During the last decade constant improvements have been made in materials and structures design and control. But now some performance objectives in particular in the field of the reliability cannot be achieved using classical technologies and require the use of the ‘smart materials concept’. Periodical maintenance NDT based inspections are today of a general acceptance for almost all complex technological structures. Nevertheless the idea that the integrated and continuous sensing techniques can optimize the operating conditions is now in progress. Different aspects of this evolution towards the desirable continuous health monitoring are discussed in relation with the smart materials concept through this non exhaustive review of some realisations or experiences. In the domain of sensitive materials, passive techniques such as Barkhausen effect, thermoelectric power, electrical impedance monitoring, acoustic emission, and active piezoelectric implant based methods, are briefly presented. Moreover, taking into account the growing demand in the field of actuators and artificial muscles for robotic and biomimetic devices, shape memory alloys and electroactive polymers are in progress. Finally the ‘self healing’ concept will be presented in the case of one ceramic-ceramic composite.

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Using a thin-film composition spread technique, we have mapped the phase diagram of the Ni-Mn-Al ternary system in search of ferromagnetic shape-memory alloys (FMSA). A characterization technique that allows detection of martensitic transitions by visual inspection using micromachined cantilever arrays was combined with quantitative magnetization mapping using scanning superconducting quantum interference device (SQUID) microscopy. A large compositional region in the Al deficient part of the phase diagram was found to be ferromagnetic and reversibly martensitic at room temperature. In addition, in the Al rich region, a new compositional range that displays marked ferromagnetism was found.

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Various engineered domain configurations were induced into barium titanate (BaTiO₃) single crystals, and their piezoelectric properties were investigated as a function of (1) the crystal structure, (2) the crystallographic orientation and (3) the domain size. As a result, the orthorhombic mm2 BaTiO₃ crystals showed the highest piezoelectric properties among three kinds of BaTiO₃ crystals such as tetragonal 4mm, orthorhombic mm2 and rhombohedral 3m phases. On the other hand, the [001]_c oriented BaTiO₃ crystals always exhibited the larger piezoelectric properties than the [111]_c oriented BaTiO₃ crystals. Moreover, the domain size dependence on the piezoelectric properties was discussed, and this result revealed that the piezoelectric property was strongly dependent on the domain size, i.e., the piezoelectric properties significantly increased with decreasing domain size. On the basis of the above results, the most suitable engineered domain configuration was proposed for the high-strain high-coupling piezoelectric application.

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We have investigated magnetic field-induced strain (MFIS) associated with rearrangement of martensite variants and its corresponding magnetization process in a disordered Fe-31.2Pd(at%) single crystal and an ordered Fe₃Pt single crystal, exhibiting a cubic to tetragonal martensitic transformation at 230 K and 85 K, respectively. When magnetic field is applied along [001] direction to a specimen with a multivariant state, it expands along the field direction for Fe-31.2Pd and contracts for Fe₃Pt, because the variants whose easy axis of magnetization (a axis for Fe-31.2Pd and c axis for Fe₃Pt) lies along the field direction is selected to grow. The fraction of such variants reaches 100% for Fe-31.2Pd but does not for Fe₃Pt. In the field removing process, a part of the MFIS recovers for Fe₃Pt but does not for Fe-31.2Pd. From the magnetization curve, the energy dissipated due to the rearrangement of variants by magnetic field is obtained to be about 260 kJ/m³ for Fe-31.2Pd and about 180 kJ/m³ for Fe₃Pt. Concerning Fe-31.2Pd, this value is roughly the same as that evaluated by stress-strain curves, suggesting that the rearrangement of variants by magnetic field takes essentially the same path as that by external stress. Based on these results and magnetocrystalline anisotropy constants of martensite phases, the mechanism of rearrangement of variants under magnetic field is discussed from a macroscopic point of view.

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Melt-spun, rapid solidified Fe-Ga ribbon sample exhibited large magnetostriction and good ductility as compared with conventional bulk sample. But the origin was not clear yet. In order to investigate the occurrence of large magnetostriction in Fe-Ga ribbon sample, the correlation between magnetostriction and the crystal grain morphology was inspected in detail by SEM/EBSP method for Fe-15 at%Ga alloy. In comparison with as-spun ribbon sample, short-time (0.5 h) heat treated ribbon had stronger [100] oriented texture and exhibited larger magnetostriction of 140 ppm (×10⁻⁶) at 800 kA/m. These phenomena suggest that such a large magnetostriction is caused by the release of considerable large internal stresses in as-spun ribbon as well as the remained strong textures after annealing.

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A ternary (Fe_0.82Ga_0.18)₈₅B₁₅ alloy was vitrified by melt spinning at wheel velocities of over 28.5 m/s. Two exothermic peaks were observed at onset temperatures of 692 K and 787 K. The melt-spun amorphous alloy ribbon exhibits saturation magnetostriction of +30 × 10⁻⁶ at the field of 80 kA/m. The magnetostriction increased by crystallization, i.e. precipitation of the bcc-Fe(Ga) phase, and reached a maximum value of +62 × 10⁻⁶ in conjunction with good response which is same as that for the as-spun amorphous sample. The maximum value is equivalent to that of the random orientated polycrystalline Fe₈₂Ga₁₈ alloy. In addition, the crystallized Fe-Ga-B alloy had better response as compared with the polycrystalline Fe₈₂Ga₁₈ alloy. The reason why the Fe-Ga-B alloy exhibits the high magnetostriction even in the coexistent state with C16-Fe₂B and L1₂-Fe₃Ga phases, seems to result from the precipitation of the supersaturated bcc-Fe(Ga) solid solution with high Ga concentrations as the crystallization -included phase.

