Mechanical properties of the brazed stainless steel joints with nickel base filler metals (BNi) were studied in relation to the microstructures at the brazing interface. The filler metals used for this experiment were BNi-1, BNi-3 and BNi-7. In this study the brazing phenomena on stainless steel joints with BNi filler metals were discussed from the viewpoints of brazability, shear strength of lap brazed joints at room temperature and elevated temperatures, and the effects of diffusion treatment on the brazed joints. The results obtained are summarized as follows: (1) The BNi filler metals showed satisfactory brazability for stainless steel, and especially BNi-7 were excellent. (2) A defect of the brazed joints with BNi filler metals existed in the brittleness at room temperature. But at elevated temperatures the shear strength of the joints were remarkably improved. (3) The brazed joints with BNi-1 and BNi-3 filler metal were improved in shear strength by the diffusion treatment. (4) The long time brazing process was effective for improving the mechanical strength of the joints.
Deformation behaviors of a commercially pure iron and a mild steel pressurized at hydrostatic pressures up to 880 MPa were examined mainly to establish a method for evaluation of the effect of pressure on the deformability encountered in some metal-formings such as explosive ones in which the work-piece is subjected to a rapid deformarion under a high pressure of short duration. Pressurization, which did not affect the fracture elongation in a quasi-static tension, sometimes caused a considerable increase of the elongation in an impact tension. This effect is attributed to an increase of the critical impact tensile speed through the lowering of yield stress. The above experiment has proposed how to evaluate the effect of pressure on the workability found in a forming such as an explosive one. In addition to the tensile ductility of pressurized specimens, the effects of grain size and ageing on the yield stress of pressurized specimens are also described in the present paper.
Phase analysis, the crystal structure of the matrix and the orientation relationships between the matrix and MnSi precipitates were examined by metallographic observation, EPMA, X-ray powder diffraction and the Weissenberg method for Mn-Si alloys with 62.5 to 63.8 at%Si. Plate-like MnSi precipitates were observed in all the crystal grains of Mn-63.1 at%Si alloy, but free-Si and free-MnSi were not. These precipitated plates were parallel to the c-plane of the matrix. In contrast to Mn-63.1 at%Si alloy, Si-deficient and Si-rich alloys produced free-MnSi and free-Si in addition to the plate-like MnSi precipitates, respectively. Mn-Si alloys containing 62.5 to 63.8 at%Si thus consisted of two or three phases, i.e. the matrix, MnSi and/or Si. Threfore, it can be said that there is not a single phase in these alloys. The matrix of these alloys was Mn15Si26(MnSi1.733). The structures of Mn11Si19(MnSi1.727), Mn26Si45(MnSi1.730), Mn27Si47(MnSi1.741), and Mn4Si7(MnSi1.750), which have been reported to be formed by a small difference in Si content near MnSi1.73, were not confirmed in this Mn-Si alloy system. The distribution of the plate-like MnSi precipitates resembles that of the eutectic lamellar structure, but there were no specific orientation relationships between the matrix and the plate-like MnSi precipitates.
The saturation magnetization at 77 K, (Ms)77, and the magnetization at high and low fields of 23.9 and 1.19 kA/m over a temperature range of 77∼273 K, MH(T) and ML(T), were measured for the present alloy aged at 723∼888 K. From the MH(T) curves, the Curie temperature, θc, and the steepest gradient of the curve, (−dM⁄dT), were estimated. Details of the M(T) curves were interpreted on the basis of the conception of magnetic mass balance. The configurations of composition variation and their changes with aging were analysed. Aging behaviour of the alloy was quite different below 793 K and above 813 K. For the specimens aged at 723 K, for example, (Ms)77 and θc, increased continuously with aging time up to 105 s. During the aging, the value of (−dM⁄dT) was relatively small, and the tails of the ML(T) curves shifted to higher temperature side. These results indicate that in these aged specimens composition fluctuations are present and grow in amplitude without any delay, where the composition of the Ti-poor regions decreases continuously with aging. For the specimens aged at 823 K, on the other hand, (Ms)77 and θc increased after an incubation time of 6 min, and became saturated after a long aging time of 30 h. For the incubation or the later stage of aging, M(T) decreased sharply at near θc. For the intermediate stage of aging where (Ms)77 and θc increased, ML(T) decreased rather discontinuously with temperature. These results suggest that some nuclei are formed during the incubation time. Thereafter, a three-phase structure is produced and the Ti-poor regions grow by enchroaching the homogeneous matrix, finally resulting in two-phase structure. It is concluded that the Ni-Ti alloy is decomposes by spinodal mechanism below 793 K and by nucleation-growth mechanism above 813 K.
