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Volume 62, Issue 4
Displaying 1-15 of 15 articles from this issue
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Hidemichi Fujiwara, Tatsuo Sato, Akihiko Kamio1998 Volume 62 Issue 4 Pages 301-309
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAn influence of the alloy content of nickel and silicon on the precipitation kinetics and precipitation hardening mechanism in Cu-Ni-Si alloys has been studied.
The degree and the rate of precipitation and the hardness change in the precipitation process increase with increasing an alloying elements. The degree and the rate of precipitation and the hardness changes show a maximum value in the condition that the atomic content of nickel is twice that of silicon.
During isothermal aging two kinds of precipitates, Ni2Si and Ni3Si, were observed. Ni2Si presipitates are plate-like in shape and have an orthorhombic type crystal structure. The orientation relationship between Ni2Si and matrix is, (110)Cu\varparallel(001)Ni2Si, [001]Cu\varparallel[010]Ni2Si. The Ni3Si precipitates are spherical and have a L12-type crystal structure coherent with the matrix.
From analysis of the hardening mechanism, it suggested that hardenability in the Cu-Ni-Si alloys during precipitation is mostly contributed to misfit-strain hardening of Ni2Si.View full abstractDownload PDF (1019K) -
Kazuto Hamaishi, Hidekazu Sueyoshi, Takayuki Shiomizu1998 Volume 62 Issue 4 Pages 310-316
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThree types of austenitic stainless steels, SUS304, SUS316 and SUS310 were preheated in air, followed by nitriding in NH3 gas in a temperature renge of 773 to 873 K. The influences of nitriding temperature and time on nitriding behavior were examined in connection with the kinetics of nitriding reaction.
The nitriding reaction occurs locally at early stage of nitriding treatment. The whole surface becomes covered with nitrided layer by coalescence of nitrided regions. Thereafter, nitrided layer with a uniform thickness is formed by the growth in the depth direction.
Diffusion of nitrogen through nitrided layer is the rate-determining process in the growth of the nitrided layer. Atmospheric preheating has no influence on the growth of nitrided layer. On the other hand the nucleation of nitriding reaction is greatly accelerated by atmospheric preheating. This is attributed to both considerably dissociation of NH3 gas and the rapid diffusion of nitrogen through surface film due to the change in the composition of the surface film with atmospheric preheating. The hardness of the nitrided layer decreases with increasing nitriding temperature.View full abstractDownload PDF (762K) -
Ryuichiro Oshima, Hisato Tokoro1998 Volume 62 Issue 4 Pages 317-326
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSWith a disorder-order transition of FePd alloys from A1 to L10, characteristic micro-twin structures are formed, and marked uniaxial magnetic anisotropy is revealed, and much work has been done regarding the relation between microstructures and magnetic properties of the alloys. Few work, however, has been reported as to the effect of magnetic field on the morphology change at the beginning of order reactions of the alloys. The present study has been carried out to examine microstructure changes of an early stage of ordering of FePd alloys with heating at various temperatures near the magnetic Curie temperature under magnetic fields by transmission electron microscopy. The results are summarized as follows: (1) By in-situ transmission electron microscope observations with a standard objective pole piece particular variant domains grow preferentially, while every variant domain nucleates homogeneously with an anti-magnetic objective pole piece. (2) Under a magnetic field parallel to the specimen surface, a variant crystal with c-axis near the direction of the magnetic field starts to grow from grain boundaries, and {011} macrotwins are formed as accommodation defects. (3) Magneto-heat treatment effect is present in a certain temperature range of ferromagnetic short range order just above the magnetic Curie temperature. (4) Magnetostriction calculated from elastic constants is an order of 10−5, which seems small but still plays an important role in the initiation of variant domains.View full abstractDownload PDF (2178K) -