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We studied the phase transformation of a new Heusler type ferromagnetic shape memory alloy, Co₂NiGa, by using an Acoustic Elastometer method. The alloy displays large magnetostriction, caused by the magnetic-field-induced rearrangement of martensite twin boundary. The ribbon samples produced by rapidly solidified melt-spinning method show large magnetostriction of about 100 × 10⁻⁶ at room temperature. While heating and cooling, the modulus defect, ΔM/M, and damping, Q⁻¹, of the ribbon sample exhibits drastic changes at A_s and M_f, which differ slightly from the magnetic results.

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Texture of Ti₅₂Ni₃₈Cu₁₀ rapidly solidified ribbons was investigated. Characterization of some of the properties such as transformation temperatures, deformation behavior, transformation strain, microstructure etc. was also carried out for the rapidly solidified ribbons in as-spun condition and after heat-treatment at 1073 K. The transformation temperatures of the ribbon specimens are found to be less than those of ingot specimens. As-spun ribbons were found to be slightly amorphous in nature, while after heat-treatment they became completely crystalline. Asspun and heat-treated ribbons show strong ‹200› fiber texture. From the thermomechanical studies it was observed that the hysteresis of the heat-treated ribbon specimen decreased whereas the transformation strain and the transformation temperatures showed an increase with increase in stress.

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The shape memory behavior, texture and microstructure were studied for Ti-Ni ribbons fabricated by a melt-spinning method where the Ni contents were designed to be 49.0 at%, 50.0 at% and 51.0 at%. The texture of the parent B2 phase was determined by X-ray diffraction pole figures. A strong ‹100› fiber texture was found in both pole figures and orientation distribution functions (ODF). TEM observation revealed that all the ribbons are fully crystallized and that disk-type precipitates of about 10 nm in length locate on {100} of B2 phase uniformly. The thermal cyclic tests under various constant stresses showed shape recoverable strains exceeding 5% and critical stresses for plastic deformation being higher than 400 MPa for Ti-49.0 at%Ni and Ti-50.0 at%Ni as-spun ribbons. These excellent shape memory characteristics of the melt-spun ribbons are due to the formation of these disk-type precipitates. In addition, Ti₂Ni precipitates of 25 nm in diameter appeared along grain boundaries of Ti-51.0 at%Ni as-spun ribbon. Since the Ni content of the matrix is condensed due to the formation of Ti₂Ni precipitates, no shape memory effect was observed in Ti-51.0 at%Ni as-spun ribbon under the experimental conditions.

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Using the ultrafine laminate method, thin foils (50 μm) of Ni-rich TiNi shape memory alloys were produced. Overall composition of the Ti/Ni laminate is Ti-50.7%Ni. TiNi (B2) phase was obtained after different diffusion treatments at 1073 K for 259.2 ks and 1173 K for 36 ks and 259.2 ks. Aging treatments at 773 K for 3.6, 18, 36, 72 and 144 ks were also performed. Multiple step martensitic transformation was observed for aged samples. The shape memory strain was 3.69 × 10⁻² in the sample aged at 773 K for 18 ks.

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TbFe₂ films prepared by a flash evaporation system onto Si(100) or polyimide substrate have been irradiated with different Ar ion doses at zero, 1.3 × 10¹⁷ and 2.7 × 10¹⁷ cm⁻² and at 10 kV. Magnetostrictive properties, i.e., saturated magnetostriction and magnetostrictive susceptibility, of TbFe₂ film with disordered structure were improved by Ar ion beam irradiation. This result was probably caused increasing of in-plane compressive stress corresponding to change of volume magnetostriction.

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To determine the collision fatigue limit for piezoelectric ceramics, an electrical nondestructive method was suggested. The materials show large changes in electrical potential induced by pressure on the collision. Measurements on this type of material found a relationship between the maximum value of electrical potential (V_m) and supplied collision energy (E_c^s) below the collision fatigue limit. It was expressed by the following simple equation.
V_m = 9.5(E_c^s)^0.5
Applying the critical differential electrical potential (V_c = 4 V), we confirmed that the collision fatigue limit was nondestructively determined for PZT materials.

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A combination of the preparation techniques for the ferroelectric films and the micro machining of Si is considered to be an effective way to fabricate microelectromechanical systems (MEMS), such as piezoelectric micro-transducer devices for the electrical and medical fields. In this study, disk shape lead zirconate titanate (PZT) thick films were successfully fabricated. 10-μm-thick PZT films were deposited onto Pt/Ti/SiO₂/Si substrate using a chemical solution deposition (CSD) process. Pt top electrode and PZT layer were etched by reactive ion etching (RIE) process, and 100 to 500-μm-diameter PZT thick film disks were fabricated. The relative dielectric constant, dissipation factor, remnant polarization and coercive field were ε_r = 1130, tanδ = 0.02, Pr = 0.14 C/m² and Ec = 2.5 MV/m, respectively. This means that the ferroelectric and dielectric properties of the PZT thick film disks were comparable with that of the bulk PZT ceramics. Moreover, the prepared PZT thick film disks showed the butterfly-shaped displacement curve, related with piezoelectric response, in the case of bipolar measurement. The PZT thick film disks could be poled with 80 V at room temperature, which is easier than the poling condition of bulk PZT. The piezoelectric constant of the poled PZT thick film disks was estimated to be AFM d₃₃ = 221 pm/V. Therefore, the micro fabricated 10-μm-thick PZT disks is considered to be applicable for piezoelectric micro devices.

