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Cu–4.2 at. % Ti alloy sheets with the dimension of 10 × 10 × 0.15 mm3 were irradiated with 2 MeV electrons at 200 and 250 °C, and the Vickers hardness was measured as a function of electron fluence. The hardness increased by the electron irradiation. The increase in hardness depends on the electron fluence and irradiation temperatures. The hardening induced by the electron irradiation was observed not only at the directly irradiated surface but also at the reverse side of irradiated surface. By masking an area of specimen surface with a thick copper sheet, we could modify the hardness only for the unmasked area. The atom probe tomography (APT) and the field-emission scanning microscope (FE-SEM) were used for the observation of the microstructures of the specimens. The image of FE-SEM suggests that Ti-rich small precipitates are produced by the irradiation. The present result shows that the electron beam irradiation at elevated temperatures can be a useful tool for improving the hardness of designated areas in bulk Cu–Ti alloys.

ABSTRUCTPositron lifetime and Doppler broadening measurements were carried out at a low temperature, 100K, for B2-type intermetallic compounds FeAl with composition ranges from 41.2 to 50.7 at%Al systematically in order to clarify the feature of lattice defects of the alloys. Quenching temperature dependences of positron lifetimes ranging from 573 to 1173 K was examined for alloys with 41.2, 49.0 and 50.7 at%Al. Two lifetime component analyses could not be made except for a few spectra, indicating a saturation trapping of positrons at atomic vacancies. The mean positron lifetimes are in a range of 175–195 psec, which are not corresponding to vacancy clusters but to mono and/or di-vacancies. The tendency for S-parameter to increase with increase in Al content was found. This suggests that such an increase of S-parameters is attributed to change in the fraction of atoms around the vacancies, not to increase in vacancy concentration.

Samples of Ti and Zr metals have been carbonized or nitrided at high temperature by means of reactive plasma processing. Thickness and hardness of modified layers increased with the processing temperature and time in an experimental range below 1500°C for less 5h. The maximum hardness of TiC-layer modified at 1300°C for 3h was about 5000Hv(kg/mm2) and the maximum thickness of ZrC-layer formed at 1400°C for 5h reached about 100μm. A TiC-layer was analyzed with EPMA, XRD, EXAFS and PAS(Positron Annihilation Spectroscopy). It was confirmed that the sub-surface layer of Ti metal was the mixture of TiC ceramics and Ti metal, and that the thickness of TiC with NaCI type structure was very large.

Change in free volume reflects various properties such as hardness and ductility of glassy alloys. The electron- and ion- irradiations affect the free volume of ZrCuAl bulk glassy alloys that is associated with the mechanical properties. In this study, as-quenched Zr50Cu40Al10 bulk glassy alloys and structural relaxed one by annealing for 5 hours at 673K below glass transition temperature (Tg) were irradiated by 8 MeV electrons with a maximum fluence of about 2×1018 e−/cm2 at room temperature. The behaviour of free volume in these samples was investigated by positron annihilation techniques. X-ray diffraction measurements showed that no crystallization occurred after the irradiation. We observed the positron lifetime increased by the irradiation for both as-quenched and structural relaxed samples. The increases in positron lifetime at 2×1018 e−/cm2 were 9 psec for as-quenched and 12 psec for relaxed sample, respectively. In addition, the increase in positron lifetime with irradiation fluence was clearly different for the two types of sample. These facts imply that the thermal relaxation before irradiation of Zr50Cu40Al10 bulk glassy alloy influences the radiation effects, especially the free volume change.

To synthesize Au nanorods without the use of seed crystals, we applied gamma-ray irradiation from 60Co radioactive source to reduce aqueous solution containing Au ions. The total dose was fixed to 6.0 kGy with various dose rates from 0.4 to 13.6 kGy/h. After the irradiation, two surface plasmon bands in the range around 530 nm and above 700 nm were observed in UV/vis spectra. We observed by a transmission electron microscopy (TEM) that rod-shaped Au nanoparticles with the length of 20–25 nm, and the width of about 7–15 nm were produced as well as a small amount of spherical particles. The size and the aspect ratio of the Au nanorods are well correlated with gamma-ray irradiation dose rate; with increasing the dose rate, their size decreases and the aspect ratio increases.