Masayuki Tabuchi, Kenzaburo Marukawa1998 Volume 62 Issue 4 Pages 327-332
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe bainitic transformation is known to have an intermediate nature between the martensitic transformation and the diffusional transformation, while its transformation mechanism has not yet been clarified precisely. If this transformation involves lattice shearing like the martensitic transformation, it should take place more easily in those alloys which have a higher tendency to transform martensitically. On this expectation, the composition dependence of bainitic transformation kinetics has been studied in Cu-Zn-Al alloys. Especially, the relation between the martensitic transformation temperature (Ms) and the bainitic transformation rate was examined. The transformation process was traced by measuring the electrical resistivity of specimens during aging. It was found that the transformation rate is higher in those alloys having a higher Ms temperature. The activation energy for the process, obtained from its temperature dependence, is independent of the alloy composition and roughly equal to that for solute diffusion in the parent alloy. This indicates that the transformation is controlled by diffusion of solute atoms. The composition dependence of the bainitic transformation rate is discussed in terms of a diffusion controlled growth theory.View full abstractDownload PDF (413K) -
Masayuki Yoshiba, Kunihiko Wada, Yoshio Harada1998 Volume 62 Issue 4 Pages 333-342
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCreep rupture properties and creep failure behavior in the hot corrosive environment by means of adopting molten salt were investigated of the plasma spray coated Ni-base superalloy systems with different spraying conditions, including the thermal barrier coating (TBC) system with the Y2O3-stabilized ZrO2 ceramic top-coat.
Characteristic manners of the coating failure were observed in the different coating systems. The most significant creep rupture property degradation was found to occur in the air plasma sprayed (APS) NiCrAlY coating system (NA) in accidental and brittle manners, although thermal cycle susceptibility of the corrosion-induced premature rupture is rather mitigated. On the other hand, the TBC system (NVZ) was confirmed to minimize the corrosion-induced strength degradation mainly by virtue of effective protection of the coating layer against a general corrosion. In this TBC system, however, the existing top-coat defect associated with a segmentation structure was revealed to cause an extremely localized coating failure because of introducing the localized and intensive attack to the NiCrAlY under-coat layer just below the top-coat crack-opened.
A possible failure mechanism and its affecting factors for the coating system failure were discussed mainly from the viewpoint of simultaneous stress-corrosion effect.View full abstractDownload PDF (1325K) -
Akira Muto, Shoji Goto, Michihiro Tagami, Setuo Aso1998 Volume 62 Issue 4 Pages 343-350
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to clarify the feature of high temperature deformation in fine-grained α Brass, a Cu-30 mass%Zn specimen with a grain size of 0.012 mm diameter was prepared by annealing for 3.6 ks at 723 K. A constant stresses creep tests were conducted for the specimen under various stresses from 9.8 MPa to 39.2 MPa at 673 K. Their creep curves were compared with each other. The test under 39.2 MPa reveals a normal type of creep curve consisting of transient creep (the 1st creep stage), steady-state creep (the 2nd creep stage) and accelerating creep (the 3rd creep stage). On the other hand, the test under the stresses less than 29.4 MPa reveal an anomalous type of creep curve in which the strain rate at the 3rd creep stage increases with increasing strain in the beginning, attains peak value and then decrease. This decreasing stage in strain rate is called the 4th creep stage.
The amounts of strain to the 2nd creep stage, the peak strain rate and the creep fracture do not depend on the stress and correspond to 0.3, 0.6, and 0.7 in true strain, respectively.