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The diagnostic algorithm introduced by Wayland et al. to test for degrees of visible determinism in complex dynamical behavior is applied to precise estimation of noise level for the gear-noise sound emanated from automobile automatic transmissions. It is shown that the method successfully captures such a small difference in acoustical characteristics indicating micro mechanical flaws on the gear surface that power spectral analysis fails to detect.

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To improve electric properties of oxide ion conducting yttria-stabilized zirconia (YSZ) films at low temperatures, a mechanical distortion was induced by a piezoelectric actuator. YSZ films containing 8 mol%Y₂O₃ were prepared by metalorganic chemical vapor deposition. The YSZ film was placed on a PZT (lead zirconate titanate) multilayer piezoelectric actuator. The effect of piezoelectric vibration on electric properties of the YSZ film was investigated. The resistivity of the YSZ film decreased with increasing amplitude of the piezoelectric vibration. Electrical conductivity of the YSZ film at 353 K vibrated by the actuator was 2 × 10⁻⁶ Sm⁻¹, 10³ times greater than that without vibration.

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Magnetostrictive thin films in electric resonant LC circuits are attractive as novel strain sensors. In order to achieve high resonance frequencies exchange coupled nanometer multilayers were used. LC circuits incorporating Fe₅₀Co₅₀/Co₈₀B₂₀ multilayers exhibited a gauge factor ((Δf/f)/Δε) of the order of 1000. This LC circuit sensor enables wireless interrogation, which is demonstrated in a torque measurement.

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Ti-aluminides-reinforced Ti-matrix composites were fabricated from 0.04 mm-thick Ti foils and 0.012 mm- and 0.024 mm-thick aluminum foils, in a process using a pulsed-current hot pressing (PCHP) equipment, and the effect of reaction temperature on properties of the composites was investigated. The composites were of laminated structure and composed of Ti and reacted layers containing Ti-aluminides. The composition of the reacted layers was dependent on the reaction temperature employed. Tensile testing at room temperature revealed that the reaction temperature was effective for the mechanical properties, including tensile strength, elongation and fracture mode, of the composites. The tensile strength and the elongation of composites fabricated at 1273 K from 0.04-mm-thick Ti and 0.012-mm-thick Al foils were 810 MPa and 3.64%, respectively, while they were 677 MPa and 3.44% for composites fabricated at 1173 K. Microstructure observations of fractured specimens showed that Ti layers of the composites fabricated at 1173 and 1273 K played a significant role in improving ductility by prohibiting the growth of numerous cracks emanating from Ti-aluminides.

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A fiber reinforced nickel was developed base on the concept of active composites due to the thermal deformation, and its reproducibility at elevated temperature has been investigated. It was reported that curvature of the composite changed non-linearly during heating/cooling cycle. This hysterisis behavior may be involved with microfracture in the composites. Acoustic emission (AE) technique is very useful to monitor a dynamic microfracture. However, conventional AE technique has a limit in application at elevated temperature. We have investigated the non-contact laser AE technique using laser interferometer as a sensor. In this study, we tried to evaluate thermal deformation process of the active composite by this method. Specimens of pure nickel plate as matrix, SiC continuous fiber as reinforcement fiber and pure aluminum plate as insert layer were prepared by hot pressing. AE signals during heating and cooling processes were detected at the reverse of the specimen using a heterodyne type laser interferometer. Observation results showed that three failure modes such as cracking in matrix layer, debonding of matrix/fiber interface, and breakage of SiC fiber occurred during thermal deformation process. These failure modes were discussed based on AE source models. AE behavior of the composite showed thermal Keiser effect. This indicates thermal stresses in the composite cause microfracture during thermal deformation process. As a result of the test with the maximum temperature of 1073 K, AE event rate increased rapidly at 960 K and AE signals were detected even in cooling process. This temperature was identified to be the transition temperature of microfracture process in this composite. AE generation temperature was also in good agreement with the critical temperature of hysterisis of curvature.

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An attempt was made to fabricate composite material of an Al alloy matrix reinforced by TiNi shape memory fiber using a hot-press method and to investigate its microstructures and mechanical properties. The analysis of SEM and EDS showed that the composite material had good interface bonding. The stress-strain behavior of the composite material was evaluated at room temperature and 363 K as a function of pre-strain, and it showed that the yield stress at 363 K is higher than that at room temperature. It is also found that the yield stress of the composite material increased with increasing the amount of pre-strain and depended on the volume fraction of the fiber and heat treatment. The smartness of the composite could be given due to the shape memory effect of the TiNi fiber, which generated compressive residual stress in the matrix material when heated after being pre-strained. Microstructural observation revealed that interfacial reactions occurred between the matrix and fiber, creating two intermetallic layers.

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Shape memory alloys (SMAs) have the features of large force-to-weight ratio and large deformation, are considered suitable for actuator uses. This paper describes the applications of an SMA material with two-way shape memory as artificial muscles for the treatment of fecal incontinences. Two designs of the proposed artificial sphincters are presented; one for a complete replacement of the anal sphincter and the other as an auxiliary sphincter to assist the puborectal muscles for maintaining fecal continence. Their functional evaluations have been conducted through fundamental experiments on the thermal responses and the mechanical deformation. The functionality of both was confirmed by in vitro experiments. The first design, the artificial anal sphincter was subjected to animal experiments for up to 4 weeks. Satisfactory results in respects of the biofunctionality of the SMA artificial sphincter imply its potential for practical uses.

