces. Furthermore, EDL force dominantly influenced its distribution near its surface compared with fluid drag force except for the case of high velocity and low ion strength. Conclusions The knowledges from the simulation might be useful for the design of biomolecules-detection devices and the simulation can be expected to be applied on its development as the design tool for high detection sensitivity and rapid diagnosis in the future.

To investigate the underlying mechanism of the effects of surface texturing on lubricated sliding friction in the metal forming operation, an in-situ observation system using transparent silica glass dies and a high speed recording camera was newly developed. To correlate the dimensional parameters of micro-dimple textured structures and tribological properties in the metal forming operation, the in-situ observation was performed during bending with the ironing process of the stainless steel sheet with a thickness of 0.1 mm. The lubrication behavior were compared between the different lubricant viscosities and the micro-dimple textures with different diameters of 10 &micro, m, 50 &micro, m, 100 &micro, m fabricated by using femto-/pico-second laser processing. As a result, the textured die with dimple diameters of 10 &micro, m and 50 &micro, m showed the lubricant flow transferred from one to the other dimples owing to the lubricant reservoir effect, while that of 100 &micro, m indicated the less supply of the lubricant. However, the textured die with a dimple diameter of 10 &micro, m demonstrated higher ironing force than that of 50 &micro, m, due to the severe adhesion of work materials inside the dimple structures. Based on these experimental findings, the dimple size dependencies on lubricant reservoirs effects and the generation of the hydrodynamic pressure were discussed by correlating with the in-situ observation results, a fluid-flow analysis and a laminar two-phase flow analysis using the finite element method.

The application of ultrasonic vibration is an effective method to overcome the processing problems in micro/meso-forming. Previously it was observed that ultrasonic vibration could reduce flowing stress in the forming process, called ultrasonic volume effect. The volume effect contains multi-mechanisms such as stress superposition leading to apparent average stress reduction, acoustic softening and ultrasonic impact leading to real stress reductin. However, the evolutional characteristics and the mechanism of acoustic softening on material deformation is still not clear. And in most previous studies only the average stress but not the oscillatory stress was measured due to the convenience of dynamic force sensing system, which confused the different ultrasonic volume effects, acoustic softening, stress superposition and ultrasonic impact. The purpose of this study is to investigate the effects of acoustic softening on micro/meso-compression behavior and microstructure evolution. An ultrasonic-assisted compression test system with dynamic force sensing technology was developed. And a series of ultrasonic-assisted micro/meso-compression tests at different amplitudes were carried out on pure copper C1100O combining the microstructure analysis by EBSD technique. By analyzing the waveform of the oscillatory stress in the process, acoustic softening was successfully separated from the stress superposition and it was found that the deformation strain plays an important role on the effect of acoustic softening. The stress reduction by acoustic softening increases with the flowing strain or ultrasonic amplitude increasing. Besides, there is an evolutionary transition of acoustic softening ratio between small strain and large strain. When acoustic softening occurs, the low-angle grain boundaries distribute randomly in grains, compared to the piled distribution without ultrasonic assistance, implying motions of the low-angle grain boundaries or dislocation is improved by acoustic softening, resulting in the real stress reduction. In addition, with small deformation strain, the elongated grain becomes equiaxed and dislocation density is significantly reduced, which may be the result of the increased dislocation annihilation due to ultrasonic-induced dynamic recovery. However, with the deformation strain increasing to some extent, acoustic hardening gradually becomes significant, leading to much less effectiveness of acoustic softening on dislocation density reduction. The findings of this study provide an instructive understanding of the underlying mechanisms of acoustic softening in ultrasonic-assisted micro/meso-forming.

This study presents a structuration approach to reach a high luminous transmittance ( T l u m) and solar modulation efficiency ( Δ T s o l) of thermochromic vanadium dioxide ( VO 2) thin films. Before starting optical simulations, we confirm that the optical properties of monoclinic VO 2 continuous films deposited by reactive magnetron sputtering show a good correspondence with numerical results. Then, calculations on ordered VO 2 nanostripes demonstrate an enhanced transmittance due to the presence of vertical openings, leading to a variety of photonic effects. A series of optimizations by varying the column width, period, and film thickness establishes that 20 nm wide and 10 nm separated nanostripes have a Δ T s o l of 14.2% and a T l u m of 47.6% for a film thickness of 250 nm. In comparison to a dense film without nanostructuring, the film transparency (related to T l u m) is significantly enhanced, while Δ T s o l remains unchanged. Furthermore, this also translates into a favorable, less opaque color, so the geometry could be useful for various thermochromic applications, such as smart windows.