Lattice relaxation around an atomic vacancy has not been considered into the conventional calculations of positron annihilation lifetime. In this work, the stable arrangement of atoms around the vacancy was simulated by using the many-body potential based on the embedded atom method, and then the positron lifetime was calculated according to the method of Puska and Nieminen. Consequently, the positron lifetime in a relaxed vacancy was worked out to 170psec, 20psec lower than that in unrelaxed one.

The magnetic Compton profiles of Fe–50 at. % Rh intermetallic compound were measured to study the ferromagnetism induced by 200 MeV Xe ion irradiation. The magnetic effect at 50 K increases with increasing the ion-fluence. The analysis of the experimental result revealed that the values of spin moment induced by the irradiation were close to the values of magnetization obtained by a superconducting quantum interference device magnetometer, suggesting that the ion irradiation mainly induces the spin magnetic moment. The difference in magnetic Compton profiles between the irradiation-induced ferromagnetism and the intrinsic ferromagnetism in pure Fe is also discussed.

It is well known that structural relaxation in a bulk metallic glass affects some properties such as viscosity, electrical conductivity, and ductility. The free volume in glassy alloy, which is open volume retained by rapidly solidification from liquid state, has a significant roll for those properties. In order to discuss the nature of free volume in a Zr50Cu40Al10 bulk metallic glass, positron lifetime measurements have been performed for this metallic glass before and after annealing, and all positron lifetime spectra have been decomposed into multi components as a size distribution function by use of CONTIN-PALS II program. The positron lifetime distribution for this metallic glass has a broad spectrum comparing to crystal metal including a single vacancy, and its average lifetime corresponds to the free volume size. This width of positron lifetime (free volume size) distribution decreases by the annealing at 673 K. This change of the positron lifetime distribution can be attributed to a free volume relaxation.

The adsorption of hydrogen on transition-metal surface has been studied by both experimental and theoretical methods. Hydrogen adsorbed Ni (111) surface had measured by using slow positron beam apparatus. The positron annihilation γ-ray energy spectra emitted from hydrogen-adsorbed Ni (111) surfaces are analyzed. We have discussed the stability of the disorder phase of adsorbed hydrogens on Ni (111) surfaces. Positron annihilation results showed that the disordered phase is unstable until about 300K.

Free volume changes in Zr50Cu40Al10 bulk glassy alloys irradiated by 200 and 2.5 MeV Xe ions, 180 keV He ions, and 2 MeV electrons were investigated at room temperature using positron annihilation lifetime and Doppler broadening techniques. In addition, a slow positron beam was used to probe the change in free volume in the 180 keV He ion-irradiated sample. X-ray diffraction revealed that no crystallization took place in any of the irradiated samples. The Doppler broadening spectra from the annihilated gamma rays remained essentially constant in all ion-irradiation cases; however, an extremely minor change of positron mean lifetime was detected in each case. For electron- and He ion-irradiated samples the positron lifetime increased, and the opposite was seen in heavy-ion irradiated samples. The Doppler broadening S parameter increased with He-ion radiation dose, and the depth profile correlated well to the damage profile.

Free volumes in Zr50Cu40Al10 bulk metallic glasses irradiated by 100 MeV and 200 MeV Xe ions and 2 MeV electrons at room temperature have been investigated by using positron annihilation techniques, the micro Vickers hardness and X-ray diffraction measurements. No crystallization took place due to both ion and electron irradiations. The coincidence Doppler broadening spectra of annihilation gamma rays also remained unchanged by ion and electron irradiation. Meanwhile, an increase and a decrease of positron lifetimes after electron and ion irradiation, respectively, were observed. This suggests the structural modification of free volumes. The response of positron lifetime to ion and electron irradiations may be connected with the tendency of hardness.

