Reorientation Of Complexes Research Articles

Internal Friction and Microstructure of Ti and Ti-Mo Alloys Containing Oxygen

Ti-Mo alloys are promising materials for use as biomaterials, because these alloys have excellent corrosion resistance and a good combination of mechanical properties such as fatigue, low elastic modulus, hardness, and wear resistance. The objective of this paper was to study the effect of heavy interstitial atoms on anelastic properties of Ti-Mo alloys using mechanical spectroscopy. The internal friction and Young’s modulus were measured as a function of temperature using dynamic mechanical analyser. The internal friction spectra were brought about by relaxation processes attributed to shortrange stress induced reorientation of interstitial and substitutional complexes in solid solution. It is suggested that the nature of the relaxing entities can be worked out in further research on Ti-Mo single crystals.

Phase transformations and relaxation phenomena induced by hydrogen in austenitic stainless steels

Stable austenitic steels were studied by means of X-ray diffraction, internal friction and Mössbauer spectroscopy. Cathodic charging induces the ε H phase. Results obtained are not consistent with the idea of spinodal decomposition as a mechanism of the formation of the γ H phase and can be interpreted in terms of inhomogeneous distribution of hydrogen and continuous sequence of hydrogen solid solutions in austenite. Nitrogen suppresses the formation of the ε H phase and increases the fraction of hydrogen-rich γ solid solution. The beneficial effect of nitrogen on hydrogen-caused losses of mechanical properties can be attributed to the suppression of the % phase formation. The internal friction spectra of hydrogenated stable austenitic stainless steels consist of five peaks, three of which are of relaxation nature and other two correspond to hysteretic processes. The hydrogen-induced relaxation in stable austenitic steels has a Snoek-like mechanism concerned with the reorientation of complexes of hydrogen atoms with substitutional solutes. The ideas of HH reorientation and hydrogen-induced Snoek-Köster relaxation in austenite are not confirmed.

Internal friction in hydrogen-charged CrNi and CrNiMn austenitic stainless steels

Relaxation and hysteretic phenomena caused by hydrogen in Crl8Ni15, Cr25Ni20, and Crl8Nil6Mn10 steels have been studied by using a low-frequency internal friction (IF) technique. Five IF peaks were observed in the temperature range of 80 to 450 K; three of them are of relaxation nature and two others have a hysteretic character. The enthalpies of activation have been evaluated by means of thermoactivation analysis. Short-range migration of hydrogen atoms has been found to be responsible for the relaxation peaks, while the hysteretic peaks have been attributed to the out-gassing processes accompanied by cracking. It follows from the data on orientation dependence of the relaxation strength and values of the activation enthalpies that relaxation has a Snoeklike nature and is caused by reorientation of complexes of hydrogen atoms with substitutional solutes causing noncubic defects, the symmetry of which is not higher than orthorhombic. Study of the composition effects has led to the conclusion that different substitutional solutes contribute to different compo-nents of the relaxation spectra in accordance with their influence on hydrogen diffusivity. Effect of electron irradiation on hydrogen-induced relaxation was studied and explained in terms of short-range atomic order. No indication of hydrogen-induced Snoek-Koster (SK) relaxation was observed in accordance with the data available evidencing absence of SK relaxation in face-centered cubic (fcc) metals having low values of stacking fault energy.

On the Motional Coupling between Chain and Junction Dynamics in Thermoreversible Networks

The dielectric relaxation of polar stickers capable of binary hydrogen bond complexation is studied theoretically and compared to experiment. In the model system, free and complexed units are considered in equilibrium. The theoretical evaluation shows that the dipole correlation function of complexes cannot be described by a simple exponential decay, as is usually assumed in dielectric spectroscopy. Complex reorientation and dissociation contribute simultaneously to the dielectric relaxation. The theoretical results are compared to experimental data obtained on polybutadiene which is functionalized at low concentration (x = 0.02, 0.03, and 0.04) by 4-phenyl-1,2,4-triazoline-3,5-dione (4-phenylurazole (PU)) units. From the comparison of recent dielectric and dynamic mechanical measurements, the relaxation times of the reorientation of dimeric complexes are calculated and compared with the lifetime of dimeric contacts. From the relaxation strength of the relaxation of complexed urazoles, the dipole moment is calculated and compared with the result of a force field calculation. Both methods reveal a slightly twisted structure of the dimeric complexes.