High power impulse magnetron sputtering (HiPIMS) is an ionized physical vapor deposition technique, providing a high flux of metal ions to the substrate. However, one of the disadvantages for industrial use of this technique is a reduced deposition rate compared to direct current magnetron sputtering (dcMS) at equal average power. This is mainly due to a high target back-attraction probability of the metal ions with typical values in the range 70%–90% during the pulse. In order to reduce this effect, we focused on the contribution of ion fluxes available immediately after each HiPIMS pulse; a time also known as afterglow. Without a negative potential on the target at this stage of the HiPIMS process, the back-attracting electric field disappears allowing remaining ions to escape the magnetic trap and travel toward the substrate. To quantify the proposed mechanism, we studied the effect of HiPIMS pulse duration on the outward flux of film-forming species in titanium discharges, which are known to exhibit more than 50% reduction in deposition rate compared to dcMS. By shortening the HiPIMS pulse length, it was found that the contribution to the outward flux of film-forming species from the afterglow increases significantly. For example, HiPIMS discharges at a constant peak current density of about 1.10 A cm−2 showed a 45% increase of the deposition rate, by shortening the pulse duration from 200 to 50 μs. Ionized flux fraction measurements, using a gridless quartz crystal micro-balance-based ion meter, showed that this increase of the deposition rate could be achieved without compromising the ionized flux fraction, which remained approximately constant. The key to the achieved optimization of HiPIMS discharges lies in maintaining a high peak discharge current also for short pulse lengths to ensure sufficient ionization of the sputtered species.

(Ti, Al)N films were deposited inside 1 mm scale small holes from a Ti 0.33 Al 0.67 alloy target by high-power impulse magnetron sputtering (HiPIMS). To investigate the transport behavior of sputtered and gas species of ternary nitride into the small hole structure and its effect on the chemical and phase compositions of the films grown on the inner side walls, the deposition was performed under inert working gas pressures of 0.5, 1, and 2 Pa with a fixed pulse length of 50 μs and a frequency of 1 kHz. Optical emission spectra revealed the pressure dependence of the ion-to-neutral fraction for titanium, showing an increasing fraction at a higher working pressure. The highest fraction of Al/(Al + Ti) was obtained at 0.5 Pa, while the lowest value was obtained at 1 Pa. This pressure dependence is discussed by considering the degree of thermalization from the viewpoint of mass differences between Al, Ti and the gas species. Under ballistic transport at 0.5 Pa, the high degree of ionization of the HiPIMS discharge further enhances the film coverage at a greater depth, resulting with an aspect ratio of 2.7, and a higher Al fraction was obtained even at a greater depth of 2 mm. The films deposited at 0.5 Pa had a high Al content with mixed cubic and wurtzite phases of (Ti, Al)N and exhibited a hardness of 35 GPa even on the inner walls of the small holes. The influence of the degrees of ionization and thermalization of the sputtered species in the growth of ternary nitride films on a high aspect ratio geometry was demonstrated.

Conventional ultrasonic-assisted forming in macro scale has been studied widely for decades. However, ultrasonic dynamic impact effect, which only occurs in micro-scale, has never been studied thoroughly. The purpose of this study is to investigate and identify the influencing parameters of amplitude and vibration time for the ultrasonic-induced stress reduction considering dynamic impact effect. As the first step for the purpose, commercially pure aluminum 1100 with specimen size of 2 mm in diameter and height were selected for ultrasonic-assisted compression tests with varying amplitude and press speed. Ultrasonic-induced stress reduction was evaluated and the contour shape of deformed specimens was compared to obtain the effect of ultrasonic vibration on material deformation. The results showed that, ultrasonic dynamic impact effect was the dominating mechanism for stress reduction in compression condition, the stress reduction which caused was nearly 5 times of the sum by stress superposition and acoustic softening. The ratio of amplitude to specimen height is identified as an influencing index for occurrence of ultrasonic dynamic impact effect, for which the critical value equals to half of yield strain. The findings showed promising prospect of ultrasonic vibration in micro-forming, which helped to provide a basis to understand the underlying mechanism of ultrasonic-assisted micro-forming and design the process in next step.

