Papers by Keyword: Snoek Relaxation

Abstract: The temperature dependence of the dynamic Young’s modulus, E, and the damping, Q^-1, of Fe-C-N and Fe-17%Cr-C-N alloys with different C, N contents were studied in the temperature range of 25°C to 600°C by the impulse excitation internal friction technique at 1KHz. Hot rolled samples were cold rolled to a thickness of 1.2mm and recrystallization annealed at 820°C for 30sec then gas jet cooled (-50°C/sec). Samples were subsequently tensile strained 6% and 16%. A Snoek peak was observed at 120°C in the undeformed sample and a Snoek-Koster peak was observed at 400°C after deformation. In the case of the Fe-Cr-C-N alloy, a high damping background due to magneto-mechanical damping was observed in the temperature range of 25°C to 400°C. A broaden Snoek peak in FeCr was observed at 300°C. The internal friction peaks observed in this study showed the strong dependence of the amount of interstitial contents and deformation and were well correlated to previous internal friction studies measured mainly by torsion pendulum and inverted torsion pendulum.

Abstract: The Fe-Mn-N alloys used in the present study showed an unexpected increase of both the yield strength and the ultimate tensile strength after prestraining and strain aging. In order to understand the mechanism of this phenomenon, which is due to solute N, static strain aging tests were carried out in combination with resonant impulse excitation internal friction analysis. It is shown that the interaction between thermal kinks and solute N atoms plays an essential role in the increase of the tensile strength.

Abstract: To establish the method for determining the amount of carbon in the ferrite phase in ferrite + martensite dual-phase low-alloy steels, mechanical loss measurements have been performed on a series of Fe–C alloys with varying constitution. The observed mechanical loss spectra of two-phase alloys turned out to be simple superposition of those of single phase alloys, of ferrite and of martensite. The concentrations of carbon in solution evaluated from the magnitude of the Snoek relaxation in the two-phase alloys agree well with those expected from the Fe–C phase diagram. It is thus possible to selectively analyse the carbon dissolved in the ferrite phase in the complex structure, at least in simple binary alloys.

Abstract: t is common knowledge that interstitial-interstitial interaction influence on the Snoek relaxation. We used a computer simulation of this effect in the Nb-O alloy to test the adequacy of various models of the O-O interaction and clarify the mechanism of this effect The energy calculations in the first twelve coordination shells have been performed by the projector augmented-wave (PAW) method as implemented in the Vienna ab initio simulation package (VASP). The energies have been calculated in different ways which vary in the method of determination the energy of non-interacting O-O pairs. The energies calculated on the various variants are similar but in one case there is O-O repulsion in all first twelve coordination shells, whereas in another one can see attraction in four of twelve shells. Internal friction Q^-1 was calculated as a sum of the contributions from individual interstitial atoms in different environments, each of which being assumed to be the Debye function. It is assumed that long-range interaction of oxygen atoms affects the distribution of these atoms and the energy of each interstitial atom in the octahedral interstices before a jump and after a jump. The Monte Carlo method is used for simulating short-range order of interstitial atoms and for calculating values of energy changes. Comparison of the calculated temperature and concentration dependence of the Snoek peak with the published data showed that the PAW supercell calculation of the O-O interactions in Nb describes the behavior of the interstitial solid solution adequately. It proves also that the impact of interstitial atom concentration on the Snoek relaxation is connected to the mutual attraction of these atoms.

Abstract: The Snoek relaxation, a specific point-defect induced anelastic relaxation phenomenon, is characteristic of an internal friction peak in bcc metals with interstitial solutes. Such internal friction mechanism has not been applied in the development of high damping alloy while grain boundary and twin boundary featured anelastic relaxations are applied in some high damping alloys. In this paper, the fundamental principles and experimental results concerning the Snoek relaxation are reviewed, and the feasibility to apply the Snoek relaxation mechanism into high damping alloys is discussed. Due to the peak-shape behavior in the Snoek relaxation type damping, composition design of a high damping alloys should takes temperature position, broadness and also peak height into account. Ti-Nb-O and Ti-V-Cr-O alloys are designed and fabricated by CCLM casting in our laboratory. It is conformed that the damping behaviors of the alloys are of Snoek relaxation type showing obvious frequency and temperature dependence. While the broadened damping peak caused by the substitutional solutes is advantage to improve the temperature stability of damping capacity, a large concentration of interstitial solute and texture control are required to improve the reduced damping capacity.

Abstract: The Snoek-Köster (SK) relaxation and the dislocation-enhanced Snoek Effect (DESE) in deformed ultra-high purity Fe-C alloys and industrial low-carbon cold-rolled steel sheets as well as a quantitative comparison between experimental data and computer simulations have been presented.