Phase transformations and relaxation phenomena caused by hydrogen in stable austenitic stainless steels

Stable austenitic stainless Cr18Nil6Mn10 steels alloyed with different nitrogen content were studied by means of X-ray diffraction, internal friction and Mössbauer spectroscopy. Cathodic charging induces the ε H phase. No evidence is obtained for occurrence of the hydrogen-induced γ H phase which could be interpreted in terms of spinodal decomposition of the hydrogen solid solution. Nitrogen retards the formation of the ε H phase and increases the fraction of the hydrogen-rich γ solid solution. The beneficial effect of nitrogen on hydrogen-caused losses of the mechanical properties can be attributed to the suppression of the ε H phase formation. The internal friction spectrum of hydrogenated stable austenitic stainless steels consists of five peaks three of which are of the relaxation nature and other two correspond to hysteretic processes. The hydrogen-induced relaxation in austenite can be described by the Snoek-like mechanism concerned with the reorientation of complexes of hydrogen atoms with substitutional solutes. The ideas of H-H reorientation and hydrogen-induced Snoek Köster relaxation in austenite are not confirmed. Short range atomic order changed by means of cold work or electron irradiation affects the relaxation spectrum. Addition of nitrogen prevents the relaxation concerned with a short range migration of the hydrogen atoms, which can be attributed to the nitrogen suppression of the ε H phase. Hysteretic damping is caused by outgassing of hydrogen from the samples.

Stress-induced reorientation of oxygen-hydrogen complexes in a Ta 75Nb 25 alloy

The anelastic behaviour of a Ta 75Nb 25 alloy containing various amounts of H and O has been investigated between 67 and 700 K at kilohertz frequencies. A relaxation process has been observed at temperatures between 74 ( f = 1.27 kHz) and 83 K ( f = 6.92 kHz), which is about two times wider than a single Debye peak. Its relaxation parameters are: W R = 0.098 eV; Γ 0 = 3 × 10 −11 s. The process appears to be related to stress-induced reorientation of O-H complexes.

Magnetic disaccommodation in cobalt following low-temperature electron-irradiation. II: Anneal above 300K

Abstract Magnetic After-Effect measurements have been made in the temperature range 4–600K on both high-purity and carbon-charged, polycrystalline cobalt and on single-crystal cobalt samples following electron-irradiation at 30K with 3 MeV electrons to a dose of 1023m−2. Attention has been focussed on the relaxation spectra following anneal above 300K. In all irradiated samples, a strong reduction in the amplitude of the relaxation spectrum in the range 250–400K occurs during anneal in this temperature range; this is attributed to the migration of the Stage III defect. In the high-purity material, no low-temperature relaxation processes evolve during this anneal. In contrast, in impurity-doped samples, low-temperature peaks evolve which are attributed to the reorientation of complexes formed by the migrating Stage III defect being trapped at interstitial carbon and at substitutional impurities.

Thermally stimulated depolarization currents in LiF+Be 2+

The reorientation of dipolar complexes in a LiF single crystal doped with Be 2+ has been studied by means of the thermally stimulated depolarization currents technique (T.S.D.C) in the temperature region 80–300 K. Three main bands were observed. The low temperature band has an enthalpy smaller by a factor of two than the intermediate band. The enthalpy of the latter is comparable to that of the migration process of the free cation vacancy but smaller (i.e. by 40%) than the enthalpy of the high temperature band. The general behaviour is similar to that of the systems: KCl + Be 2+ and NaCl + Be 2+ studies two decades ago.

