Boundary Internal Friction Peak Research Articles

A comparative study on the grain boundary internal friction peak of pure iron

The high-temperature relaxation behavior of single-crystal and polycrystalline iron is systematically investigated using the internal friction (IF) technique. A relaxation peak located at ∼0.45Tm (Tm, the melting temperature) is observed in the IF spectrum of polycrystalline iron as reported in conventional studies, but it is absent for single-crystal iron, implying that the appearance of this peak is related to grain boundaries, which provides a direct and important evidence for the origin of the peak located at ∼0.45Tm from grain boundary relaxation. At the same time, parameters of grain boundary relaxation of polycrystalline iron are carefully evaluated combined with a coupling model. This study will provide an important reference for the study of defect relaxation behavior in pure iron and ferrite steels.

Internal Friction Peaks in Mg-0.6% Zr and Mg-Ni High Damping Magnesium Alloys

Abstract A broad relaxation peak, which contributes to the high damping capacity around room temperature, has been obtained in all high damping magnesium alloys. This peak is a dislocation-related relaxation peak, which is probably caused by the interaction between dislocation and point defects (vacancy and solid atoms) during the dislocation movement on the basal plane activated by heat. The grain boundary relaxation peak also has been observed in both Mg-Ni and Mg-0.6%Zr high damping alloys. However, it is necessary to point out that microstructure can affect the gain boundary relaxation. With Ni content increasing, the grain is refined and the grain boundary internal friction peak shifts to lower temperature. Compared with Mg-0.6%Zr alloy, the grain boundary internal friction peak shifts to higher temperature after adding a little yttrium (Y).

Internal Friction Evidence on the Formation of Grain Boundary in Al Powder Sintering Process

The temperature dependence of internal friction is first investigated to understand the microstructure transition during the sintering process for the green compact of aluminum powder. An internal friction (IF) peak is observed only during the first heating process while not in the subsequent cooling and repeated heating process. The temperature position of the peak is independent of the measuring frequency and the height decreases with the increasing frequency. The appearance of the peak is closely related to the weak bonding interfaces between deformed aluminum particles and increased dislocation density induced by the pressing. The appearance of the peak well responds to a recrystallization process of deformed particles and thus the formation of the grain boundary which is proven by the appearance of the grain boundary IF peak. The peak temperature position is rationalized with the onset of the recrystallization process during the sintering process.

Grain Boundary Internal Friction Peak in Nanocrystalline Aluminum Studied by Continuously Changing-Temperature

The bulk nanocrystalline aluminum are fabricated by cryomilling and hot-press sintering. The internal friction (IF) and relative dynamic modulus measurements in the nanocrystalline aluminum (Al) have been made using a multifunction internal friction apparatus (MFIFA) at low frequencies (0.2-3.0 Hz) over the wide temperature ranges from room temperature to 450 °C, while continuously changing-temperature forced vibration measurement. In the temperature spectrums of IF during heating process and cooling process, a distinct IF peak is found. Corresponding to the IF peak, the relative dynamic modulus decreases rapidly. The peak temperature of the IF peak shifts towards higher temperature with increasing frequency, i.e., the IF peak seem due to the thermal activated relaxation process. The IF peak is a grain boundary IF peak, which is associated with the diffusive grain boundary of Al/Al. Its activation energy has been calculated to be 2.21±0.04×10-19 J and the pre-exponential factor is 10-14 s in IF measurements.

A Study on Influence of Annealing and Aging on High Temperature Internal Friction in Al-Zr Alloy

By using a low frequency inverted torsion pendulum, the high temperature internal friction spectra of Al-0.02wt%Zr and Al-0.1wt%Zr alloys were investigated respectively. In Al-0.02wt%Zr alloy, the conventional grain boundary internal friction peak (Pg) is observed with some small unstable peaks. In Al-0.1wt%Zr alloy, the bamboo peak is observed to appear at the high temperature side of the conventional grain boundary internal friction peak. The conventional grain boundary internal friction peak decreased and moved to higher temperature. The bamboo peak owns an activation energy of 1.75eV. When average grain size exceeded the diameter of samples, Pb strength was reduced and its position was shifted to a lower temperature. Based on the grain boundary sliding model, Pg and Pb peaks were explained. Their dependence on annealing temperature and time was determined by considering the effects of contained Ce atoms and other impurities on the relaxation across grain boundary.