Stress induced grain boundary migration of 〈112〉 symmetric tilt boundaries with misorientation angles ranging from 3.5° to 40° was investigated by the use of aluminum bicrystals. When the misorientation angle exceeded about 5°, grain boundaries did not migrate under the stress at room temperature. However at elevated temperatures, the grain boundaries with misorientation angles smaller than 30° migrated under the stress. The migration velocity (v) varied with tensile stress (σ) and temperature (T) according to the following equation: (This article is not displayable. Please see full text pdf.) \
oindentwhere A(θ) is a numerical factor depending on the misorientation angle (θ), n=1.0±0.2 and Q=76±8 kJ/mol. Grain boundary sliding occurred and the stress induced migration was not observed for the misorientation angles larger than 30°. On the other hand, the mobility of the grain boundary migration driven by the grain boundary energy was low for the boundaries with misorientation angles smaller than 30° but was high for the boundaries with misorientation angles larger than 30°. These results suggest that the grain boundaries with misorientation angles smaller than 30° contain dislocations and defect areas, whose migration rate is controlled by the grain boundary self-diffusion.
“Resistance-sintability of a metal powder” means a characteristic of a metal powder how easily the powder can be resistance-sintered into a dense compact which has high mechanical strength. The resistance-sintability of various metal powders (Ti, Al. Fe, Ni) were investigated through the comparisons of the heating-up-rate, the decreasing rate of electrical resistance and the dependence of physical and mechanical properties of a resistance-sintered compact on the relative temperature T⁄Tmp during the resistance-sintering operation of these powders. It was considered that, the maximum power input into a powder compact and the maximum heating-up-rate was realized when the electrical resistance of a powder compact is equal to that of the secondary circuit of the resistance-sintering machine. The result of the resistance-sintering experiments showed that Ti powder, especially dehydrided Ti powder, has the most excellent resistance-sintability. The result was discussed on the basis of the consideration mentioned above.
An investigation was made on the determination of the acid soluble and insoluble aluminum in steel by emission Spectrometry. With the sample of high insoluble aluminum content the emission signals from each discharge are distributed irregularity and their intensity is extraordinarily strong. The experiment confirmed that the phenomenon, the so-called “abnormal discharge”, originates in the presence of aluminum oxide, etc. in the sample. In this method, the above mentioned signals were discriminated from those obtained from the element which is in solid solution in the matrix by means of a PDA (Pulse Height Distribution Analyser) and the acid soluble aluminum and insoluble aluminum were determined separately. The signal distribution obtained was assumed approximately to be an exponential function and the calculated maximum was related to the aluminum content in the sample. The analytical range of the method are 0.001 to 0.10% for the acid soluble aluminum and 0.001 to 0.010% for the acid insoluble aluminum, the precision (standard deviation) being 0.0006%. The use of this method makes it possible to determine the acid soluble aluminum even when the content of acid insoluble aluminum is as much as over 0.05%.
The effect of mechanical polishing on the magnetic properties of single crystals of Mn-Zn ferrite was investigated. The following results were obtained. (1) The effect of mechanical polishing depends on the crystalline axis, and the order of effectiveness is as follows: (This article is not displayable. Please see full text pdf.) (2) The depth of the deformed surface layer (1∼2 μm) increases with increase in polishing-powder size. The magnetic properties are recovered after etching out the deformed layer. (3) The crystal structure of the deformed surface layer is found by electron beam diffraction to be amorphous or ultra fine-grained.
Mössbauer nuclei 119mSn were doped into the grain boundary of ultra fine grained iron specimens. Various parameters such as internal magnetic field, Debye temperatures and thermal jump frequency were measured. The parameters showed that tin atoms segregated at the grain boundary are contributing a less amount of outer shell electrons to bonds with the neighboring atoms and the average force constant is reduced below that of tin in solid solution in the iron matrix. The differences, however, were small while a large difference was noticed in its internal magnetic field. The absence in the internal magnetic field suggests that iron atoms next to tin in the grain boundary are in a special state with respect to their d-level and may explain the embrittlement of steel. The oxygen-induced embrittlement which was suggested from experiments of pure iron may be a different mechanism peculiar to pure iron.