Trapping and isotope effects of deuterium in Nb-5 at.% Ti

The anelastic relaxation spectrum of the Nb-5 at.% Ti system has been investigated for various deuterium concentrations, cD, between 0.07 and 1.76 at.% in the temperature range 1.2-300K. Three relaxation processes located around 170, 100 and 50K have been observed at a vibration frequency of 20 kHz, and a marked frequency-dependent rise of dissipation is measured below 5K. The maxima increase in height and shift in temperature with increasing deuterium content, but the shifts of the high- and low-temperature peaks are of opposite sign. The peak at the lower temperature grows with the square of cD and becomes the predominant process at higher concentrations. The relaxation processes are attributed to the stress-induced reorientation of titanium-deuterium complexes. These observations are interpreted under the assumption that interaction with Ti substitutionals shifts the energies of the trapping sites occupied by deuterium atoms randomly.

Relationship between frequency and activation energy for relaxation of impurity-vacancy complexes

An emperical relationship τ 0=τ 0 ∗ exp (αE) has been found between the activation energy E and the preexponential factor τ 0 for dipolar reorientation of impurity-vacancy complexes in Alkali Halides. The origin of this relationship, that is also valid for all dipolar complexes studied at present in different host crystals has been explained in terms of a monoenergetic ITC theory without recoursing to dipole-dipole interactions.

Effect of theCe3+concentration on the reorientation of dipoles in SrF2:Ce3+

The effect of the impurity concentration on the reorientation of dipolar complexes in Sr${\mathrm{F}}_{2}$, consisting of a trivalent cerium ion and a neighboring interstitial fluorine ion, has been investigated. It was found in an earlier paper that the width of the reorientation band as measured by the ionic-thermocurrents technique (ITC) increases with increasing concentration. This can be understood when it is assumed that the activation energy associated with the reorienting dipoles is modified by dipole-dipole interaction. In the present paper we propose that there is a Gaussian distribution of values for the activation energy. The width $p$ of this distribution has been calculated on the basis of a crude electrostatic interaction model. It will be shown in this paper that $p$ increases with increasing concentration of ${\mathrm{Ce}}^{3+}$. In addition, we shall see that in the interpretation given in this paper the average activation energy is independent of the ${\mathrm{Ce}}^{3+}$ concentration, whereas in earlier treatments of the ITC bands several authors have found that the activation energy decreases with increasing concentration.

Ionic thermo currents in doped CsBr and KCI

The reorientation of dipolar complexes in Ca2+, Pb2+, Ba2+, MnO24- doped CsBr single crystals and in CrO24- doped KC1 single crystals are reported in this article. The ionic thermo-current peaks were analysed using different methods. The reorientation parameters — the activation energy and the frequency factor — are calculated in each case. The results pertaining to the molecular impurities are found to be interesting.

Activation energies for reorientation of complexes in cesium halides doped with Cd2+ and Pb2+

Activation energies for reorientation of complexes in cesium halides doped with Cd2+ and Pb2+

Reorientation and degrees of binding of X2+-vacancy complexes in KCl

The reorientation of impurity-vacancy complexes in KCl crystals doped with Mg2+, Ni2+, Mn2+, Ca2+, Sr2+, Pb2+and Ba2+was studied using the ITC method. These results are analysed together with those obtained by other authors by ITC, EPR and optical methods on Cd2+, Be2+, Eu2+, Sm2+and Yb2+ions. For the first series of ions and Cd2+, it was concluded that the most favoured vacancy position is the NNN site, and that it increasingly dominates the NN site as one proceeds from Mg2+to Ba2+. The observed reorientation of complexes is mainly governed by the vacancy jump from the NNN to the NN position. In the case of Be2+it was found that the majority of vacancies are in the NN position and the special behaviour of the Eu2+, Sm2+and Yb2+rare earth ions is discussed.

Conductivity and dielectric constants of LiD

The dielectric constant of LiD has been measured in the frequency region 5-500 kHz at different temperatures up to 340 \ifmmode^\circ\else\textdegree\fi{}C. Compared to the results of other workers, the LiD conductivity curves are found to be displaced slightly to lower values than those of LiH. Furthermore, it is also proved that the high ac-conductivity values found by other workers at low temperature in the case of LiH correspond not to true conductivity but are caused by reorientation of complexes. Activation energies corresponding to the motion of a free cation vacancy or the reorientation of complexes have been determined.

