In order to clarify the contribution of grain boundary effect on the work-hardening rate without recovery effect, h, and the recovery rate without work-hardening effect, r, these two parameters in pure aluminum single crystals have been measured and compared with those in aluminum polycrystals reported so far. The measurement has been carried out by applying the strain-rate change technique to the steady-state tensile deformation at temperatures from 523 K to 673 K and at shear strain rates from 1.2×10−5 s−1 to 4.6×10−4 s−1. It is found that h is approximately proportional to the inverse of stress and depends strongly on temperature. The stress exponent of r is about 3. The activation energy of r is about 2/3 of the activation energy of lattice self-diffusion in Al. These stress and temperature dependences of h and r are almost the same as those of the polycrystals. Therefore, it is concluded that the contribution of grain boundary effect to h and r is not large.
Ti-6Al-4V alloys variously heat treated are hydrogenated by cathodic charging. The impact toughness of these alloys are evaluated using an instrumented Charpy impact testing machine. Then, the relationship between the hydrogen embrittlement and the heat treatment condition, i.e. the microstructural factor is examined. The reduction ratio of energy (ri, rp, rt) and that of fracture load (r1) which indicate the degree of hydrogen embrittlement increase with hydrogen charging time. These reduction ratios increase with the width of hydrogen embrittled fracture surface, which is equivalent to the width of hydride precipitated zone, and with the decrease of the areal percentage of primary α in the equiaxed α structure. The width of hydrogen embrittled fracture surface is in linear relationship with the hydrogen content. Ti-hydride precipitates mainly at α-β interface and also in α phase. Hydrogen embrittled cracks propagate mainly along primary α-β interfaces where much hydride exists, and sometimes propagates through primary α in the equiaxed α structure. On the other hand, cracks propagate mainly across acicular α phase in the acicular α structure.
A new scale of the theoretical optical basicity was established by means of the concept of the average electron density (D) expressecl in eq. (1). (This article is not displayable. Please see full text pdf.) \
oindentThe value of α in an oxide system was defined unity, and the values of α in alkaline earth fluoride and chloride systems were determined by measurments of Pbs-p spectra of CaF2 and CaCl2 using photoacoustic spectroscopy. The basicity moderating parameter values were found to have a linear relation with the values of the average electron density, as shown in eq. (2). (This article is not displayable. Please see full text pdf.) The theroretical optical basicity values of transition metal oxides were able to be calculated in the new scale, for example, ΛFeO=0.94, ΛFe2O3=0.72 and ΛTiO2=0.65. It was possible to explain the sulfide capacity values in the systems containing iron oxides using these optical basicity values. The theoretical optical basicity values of alkaline earth fluoride and chloride were also obtained in this study. The values of the optical basicity showed a good correlation to logarithmic values of the phosphate capacity at a constant temperature in the systems consisting of oxide and fluoride compounds. It is suggested that the theoretical optical basicity developed in this study was a resonable scale for a wide range basicity in slags and fluxes.
The activity of Zn in liquid Cu-Zn-Sn ternary alloys has been measured by the use of isopiestic method at temperatures 1423 K and 1373 K and in the composition range, NZn<0.08 and NSn≤0.08, and the first and second order interaction parameters between Zn and Sn in molten Cu have been determined. The activity of Zn in Cu-Zn binary liquid alloys is increased by the addition of a small amount of Sn. Thus, the interaction parameter, εZnSn, has a positive sign. The activity of Zn in Cu-Zn-Sn ternary liquid alloys is well expressed by a quadratic relation, (This article is not displayable. Please see full text pdf.) \
oindentin the temperature and composition ranges studied in this investigation. It has been demonstrated that the quadratic formalism proposed by Darken is also valid for Cu-Zn-Sn ternary liquid alloys in the composition range, NZn<0.08 and NSn≤0.06.