The eutectic Zr50Cu40Al10 bulk glassy (BG) alloys, which have a good glass forming ability, have been investigated for various properties, such as toughness, electronic resistivity and so on. Recently, the hypoeutectic Zr60Cu30Al10 BG alloys have been paid attention, because they exhibit no degradation of ductility and toughness after the isothermal annealing below the glass transition temperature (Tg). Although the toughness correlates with the free volume to be considered, the free volume of the hypoeutectic BG alloy has not been assessed in detail so far. In order to study the free volume in each BG alloy, therefore, positron annihilation lifetime and coincidence Doppler broadening (CDB) measurements have been performed for Zr60Cu30Al10 (hypoeutectic) and Zr55Cu35Al10 (middle-composition) and Zr50Cu40Al10 (eutectic) BG alloys. The value of the positron lifetime for hypoeutectic BG alloy is virtually the same. Additionally, the CDB ratio curve for hypoeutectic alloy dose not match that for eutectic alloy in an electron momentum region around 0.015 m0c, indicating that the fraction of Zr atoms around the free volume in hypoeutectic BG alloy is greater than that in eutectic BG alloy. Moreover, the CDB results show that the local structure around free volume for hypoeutectic BG alloy is different from that for eutectic BG alloy.

Al-Cu based alloy, which is generally called duralumin (JIS2017), was irradiated with 10 MeV Iodine ions, 200 MeV Xenon ions and 3 MeV electrons at room temperature respectively. The micro Vicker's hardness and positron annihilation coincidence Doppler broadening (CDB) measurements have been performed before and after irradiation. Only in the case of ion irradiation, the Vicker's hardness increases with increasing ion dose. Nevertheless, there was no difference in the profile CDB spectrum for before and after irradiation. On the other hand, we found that the micro hardness of this alloy, which was Xe ion irradiated and subsequently annealed at 423 K, is greater than that of age hardened alloy without irradiation. CDB ratio curve of the age hardened Duralumin is clearly different in the electron momentum range around 0.015-0.025 mc from that of the ion irradiated alloy. The results of three-dimensional atom probe (3DAP) also show that a lot of small clusters were found after ion irradiation but large precipitations have found in annealed Duralumin. These results reveal that a number of small clusters formed in this alloy after ion irradiation, and they should strongly affects the micro hardness.

The structure of Au-Pd nanoparticles prepared by the sonochemical method was observed by an analytical TEM. The core (Au)-shell (Pd) structure was confirmed by ADF-STEM images. The ratio of Au and Pd contents was controlled by adjusting the ratio of precursors, and the Pd-shell thickness was also controlled by the ratio of Au and Pd contents. The electron diffraction patterns showed that the lattice constant of the Pd shell is quite larger than that of bulk Pd and rather similar to that of bulk Au even in the systems with larger ratios of Pd, which supports the pseudomorphic growth of the Pd shell on the Au core.

Positron annihilation lifetime experiments have been performed for B-doped p-type Czochralski silicon (CZ-Si) wafers irradiated at 300 K with 1 MeV electrons with fluences between 1014 and 1017 e/cm2. In order to examine the thermal behavior of defects having shorter lifetime than that of the bulk, isochronal annealing experiments were carried out from 300 K to 900 K. The measurements were performed at 100 K to improve the positron trapping rates for defects. It is found that components having longer lifetime than that of the bulk behave differently, and they comprise by thermal donors (TD) and divacancies (V2). The short-lifetime component observed in the present experiments is responsible for a complex defect with impure interstitial oxygen atoms, doped B atoms and vacancies. The short-lifetime defects change into vacancy-type defects and thermal donors in certain ranges of annealing temperatures.

In order to obtain information on the degradation of solar cells in artificial satellites as a result of cosmic ray radiations, positron annihilation lifetime experiments were performed for B-doped p-type Czochralski (CZ) silicon wafers irradiated at room temperature with 1 MeV electrons with fluences between 1014 and 1017 e/cm2. Positron lifetime measurements were done at 100 K to improve the trapping rates of positrons with defects. The mean lifetime of irradiated Si was shorter than that of unirradiated Si. We found that short lifetime defects (approximately 100 ps) existed, which could be associated with complexes of Si with interstitial oxygen atoms, doped B and vacancies resulting from irradiation. Lifetime components longer than those of the bulk accounted for the formation of thermal donors and divacancies.

In situ observations of melting silicon have been carried out using an ultrahigh-voltage electron microscope, and lattice defects induced by rapid cooling from a partly molten state are examined in detail by conventional transmission electron microscopy. Stacking fault tetrahedra are found to form, indicating that the clustering and the collapse of thermal vacancies take place on the {111} planes at high temperatures. Their formation mechanism is discussed.