The effect of cold rolling on the physical properties and the structure of Fe79B16Si5 ribbon amorphous alloy was investigated by Mössbauer effect, X-ray diffraction, tensile test and electrical resistivity measurements. The shape of the distribution of the internal magnetic field was hardly affected by cold rolling, but the peak in the distribution, (Hpeak), shifted only slightly to the low field side. It seems that cold rolling causes the decrease of the component of magnetization parallel to the ribbon plane of the specimen. A large softening effect by about 5% cold rolling and a hardening effect by subsequent rolling were observed in the amorphous alloy. This hardening trends to increase toward that in the as-quenched state. Increase of the average Fe-Fe atomic distance would be responsible for the softening. It is suggested that the hardening is probably caused by strain hardening associated with subsequent rolling. From the topological point of view, it is likely that cold rolling produced a more disordered structure than that present in the as-quenched state. The thermal stability of the amorphous structure was not improved by cold rolling.
The present paper introduces a new statistical method of analyzing the distribution of crystal orientation in a polycrystalline material using ‘quaternion’ presentation instead of ‘matrix’ one. At first, a crystal orientation space is metrized, and the ‘mean crystal orientation (MCO)’ is defined considering the symmetry of the cubic system. In practice, the distribution of deviations from MCO is analyzed. The deviation is defined three-dimensionally and consists of the disorientation angle (1-dim) and the rotation axis of the deviation (2-dim). It is shown that the ‘quaternion’ presentation is superior to the ‘matrix’ presentation in the separation of these components. The distribution of disorientation angle is investigated at the first stage of analysis. The degree of randomness is evaluated secondly. When the material is textured in some degree, a further analysis can be made by the ‘stereographic projection of four-dimensional sphere to three-dimensional space’.
The nitriding of SUS304 steel was done by d.c. glow discharge plasma in a mixed gas (20 vol%N2+80 vol%H2) under a reduced pressure of 665 Pa at a relatively low temperature of about 623 K. In this nitriding process, the surface layer of the specimen was modified with some surface reliefs such as ion-etched grain boundaries, twins and slip-like straight traces. This layer had a depth of 15-20 μm at the nitriding time of 36.3 ks and the vickers hardness of about 1500 Hv. In this layer, an f.c.t. nitride phase was identified by X-ray diffraction studies. Subsequent annealing at 723, 823 and 923 K in a vacuum furnace gave rise to the formation of α′ martensite accompanied with the disappearance of the newly developed f.c.t. nitride, but ε martensite was not observed because of its unstability above 573 K. These processes of phase transformation induced by nitrogen in SUS304 steel strikingly resemble those of hydrogen induced phase transformation in which the f.c.c. hydride is formed by cathodic charging of hydrogen and α′ martensite is formed in its outgassing process by aging.
Low carbon steel (SM 41) was cyclically pre-loaded under a low stress amplitude in tension-compression to 1, 3, 5, 10, 15 and 30% of fatigue life. Then the effect of cyclic pre-loading on the monotonic tensile properties and Charpy impact values was investigated. The microstructures were also observed by transmission electron microscopy. The results are as follows: (1) Grains containing bundle and/or isolated dislocation structures were observed in the specimens cyclically pre-loaded to 5 to 15% of fatigue life. Dislocation network structures were also observed in some grains pre-loaded to 30% of fatigue life. In the case of cyclic loading under a low stress amplitude, the dislocation structure was quite different among individual grains in a specimen. These results suggest that the deformation was inhomogeneous among grains in contrast with monotonic tensile pre-deformation. (2) All of the cyclically pre-loaded specimens showed apparent upper yield points and Lüders strain during a monotonic tensile test. These phenomena are probably caused by a dynamic strain aging of isolated dislocations during cyclic pre-loading. (3) The increase in tensile strength of the specimens, cyclically pre-loaded up to 10% of fatigue life, is caused by the work hardening due to bundle dislocation structures, and conversly, the decrease in tensile strength of the specimens cyclically pre-loaded to 15 and 30% is caused by a certain dynamic recovery during cyclic pre-loading. (4) The maximum impact value (Imax) decreased and the temperature at the onset of ductility (Td) increased with increasing amount of cyclic pre-loading. These results suggest that cydic pre-loading always makes the specimens brittle. (5) The transition temperature (Tc) decreased with increasing amount of cyclic pre-loading. However, the decrease in Tc does not relate to the increase in toughness.