In order to develop an atomosphere assessment method, we investigated the compound corrosive action of mixed gases by analyzing the products of corrosion of exposed metals and alloys, using an electron probe microanalyzer. Test pieces were exposed to mixed gases : H2S or SO2 (10 ppm) as a background plus HCl, HNO3 (1 ppm respectively) or NH3 (100 ppm) under 90% relative humidity. Test piece metals and alloys were copper, five copper alloys, silver, aluminum, iron and 52 alloy, which are most used for electronic instruments. In H2S background gas the results are as follows: (1) When HCl gas is added, corrosion of nickel silver, cupro-nickel, iron, and 52 alloy is accelerated, and corrosion of beryllium copper, phosphor bronze and silver is suppressed. (2) When HNO3 gas is added, corrosion of all the metals and alloys is suppressed, but after corrosion once begins, corrosion of nickel silver and cupro-nickel is accelerated. (3) When NH3 gas is added, corrosion of brass, silver and 52 alloy is accelerated, and corrosion of nickel silver, and cupro-nickel is suppressed. In SO2 background gas the results are as follows: (1) When HCl gas is added, corrosion of iron is accelerated and corrosion of other metals and alloys is suppressed. (2) When HNO3 gas is added, corrosion of all the metals and alloys is suppressed. (3) When NH3 gas is added, SO2 gas is exhausted to produce ammonium compound, and no corrosive reaction occurs.
This study presents the relationship between the particle size distribution of powders and the density of the randomly packed bed. Since the binary particle groups which consist of two sized particles are the most fundamental particle ones with size distributions, the random packing models of them were made by computer simulation and investigated for the packing density dependent upon the particle size ratio and the volume fraction of the large spheres. The results are summarized as follows: (1) In the bnary random packing the density increases with the piarticle size ratio, and the maximum value exsists near the volume fraction of 0.72. (2) The maximum packing density can be expressed by a simple function of the particle size ratio. From the equation 0.75 is estimated for the maximum packing density at infinity of the particle size ratio. (3) The packing density can be mathematically expressed by the function of the particle size ratio and the volume fraction.
Effects of solidification condition and morphology of growing crystals on the formation of channel-type segregation were investigated by using unidirectionally solidified Al-Mg alloys, in which denstiy change in interdendritic liquid is similar to that in steel. Under any casting condition, channels formed at any growth rates less than a critical value R*=(2.0±0.2)×10−4 (m·s−1). Channels were mainly generated from a mixed zone of branched columnar and equiaxed crystals near equiaxed sedimental zone, and did not form in a sedimental zone. In the vicinity of the boundary region, the distribution of dendrite crystals were not uniform, and larger liquid pools existed at an early stage of solidification. The channel-type segregation was considered to originate from the stronger fluid flow through the pools. The segregation took the form of channel at fraction of solid fs=0.2-0.3.
To study the mechanism of channel-type segregation in steel ingots or unidirectionally solidified super alloys, the critical formation condition of channel-type segregation was examined experimentally and analytically by using unidirectionally solidified Al-Mg-Cu alloys. Channels formed below the critical growth rate R*, and the number of channels n (m−2) was given by the following equation at the growth rate R<R* (m·s−1). (This article is not displayable. Please see full text pdf.) \
oindentR* and A are constants which are functions of sample composition and inclination angle θt of growth interface to holizontal plane. R* was expressed by the following equations derived using nonuniform dendrite model. (This article is not displayable. Please see full text pdf.) \
oindentwhere ΔρL (kg·m−3) is the change in liquid density in the temperature range ΔTf (K) related to the channel formation, μ (Pa·s) is the viscosity of liquid and C is (1.1±0.2)×10−5 in case of Al-Mg-Cu alloy. The critical formation condition of A-segregates in steel was also successfully represented by the above equations, and C was (0.31±0.1)×10−5.
The influence of zinc concentration and drawing ratio of brass rods on the forming process of the drawing texture has been investigated by means of the determination of X-ray pole figures and the orientation distribution functions, and by transmission electron microscopy. The 〈511〉 twin component parallel to the drawing direction increases with the increase in zinc concentration and drawing ratio, and these mechanical twins are fine lamellae and consist of locally developing selected areas in the 〈111〉 orientation region. Consequently it is scarcely expected that the 〈100〉 orientation is developed by the slip rotation from the 〈511〉 twin component, because the twin component area is a microscopically laminated structure composed of alternate layers of 〈511〉 orientation and 〈111〉 preferred orientation, and the normal slip rotation toward the 〈100〉 component is disturbed by the competition of active slip systems.
