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Volume 58, Issue 4
Displaying 1-15 of 15 articles from this issue
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Sadahiro Tsurekawa, Tomoaki Tanaka, Hideharu Nakashima, Hideo Yoshinag ...1994 Volume 58 Issue 4 Pages 377-381
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA Σ17b boundary in molybdenum has high fracture strength, though this boundary has a poor atom matching compared with Σ9 and Σ11 coincidence boundaries. In order to clarify the reason from the viewpoint of grain boundary structure, the transmission electron microscopy observations have been conducted. The grain boundary of (334) Σ17b is shown to be a plane matching boundary which is regarded as one of the low energy boundaries. Interface dislocations to assure the coherency at the boundary are present in addition to DSC dislocations. Such a coherent nature of the boundary structure due to the presence of the dislocations is considered to be responsible for the fairly high fracture strength of the boundary.View full abstractDownload PDF (1186K) -
Tomoaki Tanaka, Sadahiro Tsurekawa, Hideharu Nakashima, Hideo Yoshinag ...1994 Volume 58 Issue 4 Pages 382-389
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe fracture strength in molybdenum depends markedly on the grain boundary character. In order to clarify the relationship between the grain boundary fracture strength and the grain boundary energy, purified bicrystals with ⟨110⟩ symmetric tilt boundaries were prepared and grain boundary energies were measured by the thermal grooving technique. Further, the misorientation angle, φ, dependence of the fracture strength was investigated in a range of φ from 90° to 180° over which the data are scarcely available. The main results obtained are summarized as follows.
(1) The fracture strength depends on the misorientation angle: the (111) Σ3 boundary is as strong as the single crystal, whereas the (122) Σ9 boundary is weak. The (334) Σ17b boundary is stronger than near the Σ9 and Σ11 boundaries in spite of its low coincidence density.
(2) There is a correlation between the fracture strength and the grain boundary energy though the data scattering is large. The energy cusps are observed for the (112) and (111) Σ3 boundaries which are high in fracture strength, while the energy is high for the near-Σ9 and Σ11 boundaries which are low in fracture strength.
(3) No peak in fracture strength is found around the (233) Σ11 boundary, though the boundary is regarded as a stable one in the bcc structure.View full abstractDownload PDF (1722K) -
Sadahiro Tsurekawa, Hideo Yoshinaga1994 Volume 58 Issue 4 Pages 390-396
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to clarify whether the dislocations in a titanium carbide crystal dissociate or not, single crystals with various C/Ti atom ratios, 0.59∼0.95, were deformed and dislocations introduced by deformation were observed by transmission electron microscopy using weak-beam and high resolution techniques.
It is found that the dislocations dissociate into partials. The dissociation width increases with the decrease in C/Ti ratio from 1.75 nm for TiC0.95 to 4.2 nm for TiC0.59, which leads to the stacking fault energy from 130 to 300 mJ/m2. The effects of image force and imaging conditions for the weak-beam observation on the observed dissociate width are discussed for precise estimation of the stacking fault energy.View full abstractDownload PDF (1288K) -
Yoritoshi Minamino, Toshimi Yamane, Shigeoki Saji, Keiichi Hirao, Suen ...1994 Volume 58 Issue 4 Pages 397-403
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDiffusion of Cu, Fe, and Si in the Ni3Al phase (γ′) of an intermetallic compound with L12 structure has been studied at temperatures from 1173 to 1598 K using the diffusion couples of (Ni-24.2 mol%Al/Ni-24.1 mol%Al-4.73 mol%Cu), (Ni-24.2 mol%Al/Ni-23.7 mol%Al-3.52 mol%Fe), and (Ni-24.2 mol%Al/Ni-22.3 mol%Al-3.14 mol%Si). The diffusion profiles in the annealed diffusion couples were measured by an electron probe microanalyzer. The diffusion coefficients of Cu, Fe, and Si in γ′ of 24.2 mol%Al were evaluated from the diffusion profiles by Hall’s method. The temperature dependence of the diffusion coefficients (m2/s) is presented as follows:
(This article is not displayable. Please see full text pdf.)