Tilt boundaries of evaporated gold foil with the  rotation axis perpendicular to the foil surface were examined by the multi-beam lattice image in a JEM 1250 kV transmission electron microscope. Various boundary structures such as small angle, twin, coincidence-related and near-coincidence tilt boundaries were analyzed. They were compared with those proposed or simulated by computer. It was shown that the lattice image in a HVEM is a powerfull tool to investigate the atomic configuration at the boundaries.
The present study deals with the concentration of plastic deformation into necked region in the fracture process of titanium plate and the condition for the formation of intersecting macroscopic shear bands. As reported in a previous paper, the intersecting macroscopic shear bands formed prior to the onset of fracture play an important role in the “cup and cone” fracture process of titanium plate and the formation of these shear bands is the critical stage of the fracture process. Observations on the surfaces of specimens deformed after electrolytical polishing and measurements of deformation at several stages in the deformation process to the formation of these shear bands have made clear the following points. The boundary of the plastically deformed region exists along the direction of zero extensional strain and moves toward the central part of neck with the development of necking. The formation of intersecting macroscopic shear bands is the localization of plastic deformation (plastic instability) within zones along direction of zero extensional strain that intersect in the central part of neck. The true stress in the smallest section of the neck in titanium plate was obtained by applying Bridgman’s correction method for stress in the necked portion. A maximum in true stress was found at the formation of intersecting macroscopic shear bands, and this corresponds to the condition (maximum in true stress) for the localization of flow within a plastic zone along the direction of zero extensional strain that was obtained by Chakrabarti et al. Therefore, it is concluded that the formation of shear bands in the fracture process of pure titanium plate with a large amount of necking is thought to be the plastic instability along the direction of zero extensional strain that was confirmed by Chakrabarti et al. as a second basic mode of strain localization leading to fracture initiation.
A new potentiostatic etching method using non-aqueous solutions as an electrolyte (Selective Potentiostatic Etching by Electrolytic Dissolution: abridged as SPEED Method) has been developed and applied to the observation and analysis of precipitates and metallographic grain orientation in steel samples. By the proposed SPEED Method, samples are etched at the predetermined constant electrolytical potential in non-aqueous solutions such as 10% acetylacetone-1% tetramethylammonium chloride-methyl alcohol and 3% nitric acid-2% perchloric acid-methyl alcohol. Precipitates and micro facet pits are observed and analyzed by analytical instruments such as OM, SEM and XMA, after the etched surface of the sample were washed with methyl alcohol. The advantages of the SPEED Method are as follows. (1) In situ observation of unstable precipitates in good contrast in the microstructure of the steel sample. (2) Easy estimation of the relationship between precipitates and metallographic grain orientation by a simultaneous observation of precipitates and micro facet pits. Size of facet pits are easily controlled in the range of 10 to 0.5 μm by controlled electrolytical potential. (3) Three dimentional observation of precipitates with various etching depths, controlled by the quantity of electricity. (4) Easy identification and accurate analysis of precipitates with no contamination of sample surface, easily judged by red-color of the iron chelate compound.
Effect of grain size variation between 60 μm and 350 μm on creep and creep-rupture properties was studied on Ni-base alloy Hastelloy X. Creep and creep-rupture tests were carried out at 800, 900 and 1000°C for durations up to about 103 h. At the same time, measurements of the number and size of grain boundary cavities were conducted through longitudinal sections of specimens which were unloaded during creep deformation by means of optical microscopy of 100X magnification, and the relation between grain boundary cavitavion and creep deformation was obtained. Rupture life decreased with increace of grain size at 800°C, but, at 1000°C, increased with increace of grain size. Rupture life at 900°C was little affected by grain size variation. Grain boundary cavities below 20/mm2 initiated at the time of starting of the tertiary creep range. The higher rupture strength of finer grain size materials at 800°C corresponded to the phenomena that the number and size of grain boundary cavities at costant crept time and the number of grain boundary cavities at constant creep strain decreased as grain size decreased. These phenomena at 800°C show the ease of initiation and growth of grain boundary cavities in coarser grain size materials and are considered to be due to cohesion of the carbides near the grain boundaries. The higher rupture strength of coarser grain size materials at 1000°C corresponded to the phenomena that the number and size of grain boundary cavities at constant crept time decreased as grain size increased and linkage of the cavities occurred in the eary creep region for finer grain size materials. These phenomena at 1000°C which show difficulty of initiation and growth of grain boundary cavities in coarser grain size materials may be attributed to a continuous precipitation of the carbides at the grain boundaries.