The reason for the anomalous type of creep curve is discussed mainly from view points of grain growth during creep deformation, dynamic recrystarization, work hardening and grain boundary sliding.View full abstractDownload PDF (1573K) -
Sang-Pill Lee, Gen Sasaki, Hideharu Fukunaga1998 Volume 62 Issue 4 Pages 351-357
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSBy alternating MoSi2 powder layer with Nb sheet, followed with hot pressing in a graphite mould, Nb/MoSi2 laminate composites have been successfully prepared. The volume fraction and the number of Nb sheet induced in this system are nominally 10 vol% and 4 layers, respectively. The purpose of the present work is to investigate the effect of fabricating conditions on the impact properties of Nb/MoSi2 laminate composites and to examine the variation of their impact values through the heat treatment. Lamination of the Nb sheet and the MoSi2 layer showed a sufficient improvement in the absorbed impact energy compared to that of monolithic MoSi2 material. It has been found that the impact value of the laminate composites obviously decreased when sintered at consolidation temperatures higher than 1523 K, even if the composite density contributing to impact load increased along with consolidation temperatures. The impact value of the laminate composites was also dramatically reduced with the growth of reaction layer after the heat treatment. However, it is effective in the improvement of the impact value to increase the pressure and its holding time at the same consolidation temperature.View full abstractDownload PDF (869K) -
Akira Nozue, Koji Endo, Seiji Tateishi, Tadatsune Okubo1998 Volume 62 Issue 4 Pages 358-362
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIt has been suggested that hydrogen-induced cracking may occur in titanium alloys utilized in aggressive environments. In the present study, hydrogen-induced cracking in conventionally heat-treated titanium alloys was evaluated on the basis of microstructure and stress conditions. Ti-15V-3Cr-3Sn-3Al, Ti-10V-2Fe-3Al and Ti-6Al-4V alloys with fatigue pre-cracks were tested in the compact tension specimen whilst undergoing cathode-charging in a H2SO4 solution at 200-1000 A/m2 in order to simulate an aggressive operating environment. Crack initiation and propagation were characterized by using acoustic emission, crack opening displacement and video microscopy. Under no-loading conditions, the Ti-15V-3Cr-3Sn-3Al and Ti-10V-2Fe-3Al alloys failed during cathode charging, whilst the Ti-6Al-4V alloy was uncracked. These differences are attributed to the very fine precipitation α in a matrix of β for the Ti-15V-3Cr-3Sn-3Al and Ti-10V-2Fe-3Al alloys, which may promote hydrogen-induced cracking. Acoustic emission and the crack opening displacement rapidly increased at a position close to the corresponding threshold stress intensity factor estimated in a previous study of delayed cracking by the authors.View full abstractDownload PDF (508K) -
Ryoichi Monzen, Junya Asaoka, Kazuhisa Kita, Kazuo Kitagawa1998 Volume 62 Issue 4 Pages 363-368
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effects of additions of alloying elements (Ni, Co, Ag, Bi, P) on the recovery of work hardening have been studied in Cu single crystals with nearly spherical α-Fe particles. Adding the solute elements does not change the softening mechanism; that is, Orowan loops around the particles climb and disappear by pipe diffusion through their own cores. For the alloys with Ni, Co, Ag and Bi, the loop climb rate decreases with increasing concentration of each element and eventually becomes a certain value. At the stage, the activation energies Q for pipe diffusion are approximately 70% of the activation energies for bulk diffusion of the elements in Cu. The addition of the elements also increases the frequency factor D0 for pipe diffusion. The Q and D0 values remain unchanged by the P addition. It is shown that these observations are evidently brought about by the significant presence of each element in the proximity of the dislocation core. The softening after work hardening in the Ag-added Cu alloy single crystals containing rod-shaped α-Fe particles has also been examined with respect to two kinds of geometrical relationships between the Orowan loops and the flat habit plane of the particles. In the first case the Orowan loops touch the habit plane during climbing, while in the second case they do not. Although the Ag addition results in the increase of Q and D0 in both cases, the former has smaller values of Q and D0 than the latter. This is because the amount of Ag segregation on the habit plane is lower than that on the matrix-particle interface.View full abstractDownload PDF (705K) -
Kei-ichi Fukunaga, Yasuhiro Miura1998 Volume 62 Issue 4 Pages 369-376