\ oindentThe activation energies are found to be closely related to the substitution behavior of Cu, Fe and Si atoms in the L12 lattice sites of γ′.View full abstractDownload PDF (702K) -
Keizo Kashihara, Minoru Tagami, Fukuji Inoko1994 Volume 58 Issue 4 Pages 404-410
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSEffects of free surface on the formation of recrystallized grains were discussed in terms of the differences in the deformation structure, recovery process, and total energy of grain boundaries around a recrystallization nucleus between the surface and inner layers in an aluminum single crystal with a Schmid factor of 0.5. For this purpose, the specimens were deformed in tension to the strain of 0.5 and subsequently annealed. During the annealing, the existence of the free surface promotes the formation of recrystallized grains in the surface layer. It is concluded that the recovery of deformed structures with a high density of dislocations is easier and the total energy of grain boundaries around a nucleus of recrystallization is smaller in the surface layer than in the inner layer.View full abstractDownload PDF (865K) -
Yoshitaka Iwabuchi, Isao Kobayashi, Masaki Ohmori, Masato Kikuchi1994 Volume 58 Issue 4 Pages 411-417
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe study was made of the behavior of α′→γ reverse transformation and γ→α′ martensitic transformation as a function of prior microstructure in type SCS5 soft martensitic stainless cast steel by means of dilatometric measurements and metallographic observations. The initial retained austenite decreased with the increase of heating temperature beyond TAs because of unstabilization of austenite. In the heating range between TAs and TAf, dilatometric curves showed the noticeable shrinking for the specimens with the as-quenched and quenched & tempered structures, but the monotonous expanding for the specimens which was subjected to pre-treatment in the α+γ phase range. During cooling after the α′→γ reverse transformation, martensitic transformation occurred in which Ms increased with increasing total austenite content. The increase of the total austenite content resulted in unstabilizing itself, increasing the fresh martensite and consequently the hardness.View full abstractDownload PDF (1105K) -
Manabu Enoki, Shinichi Fujikawa, Teruo Kishi1994 Volume 58 Issue 4 Pages 418-423
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSFully-lamellar TiAl has higher fracture toughness than the duplex one. Some toughening mechanisms of fully-lamellar TiAl have been proposed to explain this difference, but only few quantitative evaluations of fracture toughness have been carried out. This paper has elucidated the mechanism of fracture toughness of fully-lamellar TiAl quantitatively. The following knowledge could be revealed by the fracture test of various grain size fully-lamellar TiAl and the modeling of fracture mechanism based upon the observation of crack propagation. Fracture toughness of fully-lamellar TiAl increases in accordance with grain size coarsening. Fracture toughness of this material could be divided into the matrix fracture toughness, the microcrack stress shielding contribution and the shear ligaments contribution with which fracture toughness increase could be mainly explained. Shear ligaments are the unconnected part between microcracks in front of main crack and formed in the process zone as the result of mismatched crack planes of deflected cracks. This fracture toughness increase is mainly responsible for shear ligaments toughening, which is indicated by a fracture model given by observation of the side view of crack propagation.View full abstractDownload PDF (1378K) -
Manabu Enoki, Shinichi Fujikawa, Teruo Kishi1994 Volume 58 Issue 4 Pages 424-429
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThis study deals with the influence of microfracture mechanism to fracture toughness of fully-lamellar TiAl. It is elucidated from the evaluation of grain size dependence of dynamic fracture toughness KId and the comparison of KId with static fracture toughness KIC. The KId of fully-lamellar TiAl decreased with increasing grain size increase. This result could be explained by the comparison between the dynamic and static fracture surfaces and the evaluation of both the microcrack nucleation time from the acoustic emission (AE) method and the stress intensity factor corresponding to the initiation of AE. That is, there was not enough time to create microcracks which could induce shear ligament toughening in the dynamic condition. It was concluded that shear ligament toughening could not emerge in the dynamic condition and also that KId could not increase with grain size increase.View full abstractDownload PDF (811K) -
Masato Murata, Yoshihiko Mukai1994 Volume 58 Issue 4 Pages 430-435
