The effect of quenched and tempered structure on the diffusion coefficient and solubility of hydrogen in high-strength alloy steels, such as Cr, Cr-Mo, Ni-Cr and Ni-Cr-Mo steels, have been investigated at room temperature by means of electrochemical permeation technique. The diffusion coefficient and the solubility of hydrogen vary with the structure of the steel; the former shows a minimum, when the steels are quenched and tempered at 300°C except for a case with high Mo content, while the latter exhibits a maximum at that temperature. In the case of steels having comparatively higher Ni, Cr and Mo contents, the structure of bainite plus martensite obtained by furnace cooling from the temperature above Ac1 have lower values of diffusion coefficient which are comparable with that of the as-quenched martensitic structure. The dependence of hydrogen diffusion on the quenched and tempered structure can be explained by postulating that both the lattice imperfections, such as dislocations, faults, lattice vacancies and subgrain boundaries introduced by the martensitic and/or bainitic transformation, and the interfaces between the ferrite phase and carbide precipitates, provide regions for the occupancy of hydrogen.
The diffusivity and solubility of hydrogen in both annealed and cold worked polycrystalline nickel were determined in the temperature range of 10 to 60°C by means of an electro-chemical permeation technique. The following results are obtained. The diffusivity increases slightly with increase in grain size, whereas there is an enhanced solubility of hydrogen at grain boundaries. The cold working of nickel results in a lower value of diffusivity and that brings about not only an increase in the solubility of hydrogen but also a change in the mode of absorption from the endothermic to exothermic. These behaviors of hydrogen transport, likewise cold worked iron, can be interpreted in terms of a hydrogen trapping process involving the lattice imperfections such as dislocations, faults, lattice vacancres and subgrain boundaries, etc., introduced by cold working. The changes in free energy of hydrogen trapping reaction were evaluated to be comparable with the average hydrogen-dislocation binding energy in α-iron.
The measurements of internal friction Q−1 under tensile loading and mechanical properties have been carried out on open-melted Fe-Co alloys containing 5∼25%Co subjected to annealing at 900∼1200°C. The value of Q−1 at a frequency of 0.3∼1.1 Hz first increases sharply to a maximum with an increase in maximum shear strain amplitude and then decreases gradually. The higher the annealing temperature and the Co content, the greater becomes Q−1. An Fe-25%Co alloy exhibits the highest Q−1 value of 75×10−3 when annealed at 1200°C for 1 h. When the measuring temperature becomes higher, the Q−1 value at first decreases from about 400°C and sharply increases after reaching a minimum in the vicinity of 550°C. Moreover, the Q−1 value decreases rapidly with an increase in external d.c. magnetic field. The mechanical strength of Fe-Co alloys increases considerably with Co content.
For the composites, the strength and the site of crack nucleation are determined by a combination of mechanical and physico-chemical factors. The former provides the required stress concentrations and local plastic deformation, while the latter is represented by the strength of inclusion, interface and matrix, respectively. So, this problem may be solved by investigating the strength and mechanical properties of each alloy element and by calculating the stress distribution in plastic deformation. But the micromechanical calculations during plastic deformation were solved by the finite element method, that has been applied to the fracture mechanics. On the assumptions of the three different crack initiation modes, two-phase model alloys which were the Al matrix with Si, the Al matrix with Cu and the Cu matrix with Fe, were prepared by the hot-press method and the tensile behaviour was observed. On the other hand, the elastic-plastic finite element simulation was used for the micromechanical stress and strain calculations of these composite models in tension. There was good agreement in the load and the site of initiation of fracture voids between the results calculated from the simulation and experimental data on Si/Al, Cu/Al and Fe/Cu composite alloys. And the available results were computed for the initiation of ductile fracture voids.
