Search

Article

x

Vol. 13, No. 2 (1957)

1957-01-20
Topics
CONTENT
INTERNAL FRICTION PEAK ASSOCIATED WITH THE STRESSINDUCED DIFFUSION OF HYDROGEN MOLECULES IN HIGH CHROMIUM-NICKEL ALLOY STEELS
KUNG CHING-PING, KE TING-SUI
1957, 35 (2): 130-141. doi: 10.7498/aps.13.130
Abstract +
Internal friction peaks associated with the presence of hydrogen in eight types of high chromium-nickel alloy steel were observed in measurements with a torsion pendulum. The optimum temperature for maximum internal friction lies between 610-640℃ for a frequency of vibration of about 1.5 cycles per second. Systematic investigations were made with specimens containing 18% of Cr and 12% of Ni. The elementary process for this internal friction peak was found to be a relaxation process, associated with an activation energy of about 46,000-50,000 calories per mole. Judging from the value of this activation energy, as well as from the behavior of the internal friction peak when the measurements were taken while the temperature was raised, lowered and kept constant, the conclusion was reached that the new internal friction peak is associated with the stress-induced micro-diffusion of hydrogen molecules in high alloy steels.Internal friction measurements were also able to disclose the temperature range in which transformations between hydrogen molecules and hydrogen atoms are taking place in 18 Cr 12 Ni alloy steel specimens for a given rate of heating and cooling. The results obtained are in agreement with those found in the literature.
A STUDY ON THE ACOUSTIC INTERNAL FRICTION OF IRON VIBRATING TRANSVERSELY IN A STEADY MAGNETIC FIELD BY PIEZO-ELECTRIC CRYSTAL PLATES
KE TING-SUI, CHOW PEN-LIEN
1957, 35 (2): 142-149. doi: 10.7498/aps.13.142
Abstract +
The acoustic internal friction of iron vibrating transversely in a steady magnetic held was measured by means of Rochelle salt (NaKC4H4O6·4H2O) crystal plates, the frequency of vibration used was 1633 cycles/sec. When the strength of the magnetizing field is lower than 40-50 oersteds, the curve showing the dependence of internal friction on magnetic field strength is almost flat, and becomes steeper for a higher field strength. However, as the field intensity exceeds 150 oersteds or so, the change of internal friction with field strength becomes slower again, and finally approaches to a maximum value. This maximum value of internal friction does not decrease under a saturation magnetic field. Such a phenomenon has not been observed before.According to a preliminary analysis, the observed internal friction may possibly be associated with the rotation of the magnetization vector of the magnetic domains in iron vibrating transversely in a steady magnetic field. The magnetization vector of the magnetic domains is turned because of the bending of the specimen. The action of the magnetizing field, however, tends, to turn the magnetization vector back so as to be parallel with the field direction. Through magnetostriction, the rotation of the magnetization vector induces an auxiliary strain in the specimen. A definite amount of time is required in the process of the coupling between the magnetic and elastic phenomena. This creats a condition for which the strain lags behind the stress, and gives rise to internal friction under periodic stress.
CRYSTAL STRUCTURE CHANGES IN THE T-PHASE OF Al-Cu-Ni ALLOYS
LU HSUEH-SHAN, CHANG TSUNG
1957, 35 (2): 150-176. doi: 10.7498/aps.13.150
Abstract +
A thorough investigation by means of X-rays has been carried out with the purpose to determine the nature of the ternary phase τ in Al-Cu-Ni alloys. In contrast with the conventional concept of alloy phase which is characterized by a definite type of crystal structure, systematic structure changes are found in the single phase field of τ which occupies quite an extensive area in the isothermal section of the phase diagram at room temperature. There are eight types of structures altogether, all derived from a basic rhombohedron with corners occupied by Al atoms and centres either occupied by the heavy atoms or remaining vacant. The basic rhombohedron is the building stone in the crystal architecture. By transforming the basic rhombohedron into a hexagonal prism in the usual way, all structures may be considered to be built up by stacking together a number of these hexagonal prisms along the triad. The transformation of one structure into another is quite systematic in the way that the number of the stacking stories in the unit cell increases according to the order 10, 11, 12, 13, 14, 15, 16, 17. The atomic arrangements in the different structures are closely related too, in the respect that they are all superstructures due to the presence of ordered vacancies in the rhombohedral centres.The principal factor controlling the formation of these structures has been fully considered. In view of the fact that the change of structure types follows closely with the content of Ni or Cu for alloys of constant Al content, the atomic size factor appears to be unimportant in the formation of these alloys. It has been shown that for alloy phases of the defect lattice type as the r-phase, the most fundamental factor is the average number of valency electrons per structural unit which is the basic rhombohedron in the present case. By assuming Hume-Rothery's valencies, the average number of valency electrons remains remarkably constant throughout the entire phase field, while the electron concentration varies with compositions. It has also been pointed out that for alloy phases where there is no unit cell change, the average number of electrons per structural unit is equivalent to the number of electrons per unit cell, and for alloy phase where there is no defect, this is in effect equivalent to the electron concentration.