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe appearance of SCC initiation in SUS304 (smooth specimen, in 42%MgCl2) was found to resemble that of a crack initiation of the Stroh model. The applicability of the Stroh model to SCC initiation was discussed by fracture mechanics simulation. In this study, a finite element program with the modified bond element was developed to analyze the heterogenious slip deformation. As the result, the regidity of the slip plane decreased with the slip line corrosion occurring on the slip line and a singular stress induced by slip line corrosion increased at the slip tip. In addition, the limit stress for SCC, σth, was regarded as the stress which could induce the lower limit of stress intensity, such as KISCC, at the slip tip.View full abstractDownload PDF (611K) -
Masahito Sugiura, Akio Fuwa1994 Volume 58 Issue 4 Pages 436-441
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSUsing a hot-wall CVD reactor, silicon precipitation rates in the SiHCl3-Ar and SiHCl3-H2-Ar systems were measured in order to elucidate the reaction kinetics in these systems. Silicon precipitation in the former system takes place through the thermal decomposition reaction of SiHCl3 and its rate is a function of reactant SiHCl3 mole fraction and reaction temperature. That in the latter system takes place through the hydrogen reduction of SiHCl3 in addition to the thermal decomposition reaction and its rate can be expressed as a function of SiHCl3 and H2 mole fractions and temperature. In both systems, the transition temperature from chemical reaction control region to mass transfer control region is around 1173 K. From the observed reactant concentration dependence on these rate expression, a plausible reaction mechanism is proposed where SiCl2(g) and its adsorbed species are the reaction intermediate in the precipitation reaction scheme.View full abstractDownload PDF (541K) -
Noboru Yoshikawa, Kazuyuki Higashino, Atsushi Kikuchi1994 Volume 58 Issue 4 Pages 442-447
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSReactant gas mixture composed of TiCl4, H2, and N2 was introduced to the tubular reactor and TiN was deposited on the inner wall of the reactor.
Relationships between gas flow rates and growth rates of the films were examined at 1273 K and at various gas compositions in order to determine the gas flow rates required for the reaction controlled conditions.
Under these conditions, the following empirical rate equations were obtained:
1) R=k1·PN2·PH20.5·PTiCl4−0.2 1.52kPa≤PTiCl4≤4.05kPa,PN2⁄(PN2+PH2)≤0.5
2) R=k1·PN20.5·PH2·PTiCl4−0.2 1.52kPa<PTiCl4≤4.05kPa,0.5≤PN2⁄(PN2+PH2)<0.67
3) R=k3·PN20·PH20 PTiCl4∼1.52kPa,PN2⁄(PN2+PH2)≥0.5
4) R=k2·PN20.5·PH2·PTiCl4−0.3 1.52kPa<PTiCl4≤4.05kPa,PN2⁄(PN2+PH2)≥0.67
\ oindentwhere k1=1.3×10−2 nm· s−1 (kPa)−1.3, k2=1.71×10−2 nm· s−1 (kPa)−1.2, k3=3.83 nm· s−1
The apparent activation energy at PTiCl4=2.43 kPa and PN2⁄(PN2+PH2)=0.5 was determined to be 230 kJ/mol (1193∼1273 K).
From an examination of the reaction mechanism, it is concluded that the reaction rate is expressed in the following equation:
(This article is not displayable. Please see full text pdf.)
\ oindentwhere Piin (i=H2, N2, TiCl4) is the partial pressure of i component in the reactant gas mixture, PHCl′=(PTiCl4in)0.5·(PH2in)0.25, k#, KH2, KN2, KHCl are constants proportional to the reaction rate constant, adsorption equilibrium constants of H2, N2, HCl, respectively, and K* is a constant that is related with the partial pressures and adsorption equilibrium constants of TiCln (n=1, 4).View full abstractDownload PDF (415K) -
Tetsu Go, Nobuyoshi Hara, Katsuhisa Sugimoto1994 Volume 58 Issue 4 Pages 448-454
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe formation process of a TiO2 thin film on a Si(100) substrate by low-pressure CVD with tetraisopropyl titanate (TPT) has been studied by in-situ ellipsometry. Changes in the growth rate and the refractive index of the film obtained from ellipsometry were examined as a function of the substrate temperature, the vaporization temperature of TPT, and the flow rate of O2 reactant gas. The formation process of the film at the substrate temperatures below 569 K can be divided into two regions; the initial region corresponding to the nucleation of TiO2 and the steady state region corresponding to the growth of the TiO2 layer after coalescence of the nuclei. The initial region was undistinguishable at the substrate temperatures higher than 600 K. The growth rate in the steady state region increased with increasing substrate temperature and the refractive index decreased. At a constant substrate temperature of 695 K, both the growth rate and the refractive index increased with increasing vaporization temperature of TPT. A Raman spectroscopic analysis indicated that the film has an anatase structure. An infrared spectroscopic analysis suggested that the more ordered anatase is formed with the higher substrate temperature.View full abstractDownload PDF (532K) -
