Zenjiro Yajima

Effects of microstructure on mechanical fatigue crack growth characteristics of a Ti–Ni–Co shape memory alloy

Abstract Crystal structure and mechanical fatigue crack growth characteristics of a Ti–49.7at.%Ni–1.38at.%Co alloy at 295±1 K were investigated as a function of heat-treatment. The crystal structure of the alloy aged at 723 K was examined by using an X-ray diffractometer, and the lattice constant and crystallographic axis angle were determined to be a=0.3014 nm and α=β=γ=90, respectively. The fatigue crack growth characteristics of the alloy were examined for center-cracked-tension type specimens by using a computer controlled servo-hydraulic type machine. The fatigue crack growth characteristics of the 723 K aged alloy were comparable to those of the as-rolled alloy, and, for the same stress intensity factor range, the crack growth rates of the aged and as-rolled alloys were equivalent within experimental error. Therefore, the martensitic transformation temperature appears not to influence the fatigue crack growth characteristics. Fatigue fracture surfaces of the two alloys were examined by using a scanning electron microscope with a field emission electron gun, and striation patterns were observed on them. The micro crack growth rate estimated from the striation patterns was in good agreement with the crack growth rate, dl/dN, obtained from the examination of center-cracked-tension type specimens.

Magnetic Properties and Microstructures of Rapidly Solidified FePd Alloy Ribbons

It is well known that FePd alloys are effective as a magneto-thermoelastic actuator material, because they have large magnetostriction and shape memory effect. In order to use the alloys for a micro-actuator, magnetic properties and microstructures have been examined as for rapidly solidified Fe-29.6 at% Pd alloy ribbons. The ribbons exhibit a large magnetostriction at room temperature and good shape memory effect. Magnetostriction and coercive force of the ribbons markedly depend on the direction of the applied magnetic field. Maximum values of magnetostriction and coercive force are obtained at θ = 85 degree (θ is the angle between the magnetic field and the ribbon plane). Relief effects corresponding to the formation of FCT martensite variants are observed on the grains. X-ray diffraction profile at room temperature shows that FCT martensitic phase and FCC parent phase coexist in the ribbon. Dense striations are observed in the TEM bright field images of FCT martensite plates. Selected area electron diffraction patterns revealed the striations to be thin twins.

Simultaneous Sterilization With Surface Modification Of Plastic Bottle By Plasma-Based Ion Implantation

Dry sterilization of polymeric material is developed. The technique utilizes the plasma‐based ion implantation which is same as for surface modification of polymers. Experimental data for sterilization are obtained by using spores of Bacillus subtilis as samples. On the other hand we previously showed that the surface modification enhanced the gas barrier characteristics of plastic bottles. Comparing the implantation conditions for the sterilization experiment with those for the surface modification, we find that both sterilization and surface modification are simultaneously performed in a certain range of implantation conditions. This implies that the present bottling system for plastic vessels will be simplified and streamlined by excluding the toxic peroxide water that has been used in the traditional sterilization processes.

Magnetoelectric Effect of Fe70Pd30 Ferromagnetic Shape Memory Alloy Film: Lead Zirconate Titanate Trilayer Composites at Low and High Magnetic Field Frequencies

Magnetoelectric (ME) coupling in multiferroic composites of Fe70Pd30/lead zirconate titanate (PZT)/Fe70Pd30 trilayers was investigated. An Fe70Pd30 ribbon and Fe70Pd30 films were prepared by rapid solidification and sputtering techniques, respectively. The saturated value of magnetostriction of the ribbon 30 µm in thickness was 95 ppm at a steady magnetic field of 200 Oe. Those of the films were 22 to 67 ppm depending on the film thickness. The output ME voltage VME of the trilayer composites, which was measured at a driving ac magnetic field Hac at 1 Hz, increased with increasing magnetostriction. The VME of the ribbon/PZT/ribbon composite exhibited a very large peak at a resonant frequency of 64 kHz and responded to an Hac of 0.0025 Oe. However, for the film/PZT/film composite, VME linearly increased with increasing Hac in a wide frequency range of 1 to 104 Hz.

