Vol. 22, No. 6 (1966)
1966-03-20
CONTENT
1966, 22 (6): 647-658.
doi: 10.7498/aps.22.647
Abstract +
The grain boundary peak in molybdenum was measured by a torsion pendenlum, when the frequency of vibration is 1 cps, the peak occurs around 1020℃. This G. B. peak is reduced by oxygen or carbon additions, but an "alloy grain boundary peak" appears at the lower temperatures on the same damping curve. Using frequency of 1 cps, "Oxygen peak" occurs around 890℃; and "carbon peak" occurs around 925℃. Since no peak is evident on the damping vs temperature curve of molybdenum single crystals, it may be concluded that these peaks are all associated with the stress relaxation across grain boundaries. If some carbon is also present in the sample containing oxygen, the other two "alloy grain boundary peaks" appear around 960℃ and 985℃. The activation energys of all the peaks were determined. The higher is the peak temperature, the larger is the value of activation energy, i.e. the activation energy of "oxygen peak" is the smallest one (80 kcal/mol); that of "carbon peak" is somewhat larger (98 kcal/mol); that of "pure grain boundary peak" is the largest (119 kcal/mol); and the activation energies of the other two "interaction peaks" are somewhat less than that of "pure grain boundary peak".Fractographic work was made after the damping measurements had been taken. Many black oxide spots were observed on the intergranular facets of the specimen, by which the "oxygen peak" had been measured; the feathery carbides were observed on the intergranular facets of the same specimen as we had measured the "carbon peak". When both oxygen and carbon are present in the specimen, which gives the "interaction peaks" around 960℃ and 985℃, many white precipitations embeded by black rings were observed on intergranular fracture facets.Based on the results presented above, the mechanism of the embrittlement of molybdenum by a small amount of interstitial solute elements was discussed, especially the fact that carbon counteracts the severe embrittling effect of oxygen was also explained.
1966, 22 (6): 659-668.
doi: 10.7498/aps.22.659
Abstract +
A thorough investigation of the structural changes in the δ phase of Al-Ni alloys has been taken by measuring the lattice spacings, densities, and intensities of diffraction lines. The determination of the lattice spacings shows that, within the narrow homogeneity range less than four atomic per cent, a and c decrease at first with the increase of the Ni content, while after the ideal composition Ni2Al3, they increase with the increase of the Ni content; in other words, both a and c reach minimum simultaneously at the ideal composition. All density and intensity measurements prove unequivocally that when the Ni content is less than that in the ideal composition, the number of atoms contained in each unit cell always remains five, the Al atoms substituting at random some of the Ni atoms at the centres of the pseudo-cubes; and when the Ni content exceeds that in the ideal composition, the number of atoms per unit cell is more than five, the superfluous Ni atoms filling up randomly part of the interstices forming centres of the pseudo-cubes in the ideal structure.The principal factor governing these changes is the mean number of valence electrons in the fundamental structural unit. In the δ phase, the mean number of valence electrons per fundamental structural unit, the pseudo-cube, could not be greater than three.Complementary to the corresponding β phase in the same system, the δ phase forms a new type of defect lattice in alloy phases.
1966, 22 (6): 669-697.
doi: 10.7498/aps.22.669
Abstract +
A thorough investigation of the Cu-Au system has been taken by means of X-ray diffraction studies. Alloys were annealed at appropriate temperatures for different periods (one month, three months, six months and one year) and slowly cooled down to room temperature, or quenched at 300° and 600℃, with the purpose to elucidate the phases and the phase transformations that might occur. Lattice parameters were accurately determined in order to study their variations with compositions and heattreatments. The stacking periods of the ordered structures with long periods were investigated, particularly in their relations to compositions and temperatures, and by means of quenching alloys after having been annealed for various periods of time, the ordering process near the equiatomic composition was studied. Under the conditions of heattreatment mentioned above, the entire system consists of six different phases: α1 is the primary solid solution of Au in Cu, α′1 the superstructure corresponding to Cu3Au, α2 the primary solid solution of Cu in Au, α′2 the superstructure corresponding to CuAu3, k the superstructure corresponding to CuAu I, and k′ the superstructure corresponding to CuAu II. The most noteworthy is the fact that with the increase of the period of annealing, the ordered regions extend gradually, while the two-phase regions gradually narrow down, and in the slowly cooled alloys after one year's treatment, the two-phase regions almost disappear. This leads the authors to conceive that the two-phase coexistence in the Cu-Au system is in a state of metastable equilibrium. As for the α′2 phase, the most clear superlattice lines appear not at the stoichiometric composition but at 68 at.% Au. The k′ phases which appear at both sides of the equiatomic composition are partially transformed into k phases after the alloys being treated for one year. By the equiatomic composition, both the maximum transformation temperatures of the k phase and the k′ phase are not exactly at the equiatomic composition but at 49 at.