Creep tests at high temperatures have been carried out in an Al-Al2O3 binary alloy and an Al-Al2O3-Si ternary alloy with different grain sizes. Dislocation structures after the steady-state creep have been observed in the temperature range from about 473 K to 873 K. The creep behaviour and the contribution of grain boundary sliding in a low stress range at temperatures above 773 K have been examined in details in the Al-Al2O3 alloy. Dislocations were generally distributed rather uniformly, being pinned to the dispersed particles when crept at temperatures below 673 K, though incomplete subboundaries were occasionally observed in a high stress range. On the other hand, when crept at temperatures above 773 K, sharp subboundaries, which appeared to be formed associated with the grain boundary sliding, were often observed with the uniform distribution of dislocations. At temperatures above 773 K, the Al-Al2O3 alloy was deformed at relatively large creep rates under stress lower than the threshold value which was estimated at temperatures below 673 K, that is, the temperature compensated creep rate \dotεs⁄D in the low stress range deviated upwards from the \dotεs⁄D vs. σ⁄E relation obtained at temperatures below 673 K, where \dotεs was the steady state creep rate, D the self-diffusion coefficient of aluminium, σ the applied stress and E the Young’s modulus. The deviation increased with increasing testing temperature and with decreasing grain size. The contribution of grain boundary sliding to the total creep strain ranged from about 10 to 30% when crept at temperatures above 773 K, and the mechanism of creep deformation occurring in this temperature range was discussed.
The delayed fracture of a nickel coated ultrahigh strength maraging steel was studied in hydrogen gas pressure of 6.67 kPa and 66.7 kPa using notched tensile specimens. The delayed fracture strength for 180 ks increased with the increase in the thickness of a nickel coating and was lowered with increasing hydrogen gas pressure. The effect of coating on the hydrogen gas embrittlement of maraging steel varied drastically from reduction of embrittlement to its enhancement with the change in the thickness of coating from 10-20 μm to 2.5 μm. Hydrogen absorption into the specimens was active at the fresh surface of the coating that was produced by plastic deformation during loading the specimens, but it was extremely suppressed after the fresh surface had once been exposed to the air. A delayed fracture model in which the degree of hydrogen absorption at the surface was varied was discussed, and the delayed fracture behaviors were successfully explained by the consideration that the nickel coating layer had an effect of storing hydrogen because the distribution of hydrogen was much richer in nickel than in steel.
Internal friction was measured from 150 K to 370 K in transverse vibration for Fe-36%Ni invar alloy charged with hydrogen and deuterium. A hydrogen peak of internal friction was found around 250 K at about 700 Hz and its activation energy was 43 kJ/mol, closely related to that for hydrogen diffusion. This internal friction peak seemed to be of the same origin as the hydrogen peak found previously in austenitic stainless steels. A deuterium peak of internal friction was also detected but located at a temperature 2-3 K higher than the hydrogen peak. Such an isotope shift of the peak temperature can be interpreted in terms of the isotope effect of hydrogen diffusion. This suggests that the hydrogen peak is attributed to a Snoek-type relaxation caused by hydrogen diffusion in Fe-36%Ni invar alloy, as has been proposed for austenitic stainless steels.
The carbon deposition on iron, Fe-Cr, Fe-Si and Fe-Cr-Si alloys has been studied by means of metallography and thermogravimetry, in order to elucidate the effects of chromium and silicon on the carbon deposttion behavior on iron and to get a better understanding on the mechanism of the carbon deposition. Chromium retards the carbon deposition by forming the carbide, (Fe,Cr)3C, more stable than Fe3C, whereas silicon accelerates the deposition of filamentous carbon, and in particular on an Fe-3.0 mass%Si alloy only deposition of filamentous carbon is observed. This behavior on the Fe-Si alloys is probably ascribed to the effect of silicon on the stability of Fe3C and the diffusion rate of carbon atoms. The carbon deposition behavior on Fe-Cr-Si alloys containing 0.8-1.5 mass%Cr changes according to the proportion of chromium to silicon; at Cr%≥Si% only filmy carbon deposits, while at Cr%<Si% only filamentous carbon does. Silicon in high chromium alloys containing ca. 12 mass%Cr has an effect to refine and disperse carbides, and further addition of silicon may result in the deposition of filamentous carbon. The deposition behavior of filamentous carbon on all these alloys can be explained by the mechanism of formation and decomposition of Fe3C.
Corrosion experiments of cobalt were carried out at 873∼1173 K in various Ar-O2-SO2 atmospheres. The change in the corrosion amounts was automatically recorded by massgravimetry. Scale structures were examined by X-ray diffractometry, optical microscopy and EPMA. The corrosion kinetics followed the parabolic rate law. The rate-controlling process of the reaction was considered to be mainly the outward diffusion of Co ion. The corrosion products consisted of CoO, Co3O4, CoS1.035, Co9S8 and α-CoSO4. The corrosion amounts reached a maximum at about 948 K in almost all atmospheres. Duplex scale structures consisting of oxides and sulfides were formed at lower temperatures, and a single oxide layer was formed at elevated temperatures. The activation energy was found to be about 140 kJ/mol at temperatures above 1000 K.