In the present study, to observe the contact interface during sheet metal forming process, in-situ observation system using transparent silica glass dies and high speed recording camera was developed. To correlate the dimensional parameters of micro-textured structures and tribological properties during the forming operation, in-situ observation during ironing process of stainless steel sheet with a thickness of 0.1 mm was performed. Tribological behavior was compared between the different dimple structures under different contact state. Dimple structure arrays with diameters of 10, 50, 100 µm were achieved by using femto-/pico-second laser processing. As results, the textured die with dimple diameters of 10 and 50 µm showed the lubricant flow transferred from one to the other dimple structures, in which hydrodynamic pressure seems to generate inside the dimples, while that of 100 µm indicated the less supply of lubricant. However, for the textured die with a dimple diameter of 10 µm demonstrated higher ironing force than that of 50 µm, due to the coverage of dimple structures by generated wear debris during the forming process. Based on these experimental findings between different contact states, the principle in generation of hydrodynamic pressure, the function of micro-trap for wear debris and the micro-reservoirs effect for lubricant retention depending on the size of dimple structures were discussed by correlating with the in-situ observation results.

Application of resistance heating in micro forming processes is effective for improving formability of thin foils and accuracy of products. Current flows to thin foils can achieve a rapid heating time with very low heating energy owing to the size effect of heat capacity and electrical resistance. To control the temperature distribution of such as thin foils, the heating property depending on the dimensions and electrical resistance of the workpiece has to be taken into account. Furthermore, the positioning of electrodes and shape of the products might affect the current distribution. In this study, a novel heating system, controlling the electrical resistance of die surface by using high density plasma nitriding and annealing processes, was proposed. In addition, finite element (FE) analysis was applied to simulate the heat temperature evolutions in dies and heat transfer to workpieces for designing this heating system. As results, the nitrided layer in depth of 50 μm with a nitrogen concentration of 9 at.% in a steel die was achieved by this nitriding process. After annealing of this nitride layer, the electrical resistance increased to 3*106 Ω. By using this nitrided tool steel die a workpiece of a SUS304 sheet in thickness of 0.1 mm was successfully heated to around 700 °C with the heat convection from the die, which a current of 40A was applied.

Strain gradient is known as an important factor that influences springback of bent components in microscale. Compared with thicker foils, thinner foils usually indicate more strain gradient due to non-uniform material deformation. A resistance heating (RH) method is an effective approach to obtain homogenous material flow by heating foils within only several minutes. To predict springback of foils bent at elevated temperatures, an investigation of the influence of strain gradient on springback is indispensable. To achieve this, microbending tests assisted by RH were conducted at different temperatures ranging from 298 to 723 K in the present study. 0.05 mm-thick pure Ti foils with varying grain sizes of 2.7, 14.7, and 24.5 μm were used. As results, normalized bending moment decreased with increasing temperature and with increasing grain size. The less strain gradient of the foils with larger grain size and at elevated temperatures was confirmed to be the reason according to a theoretical analysis of springback using the constitutive model considering statically stored dislocations (SSDs) and geometrically necessary dislocations (GNDs). The predicted normalized bending moment by theoretical calculation showed good agreement with experimental results at the temperature of 573 K or higher but not at the temperature lower than 573 K. It was found that the springback of the foils was influenced by the strain gradient at low temperatures. Furthermore, the size effects caused by strain gradient reduced as the bending temperature increases.