Further evidence of grain boundary internal friction in bicrystals

In order to further confirm the origin of grain boundary (GB) internal friction peak in bicrystals, the effect of GB density (i.e., GB area in unit volume of specimen) on the internal friction peak in pure aluminum is studied. It is found that the increment of GB density leads to a proportional increment of the peak height (or relaxation strength), while the activation parameters remain unchanged. The results further confirm that the observed internal friction peak in bicrystals is induced by the GB, rather than lattice dislocations in grain interior. By analyzing the stress components acting on the GB plane in bicrystals, the internal friction peak is interpreted by stress induced GB sliding. The restoring force to sliding is assumed due to the faceted junctions or steps in GBs.

Internal friction in Al bicrystals with ⟨111⟩ tilt and twist grain boundaries

Internal friction measurements were performed on various ⟨111⟩ tilt and twist grain boundaries in high-purity Al bicrystals. The temperature dependence of the grain boundary internal friction peak was determined, and the activation parameters of grain boundary relaxation were obtained. These parameters were found to change in a wide range depending on boundary geometry. The activation enthalpy of boundary relaxation and the pre-exponential factor of the relaxation time are related according to the compensation effect. The results are discussed in terms of the model of correlated relaxations. Bicrystals with vicinal Σ3 boundaries were observed to behave like single crystals, i.e. an internal friction peak did not appear. This evidences that both coherent and incoherent (60° ⟨111⟩ tilt) twins possess a high mechanical resistance.

Grain boundary internal friction in bicrystals with different misorientations

The grain boundary (GB) internal friction peak has been observed in pure aluminum bicrystals containing 〈1 0 0〉 and 〈1 1 2〉 tilt GBs with different misorientations. It is found that the apparent activation parameters are different among low-angle, high-angle random and special GBs, and different extents of coupling effect are involved in different types of GBs. The results reveal that the basic mechanism for low-angle GBs can be attributed to dislocation climb, while that for high-angle GBs can be attributed to GB diffusion. The previously puzzling behaviors (apparent high activation energy and broad peak-width) of GB internal friction in polycrystals can also be explained in the light of the coupling model.

Structure of Grain Boundaries of a General Type and Mechanisms of the Grain Boundary Internal Friction Peak

Structure of Grain Boundaries of a General Type and Mechanisms of the Grain Boundary Internal Friction Peak

Damping Behavior and Mechanism of Foamed Zn-Al Eutectoid Alloy

The present work investigates the damping behavior and mechanisms in foamed Zn–Al eutectoid alloy prepared by air pressure infiltration process. Pores in the foamed Zn–Al eutectoid alloy have macroscopic size of the order of a millimeter (0.5–1.0 mm) and in large proportions, typically up to 65 vol%. The damping behavior of the foamed Zn–Al eutectoid alloy is characterized by internal friction (IF). IF and relative dynamic modulus measurements at maximum surface shear strain of 20 × 10—6 have been made using a multifunction internal friction apparatus (MFIFA) at three discrete frequencies of 0.5, 1.0, and 3.0 Hz over a temperature range from room temperature to 400 °C, while continuously changing temperature. Two IF peaks were found in the IF–temperature curves. The first is a grain boundary IF peak, which is associated with the diffusive flux on a crystalline boundary of Al. Its activation energy has been calculated to be (1.12 ± 0.04) eV and the pre-exponential factor τ0 is 10—14 s in IF measurements. The second is a phase transition peak, which results from the transformation of Zn–Al eutectoid. Experimental results show that this phase transition IF peak is a function of Ṫ/f (Ṫ rate of temperature change, f vibration frequency), but is not proportional to Ṫ/f. Finally, the damping capacity of the foamed Zn–Al eutectoid alloy, with different macroscopic pore volume fractions and two different macroscopic pore sizes, were compared with that of bulk Zn–Al eutectoid alloy specimens. The damping capacity of the materials is shown to increase with increasing volume fraction of macroscopic pores and increase with decreasing macroscopic pore size. The operative possible damping mechanisms in the foamed Zn–Al eutectoid alloy were discussed in light of IF measurements.