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Potentiostatic cathodic electrodeposition of ZnTe was investigated from the viewpoint of the effect of pH on the deposits' composition and crystallinity using citric acidic electrolytic baths, in which Zn(II) and Te(IV) species were dissolved to form ZnH₂Cit⁺, ZnHCit, ZnCit⁻, Zn(Cit)₂⁴⁻ and HTeO₂⁺, HTeO₃⁻, respectively (Cit: citrate) at various pH. The complex equilibrium calculation was carried out to examine the most predominant complex ion for Zn-Cit system at different pH. Deposition of three kinds of deposits, i.e., polycrystalline ZnTe with closely stoichiometric composition, crystalline Te, and the mixed crystal due to Te and ZnTe, can be controlled by changing the pH and [Zn(II)]/[Te(IV)] concentration ratio of the baths. All the deposits obtained at pH 4.0 were well crystallized with a ZnTe cubic preferential orientation along the (111) plane without any post-treatment. The difference of the electrodeposition behavior at various pH was also discussed.

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Water vapor corrosion behavior of rutile TiO₂ was examined at 1773 K in 30 mass% H₂O environment. The corrosion rate for this sample was 2.2 × 10⁻⁴ kg·m⁻²·h under this experimental conditions. Anisotropic corrosion behavior was recognized in the planes that are parallel to c-axis. Many rectangular shaped etch-pits were generated at the grain surfaces. The corrosion proceeded from the side wall of the etch-pits and then, terrace fields were grown on the grain surface. Ridge-shaped microstructure was observed on the side wall of the terrace owing to the anisotropic corrosion.

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This article was retracted. See the Notification.

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As the automotive industry trends towards increased use of aluminum, the friction stir welding process offers many potential benefits for joining of aluminum. In this study, the microstructure in friction stir welded 6061 aluminum alloy was observed by metallographic technique, electron backscatter diffraction pattern (EBSD) and optical microscopy. The microstructure in the heat affected zone (HAZ) was significantly different from that in a thermo-mechanically affected zone (TMAZ). EBSD indicated that many more low-angle grain boundaries in TMAZ, i.e., subgrains with a recovered granular structure, were observed than in HAZ. Friction heating and plastic flow during friction stir welding created fine recrystallized grains and recovered grains in the TMAZ. The friction stir welding process produced a softened region in the 6061 Al welded alloy. In the stir zone, equiaxed grains were created and the grain size was smallest in the bottom area.

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We systematically investigated the hydrogenation and dehydrogenation properties for heavy rare earth-based binary R_HNi₅ (R_H = Gd, Tb and Dy) intermetallic compounds and evaluated the correlations between crystallographic and thermodynamic properties. XRD analysis shows that all R_HNi₅ compounds crystallize in the hexagonal CaCu₅-type crystal structure. In analogy to the light rare earth-based R_LNi₅ (R_L = La, Pr, Nd and Sm) compounds both lattice constants of R_HNi₅ compounds decrease with increasing the atomic number of R_H element due to the lanthanide contraction. On the pressure-composition (P-C) isotherms, GdNi₅-H₂ system shows two well-separated pressure plateaux qualitatively similar to R_LNi₅-H₂ systems. Looking over from Gd to Dy in the R_HNi₅ compounds, we find three specific dehydrogenation properties on the P-C isotherms: 1. The first plateau pressure (p_P1) increases in this order (at around H/R_HNi₅ = 2.5) due to less stability of hydrogen in the unit cell by the lanthanide contraction. Linear correlations are also observed between log p_P1 and the unit cell volume (V) which fall onto the same lines extrapolated from those observed in case of the R_LNi₅ compounds. 2. The second plateau (P2) tends to disappear because the P-C isotherm goes beyond the critical point of the phase transition. 3. Fairly flat first plateau separates into two parts in which a new plateau (PN) appears at low hydrogen content (H/R_HNi₅ ≤ 2) with hysteretic phase transition. So long as the first plateau of dehydrogenation is concerned, from LaNi₅ to DyNi₅ we can predict the first plateau pressure from the unit cell volume of compounds and temperature.

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The metallographic factor controlling the strength of friction-bonded interface of low carbon steel (approximately 0.10 mass%C) to aluminum-magnesium (Al-Mg) alloy (equivalent to AA5083) has been investigated by TEM observations. The bond strength, estimated from the tensile strength of a specimen with a circumferential notch at the interface, rose rapidly with an increase in friction time, and then reduced. A maximum strength of 306 MPa was obtained at a friction time of 2 s (rotation speed = 20 s⁻¹, friction pressure = 40 MPa, and forge pressure = 230 MPa). At a friction time of 1 s, an IMC layer about 100 nm wide that consisted of (Fe,Mn)Al₆ and Mg₂Si was formed at the interface, and an Al-oxide layer of a width less than 10 nm was observed between this IMC layer and low carbon steel substrate. In a joint showing the highest bond strength (friction time = 2 s), no Al-oxide layer could be detected between the low carbon steel substrate and IMC layer which consisted of (Fe,Mn)Al₆, Fe₄Al₁₃, Fe₂Al₅, and Mg₂Si. The width of the interfacial layer was increased to about 300 nm. At a friction time of 4 s, a layer of MgAl₂O₄ was observed in addition to intermetallic compounds of (Fe,Mn)Al₆, Fe₄Al₁₃, Fe₂Al₅ and Mg₂Si. The width of this layer was about 700 nm. Thus the phases formed in the interfacial layer as well as its width were altered depending on the friction time. The change in the bond strength with friction time was discussed in view of these differences in the interfacial microstructure.