% Au or even less.The measurement of lattice spacings shows that: the relation between the mean lattice spacings of the fundamental unit cells and the compositions is a continuous curve indicating positive deviation from Vegard's law. In the a and a′ regions, a increases with the Au content. In the k′ regions, for alloys where the Au contents are less than that in the equiatomic composition, a increases with the Au content while c decreases, and meanwhile c/a deviates gradually from 1 ; and for alloys where the Au contents are more than that in the equiatomic composition, a decreases gradually with the increase of the Au content, while c increases abruptly, and c/a gradually approaches 1. At the compositions where k′ transforms into k or vice versa, both a and c undergo abrupt changes.The influence of the period of annealing to lattice spacings has been fully considered. The lattice spacings in those parts of the phase regions wherein the phases do not change with the heattreatment are practically unchanged within the experimental conditions cited above. In the α′2 region, the transformation from disorder to order causes sharp drop in the lattice spacing. In the k regions, for alloys where the Au contents are less than that in the equiatomic composition, a increases with the period of annealing; and for alloys where the Au contents are more than that in the equiatomic composition, both a and c decrease with the increase of the period of annealing. But in all k regions, the volume of the fundamental unit cell decreases with the increase of the period of annealing. The authors are therefore of the opinion that the volume of the fundamental unit cell should be taken as a general measure of the degree of order.The law governing the indices of the superlattice lines present in the k′ structures has been discussed in details as well as their correspondence to those present in the k structure. The stacking periods in the k′ structures have been accurately determined by measuring the distances between the doublets arising from the splitting of the k superlattice lines as k is transformed into k′. The variation of stacking periods with compositions is continuous. The farther the alloy is from the ideal composition, the longer is the stacking period. And for the same alloy, the higher the temperature, the longer the stacking period. The stacking period may be odd, and may be a non-integer.In the metastable two-phase regions, not only the lattice parameters, but also the stacking periods of the k′ phase vary with compositions. The two-phase coexistence is composed really of two structural forms with the same composition. Purely from ther-modynamic considerations, it has been shown that the order-disorder transformations in the Cu-Au system are transformations of the second order.
1966, 22 (6): 698-707.
doi: 10.7498/aps.22.698
Abstract +
This article describles that N-type indium antimonide single crystal and twin crystal involving larg grain samples (n≈1.23×1014—2.40×1015cm-3,μe≈5.15×105—2.10×105cm2/V·sec) are converted into P-type samples by heat treatment in different kinds of gases at 500℃. During this heat treatment, if the temperature rises to above the melting point, the thermal acceptors in the P-type sample disappear, and the sample is converted back to N-type. If this converted N-type sample is again heated at 500℃, it will be converted to P-type once again. We have investigated this new discovered process which is related to the varying preparation conditions of indium antimonide and the varying gas ambients of the heat treatment, and we have also discussed the process of thermal conversion cycle and melting effect.By the fact that the thermal acceptors has been introduced into N-type indium antimonide as a function of annealing time at 500℃, it is found that the rate of thermal acceptors formed is greater at the beginning period of annealing time; when the annealing time is increased, the thermal acceptor concentration rises to maximum and then subsequently diminishes. This phenomenon is similar to that when silicon is subjected to heat treatment.From the analysis of new results of experiments, it is considered that this effect of heat treatment of indium antimonide is likely carried out by internal factor which is already existed in indium antimonide. We think that can be related with oxygen and hydrogen. Finally the possible mechanism of the heat treatment of indium antimonide is discussed.
1966, 22 (6): 714-718.
doi: 10.7498/aps.22.714
Abstract +
The correlations between the Raman band intensities, concentrations, refractive indices and the absorption frequency of benzene were studied by measuring the integrated intensities of the Raman band 992 cm-1 of benzene in 8 solutions of different concentrations and the refractive indices of the solutions. It is shown that the intensity deviation is proportional to the difference between the refractive index of the solution and that of pure benzene. The band intensities of different solutions depend linearly on their refractive indices, that is, the intensity does not depend on the nature of the solvent, but on its refractive index. The relationship between the band intensities and the resonance frequency factors of benzene in the solutions is also linear. The experimental results are discussed from the point of view of perturbation of the medium on the electronic absorption band.