The change of grain boundary internal friction peak during high temperature deformation at different modes

The change of grain boundary internal friction peak during high temperature deformation at different modes (i.e., static tensile creep, cyclic tensile creep, and cyclic reverse torsion) in high purity aluminum was studied in conjunction with microstructure examinations. It was observed that the internal friction peak decreased with increasing plastic strain for all the modes, indicating that grain boundary sliding was degraded by the deformation. Nevertheless, at the same strain the decrement of internal friction was different for different modes, in particular smallest for reverse torsion. The origin of the decrease of internal friction and the difference among different modes is interpreted in the light of microstructure observations.

Grain Boundary Internal Friction of Hydrogen Precharged 13CrMo44 Steel

Pipeline steel, hydrogen charged to a content lower and higher than the critical one for void formation (established in electrochemical tests) and then degassed, was subjected to internal friction measurements. Undercritical hydrogen pretreatment was found to modify the internal friction spectra, revealing the irreversible change of the grain boundary structure produced by hydrogen. The components, corresponding to the relaxation at ferrite-ferrite, ferrite-pearlite and ferrite-cementite grain boundaries could be distinguished in the grain boundary internal friction peak.

Further experiments on the bamboo boundary internal friction peaks in high-purity aluminium

The bamboo boundary internal friction (BB) peak observed in high-purity aluminium was shown to be connected with the existence of dislocation substructures nearby the bamboo boundary. It is shown that the BB peak is reduced in specimens quenched from high temperatures and changes when the quenched specimen is aged at various temperatures, and disappears when aged at lower temperatures. TEM observation made after internal friction measurement shows that the configuration of the dislocation substructures changes after quenching and aging treatments. The configurations responsible for the BB peak and for the complementary peak appearing at a much higher temperature (HT peak) are determined by comparing the results of internal friction measurement and TEM observation. The condition of appearance of the BB peak predicted by the four-parameter mechanical model is confirmed.

Mechanism of the bamboo boundary internal friction peak

At the beginning of the 1980s, an internal friction peak situated below the optimum temperature of the grain boundary peak of fine grained specimens (the Kê peak) was observed in high-purity aluminium consisting of bamboo crystals. This discovery has given rise to much controversy, and the opinion has been expressed that this peak is only the Kê peak shifted toward lower temperature, and is not a new peak. However, our systematic study shows that the behaviour of this peak is quite different from that of the Kê peak. Recently, the bamboo boundary internal friction peak and the Kê peak were observed separately on one internal friction curve in sheet specimens consisting of mixed grains. This shows that the bamboo boundary peak is a new peak. TEM observations showed that dislocation substructures exist near the bamboo boundaries. Accordingly, we propose that such substructures intersecting and interacting with the bamboo boundaries are dragged along with the bamboo boundary during the viscous sliding of the boundary, so that the sliding process is limited with the appearance of an internal friction peak. A four-parameter mechanical model is suggested for describing the relaxation behavior of the bamboo boundary peak. The mathematical formulations and the experimental conditions for the appearance of the bamboo boundary peak derived according to this model agree with experiments.

