Selective laser melting (SLM), a kind of additive manufacturing (AM) technologies, enables to fabricate highly complicated 3-dimensional structures from a powdered metallic materials. Recent investigations demonstrated the ability of SLM to form crystallographically texturized parts. Highly texturized materials exhibit anisotropic functions; therefore, control of texture via AM is becoming attractive strategy for developing functionalized materials. In the present study, we tried to find laser conditions for formation of randomly and highly texturized parts in SLM of T-15Mo-5Zr-3Al biomedical alloy. We successfully achieved randomly and highly texturized parts under the conditions of (low laser power and low scan speed) and (high laser power and high scan speed), respectively. The highly texturized part showed anisotropy in Young’s modulus in which the value in <001> oriented direction was significantly lower than that in <011> oriented direction, the similar trend to those reported in single crystal of this alloy. The evolution of crystallographic texture was thought to be related with melt-pool shape, which needs further investigations.
Fluctuated structures were designed and fabricated by using stereolithographic additive manufacturing for fluid flows control in living environments. Through the inverse Fourier transformation, fluctuated patterns can be introduced effectively into surfaces of designed solid models automatically. Geometrically modulated artifacts composed of alumina dispersed resin were reproduced by computer aided- design, manufacture. The photo sensitive resin with alumina particles at 55 vol.% were spread on a metal substrate by a knife edge, and an ultra violet laser beam was scanned to create a two-dimensional cross section. Through automatically layer laminations, a three-dimensional object with fluctuated patterns could be fabricated. Water flows on the formed fluctuated components were simulated theoretically and evaluated experimentally.
Complicated ceramics structures were designed by three-dimensional computer graphics and fabricated by using
Stereolithographic processes. Photosensitive acrylic resin including with the ceramics particles were spread on a substrate by using a mechanical knife edge. An ultraviolet laser beam of 355 nm in wavelength was focused into 100 μm in diameter and scanned to draw a cross sectional solid pattern. A composite precursor was obtained successfully thorough continuous laminations. The ceramics component could be created by dewaxing and sintering. In this investigation, sound absorption structure with structural property of Helmholtz chamber were designed and fabricated by this process. Sound wave generated by thermal spraying was controlled by the Helmholtz structure. The frequency spectra were plotted by computational fluid dynamics and acoustic simulation. According to the theoretical procedure, a soundproof equipment for gas flame noise from thermal spraying were designed and fabricated by stereolithography.
Alternative current TIG welding is a common way to joint aluminum for the use of the oxide cleaning action by cathode spots. In order to improve the efficiency of the oxide cleaning through the control of the cathode spot, the cathode spot behaviors should be clarified in detail. For this purpose, an observation of the oxide cleaning action in helium TIG welding was carried out by a highspeed camera. Here, the behaviors of cathode spots were elucidated by tracking the movement of them in the observation. As a result, the new cathode spots were found to be generated only from the division of the old cathode spot. This division took place continuously around the radial distance of 3.5mm from the center of weld pool. Most of the cathode spots generated there tended to move outward at average velocity decreasing from 200 m/s to 20 m/s with the radial distance. Arriving at the white zone, they suddenly decelerated around the radial distance of 5.5 mm to become gradually weak and then finally disappear. The probability of the generation of the cathode spot except for in the vicinity of the weld pool center was hence seen to be very low. Consequently, the general tendency of the life cycle of the cathode spot from the generation to the disappearance was clarified through the quantitative evaluation of the distribution and velocity of the cathode spot.
The aim of this study is to obtain the high fatigue strength of 0.35%C-1%Mo sintered steel by the combination process of primary-sintering（PS）, cold-forging（CF）, carburizing and carbonitriding, quenching and tempering.
The impact energy of the PS specimen increases exponentially at high PS temperatures. It becomes very high in case of the conditions of PS density of 7.4 Mg/m3 and PS temperature ranging from 1075℃ to 1100℃. Also, the impact energy depends on the volume diffusion in the sintered material and it was found that the impact energy is directly proportional to logarithm of the diffusion length of Fe atoms in γ-Fe.
From investigations of both the impact load profile and the microstructure of PS-CF specimens, it was found that micro-cracks occur on the surface layer of specimens by CF load, irrespective of PS conditions: PS temperature, PS time and the density. These micro-cracks weaken the heated PS-CF specimens. Since the heat treatment leads the diffusion bonding of micro-cracks in the surface layer, the cracks can be recovered. When the PS-CF specimens were heated by the suitable second sintering and vacuum carbonitriding, both the superior impact energy and the superior fatigue limit of bending strength were obtained compared to those of wrought steel SCr420H. The results would not be obtained only by the suitable PS-CF processes, and show that the combination of heat treatments have the synergistic effect of micro-cracks recovery and pore spheroidizing, along with microstructure modification.
In the field of circuit boards, a paste technology making it possible to develop a new interconnection technology is highly requested. In this study, we worked on the realization of a new metal-bonding-type conductive paste supplementing the weakness of the conventional via-filling one. This conductive paste is a complete melting-point-changing-type paste in which large spherical copper (Cu) powder (particle diameter of 25 to 50 μm) is used as a conductive filler and an alloy of tin (Sn) and bismuth (Bi) is coated on its surface. It distinguishes itself from the previous ones by the absence of metallic components since it is only composed of Cu coated with Sn-Bi. This paste not only ensure a high connection reliability between multilayer circuit boards, but also does not re-melt after two or more unavoidable thermal exposures needed throughout the production process. In this paper, we evaluated the thermal properties of the Cu filler alloying used in this conductive paste. An observation of the alloying made of a Cu core coated with Sn-Bi showed that its thermal property depended on the thickness of the layer. Provided this result, a Sn-Bi alloy which doesn't re-melt was found by analyzing the thermal properties of different thicknesses of the same alloy and observing the variation of the melting-point during the re-heating.
Nowadays advanced board structures are made of two different circuit boards interconnected to each other. As these circuit boards are made of different materials and have to go through different manufacturing processes, the use of a specific conductive paste is needed for a reliable interconnection. To realize this complex structure, we worked on the development of an innovative conductive paste overcoming the weaknesses of the conventional one. It is a melting-point-change type conductive paste in which a large spherical copper (Cu) powder is used as a conductive filler and an alloy of tin (Sn) and bismuth (Bi) is coated on its surface. The conductive paste is expected to stabilize the bonding by tolerating the scatter of the thickness, it also has to maintain a long-term electrical reliability. In this paper, we determined the fundamental composition of the paste to answer these needs. To evaluate the performance of the bonding we studied the influence of the electrical reliability of the paste at its optimum bonding condition, the aggregability of the resin and the bonding strength. Finally, we created a complex structure with the paste to analyze the tolerance of the bonding height and its electrical resistance through a thermal cycle (TC) test.