Relations between weld heat-affected zone cracking and microstructures of several nickel-base superalloys by the hot ductility test, i.e. the Gleeble test, were determined in comparison with the brittle temperature range between the nil-strength temperature (N.S.T.) and the temperature at which the ductility begins to recover on-cooling from N.S.T. and the recovery velocity of ductility. The conclusions obtained are as follows. (1) In the wrought alloys, constitutional liquation of grain boundaries begins at the nilductility temperature (N.D.T.) and the liquation spreads out to all grain boundaries at N.S.T. and the brittle temperature range is determined by the degree of the solidification temperature drop caused by the constitutional liquation. (2) In the cast alloys, constitutional liquation produces solute-rich regions around and between the preciptates, along which fracture propagates. Consequently the ductility is lost completely and its recovery is slower than the wrought alloys. (3) The recovery velocities of ductility of all the alloys tested are almost the same, but the brittle temperature range is 60°C for Hastelloy X cast alloy, 70°C for Inconel 718 wrought alloy and Inconel 706 wrought alloy, and 170°C for Inconel 718 cast alloy. The results coincide well with our job experiences of hot cracking tendencies of the heat-affected zone in TIG arc welding. (4) Even with the same chemical composition, the cast alloy has a wider brittle temperature range than the wrought alloy. (5) Inconel 706 wrought alloy, obtained by improving the fogeability and machinability of Inconel 718 wrought alloy, exhibits low hot cracking sensitivity nearly equal to Inconel 718 wrought alloy.
Strain-rate cycling tests, double strain-rate cycling tests and stress relaxation tests were performed during the tensile deformation of iron, internally oxidized Fe-Al alloys containing 0.069 and 0.158 wt%Al in the temperature range 177 and 293 K. The effective stress, σ*, the internal stress, σi, developed during deformation, the effective stress exponent of the average dislocation velocity, m*, and the activation enthalpy, ΔH, were obtained. In all materials tested, σ* is independent of strain at all temperatures. The work-hardening is associated with the increase in σi. The difference in the flow stress between iron and the alloys is due to the difference in σi. The values of m* and ΔH0 (ΔH at σ*=0) for the alloys are nearly equal to those for iron. These results suggest that the mechanism controlling the low temperature deformation in the alloys is similar to that in iron.
Polycrystals of Cu-Mn solid solutions containing 3 to 20 at%Mn were deformed in tension at 873, 923 and 973 K, at strain rates of 1.7×10−5∼1.7×10−3 s−1. The results obtained are as follows: (1) In the steady state deformation stage, the strain rate is represented by the relationship, \dotε=Aσnexp(−Q⁄RT), where n=2.7∼3.7 in high manganese alloys and n=4.3∼5.7 in low manganese alloys. The apparent activation energies for the high temperature deformation, Q, are 203∼214 kJ/mol and consistent with the activation energies for the inter-diffusion in Cu-Mn alloys. (2) In the high Mn alloys showing the alloy-type behavior, yielding phenomena at high temperature were always observed. (3) The high temperature deformation in Cu-Mn alloys is controlled by the dragging of solute atomosphere for dislocation motion. The normalized strain rate in Cu-Mn alloys is about ten times as large as that in Cu-Sn alloys under the same normalized stress. The difference in the normalized strain rate between Cu-Mn and Cu-Sn alloys is derived from the difference in the size factor between these alloy systems.
Partial pressures of the constituent elements over CdSe(s) and CdTe(s) have been measured by an optical absorption method. One set of measurements used optical cells consisted of an optical path chamber and a sample chamber. Dissociation constants were logKCdSe=logPCd2×PSe2(atm3)=−33416⁄T+20.43(707∼936°C) and logKCdTe=logPCd2×PTe2(atm3)=−29979⁄T+19.62(763∼908°C). Using another type of optical cell having also a reservoir chamber, control of partial pressure over the sample (CdSe(s) or CdTe(s)) was attempted by regulating saturated pressure of one of the constituent elements at the reservoir temperature, TR. When PiTR (i: Cd, Se2, Te2), the partial pressure at the reservoir, is larger than Pi*, the partial pressure corresponding to the total pressure minimum at a given temperature, partial pressure control is effective with such a reservoir. However, when PiTR is smaller than Pi*, partial pressure control by a reservoir is not effective, and the condition of the total pressure minimum dominates in the system.
Hydrogen permeation through materials is one of the major problems in the fusion reactor design. In this study, hydrogen permeabilities of nickel and Hastelloy X were measured with a permeation method. For nickel, the dependence of hydrogen permeability on hydrogen pressure and sample thickness was investigated systematically, and for Hastelloy X, the effects of sample treatments, mainly heat treatment, were studied. Main results are as follows: (1) Hydrogen permeability in nickel was obtained within the temperature range of 473 to 973 K, the hydrogen pressure range of 3.4×102 to 8.67×104 Pa and the sample thickness of 0.20 to 0.80 mm, which is as follows: (This article is not displayable. Please see full text pdf.) (2) Because of the good reproducibility of the data, the effectiveness of the apparatus was established. (3) It was confirmed that the bulk diffusion is the rate-limiting step of hydrogen permeation through nickel and the dissolution of hydrogen into nickel depends on Sieverts’ law. (4) Within the temperature range of 673 to 873 K, hydrogen permeabilities of Hastelloy X were obtained as follows: \
oindentFor a sample without heat treatment (This article is not displayable. Please see full text pdf.) \
oindentfor a sample heated at 1023 K for 30 h before measurements (This article is not displayable. Please see full text pdf.) \
oindentfor a sample heated at 1023 K for 100 h before measurements (This article is not displayable. Please see full text pdf.) (5) Activation energy of hydrogen permeation in Hastelloy X was increased by the heat treaments, and this was qualitatively explained connecting with some precipitates.