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The microstructure of the solid-state diffusion-bonded interface of tin has been investigated by TEM observations in order to reveal the evolution of the superficial oxide film of tin with the progress in bonding. The diffusion bonding was carried out in a vacuum chamber at bonding temperatures T_j of 373—493 K and at bonding pressures P_j of 90—170 MPa (bonding time = 1.8 ks). The tensile strength of the joint was increased with bonding temperature and pressure; joints having tensile strength comparable with the base metal were obtained at T_j = 493 K at P_j = 130 MPa and at T_j = 443 K at P_j = 130 MPa. When the joint strength was much lower than the base-metal strength, an interfacial region ∼500 nm in width was observed where a number of very fine inclusions that could be regarded as tin oxide were distributed. As the joint strength increased with bonding temperature, these inclusions were coarsened, and their number density was decreased. The increase in the bonding pressure enhanced these changes in the inclusion. The rise in the joint strength with bonding temperature corresponded well with the observed change in the size and density of the inclusion.

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The microstructures of an A₂O₃/YAG/ZrO₂ eutectic Melt-Growth-Composite (MGC) solidified unidirectionally by the modified-pulling-down method were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and electron backscattered pattern (EBSP) method. The anisotropy of strength was investigated by hardness tests and compression tests at various directions of the composite at elevated temperatures. The eutectic MGC has strong preferred growing orientation and the constituent phases hold the orientation relationship. The eutectic MGC shows excellent high-temperature strength and can deform plastically above about 1500 K. High-temperature strength above 1500 K depends on strain rate, temperature and orientation.

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Polymer impregnation and pyrolysis (PIP) is one of the most attractive fabrication processes for silicon carbide (SiC) composites due to the shape flexibility, mass production and relatively low cost. In particular, advanced PIP SiC/SiC composite with high-crystallinity and near-stoichiometric composition is expected to have superior thermo-mechanical properties including good oxidation resistance, due to the reduction of impurities and well-organized crystal structure. Additionally, by applying a thin carbon interphase by chemical vapor infiltration (CVI), control of the crack propagation and oxidation resistance are also achieved. In this study, a CVI + PIP hybrid process based on the recently developed stoichiometric PIP process was performed. Specifically, matrix crystallization was enhanced by heat treatment in Ar, and its effect on microstructures and mechanical properties were evaluated. Stoichiometric SiC/SiC composites exhibit superior flexural strength up to 1573 K in Ar and 1273 K in air. This is because the stoichiometric composition in PIP-SiC matrix reduces inner oxidation by impurities. Also, the thin pyrolytic carbon interphase tailored by CVI process effectively controls crack propagation at fiber and matrix interphase. In a similar manner, the microstructure of the stoichiometric PIP-SiC matrix, constructed by the mixture of amorphous SiC and highly crystalline SiC, was stable against the high-temperature heat exposure up to 1773 K in Ar. In particular, stoichiometric SiC/SiC composites heated at 1773 K in Ar provides superior stability of mechanical properties up to 1573 K even in air atmosphere, although extensive crystallization, in the case of heat treatment at 1973 K in Ar, caused brittle composite fracture.

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Structural transformation induced by magnetic fields on MnAs and MnAs_0.9Sb_0.1 was investigated by the X-ray diffraction measurements in high magnetic fields up to 5 T. The X-ray diffraction profiles at 319 K for MnAs showed a single phase of the orthorhombic MnP-type structure in zero field, and applying a magnetic field of 3 T caused an appearance of the hexagonal NiAs-type structure. On further increase of magnetic fields, the single phase with the hexagonal structure was confirmed above 3.5 T in a forced ferromagnetic state. The X-ray diffraction profiles at 295 K for MnAs_0.9Sb_0.1 showed the hexagonal NiAs-type structure. However, the coexistence of two kinds of the NiAs-type structure with different lattice parameters was confirmed in the magnetic field of 2.5 T. The two phase coexistence was also confirmed in the temperature variation measurements in zero magnetic field. The lattice volume of the ferromagnetic phase was 1.1% larger than that of the paramagnetic phase. These results imply that the transition at T_C for MnAs_0.9Sb_0.1 is of the first-order.

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Hydrogen distribution in high-purity-based polycrystalline Al-5%Mg alloys prepared by changing the melting atmosphere was visualized by means of hydrogen microprint technique with electron backscattering pattern analysis after a tensile deformation at room temperature. The number of hydrogen atoms observed as silver particles on the slip lines was increased when the applied strain was increased. Hydrogen atom observed on the slip lines was totally increased when the melting atmosphere of the alloys was changed from argon to air. Hydrogen atom was observed at both slip lines and special grain boundaries when an air-melted specimen was deformed. It was shown that hydrogen atom accumulation at grain boundaries varied with the misorientation of grains and the angle to the tensile direction.

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Dense forming of shoulder components through the pulse discharge sintering process was examined. A new technique of multi-way loading system is proposed. This loading system is able to control the pressure in a powder compact body equally even if it has an irregular sectional profile. The traveling zone heating method combined with this loading system will allow the successful sintering of shoulder components through the PDS process, since no sinking due to pressure difference occurs in a powder compact. Based on this idea, the conventional sintering procedure with a perforated spacer was applied to production of a shoulder component. The spacer dictated the loading stroke on the thin side. The result was that an aluminum shoulder component with diameters of φ15 mm at the thin side and φ25 mm at the thick side was satisfactorily produced. The relative density of the component exceeded 99%. Some problems remain to be solved, but this procedure has potential for achieving high reproducibility by developing a precise load control system and stable contact between the electrode and the cylinder.