Influence of Substrate Temperature on Texture for Deposited TiNi Films

In order to fabricate two-dimensional micro actuators with shape memory alloy films, it is especially important to evaluate the anisotropy of transformation strain that is caused by texture. In this paper, microstructures of sputter-deposited TiNi films are examined. The films of 1 μm in thickness are sputter-deposited on Si(001) substrates by RF magnetron multi-sputtering system equipped with four separate confocal sources as well as with substrate heating. Pure Ti and Ni targets of 50 mm in diameter are used for the sources. The films deposited at ambient temperature have been generally amorphous. However, we find that some films which are deposited at 773K of substrate temperature are crystalline, when we appropriately choose sputtering parameters such as source voltage and the distance between a target and the substrate. X-ray powder diffraction and pole figure measurements reveal that these films are oriented with {110}B2 parallel or inclined at 45 degree to the substrate. Furthermore, we also find that crystallized film is deposited even at 673K of substrate temperature by applying pulse bias voltage to the substrate.

X-RAY EXAMINATION OF FATIGUE FRACTURE SURFACES OF NODULAR CAST IRON

ABSTRACT The fatigue tests were conducted by using compact tension (CT) specimens of nodular cast iron. The line broadening of X-ray diffraction profiles was measured on and beneath fatigue fracture surfaces. The amount of plastic strain and the depth of the plastic zone left on the surface were evaluated from the line broadening. The main results obtained in the present study are summarized as follows: (1) The depth of the maximum plastic zone wy was determined on the basis of the distributions of the half-value breadth. It was related to the maximum stress intensity factor Kmax (MPam) divided by the monotonic yield strength σY (MPa) by where α=0.08 for the case of fatigue and α=0.13 for the case of monotonic fracture. (2) The published data on the α-value determined for various kinds of steels are the following function of the yield strength σY (MPa): α = 0.15 [σY/(143 + 0.772σY)]2

Crystallizing compound film on plastics by ion irradiation in plasma

Micro machines are expected in advanced medical instruments for micro surgery. Typical materials for the actuators are shape memory alloys such as TiNi(titanium nickel) and piezoelectric compounds such as PZT(lead zirconate titanate). For future medical application the materials will be required to be deposited directly on the surfaces of plastics in the form of crystalline thin film, since most medical instruments such as catheters for blood vessel surgery are made of polymeric plastics. Then the film will be finished into some micro actuators.

Low Temperature Crystallization of Sputter-Deposited TiNi Films

We have found that deposited film can be crystallized without the post-annealing treatment but with the simultaneous ion-irradiation during sputter-deposition at very low substrate temperature. The present paper reviews the low temperature crystallized TiNi films deposited by the above technique. An RF magnetron sputtering apparatus equipped with separate confocal sources as well as with a heating and ion-irradiating system for substrates was used to make the films crystalline. Without using the ion-irradiating system, the films deposited on ambient-temperature substrate have been amorphous. However, crystallized film is deposited even at 353 K of substrate temperature with using the system. Appropriate ion-irradiation is considered to be help to crystallize the film at low substrate temperature. Broad and doublet X-ray diffraction profile of the film, which was diffracted from B19’ and/or R phase, was recorded between 42 degree to 45 degree in 2 theta. The crystallized film deposited on a polyimide sheet was cut into the shape of a double-beam cantilever and the ends of the two beams were connected to an electrical power supply. The cantilever shows a repeatable two-way motion by electrical cycle of 0.1 Hz at room temperature.

Load Variation Effect on Crack Growth of Stress Corrosion in High Strength Steel

The effect of the load variation on the crack growth behavior in stress corrosion cracking (SCC) was examined. When the K-value was raised, the crack growth rate immediately became the rate obtained in constant X-tests. On the other hand, when the X-value was partially reduced from to k2 to k1 the incubation time was observed before the crack started growing under k1-value. The threshold stress was also found to increase due to over loading. The incubation time tin was expressed as a second power function of ΔK=k2-k1 the relation between tin and ΔK was unaffected by stress variation sequences tested, i.e. K2→K1, K2→O→K1 and K1→K2+K 1 . The experimental relation was discussed in relation to the residual distribution due to load variation.

Crystallizing metal compound film on plastics by plasma-based ion implantation

It has been difficult to sputter-deposit crystalline compound directly on a substrate of low heat-resistant material like polymer. In this study a new apparatus is developed which deposits metallic compound film in crystalline structure directly on a substrate at lower temperature than 200°C (473K). The apparatus consists of a magnetron-sputtering deposition system with multi targets as well as of an ion irradiation system which has the same constitution as the plasma-based ion implantation, although the applied voltage is much lower. The crystallization on a low temperature substrate is assumed to arise from the simultaneous irradiation of ions extracted from plasma. In this report very low temperature crystallization of titanium nickel on polyimide substrate at 80°C (353K) was achieved by reducing the substrate heating due to the ion irradiation. The shape memory effect of the sheet was confirmed.