In order to clarify the fluidity of interdendritic liquid contributing to the formation of macrosegregation and the castability in an ingot, an artificial hole was made in the zone of coexistence of the solid and the liquid so as to make only the liquid flow into the hole. Then the relation among the fluidity of the liquid, the fraction of solid and the dendrite morphology in the solid-liquid coexisting zone was examined. Furthermore the fluidity of the interdendritic liquid was estimated by the effective permeability. The results on an Al-2.4 wt%Si alloy are summarized as follows: (1) The fraction of solid at which dendrites begin to form networks is about 31%, and the fraction of solid above which the interdendritic liquid cannot flow is 67%. These fractions of solid are consistent with those at the boundaries between the q1 and the q2 zones and between the q1 and p zones, respectively, which have been previously found from the hydrodynamic examination on the process of solidification by one of the authors. (2) The effective permeabilities in the fraction of solid of 0.35 and 0.65 are 6.1×10−4 and 6.2×10−6 cm/s, respectively. The latter is the value that the seepage of the interdendritic liquid can hardly occur. It is equal to the value that the seepage of water in the soil can be scarcely occurred. (3) It is practical that the fluidity of the interdendritic liquid is evaluated with the effective permeability obtained by this experimental method, because the effective permeability consists of the viscosity and the density in the liquid and the permeability depending on the dendrite morphology.
The thermal defects in NiAl were investigated by the measurement of the dilatometric expansion coefficient over the range of composition from 48.5 to 60.3 at%Ni. The apparent formation energy of the thermal vacancy, Ef, decreased with an increase of the Ni content and the decrease was much more pronounced at the Al-rich side of the stoichiometry than at the Ni-rich side. Considering the nature of compositional defects, the amount of antistructure atoms thermally formed would account for a half of the number of thermal vacancies, but these atoms might have a minor contribution to the thermal expansion. The concentration of thermal vacancies at the melting temperature was on the order of 10−2 which was larger than those formed in pure metals by a factor of 100.
Ag-2∼12 at%Zn alloys containing a small amount of several metals such as 1∼3 at%Sn, 1∼4 at%In, 0.1∼1 at%Te, 0.5∼3 at%Cu and 0.5 at%Li were internally oxidized in air, and at 1 and 5 atm oxygen pressures at 800 and 850°C. The microstructures in oxidized layers of the alloys were observed using an optical microscope. (1) The concentration range, in which oxide particles are uniformly dispersed in a silver matrix, has been estimated for internally oxidized Ag-Zn-Te, Ag-Zn-Sn-Te, Ag-Zn-In-Te and Ag-Zn-Sn-In-Te alloys. (2) An addition of Te disperses oxide particles uniformly, leading to a wide concentration range in which the internal oxidation proceeds. (3) A replacement of Te by Cu or Li has a similar effect on the dispersion of oxide particles as the addition of Te. (4) An addition of Sn results in a fine oxide particle size.
A high temperature X-ray diffraction technique has been used to determine the structure of molten FeO-Fe2O3-SiO2 from 1250 to 1350°C. The SiO2 content and oxygen partial pressure were in the range of 22.5 to 35 wt% and 2.0×10−7 to 2.0×10−3 Pa. From an analysis of the scattering intensity, the radial distribution function was calculated from which the interatomic distance and coordination numbers were estimated. The following characteristic features emerge from these results. A constant coordination number of about four and an interatomic distance of about 0.162×10−9 m are found for Si-O pairs in the composition and temperature range investigated. This supports that the fundamental local ordering unit is SiO4 tetrahedra in molten FeO-Fe2O3-SiO2. The Si-Si distance, which corresponds to the inter SiO4 distance, gradually decreases as the SiO2 content increases and then approaches a nearly constant value at composition beyond about 30 wt%SiO2. This constant value is rather comparable with the value of the Si-O-Si distance in polymerized ring and branched chain structures and suggests that some of the SiO4 tetrahedra polymerize to form silicate anions. The Fe-O distance also gradually decreases as the SiO2 content increases and becomes nearly constant beyond about 30 wt%SiO2. The coordination number of Fe-O pairs varies from six to four. This variation of the Fe-O correlation corresponds to a change in the position of Fe from an octahedral site to a tetrahedral site. The viscosity maximum near the fayalite composition has been also discussed by means of a combination of the silicate anion polymerization effect and the cation effect which are connected with the present structural information.