Shigekazu Otomo1994 Volume 58 Issue 4 Pages 455-460
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effects of the addition of Cr and Ti on wear and soft magnetic properties has been investigated for Fe-Al-Si alloys in order to improve the wear resistance of heads for VTRs. We find that the head wear rate increases greatly with increasing relative humidity, and varies depending on the tape properties. The surface hardness of magnetic tapes increases with increasing relative humidity and is high in the case of highly abrasive tapes. Addition of Ti and Cr increases the hardness and the corrosion resistance of the Fe-Al-Si alloy and reduces the wear rate, especially for the highly abrasive tapes, and the high relative humidity. A minimum coercivity and a maximum permeability have been obtained in the 7.5∼8 mass%Si and 7.5∼9.5 mass%Al Sendust alloy with 3 mass%Cr and 1 mass%Ti. This optimum composition coincides with that in which the magnetocrystalline anisotropy constant, K1, and the magnetostriction constant, λs, is close to zero. The alloy with 3 mass%Cr and 1 mass%Ti and with optimum Si and Al concentrations shows lower coercivity, higher permeability and higher electrical resistivity, ρ, than the conventional Sendust alloy. The heads for broadcast VTRs using this alloy are 20∼30% higher in output than the conventional head.View full abstractDownload PDF (501K) -
Ken’ichi Miura, Tomoyuki Mizukoshi, Itsuo Ishigami, Masato Kuno, ...1994 Volume 58 Issue 4 Pages 461-467
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSElectron-probe X-ray microanalysis is convenient and practical for quantitative analysis of titanium nitride films as hard coatings. However, the conventional ZAF correction method is not applicable to thin coatings because the electron beam penetrates into a substrate. This paper concerns a quantum-theoretical analysis of thin coatings by EPMA and verification of its validity. The new analysis has been established based on the ZAF method; the analysis is given as a function of mass thickness, ρ×t, where ρ and t are the density and the thickness of coatings respectively. Analysis of titanium nitride coatings was carried out at electron beam voltages over the range of 6 to 28 kV. For a coatings as thin as 0.54 μm, the chemical compositions of Ti calculated from the present analysis remained constant in the above voltage range, whereas those from the ZAF method decreased monotonically with increasing in voltage over 12 kV. On the contrary, for a thick coatings 12.55 μm in thickness, the compositions obtained from both models were independent of the beam voltages. These results show that the present method is effective in the analysis of thin coatings.View full abstractDownload PDF (806K) -
Hiroyuki Toda, Toshiro Kobayashi, Mitsuo Niinomi1994 Volume 58 Issue 4 Pages 468-475
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effect of matrix microstructure on fracture characteristics of 6061 aluminum alloy reinforced with SiC whisker was investigated.
The underaged composite exhibits stable slow crack growth behaviour and possesses a high fracture toughness value of 20.0 MPa\sqrtm. On the other hand, with increasing aging time, the fracture characteristics changes drastically to low stress type brittle fracture without stable crack growth, and the fracture toughness is degraded to the minimum level of 13.6 MPa\sqrtm in the peakaged composite. Detailed SEM observations of the fracture surfaces and cross-section of a specimen show that the microscopic fracture mechanisms of the underaged composite has the tendency of void nucleation and growth at the sharp corners of whiskers, and it is considered due to severe stress concentration. Meanwhile whisker breakage is mainly observed in the peakaged and overaged composites, and it is considered to be attributed to immediate rapid and unstable fracture.
From the microstructural observations carried out using TEM, narrow PFZ is observed around whiskers and it is accompanied by coarse precipitates on their surfaces in the peakaged composite. Further, the density and size of the precipitates, according to direct and high-magnification observations on the surfaces of whiskers, increase with increasing aging time. The change of the microscopic fracture mechanism with increasing aging time in the mechanical property tests is attributed to both lowering of whisker fracture strength due to existence of coarse precipitates on its surface and depression of hydrostatic stress around sharp edges of whiskers due to existence of ductile PFZ layers. Therefore the premature fracture of whisker is considered to occur at a lower load level than nucleation of voids at the corners of whiskers in the peakaged and overaged composites.View full abstractDownload PDF (2145K)
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