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAn X-ray diffraction study and measurement of compressive yield strength were made on L12-Al3Sc intermetallics, and the nature of dislocations was determined by transmission electron microscopy. The main results are as follows. The lattice constant of Al3Sc determined by the X-ray powder method is 0.4103 nm. The long range order parameter at 1273 K is estimated to be 0.92. The yield strength of the Al3Sc alloys showed a decrease in the low temperature range (77 K∼room temperature) and a slight increase in the higher temperature range. At low temperature deformation, a⟨110⟩ superdislocations glide on a{111} plane, and dissociate into two a/3⟨112⟩ superpartials separated by a SISF(superlattice intrinsic stacking fault). The SISF energy estimated from the dissociation distance is 170 mJ/m2 at 77 K, 230 mJ/m2 at 210 K and 290 mJ/m2 at 293 K. An in-situ high temperature observation revealed that the width of the SISF on {111} decreases with increasing temperature, until the superdislocations begin to dissociate on {100} planes into a/2⟨100⟩ partials at 873 K.View full abstractDownload PDF (1513K) -
Hiromitsu Takeuchi, Yoshiki Tsunekawa, Masahiro Okumiya, Yutaka Kawai1998 Volume 62 Issue 4 Pages 377-382
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThis paper presents a novel selective electroplating method that utilizes an electrolyte jet, instead of insulation masking on a substrate. The deposits have a convex shaped cross-section in the jet electroplating, so that the electrolyte jet is appropriately applied to selective electroplating. Even without masking process, a definite boundary between plated and non-plated area needs to be achieved in selective electroplating. The flat electroplated area, in which the current density distribution is nearly uniform, is deposited by using the nozzle with a center bar. However, the boundary becomes indistinct with this nozzle. The current density distribution on a cathode surface can be simulated by applying a finite element method based on the Laplace equation in steady state. The calculations suggest that the flat deposit area with a definite boundary will be created, if the electrolyte jet is limited to strike only on the projected nozzle area of a substrate. A modified nozzle with high velocity air holes adjacent to an electrolyte jet is designed, which successfully creates the flat deposit similar to the simulated cross-section profile.View full abstractDownload PDF (553K) -
Naoki Matsuoka, Koji Hayashi1998 Volume 62 Issue 4 Pages 383-389
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA difference equation for the growth of large grains in a grain-dispersed alloy model, where a large amount of uniform fine grains and an extremely small amount of large grains {the initial sizes (diameter) are dF,0 and dL,0, respectively. dL,0⁄dF,0≥2} are dispersed in the liquid phase was derived on the assumption that the rate-determining step of Ostwald ripening is the interface reaction. Next, the numerical calculation of the size (dL,3.6) of WC large grains after the sintering of 1673 K-3.6 ks in the fine grained WC-10 mass%Co hardmetal with the addition of VC (5 mass% in Co) which is most effective among the well-known grain growth inhibitors and with two kinds of grain sizes was carried out to estimate the values of dF,0 and dL,0 where abnormal grain growth (dL,3.6⁄dL,0≥2) becomes to occur.
The results obtained were as follows: (1) The equation derived is dL,t+Δt=dL,t+(81⁄32)K(1⁄dF,0−1⁄dL,t)Δt, where K is the same as in the well-known grain growth equation of \bardt2−\bard02=Kt. (2) The calculation by using the differential equation, in which the measured K value (2.18×10−2 μm2/ks or 2.18×10−14 m2/ks) of the hardmetal with the same chemical composition but usual grain size distribution was substituted, showed the following; (2-1) The abnormal grain growth occurs irrespective of dL,0, for example, in the case of dF,0≤0.1 μm. The abnormal grain growth in this case was considered to be a substantial phenomenon. (2-2) The abnormal grain growth does not occur irrespective of dL,0 in the case of dF,0≥0.3 μm. These indicate that the present design criterion of commercial fine grained hardmetal that the average grain size, i.e., dF,0 is fixed near 0.5 μm in minimum is rational from the viewpoint of the stable production. (3) The value of K necessary for inhibiting the abnormal grain growth even in the case of dF,0=0.1 μm is calculated to be less than 0.336×10−2 μm2/ks.View full abstractDownload PDF (895K) -
Yasuhiro Maeda, Hidenori Ogawa, Hiroyuki Nomura1998 Volume 62 Issue 4 Pages 390-396