The demand of microforming is increasing as one of the economical production methods for small metallic parts. However, the formability of metallic foils decreases with decreasing ratio of thickness to grain size. In the present study, a process combining step motion and ultrasonic vibration is proposed to enhance the formability by stress relaxation. To investigate the effect of stress relaxation on forming limit of metallic foils in different stress states, micro bulge tests were carried out. The material used was brass foils with a thickness of 0.03, 0.05 and 0.08 mm. For calculating the strains of the deformed specimens, a pattern of dots with a diameter and a pitch of 50 and 60 μm was fabricated on the surface of the specimens by photolithography. The results of micro bulge tests showed that the forming limit increases by the stress relaxation regardless of stress states, except for the foil with a thickness of 0.03 mm. The possibility of enhancing the formability of metallic foils by stress relaxation was experimentally demonstrated.

The occurrence of size effects in microforming process influences the accuracy of the products significantly. To investigate the scale effect and the mechanism of springback behavior of thin pure titanium (Ti) foils bent at elevated temperatures, scaled microbending processes assisted by resistance heating are performed for the foils with different thickness of 0.02, 0.05, and 0.1 mm. It is found that the springback angle increases with decreasing foil thickness at room temperature. However, after bending at elevated temperatures, the springback angle is found to decrease with decreasing foil thickness. Due to the lower flow stress of surface, the influence of surface area is thought to be the dominating factor that results in the less springback of thinner foils at elevated temperatures. To confirm this and to predict the springback angles at elevated temperatures, a new theoretical model of surface area increasing with increasing temperature is proposed. The springback angles are calculated by theoretical analysis using conventional plastic theory and the proposed model. As temperature increases, the large reduction of springback angles compared to 298 K can be captured by using the proposed model successfully. The validity of the proposed model is confirmed.

This chapter introduces several investigations including development of novel processes including combining micro press-forming and automatically assembling in a progressive die for fabrication of micro devices, heat-assisted forming, dieless tube forming, and coating system for micro-die adapted to microforming. Micro parts in several hundreds of micrometers and a micro pump in several millimeters were made by using this microforming technology. Several investigations were carried out to indicate the advantages of heating-assisted microforming for improving and formability of workpiece and accuracy of the product. The heat-assisted microforming system with resistance heating was designed to satisfy low energy consumption and high forming accuracy to heat only the workpiece material and to limit the heat transferring to tools. Microtube which is one of the important micro components is used in various applications such as a painless injection needle and stent, heat exchanger, and micro nozzle. The chapter discusses the die surface treatment toward the final goal of the achievement of lubricant-free microforming.

Anisotropic heterogenous Ni/NiO nanoparticles with controlled compositions are grown using a high-power pulsed hollow cathode process. These novel particles can be tuned to consist of single-phase Ni via two-phase Ni/NiO to fully oxidized NiO, with a size range of 5-25 nm for individual crystals. A novelty of this approach is the ability to assemble multiple particles of Ni and NiO into a single complex structure, increasing the Ni-NiO interface density. This type of particle growth is not seen before and is explained to be due to the fact that the process operates in a single-step approach, where both Ni and O can arrive at the formed nanoparticle nuclei and aid in the continuous particle growth. The finished particle will then be a consequence of the initially formed crystal, as well as the arrival rate ratio of the two species. These particles hold great potential for applications in fields, such as electro- and photocatalysis, where the ability to control the level of oxidation and/or interface density is of great importance. Funding Agencies|Knut and Alice Wallenberg Foundation [KAW 2014.0276]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Tokyo Metropolitan University; Linkoping University

Magnetic nanoparticles with average size 30 nm were utilized to build three-dimensional framework structures—nanotrusses. In dual-phase Ni/NiO nanoparticles, there is a strong correlation between the amount of magnetic Ni and the final size and shape of the nanotruss. As it decreases, the length of the individual nanowires within the trusses also decreases, caused by a higher degree of branching of the wires. The position and orientation of the non-magnetic material within the truss structure was also investigated for the different phase compositions. For lower concentrations of NiO phase, the electrically conducting Ni-wire framework is maintained through the preferential bonding between the Ni crystals. For larger concentrations of NiO phase, the Ni-wire framework is interrupted by the NiO. The ability to use nanoparticles that are only partly oxidized in the growth of nanotruss structures is of great importance. It opens the possibility for using not only magnetic metals such as pure Ni, Fe, and Co, but also to use dual-phase nanoparticles that can strongly increase the efficiency of e.g. catalytic electrodes and fuel cells.