In order to establish a method of measuring the potential distribution in the corrosion study, three apparatus of different types were designed; the first one is applicable to samples of any shape, the second to cylindrical samples, and the last to plate samples. These apparatus were used in the measurement of the potential distribution at the curved surface of a deformed steel, at the cylindrical surface of a copper-zinc galvanic couple and at the plane surface of a welded mild steel, respectively. The local anodic and cathodic sites and the boundary between the two sites could be easily detected and the local corrosion current could be estimated by analysing the potential distribution. The technique was also applied to the study of the effect of anodic polarization on the potential distribution. The result showed, that the measurement of the potential distribution under external anodic polarization was very useful for detecting the anodic and cathodic sites. The present study indicates that the method of measuring the potential distribution provides important information in the study of corrosion phenomena from the standpoint of the local cell theory.
High purity Al-Zn-Mg alloys often exhibit low tensile ductility and typical grain boundary embrittlement occurs when aged to maximum strength levels. The influence of cold work and aging on the mechanical properties and the fracture behaviour of high purity Al-6%Zn-1.5%Mg base alloys has been investigated to improve the low ductility of the alloys. Marked improvement in the ductility of coarse grained alloy can be obtained by proper cold working and aging, and the fracture mode changes from brittle grain boundary fracture to ductile dimple-type transgranular fracture. These phenomena are observed only in the coarse grained alloy and not in the Zr-added fine grained alloy. Preaging treatment after quenching is not desirable because of a drastic loss of ductility. The cause of the marked improvement in the ductility is attributed to the absence of precipitate free zones along grain boundaries and coarse grain boundary precipitates and the precipitation of coarse intermediate precipitates in the matrix.
The aging behaviour and age-hardening of Al-10%Mg alloys with and without 0.5%Ag were investigated by means of hardness, electric resistivity measurements and optical and electron microscope observations. A fine and homogeneous distribution of small precipitates and the higher hardness were recognized in the alloys containing Ag. Furthermore, the addition of Ag to the binary alloys prevented the formation of precipitate-free-zones and brought about a remarkable increase in hardness on the two-step aging. G.P.zones in the binary alloys formed only on the aging below 50°C. In the alloys containing Ag, however, G.P.zones formed up to the higher temperature compared with that in the binary alloys; namely they formed even at about 100°C. The remarkable increase in hardness of the alloys containing Ag was due to the fine and homogeneous distribution of intermediate phases. It was considered that the exisistence of G.P.zones which act as nuclei of the intermediate phase caused these structures.
Pure nickel-pure zinc diffusion couples were annealed in the temperature range from 483 to 873 K. Diffusion layers were formed step by step as in the case of the iron-zinc system. Above 613 K five layers, δ, γ′, γ'″, γ″ and γ1, were detected, although γ′, γ'″ and γ″ layers were not presumed to be formed from a point of view of the equilibrium phase diagram. Anantatmula et al. measured the thermodynamic activity in the nickel-zinc system and found that the value of lnγZn changed abnormally at about 17 at%Ni in the homogeneous region of the γ phase. They concluded that the abnormal change of the activity would be caused by an interaction between the Fermi surface and the Brillouin zone in the γ phase of γ brass structure. The concentration gap at the boundary of γ′⁄γ'″ layers ranged from 16 to 18 at%Ni and within this composition the activity showed an abnormal behaviour. There are two possible interpretations of the formation of the γ′ and γ'″ layers; one is that the interdiffusion coefficient reaches a minimum at 17 at%Ni, and the other is that there is a miscibility gap around the same composition mentioned above.