Migration polarization study in alumina phosphate glasses by the ionic thermocurrent technique

Ionic thermostimulated currents (ITC) of several alumina phosphate glasses are measured and analysed in terms of distributed polarizations. The relaxation spectrum analysis yields the value of the activation energy for reorientation of complexes 0·73 eV for all subpolarizations distributed in frequency factor with the most probable value ∼1·25×1012 sec−1. The ITC experimental results are confronted with the dc conductivity measurements within the framework of the used model of alkali ion migration in glass.

Internal friction and strain aging of ferrous austenite

The effects of quenching, cold work, and electron irradiation on Snoek-like (bound pair) carbon internal friction peaks in some Fe-base austenitic alloys have been examined and correlated with previous studies of dynamic strain aging and self diffusion in similar materials. The results imply that i) the bound pair peaks have their origin in the stress-induced reorientation of carbon-vacancy complexes, ii) the binding energy of these complexes is large and possibly precludes the occurrence of cold-work-type peaks observed in bcc materials, and iii) the carbon-vacancy interaction controls many aspects of strain-aging and self diffusion in austenites which contain carbon.

Etude de la reorientation des complexes lacune-impurete divalente dans NaCl dope

We study, by means of the depolarization thermocurrent method (I.T.C.), the reorientation of impurity-vacancy complexes in NaCl containing divalent substitutional ions such as Ca 2+, Cd 2+, Mn 2+ and Mg 2+. Two thermocurrent peaks are noticeable: the greater one (monoenergetic) is ascribed to vacancies in nearest neighbour positions; the other (not compatible with a single relaxation time) to vacancies in more distant sites. This interpretation (given using a three-shell model) is extended to the case of NaCl doped with any divalent impurity: for this purpose, it is taken account of the results published by other authors concerning Be 2+, Co 2+, Sr 2+, and those obtained from diffusion, conductivity and E.P.R. measurements.

Study of the reorientation of impurity-vacancy complexes in KCl containing divalent substitutional ions

The dielectric relaxation of KCl containing impurities such as Ba++, Pb++, Sr++ and Ca++ has been investigated, using the depolarization thermocurrent method. The results are difficult to reconcile with Dreyfus' model.

Anelastic and Dielectric Relaxation due to Impurity-Vacancy Complexes in NaCl Crystals

Appreciable pairing of divalent metallic impurities with ${\mathrm{Na}}^{+}$ vacancies occurs in NaCl below 300\ifmmode^\circ\else\textdegree\fi{}C. The reorientation of such pairs or complexes had previously been observed under an applied electric field. In the present work stress-induced reorientation of pairs in NaCl doped with Ca${\mathrm{Cl}}_{2}$ and Mn${\mathrm{Cl}}_{2}$ has been studied by means of internal friction measurements. An internal friction peak attributed to pair reorientation under stress was observed near 100\ifmmode^\circ\else\textdegree\fi{}C for a vibration frequency of \ensuremath{\sim}10kc/sec. Data obtained for longitudinal stress along both the $〈100〉$ and $〈111〉$ crystal directions yields information about the rates of relaxation corresponding to various mechanical relaxational modes. The data can be interpreted consistently in terms of an extension of the theory previously applied to dielectric relaxation, according to which the paired vacancy occupies only nearest-neighbor (n.n.) and next-nearest-neighbor (n.n.n.) sites to the impurity. Relations obtained between the relaxation rates and the various possible jump rates for a ${\mathrm{Na}}^{+}$ ion into the vacancy enable each of the specific vacancy jump rates to be determined. It is concluded that the most rapid means for the reorientation of an impurity-vacancy pair between two n.n. sites is for the vacancy to move via a n.n.n. site. The rate of jump of the impurity ion into the vacancy is found to be a relatively slow process.