Toshio Sakuma

Influence of Cold Working on Deformation Behavior and Shape Memory Effect of Ti-Ni-Nb

Thermo-mechanical characteristic of shape memory alloy depends on cold working and heat treatment, because these processes can control the amount of defects including dislocation and precipitation [1]. In this study, the influence of cold working on the deformation behavior and the transformation characteristics was investigated on the Ti-Ni-Nb shape memory alloy (SMA). Both the tensile test and the shape recovery test were performed for the wire specimens of 1mm in the diameter with some different rates of cold working. The shape recovery tests were performed for the wire specimens of different cold working rates until the various levels of maximum applied strain, and the reverse-transformation characteristics on the process of heating after unloading were studied. It is clarified that the higher cold-working rate improves the shape memory properties of the alloy.

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.

Effects of Pre-Strain and Nb Content on Transformation Temperatures in Ti-Ni-Nb Shape Memory Alloy

Ti-Ni-Nb shape memory alloy has a wide transformation hysteresis, and has been used as coupling devices and so on. However systematic researches of the influence of the amount of Nb addition on transformation temperatures are few. The purpose of this work is to clarify the influences of pre-strain and Nb content on transformation temperatures in Ti-Ni-Nb shape memory alloys. The specimens were Ti-Ni-Nb alloys (Ni/Ti=1.0, Nb=0-15at%), annealed at 1223 K for 0.3 ks. The variation of transformation temperatures with pre-strain and Nb content were investigated experimentally. The variation of As, Ms and transformation temperature hysteresis with pre-strain and Nb content will be discussed in relation to the elastic strain energy and the volume fraction of slip-deformed martensite.

Thermo-Mechanical Characteristics of Ti-Ni-Cu Shape Memory Alloy Fabricated by Pulse-Current Pressure Sintering Method

The Ti-Ni-Cu shape memory alloy by elemental powders was fabricated by means of a pulse-current pressure sintering method that can produce high-density sintered compacts in a very short sintering time. The fabrication conditions of Ti-Ni-Cu alloy and the influence of Cu content in Ti-Ni-Cu alloy on the tensile properties and thermo-mechanical characteristics were investigated. The relative density of the as-sintered compacts was around 97% at any Cu content. The microstructure, tensile properties and thermo-mechanical characteristics of the as-sintered compacts were improved greatly by performing a solid solution heat-treatment. The yielding behavior due to the stress-induced martensite in stress-strain curves of the alloy took place after elastic deformation at any Cu content. The deformation resistance of the alloys changed with Cu content, and it was lowest around 9at% in Cu content. The tensile strength and elongation of the alloy with Cu content around 9at% were more than 400 MPa and 6%, respectively. It was found that the thermo-mechanical behavior of the alloy becomes stable by performing cyclic deformation.

Sound Attenuation due to Plural Plates in Water.

In order to prevent the expansion of tube damage and to maintain structural safety in steam generators(SG) of a liquid metal fast breeder reactor (LMFBR), it is necessary to detect precisely and immediately the leakage of water from tubes of heat exchangers. The active acoustic detection method, which detects the sound attenuation due to bubbles generated by the sodium-water reactions, has attracted interest owing to its short response time and being least affected by background noise. Sound attenuation is also subjected to structures such as heat transfer tubes and shrouds. Accordingly, it is necessary to evaluate the sound attenuation due to structures. However, studies concerning these aspects are very few. In this paper, using the water bath, the attenuation characteristics of sounds due to flat plates are investigated and discussed under various conditions such as thickness, location, and number of flat plates.

Evaluation of Static Strength of Cu/Si3N4 Functionally Gradient Materials.

In order to ensure reliability of the thermoelectric module, we had applied a FGM layer with composition of Cu and Si3N4 to the bonding parts in the module and decided the functionally graded compositional profile based on numerical analysis. In this study, Cu/Si3N4 functionally gradient material and Cu/Si3N4 composite materials were fabricated by hot press (HP) and static strength at room temperature was evaluated. As a result, it was found by observation with an optical microscope that neither FGM nor the composite materials produced by HP had internal defects. Static strength of composite materials obtained by the 4-point bending test exhibited a lower value as compared with those based on the rule of linear mixture. Finite element analysis for the FGM was performed. It was shown that fractured stress and initiation site of cracks could be predicted by using the fracture criterion for the bending strength of the composite materials.

Active Acoustic Leak Detection for LMFBR Steam Generator. Sound Attenuation due to Bubbles.

In the steam generators (SG) of LMFBR, it is necessary to detect the leakage of water from tubes of heat exchangers as soon as it occurs. The active acoustic detection method has drawn general interest owing to its short response time and reduction of the influence of background noise. In this paper, the application of the active acoustic detection method for SG is proposed, and sound attenuation by bubbles is investigated experimentally. Furthermore, using the SG sector model, sound field characteristics and sound attenuation characteristics due to injection of bubbles are studied. It is clarified that the sound attenuation depends upon bubble size as well as void fraction, that the distance attenuation of sound in the SG model containing heat transfer tubes is 6dB for each two-fold increase of distance, and that emitted sound attenuates immediately upon injection of bubbles.

The Principle and Trial Apparatus of Piston Type Shape Memory Heat Power Generation.

In this paper, the new electric power generation system by piston type solid phase heat engine using shape memory alloy is proposed. The proposed system is developed by authors for the purposes not only of establishing new power generation technologies utilizing thermal energy of low temperature region but also of making this new technologies available for practical use. The followings are described.(1) The trial apparatus based on the proposed principle is manufactured as a new power generation system, whereby life becomes long, is made compact size and thus weak points of prevailing systems are corrected. Furthermore, proposed principle is proved by generating successfully the trial appartus.(2) The test results show that the proposed system can be useful for middle load power station when the system is connected to power transmission line.(3) Valuable test results are obtained regarding characteristics on a method of using shape memory alloy for heat engine.