Extraction of Nb and Ta from acid solutions with bis-2-ethylhexyl acetamide and stripping of these metals with sulphuric acid solutions were investigated. The organic phase was a binary solution of bis-2-ethylhexyl acetamide and xylene, while the aqueous phase was composed of hydrofluoric acid solution or hydrofluoric-sulphuric acid solution containing 3.5-13 kg/m3Nb and 5-10 kg/m3Ta. Sulphuric acid, hydrochloric acid and nitric acid were used as salting out agents to understand the effect on the extraction. Both metals were not sufficiently extracted from hydrofluoric acid solutions, whereas the extraction of both metals remarkably increased with an addition of sulphuric acid to the aqueous phase. The separation factor decreased with an increase in the concentration of hydrofluoric acid at the constant sulphuric acid concentration of 5.8N, and both metals were completely coextracted in the aqueous condition of 6N hydrofluoric acid and 8N sulphuric acid. The stripping occurred for both metals with a high efficiency, when water or dilute sulphuric acid solution was used as a stripping agent. The increase in sulphuric acid concentration caused less stripping of Ta, while the stripping of Nb was maintained at 80% up to 7N sulphuric acid. The separation factor reached the maximum with the value of 116 in the use of 6.5N sulphurtc acid. The extraction behavior of Fe(II), Fe(III), Sn(IV) and Mn(II) was also examined with the results that these metals were not extracted even to the extent of the lowest limit of atomic absorption spectrophotometer. Moreover, the comparison of this extractant with MIBK and TBP, which were in common use, was carried out.
An investigation was made on the viscous flow and microstructure in hypereutectic alloys by rheocasting with the rotation of a stirrer at a high speed in the range from 30 to 70 rev/s. The value of apparent viscosity in hypereutectic Al-Si alloys solidifying with the rotation of stirrer at a speed above 30 rev/s remained almost unchanged to a certain level except a rapid change in the initial stage of solidification. The average size of primary silicon was 66±19 μm in an Al-17%Si-4%Cu-0.5%Mg-0.3%Fe alloy ingot rheocast at 70 rev/s under the cooling condition of 0.6 K/s in the melt. The primary silicon size became finer by the modification of microstructure with an addition of 0.01%Na or 0.01 and 0.1%P in rheocast and conventionally cast hypereutectic Al-Si alloy ingots. A constant level of apparent viscosity was also observed during the high-speed rheocasting of an Al-17%Si-4%Cu-1.2%Fe-1%Mg-1%Ni-0.5%Mn-0.5%Zn-0.2%Ti-0.01%Na alloy ingot. It was depressed with the increase in stirrer speed from 30 to 50 rev/s. The primary silicon size of the alloy ingot was 101±27 μm at a rotation speed of 30 s−1, 96±25 μm at 40 s−1 and 93±25 μm at 50s−1.
In this study computer simulation was carried out to make randomly packed beds of powder with a particle size distribution, and to analyze the internal structures formed. The simulation of the packing process had two kinds of boundary condition, the fixed and the periodic one, and the particle size distribution was assumed to be discrete Forsfield’s distribution consisting of five different size spheres which can make the most dense packing in the geometrically regular arrangement of spheres. The results are summarized as follows: (1) In the packed bed larger spheres are uniformly dispersed, while smaller ones unevenly fill up gaps made by larger ones. (2) In case of the packing into a container with fixed walls, abrupt lowering of the density of packing is obtained near the walls and corners leading to the loose packing structure there. (3) In the process of random packing, larger particles having a large volume fraction build up the fundamental structure, while smaller ones rolling down through the gaps among larger ones to the stationary positions contribute to the increment of the density with the lapse of time. (4) For the random packing of the powder with such a particle size distribution the mean density is strongly influenced by the packing state of larger particles with a large volume fraction, while both the distribution and the mean value of coordination number are dependent upon the packing state of smaller particles with a large fraction in number. (5) Under the periodic boundary condition excluding a wall effect, the mean values of the packing density and the coordination number were 0.622 and 5.92, respectively.
The effects of the sputtering conditions such as substrate temperature, partial pressure of argon gas and sputtering power on the structures of sputter-deposited Cu-14 mass%Al-4 mass%Ni films were investigated by X-ray diffraction. The grain sizes of the films were very fine and less than about 1.0 μm in diameter. In the substrate temperature range from 373 to 573 K, the film structure was identified with a DO3-type ordered bcc similar to that of the β1 phase(Cu3Al). The degree of ordering of the DO3 structure decreased with decreasing substrate temperature and with decreasing partial pressure of argon gas. On the other hand, the crystal structure was independent of the sputtering power, remaining unchanged as to DO3-type. The martensite transformation occurred between 293 and 123 K for the DO3-type ordered films. The films sputter-deposited on an aluminum foil exhibited a good shape memory effect. Thus, these films may be useful as a shape memory composite material.
Ribbons with a composition of Sm(Co,Fe,Cu,Zr)7.4 have been prepared by the melt-spinning technique, to examine their magnetic properties and structures. In the as-prepared state, the ribbon specimens are composed of a single phase with a very low coercivity. With appropriate heat treatments, however, the specimen is transformed into a two-phase structure in which a celullar structure of 2-17 phase is divided by boundaries of 1-5 phase. As a result, the maximum value, 460 kA/m, may be achieved. These results obtained for the melt-spun ribbons are very similar to those for the sintered magnet alloy of the same composition.