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The effects of different concentrations of individual additions of rare earth metals (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) on eutectic modification in Al-10 mass%Si has been studied by thermal analysis and optical microscopy. According to the twin-plane reentrant edge (TPRE) and impurity induced twinning mechanism, rare earth metals with atomic radii of about 1.65 times larger than that of silicon, are possible candidates for eutectic modification. All of the rare earth elements caused a depression of the eutectic growth temperature, but only Eu modified the eutectic silicon to a fibrous morphology. At best, the remaining elements resulted in only a small degree of refinement of the plate-like silicon. The samples were also quenched during the eutectic arrest to examine the eutectic solidification modes. Many of the rare-earth additions significantly altered the eutectic solidification mode from that of the unmodified alloy. It is concluded that the impurity induced twinning model of modification, based on atomic radius alone, is inadequate and other mechanisms are essential for the modification process. Furthermore, modification and the eutectic nucleation and growth modes are controlled independently of each other.

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The cellular aluminum materials with relative densities of 0.1∼0.25 were fabricated by the sintering method and effects of the density on mechanical properties of the cellular aluminum were investigated by compressive tests. The cellular aluminum exhibited a plateau region with a nearly constant flow stress. The stress in the plateau region increased with increasing relative density, on the other hand, the densification strain decreased with increasing relative density. Observation of the deformed cells revealed that the cell walls were bent. Besides, the stress in the plateau region was proportional to 1.9 power of the density. These suggest that plastic collapse is dominated by bending of the cell walls for the cellular aluminum produced by the sintering method.

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The (Ni_0.6Nb_0.4)₄₅Zr₅₀X₅ (X = Al, Co, Cu, P, Pd, Si, Sn, Ta or Ti) alloy ribbons were produced by the melt-spinning technique. All ribbon specimens were confirmed to have a single amorphous phase by XRD analysis. The crystallization temperatures of the melt-spun (Ni_0.6Nb_0.4)₄₅Zr₅₀X₅ (X = Al, P, Pd, Si or Sn) amorphous alloys are higher than that of the (Ni_0.6Nb_0.4)₅₀Zr₅₀ amorphous alloy (727 K). Although the hydrogen permeability of the (Ni_0.6Nb_0.4)₄₅Zr₅₀X₅ (X = Si, Sn, Ta or Ti) amorphous alloys could not be measured due to severe embrittlement during the permeation test, the (Ni_0.6Nb_0.4)₄₅Zr₅₀X₅ (X = Al, Co, Cu, P or Pd) amorphous alloys had high ductility which was enough to measure the permeability. The hydrogen permeabilities of the (Ni_0.6Nb_0.4)₄₅Zr₅₀Co₅ and the (Ni_0.6Nb_0.4)₄₅Zr₅₀Cu₅ amorphous alloys were 2.46 × 10⁻⁸ and 2.34 × 10⁻⁸ [mol·m⁻¹·s⁻¹·Pa^−1/2] at 673 K, respectively. The (Ni_0.6Nb_0.4)₄₅Zr₅₀P₅ amorphous alloy possesses the lowest permeability of 1.36 × 10⁻⁸ [mol·m⁻¹·s⁻¹·Pa^−1/2] at 673 K among the alloys where the permeability was measured. The reduction of the permeability in the (Ni_0.6Nb_0.4)₄₅Zr₅₀P₅ amorphous alloy is thought to be due to a preferential development of Zr-P atomic pairs which may suppress hydrogen solubility and hydrogen diffusivity in the alloy, because the heat of mixing for Zr-P atomic paris is negatively larger than those of other pairs such as Ni-P and Nb-P. It is concluded that the Ni-Nb-Zr-X (X=Co or Cu) amorphous alloys have high potential to hydrogen permeable membranes.

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In order to clarify the influence of water vapor on evaporation and crystallization of an amorphous SiO₂ scale formed on SiO₂-formers, fused silica was exposed for up to 49 h at 1373—1673 K in N₂-O₂-H₂O atmospheres. The water vapor concentration was regulated to 19.6 and 46.7% (vol%). Under conditions of low water vapor concentration, the mass change in the fused silica was negligible. On the other hand, the mass linearly decreased with the duration of exposure under high water vapor concentration. From the temperature dependence of the evaporation rate, it was speculated that the main volatile species were Si(OH)₄ and SiO(OH)₂ in N₂-H₂O and N₂-O₂-H₂O, respectively. Moreover, although crystallization of fused silica was observed in both atmospheres, air and N₂-O₂-H₂O, the rate of crystallization in the N₂-O₂-H₂O atmosphere was much higher than that in air. These results indicate that crystallization is accelerated by the presence of water vapor.

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The factors controlling irradiation hardening and their contributions to the hardening in electron irradiated pure-iron and Fe-0.15 mass%Cu alloy were determined by means of post-irradiation annealing experiments, such as hardness measurements, positron annihilation spectroscopy (PAS) measurements, transmission electron microscope (TEM) observations and three dimensional atom probe (3DAP) analyses. In pure-iron, almost complete recovering of the hardness was observed after the annealing to 773 K, which was accompanied by disappearing of the interstitial type dislocation loops (I-loops) that were observed in as-irradiated specimen. In contrast, the hardening of Fe-0.15 mass%Cu alloy recovered in a two-step mode; about a half of the hardening recovered by the 773 K annealing, and a complete recovery was observed after annealing to 973 K. Most of the I-loops observed in as-irradiated specimen again disappeared after the annealing to 773 K. These clearly show that the I-loops are one of the main factors controlling irradiation hardening in iron-copper alloy. The residual hardening in the Fe-0.15 mass%Cu alloy after the annealing to 773 K, which is about a half of the irradiation hardening, was attributed to the copper-rich precipitates (CRP) through the direct observation by 3DAP analysis. PAS measurements revealed the disagreement between the recovery behaviors of the hardness and lifetime parameters. Based on the quantitative data analysis, it was concluded that the factor controlling the irradiation hardening of pure-iron is the I-loops, and those in Fe-0.15 mass%Cu alloy are both the I-loops and CRP of which the contributions to the hardening are almost same.