The oxidation behavior and mechanism of an Fe-30 mass%Cr-4 mass%Al alloy and similar alloys containing 0.06, 0.09, 0.19 and 0.38 mass%Hf were studied at temperatures between 1273 and 1573 K for times up to 79.2 ks in stagnant air by thermogravimetric method, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The oxide formed on these alloys was mainly α-Al2O3, though the inclusion of HfO2 particles in scales increased with an increase in hafnium content in the alloy. Oxidation kinetics and scale adherence were discussed in terms of the morphological details of the scale and the structural change in the scale-alloy interface. The addition of a small amount of hafnium lowered the oxidation rate, but further hafnium addition tended to increase the oxidation rate by providing rapid diffusion paths in the form of HfO2 stringers. The scale adherence, on the contrary, showed a reverse trend, i.e., the higher the hafnium content, the stronger the adherence of scale in the experimental addition range. Metallographic evidence suggested that the improved scale adherence was due principally to a pegging mechanism; hafnium promoted the growth of stringers of α-Al2O3 into the alloy.
A study has been made on effects of C, B, Al, and Mo on cellular precipitation, grain-boundary and intragranular microstructures, and mechanical properties at 4 K of an A286-type iron-base superalloy. Base composition was low C (≤0.005) and Si (≤0.1) Fe-25Ni-15Cr- (2.4 and 3) Ti (mass%), and 0.06C, 0.006B, 1Al, 1-1.5Mo, and 1.4Mo+0.006B were independently added to the alloy in order to explicitly examine the effects of the respective elements. The independent addition of C, B, Mo and Mo+B suppressed the cellular precipitation in the alloy aged at 973 K after solution-treatment at 1373 K for 3.6 ks followed by water quenching. Particularly, C and Mo completely retarded the precipitation for times up to 720 ks. Aluminum, however, showed no retarding effects on the cellular reaction. Microstructural observations and fractographs revealed that there were three metallurgical factors which degraded the low temperature ductility (reduction of area and total elongation in tensile tests) and toughness (Charpy absorbed energy) of the nearly peak-aged alloy: (a) Cellular precipitates, (b) grain-boundary precipitates such as TiC and Fe2B which are responsible for intergranular fracture, and (c) coarse intragranular precipitates which consist mainly of TiC and act as nucreation sites for intragranular voids or cracks. The C addition can only suppress (a), but introduces (b) and (c). The B bearing alloys of which ductility and toughness are higher than those of the C bearing alloys are free from (a) and (c), but not from (b). The Mo addition to low C alloys eliminates these three factors, which results in marked enhancement in ductility and toughness at 4 K.
Fully stabilized zirconia with 10 mol% Y2O3 was implanted with 1 MeV nitrogen ions (15N2+) to doses ranging from 1.3×1014 to 4×1016 N/cm2 by using a Van de Graaff accelerator. Changes in the crystal structure of the implanted surface layer were investigated by X-ray diffraction, and the following were obtained. (1) A new phase transformation from cubic to rhombohedral symmetry was found to occur in the implanted surface layer. The rhombohedral phase (R-phase) is not a stable compound containing nitrogen atoms, but is thought to be a metastable phase induced by the surface stress arising from the radiation damage due to ion implantation. (2) The lattice parameters of the R-phase are described as a′=0.5179 nm and α′=89.8° (Z=4) for the specimen implanted to a dose of 1×1016 N/cm2. The depth distribution of the implanted nitrogen was approximately a Gaussian profile with the projected range of 500±30 nm and the maximum concentration of 2.6×1020 atoms/cm3. The transformed zone for the specimen was estimated to extend from the surface to a depth of 1 μm, which was about twice as deep as the projected range, and the fraction of the transformed material was estimated to be 74%. (3) Transmission electron microscopic observation of the implanted surface layer rewealed that no damage in the form of precipitates, large bubbles or voids existed and that the layer was crystalline. (4) By thermal annealing at temperatures up to 973 K, the R-phase disappeared with little change in the depth profile of the implanted ions. This is attributed not to the diffusion of nitrogen ions but to a reverse transformation from the metastable R-phase to C-phase. The reverse transformation is thought to occur by the thermal relaxation of the stress arising from the radiation damage.