Effect of solute atoms and precipitated particles on the optimum temperature of the grain boundary internal friction peak in aluminium

Effect of solute atoms and precipitated particles on the optimum temperature of the grain boundary internal friction peak in aluminium

Internal friction associated with formation and dissolution of metastable phase particles at grain boundaries in AlMg alloys

The grain boundary internal friction peak (GBP) of AlMg polycrystals has been measured in an inverted torsion pendulum. The height of the GBP is greatly suppressed GBP recovers after annealing at an Al-2.4wt.%Mg and Al-6.0wt.%Mg specimens. This suppressed GBP recovers after annealing at an elevated temperature. Phase analysis by X-ray diffraction techniques indicates that this process is accompanied by formation and dissolution of AlMg metastable phase particles which are introduced by non-equilibrium segregation of magnesium atoms at grain boundaries after quenching. A suitable interpretation based on numerical estimation is given.

On the grain boundary internal friction peak of ?-brasses

A conventional Ke pendulum was used to investigate the temperature dependence of internal friction for thoroughly annealed samples of Cu−30% Zn. The relaxation peak observed at 330 o C at a frequency of vibration 0.60 Hz was attributed to grain boundary diffusion. The energy activating the process amounted to 1.84 eV and characterized the activation energy for self diffusion in copper. The relaxation strength showed strain amplitude dependence, however, the activation energy and peak temperature did not show any amplitude dependence. The effect of solute atom concentration, cold work and vacancies was also tested

Experimental evidence on the existence of the bamboo boundary internal friction peak

Experimental evidence on the existence of the bamboo boundary internal friction peak

On the grain boundary internal friction peak of α-brasses

Abstract A conventional Ke pendulum was used to investigate the temperature dependence of internal friction for thoroughly annealed samples of Cu30wt.%.Zn. The relaxation peak observed at 300 °C at a vibration frequency of 0.60 Hz was attributed to grain boundary diffusion. The energy activating the process was 1.84 eV and characterized the activation energy for self-diffusion in copper. The relaxation strength showed a strain amplitude dependence, but the activation energy and peak temperature did not. The effects of solute atom concentration, cold work and quenching were also tested.

Bamboo boundary internal-friction peak in 99.9999% aluminium and the effect of cold work on the peak

An internal friction peak is observed in zone-melt 99.9999% aluminium wire specimens with bamboo crystals. The height of the peak (Q) is found to be proportional to the number of bamboo boundaries N contained in the specimen with the straight line passing through the origin. The activation energy associated with this bamboo boundary peak is found to be 1.44 eV. These results confirm the previous findings in the case of 99.999% aluminium. A systematic study is made on the effect of cold deformation on the bamboo boundary peak. Results show that the internal friction peak previously observed in cold-worked 99.9999% aluminium by some authors and claimed to be due to lattice dislocations is actually a composite peak consisting of PH, PB, and PL, where PB is the bamboo boundary peak, PH and PL are two peaks originated from cold deformation and are situated at higher and lower temperatures than that of PB. Conditions for the appearance of PH and PL are discussed. In zonengezogenem 99,9999%-Aluminiumdrahtproben mit Bambuskristallen wird ein Maximum der inneren Reibung beobachtet. Die Peakhohe (Q) ist proportional zur Zahl der Bambusgrenzen in der Probe, deren gerade Linie durch den Ursprung gehen. Die mit diesem Bambusgrenzenpeak verbundene Aktivierungsenergie betragt 1,44 eV. Diese Ergebnisse bestatigen fruhere Ergebnisse im Falle des 99,999%-Aluminium. Der Einflus einer Kaltdeformation auf den Bambusgrenzepeak wird systematisch untersucht. Die Ergebnisse zeigen, das das Maximum der inneren Reibung, das fruher in gewalzten 99,9999%-Aluminium von einigen Autoren beobachtet und Gitterversetzungen zugeschrieben wird, tatsachlich ein zusammengesetztes Maximum ist, das aus PH, PB und PL besteht, wobei PB der Bambusgrenzenpeak ist und PH und PL zwei Maxima, die von der Kaltdeformation herruhren und bei hoheren und tieferen Temperaturen als die von PB auftreten. Die Bedingungen fur das Auftreten von PH und PL werden diskutiert.