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High-cycle fatigue properties at 4 K, 77 K and 293 K were investigated in forged-INCONEL 718 nickel-based superalloy with a mean gamma (γ) grain size of 25 μm. In the present material, plate-like delta phase precipitated at γ grain boundaries and niobium (Nb)-enriched MC type carbides precipitated coarsely throughout the specimens. The 0.2% proof stress and the ultimate tensile strength of this alloy increased with decreasing temperature, without decreasing elongation or reduction of area. High-cycle fatigue strengths also increased with decreasing temperature although the fatigue limit at each temperature didn't appear even around 10⁷ cycles. Fatigue cracks initiated near the specimen surface and formed faceted structures around crack initiation sites. Fatigue cracks predominantly initiated from coarse Nb-enriched carbides and faceted structures mainly corresponded to these carbides. In lower stress amplitude tests, however, facets were formed through transgranular crack initiation and growth. These kinds of distinctive crack initiation behavior seem to lower the high-cycle fatigue strength below room temperature in the present material.

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In order to improve the environmental barrier property of coatings fabricated by the HVOF spray process with a gas shroud, their oxygen content of 0.19 mass% as the lowest conventional figure was still more reduced by changing the composition of combustion gas. Introduction of nitrogen gas to the combustion chamber lowered the temperature of the in-flight spray particles while maintaining their high velocity. This method could reduce the oxygen level of a HastelloyC coating to 0.063 mass% at the lowest present value, which is comparable to that of the feedstock with 0.042 mass%. Other coating with 0.14 mass% could be obtained along with the open porosity below 0.1 vol%. The latter coating exhibited the improved environmental barrier property in artificial seawater.

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Effect of adding cobalt on the shape memory properties of Ni-Mn-Ga sputtered films was investigated. It was found that the films containing cobalt less than 5.1 mol% has a single phase and those with more than 6.8 mol%Co has two phases. The Curie temperature increased and the saturation magnetization decreased with increasing cobalt content. These films exhibited one way shape memory effect. The shape recovery start temperature increased and the temperature range of shape change broadened with increasing cobalt content.

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The vertical Ohno Continuous Casting (OCC) process was used to examine the possibility of casting Al-In monotectic alloys with a homogeneous microstructure. Three compositions, Al-17.3 mass%In, Al-20 mass%In, and Al-25 mass%In were used in this study. Al-In alloy ingots with a diameter of 8 mm and a length of 400 mm could be continuously cast by controlling the temperature and solidification velocity of the melt regardless of the alloy compositions. The Al-In alloy ingots had a very beautiful surface and a unidirectional macrostructure. Furthermore, the Al-In alloys exhibited a good distribution of β-In particles throughout all sections without any segregation of β-In phase.

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Precipitation behavior of intermetallic phases in ferrite matrix is investigated by transmission electron microscopy (TEM) in Fe-10Cr-1.4W-4.5Co (at%) alloys with and without 0.3 at%Si. It is intended to provide basic information for the alloy design of ferritic heat resistant alloys strengthened by intermetallic compounds. In the alloy containing Si, icosahedral quasicrytalline phase (I-phase) is found to precipitate during aging at 873 K. It is confirmed that selected area diffraction (SAD) patterns of the precipitates exhibit two-, three- and five-fold symmetry and have diffraction spots in the positions related to the golden section. In the Si-free alloy, the R-phase precipitates instead of I-phase at 873 K, and the Laves phase precipitates in both alloys during aging at higher temperature, 973 K. The Laves phase formed at 973 K transforms to the I-phase in the alloy containing Si but to the R-phase in the Si-free alloy during subsequent aging at 873 K. It is found that the structures among icosahedral quasicrystalline and crystalline R- and Laves phases are closely similar by comparing the orientation relationship, precipitate morphology and stability of I-phase with those of R- and Laves phases.

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Blow forming characteristics of AZ31 Mg alloy recycled by solid-state recycling were investigated. Cylindrical scraps and machined chips were recycled by hot extrusion and hot rolling in air. Oxide layers were observed in the recycled specimens by oxygen mapping with EPMA (Electron Probe Micro Analyser). The interval of the oxygen layers for the specimen from machined chips was much shorter than that for the specimen from cylindrical scraps. As a result of tensile tests, the mechanical properties of the specimen from cylindrical scraps were found to be almost the same as those of a rolled specimen from a virgin ingot. On the other hand, at elevated temperatures, the elongation of the specimens from machined chips was low, compared with those of the rolled specimens from a virgin ingot. The large amount of oxide contamination is likely to be responsible for the lower elongation of the specimens from machined chips. In blow-forming tests, the specimen from cylindrical scraps exhibited excellent formability similar to the rolled specimen from a virgin ingot. However, the specimen from machined chips showed poor formability. Thus, oxide contamination adversely affected the formability of recycled Mg alloy.

