Hideki Kyogoku

Shape Memory Characteristics of Ti-Ni Alloy Using Mechanically-Alloyed Powder

In this research, we investigated the fabrication conditions of Ti-Ni alloy powder by MA process and the shape memory characteristics of the sintered alloy by a pulse-current sintering equipment using mechanically alloyed powder (MA powder). The microstructure of the sintered alloy of the MA powder was more homogeneous than that of the alloy of the elemental powders. The application of the MA powder makes the width between transformation temperatures of the shape memory treated alloy of the MA powder became narrower, that is, it improves the temperature response of the compact. The tensile strength and elongation of the shape memory compact of the MA powder were approximately 780 MPa and 7.5 %, respectively. This is one of the superior tensile properties of SMA compact fabricated by powder metallurgy process. The superelastic behavior took place in the alloy of the MA powder. Thus, the MA process in short process time resulted in lower contamination of the MA powder and the application of the MA powder resulted in superior shape memory characteristics of the sintered alloy.

Fabrication of Ti-Sn-Cr Shape Memory Alloy by PM Process and its Properties

Ti-Sn-Cr shape memory alloys were fabricated by the powder metallurgy (PM) process. The mixed powders in composition of Ti-3at%Sn-7at%Cr were prepared using a V-blender. The mixed powders were filled into a graphite die, and then sintered at a temperature between 1023 K and 1223 K using a pulse current sintering equipment. The sintered alloy was solution-treated and then aged. The phase structure and the tensile properties of the alloy obtained were investigated. The relative density of the as-sintered alloy increased with elevating sintering temperature, and the maximum relative density was 99.5 % at a sintering temperature of 1223 K. Although the as-sintered alloy was high density, the microstructure of the alloy was inhomogeneous. Thus it was found that the solution treatment was needed to obtain the homogeneous microstructure of the alloy. The alloy which is mainly consisted of the β phase was obtained by performing solution treatment. The plateau region due to the slip deformation was observed in the stress-strain curve of the solution treated alloy, but that due to the stress induced martensite transformation could not be done. The plateau region due to the stress induced martensite transformation, however, was appeared in the stress-strain curve of the aged alloy. This means that the aged alloy has shape memory properties. It was also found from the result of bending test that the alloy fabricated by the PM process has obviously shape recovery properties.

Influence of Cyclic Deformation on Shape Memory Characteristics of Ti-Ni-Cu Alloys Fabricated by Pulse-Current Pressure Sintering Method

Ti-Ni-Cu shape memory alloy by elemental powders was fabricated by using a pulse-current pressure sintering method, and it was subjected to solid-solution heat treatment after sintering to homogenize the microstructure of the alloy. The influence of the thermo-mechanical cyclic deformation on the shape memory and thermo-mechanical characteristics of Ti-Ni-Cu alloy was investigated. The thermo-mechanical cyclic deformation improved the deformation behavior of the sintered alloy and made the thermo-mechanical behavior of the alloy stable caused by the introduction of dislocations. As a result, the recovery stress of the alloy after the cyclic deformation fairly increased. The transformation temperatures of the alloy after the cyclic deformation became lower than those of the alloy before the cyclic deformation. Therefore, the superelastic-like behavior of the alloy after the cyclic deformation appeared in an isothermal tensile test at lower holding temperature.

Production of Cemented Carbide-Alumina Composite Material by Wet-Shaping Process

In this study, the characteristics of the production process of cemented carbide-alumina composite material made using the wet-shaping process were investigated. The production process in this study produced a green compact of composite material by repeating the wet-shaping process for the molding of each material, and it made possible the sintering of plural materials with varying sintering conditions at the same time, a process that was difficult until now. By using wet-shaping and ultra-fine powder, which have superior sintering characteristics, sintering conditions were found in which it was possible to sinter cemented carbide and alumina at the same time, with a sintering temperature of 1723 K and a sintering time of 5.4 ks. With these sintering conditions, the relative densities of the sintered compact of cemented carbide and alumina were 99.0 % and 98.9 %, respectively. It is clear that the characteristics of sintered compact made with these sintering conditions are superior. When the cemented carbide slurry and the alumina slurry were layered by repeating the wet-shaping process, a composite material was able to be produced by inserting an active brazing filler metal in the interface to improve the bondability of the cemented carbide and the alumina during the sintering. However, it was observed that the active brazing filler metal and the cobalt in the cemented carbide flowed out from the interface between the cemented carbide and the alumina in the sintered compact of the composite material.

Production Processes and Characteristics of Porous Alumina with Air Bubbles Introduced into Slurry

In this study, production processes for porous alumina, and the characteristics of the material, were investigated. Porous alumina was produced by a wet-shaping process in which air bubbles were introduced into the slurry. The feature of this production process is that many pores are produced by slip casting carried out using whipped slurry, where only the conditions of the slurry are adjusted. The advantage of this process is its simplicity. From the results, it is made clear that a green compact of porous alumina can be produced by changing the amount of solvent and binder, and also that a sintered compact of porous alumina can be produced by a low sintering temperature, such as 1473 K. The four point bending strength of porous alumina is about 515 MPa when the porosity is about 30 %. The excellent characteristics of the sintered compact of porous alumina are shown by the observation results of the fracture surface in this production process. The dense alumina body is sintered while maintaining the fine grains, and with the micro pores remaining in the grain boundary.

S041015 Direct Selective Laser Sintering of Tool Steel Powder

In this study, the fabrication conditions of tool steel by direct selective laser sintering were investigated. The effects of powder size, additives such as Cu and Ni powders, and laser sintering conditions on the state of laser-scanned body were examined to fabricate a sound laser-scanned body of tool steel. The optimum laser power, scan speed and scan pitch were examined by experiments. As a result, it was found that the continuously smooth single-scan track can be obtained at wider range between laser power and scan speed by using SKD11 powder below 45 μm. The smooth surface of the laser-scanned body could be fabricated at a laser power of 10 W, a scan speed of 10 mm/s and a scan pitch of 0.08 mm by using SKD11 powder below 45 μm.

Direct Selective Laser Sintering of WC-Co Cemented Carbide by Premixing of Additives

In this study, the fabrication conditions of WC cemented carbides by direct selective laser melting were investigated. The effects of additives, such as Co, Cu-20%Sn and Cu powders, and laser scanning conditions on laser sintering process were examined to fabricate a sound laser-scanned body of WC cemented carbides. The optimum laser power, scan speed and scan pitch were found out by experiments. It was found that the continuously smooth single-scan track can be obtained at a lower laser power and a higher scan speed by the addition of 30% Cu powder. The smooth surface of the laser-scanned body could be fabricated at a laser power of 9 W, a scan speed of 20 mm/s and a scan pitch of 0.05 mm.Copyright

Identification of material parameters in constitutive model for shape memory alloy based on isothermal stress-cycle tests

Publisher Summary When a shape memory alloy (SMA) is isothermally loaded, it exhibits pseudoelasticity at high temperature and reversible shape memory effect at low temperature. Such thermo–mechanical behavior, which is due to the martensitic transformation and its reverse transformation, is described by a thermo–mechanical constitutive model. In general, all constitutive models incorporate some material parameters to be determined from experiments. In the present work, sets of material parameters in a modified constitutive model for Ti-Ni-Cu SMA are identified. For the identification, the whole experimental data obtained from isothermal stress-cycle tests conducted at various temperatures are employed simultaneously. This approach allows one to determine the phase transformation temperatures directly from the identification as two additional material parameters, while they are usually obtained only by some special experimental techniques such as DSC (differential scanning calorimetry).