Suitable metallic standard samples are not often obtained in photo-electric emission spectrochemical analysis. In this investigation the method for preparing samples which were used for working curves was studied. At first, iron base samples containing a series of small amounts of one element (W, Co, Ni, Mo, Nb, Cr, V systems) were made. These samples were compared with NBS 1161∼1168, and both showed good coincidence when influences of adjacent spectral lines were corrected for NBS standard samples. The remelting samples containing niobium, chromium or vanadium which have low ionization potentials were necessary to contain carbon. Next, it was examined that a series of samples for the working curve were prepared by an iron dilution method from a high alloy standard steel and that iron dilution samples of same kind of alloys were analysed with them. As high alloy steels, stainless steels (JSS 651, 652, 654) (Cr, Ni, Mn, Mo) and high speed steels (JSS 608, 610, 611) (W, Co, Mo, Cr, Mn) were chosen and two series of samples were compared with each other. When the effect of interfering lines were large, they were corrected. Satisfactory results were obtained. The equation of working curves were derived by a curve fitting with orthogonal poly-nominals. The F-test was performed for comparison of mean squares of data from the equations of working curves.
Lead (99.9%Pb) melted in a crucible of SUS 27 was ejected by argon gas pressure through various nozzles of 0.07 to 1.13 mm diameters into water or the atmosphere. The shape, length, diameter and surface- and edge-structure of the filament produced were examined by optical and scanning electron microscopy. Furthermore, the stability of the jet was examined by stroboscopic and high-speed photography. The breakup length of the jet was measured from the variation of electric current with time, which was applied to the jet, and the jet velocity. Continuous wires of 0.4 to 1 mm diameters were produced by the ejection into water. By the ejection into the atmosphere, continuous filaments of about 0.07 to 0.1 mm diameters were produced and the length of filaments of about 0.2 mm diameter was lengthened from about 0.3 to 2 m by changing the direction of ejection from vertical to horizontal. Filaments of more than 0.4 mm diameters could not be produced. These facts were explained in terms of stability and solidification of jet. The observation of the jet and the measurement of breakup length revealed that the breakup behavior of the jet was different from those jets of water or oil. The breakup length was about from two to four times as large as the value calculated by Weber’s equation. The most important factor for the stability of the jet was the accelerating effect by the gravity and the cause was supposed to be the oxide film on the jet. It is concluded that keeping the velocity at the nozzle and the velocity in cooling medium as equal as possible is most important for the production of continuous filament in the process mentioned here or in the melt spin process.
Superconducting Nb-Zr alloy films have been prepared by a continuous high-rate sputtering on tantalum substrates. A deposition rate of 330 nm/min has been attained. The compositional profile in the Nb-Zr film is quite uniform and the film has nearly the same composition as that of the target. The films deposited in a pure argon atmosphere show a columnar structure grown perpendicular to the substrate. The grain size strongly depends on the substrate temperature. The phase transformations in the Nb-Zr film become more apparent and the structure becomes closer to the equilibrium state as the film is deposited in higher atmosphere pressures and/or at lower target voltages. The superconducting transition temperature Tc of the films is about the same as that of bulk samples. The dependence of Tc on the substrate temperature is explainable on the phase transformations in the film. Critical current density Jc and its anisotropy is closely related to the grain structure of the film. Grain boundaries seem to act as the most predominant flux pinning centers in the films. Effects of oxygen in the sputtering atmosphere on the structure and superconducting properties of the Nb-Zr films have been also investigated. Oxygen significantly decreases the grain size of the film. Oxygen increases Jc but decreases Tc of the film.
By a new method using the stress relaxation test, the coefficient of strain hardening without recovery (h) and the rate of recovery without strain hardening (r) are estimated in high-temperature deformation of fcc aluminum and bcc iron, where the internal stress is confirmed to be nearly 100% of the flow stress. Both h and r are dependent on applied stress σ and temperature T in a steady-state deformation, and are represented by h=h0(σ⁄E)mexp(−Qh⁄RT) and r=r0(σ⁄E)lexp(−Qr⁄RT), where h0 and r0 are constants, E is Young’s modulus and m=−0.88(−1.5), l=4.3(3.2), Qh=−22(−76) kJ/mol, Qr=88(132) kJ/mol for aluminum (iron). During a transient state of tensile deformation in the constant strain-rate test, h and r are nearly independent of strain. The activation energy for recovery (Qr) is found to be appreciably smaller than that of self-diffusion, and then possible roles of pipe-diffusion and strain-enhanced diffusion in dynamic recovery are discussed.