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In order to investigate the effect of aging heat treatment and surface orientation on oxidation during the nanopore formation of B2-type FeAl, the surface of Fe-48 mol%Al single crystal was analyzed by Auger Electron Spectroscopy (AES). Electropolished and plasma-cleaned surfaces were aged for 18 ks at 723 K, in vacuum (about 5 × 10⁻⁴ Pa). A thin oxide layer was already formed on the non-aged surface. A thicker oxide layer was grown on the aged surface, but the difference in thickness of the oxide layers was slight. Further, the orientation dependence of the thickness of the oxide layers was even smaller. The thickness of the oxide layer on the FeAl single crystal is comparable to that of the passive film on the aluminum foil. Therefore, it is concluded that the influence of the aging heat treatment on oxidation during the nanopore formation of B2-type FeAl is negligible.

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This paper describes magnetic properties and microstructures of Sm-Fe-N thick films prepared by the aerosol deposition (AD) method. The maximum thickness (d) of 77 μm was obtained in the AD conditions of gas flow rate (gfr) = 6 × 10⁻³ m³/min for 4 min. From this result, the deposition rate was estimated as 19 μm/min. The density (ρ) of Sm-Fe-N films were in the range of 4.9 × 10³−5.9 × 10³ kg/m³, which were 64—77% of the X-ray density of the Sm₂Fe₁₇N₃ compound reported (7.67 × 10³ kg/m³). However, they were higher than the density of the green compact of Sm-Fe-N host powders (3.86 × 10³ kg/m³). The Sm-Fe-N AD films showed the remanences (B_r) of 0.36—0.42 T, which were 58—68% of that of host powder (0.62 T). The coercivities (μ₀H_cJ) increased from 1.16 T to 1.69—1.86 T after the deposition because the average grain size decreased from 1.94 to 0.32 μm. XRD analysis revealed that the ratio of peak intensity of (006) to (033) in the Sm-Fe-N AD films was higher than that in the host powder. In addition, the remanence measured in perpendicular to the film plane was higher than that in parallel after the compensation of demagnetizing field. Therefore, it is considered that the c-axis in Sm-Fe-N AD films has a tendency to align in perpendicular to the film plane.

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Ternary compound Ti₃SiC₂ has been successfully synthesized and concurrently consolidated by sintering green compact of starting powder mixture. 3Ti/SiC/C powder mixture was compacted and heated in vacuum or in Ar atmosphere at temperatures from 1573 to 1773 K for a time period ranged from 2 to 6 hours. It has been found that either in vacuum or in Ar atmosphere the Ti₃SiC₂ content reached 100% in the surface layer. The growth of Ti₃SiC₂ in a layered manner on the surface of the sample was observed. It was also found that the sample sintered in Ar atmosphere is denser than those sintered in vacuum. After sintered in Ar atmosphere at 1773 K for 2 hours, the relative density of the compound reached 97%. Occurrence of liquid phase during sintering contributed to the densification of the compound.

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Surface nanocrystallization in various steels by shot peening (both air blast (ABSP) and ultrasonic (USSP)) was investigated. In all the shot-peened specimens, the equiaxed nanocrystals with grain size of several 10 nm were observed at the surface regions. The depth of nanocrystalline (NC) layers was several μm. The NC layers have extremely high hardness and were separated from the deformed structure regions just under the NC layers with sharp boundaries. By annealing, the NC layers show the substantially slow grain growth without recrystallization. These characteristics are similar to those observed in the specimens treated by ball milling, ball drop and particle impact deformation. Comparing ABSP and USSP at the similar peening condition, the produced volume of NC region in ABSP is larger than that in USSP.

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The phase equilibria in the Sn-Ag-Bi-Cu quaternary system have been studied experimentally and using thermodynamic calculations. The phase boundaries in some vertical sections of the Sn-Bi-Cu and Sn-Ag-Bi-Cu systems were determined using differential scanning calorimetry. The experimental values of the thermodynamic parameters were used in the calculations of the phase diagrams for the quaternary system. Thermodynamic evaluation of the Sn-Bi-Cu system was performed by considering a two-phase separation of the liquid phase. The phase diagram calculations showed that the Cu-Sn-based compounds form as the primary crystals, even for low Cu concentrations, and accordingly, the melting point of the alloys rises markedly. The microstructure of the solidified alloys was observed using a scanning electron microscope. We observed that coarsened Bi particles existed alongside the Cu-Sn-based primary crystals. Based on these results, a non-equilibrium solidification process using the Scheil model was simulated and compared with the observed structures. Our calculations reasonably explain the Bi-enrichment in the final solidification zone.

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The present paper describes the grain size refinements of Mg alloys (AZ61, AZ91, ZK60) by HDDR treatment. As a result of the HDDR treatment at 350°C under a hydrogen pressure of 7 MPa for 24 h, following by evacuation at 350°C for 3 h, the grain size of AZ61 alloys was reduced from 10∼20 μm to 100∼200 nm. At the hydrogenation stage for the AZ91 alloys, the disproportionation reaction occurred with forming MgH₂, Mg₂Al₃ and Al phases. At the following desorption stage, the three phases were recombined and the Mg-Al-Zn solid-solution alloy was reformed. After the HDDR treatment, the grain size of AZ91 alloys was reduced to 100∼200 nm. For the ZK60 alloy without Al, the grain size was reduced from 2∼20 μm to about 300 nm by the HDDR treatment.

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In this work, a growth analysis is made on the banded microstructure formation during directional solidification of peritectic alloys. The convection model, which has been proposed to explain the discrete banded microstructure formation, is extended in the part of the nucleation condition. Applying the nucleation and constitutional undercooling criterion, a new calculation was developed. Concentration profile calculated by the model was compared with experimentally obtained banded microstructure in Fe-Co and also with those of the convection and the diffusion models. Consistent agreement with experiments is shown. In comparison with the other models, interesting difference in predictions of concentration profile is obtained between them.

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