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTo obtain the sound green compacts in metal injection molding (MIM), it is very important to know the optimal injection molding conditions using the slurry flow analysis such as a Flow Analysis Network (FAN) method. The flow analysis method requires several basic parameters including the rheological properties, e.g. viscosity, density and thermal conductivity of the slurry or green compacts. The physical properties of the MIM materials using a stainless steel SUS304 powder have been measured in this study, particularly for the temperature dependence of density, thermal conductivity and viscosity. The slurry viscosity was measured by the capillary test using the injection molding machine. From the experiments, the clear relations were obtained between the parameters and the temperature or share rate. Furthermore, from the flow analysis using the FAN method and the measured parameters, the detailed flow pattern was obtained in the wide range of temperatures during slurry filling in the mold cavity. The rheological properties of slurry depending on the temperature were found to be very important factors in the numerical simulation for the optimization of injection molding conditions.View full abstractDownload PDF (675K) -
Transition in Flattening Behavior of Thermally Sprayed Particles Impinging on Flat Substrate SurfaceYahui Huang, Masahiro Fukumoto1998 Volume 62 Issue 4 Pages 397-403
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTransition behavior of flattening Ni sprayed particles on a flat substrate surface nearby the transition temperature was investigated. The results obtained are summarized as follows:
(1) As for a splat morphology, intermeditate states that have both disk-splat and splash-splat characteristic were existent nearby the transition temperature.
(2) Auger analysis of the splash-splat and SEM observation of the splash-splat on Au coated substrate suggested that the splash was formed by the scattering of the liquid droplet from the center part of the splat. Therefore, the initial rapid flow of the splash-splat is considered to hardly depend on the sliding of the flow on the substrate surface due to the poor wettability at the splat/substrate interface.
(3) From the bottom surface observation of the splat, while the homogeneous solidification structure was recognized in the disk-part of the splat, remarkable radiated flow pattern was observed in the periphery of the splash-part. Moreover, from the observation results of etched splat surfaces, while the coarse structure was observed in the disk-splat, quite fine structure was recognized in the radiated flow pattern of the splash-splat. The fine structure indicates that the center part of the splash-splat was formed under the rapid solidification condition.
(4) From the fact that the splash-splat pattern was recognized only in the direction perpendicular to the scratching in the splat on the unidirectionally scratched substrate, it was confirmed that the splashing was caused by stumbling due to some kinds of deterrent to the liquid flow, such as poor wettability at the flow tip or the rapid solidification of the splat.
(5) Splashing seems to be the breaking phenomenon of the flowing liquid film, which is caused by the rapid flow due to the occurrence of the initial rapid solidification of the splat. The drastic change of the flattening pattern nearby the transition temperature seems to occur when the We number of the liquid flow coincide with some critical value.View full abstractDownload PDF (1071K) -
Takuya Aoki, Hiroshi Hatta, Yasuo Kogo, Hiroshi Fukuda, Yasuhiro Goto, ...1998 Volume 62 Issue 4 Pages 404-412
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHigh-temperature oxidation behavior of the SiC-coated Carbon/Carbon (C/C) composites was examined in the temperature range between 873 and 2273 K under open air environment. From the oxidation tests, three kinds of oxidation regimes were identified: i.e., oxidation reaction rate controlling regime; 873 K to 1173 K, oxygen diffusion controlling regime; 1173 K to 1973 K, and SiC sublimation regime; above 1973 K. Weight loss below 1973 K was due to the oxidation of the C/C substrate by oxygen diffusion through coating cracks. To understand the oxidation behavior, a morphological characterization of coating cracks has been done from the results of the microscopic observation of SiC coating. In particular, in the oxygen diffusion controlling temperature range, an analytical model was developed for the prediction of weight loss due to oxidation of the SiC-coated C/C composites. This model was derived from considering the oxygen diffusion in the coating cracks with the aid of statistical information on coating cracks, such as the distribution and temperature dependence of the coating crack width. Furthermore, considering the effect of silica growth at the crack walls during the oxidation, the weight loss curves were also predicted as a function of oxidation time. The oxidation rate and weight loss curves derived from this model are in fairly good agreement with the experimental results.View full abstractDownload PDF (962K)
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