A study of internal friction in polypropylene (PP) filled with nanometer-scale CaCO3 particles

The internal friction and relative elastic modulus of polypropylene (PP) filled with nanometer-scale calcium carbonate (nm-CaCO₃) particles in different contents (0, 4, 7, and 15 vol.%) are measured in the temperature range 150–400 K with a torsion pendulum. The peak associated with the glass transition and a small peak (′ peak) associated with the pre-melting process in crystalline parts of PP was observed around 290 and 370 K, respectively. At temperatures lower than 270 K, no peaks were observed. With increasing content of nm-CaCO₃ particles, the apparent activation energy of the peak decreases, and after passing a minimum of 4.7 eV at 4 vol.% of nm-CaCO₃, it increases. In contrary to this behavior, the peak temperature has a maximum of 289 K at the same filler fraction. Correspondingly, the highest tensile and flexural strength of PP were obtained around this content. These observations may be understood through the influences of fillers on the degree of crystallization of PP and on the mobility of molecules of PP.     

Internal friction associated with phase transformation of nanograined bulk Fe–25 at.% Ni alloy

The internal friction and modulus of a nanograined bulk Fe–25 at.% Ni prepared by an inert gas condensation and in situ warm consolidation technique were measured in temperature range −100 to 400 °C by means of a dynamic mechanical analyzer (DMA). An internal friction peak at around −75 °C associated with martensitic transformation was observed. During heating, an internal friction peak at about 200 °C accompanied with the decrease of modulus was also observed, which was proved by XRD that this may mainly be attributed to the reverse phase transformation of stress-induced martensite (SIM). Some abnormal features of modulus versus temperature were observed and discussed.     

High temperature deformation mechanisms in cemented carbides and cermets studied by mechanical spectroscopy

Two model hardmetals, a pure WC–Co and a TiWCN–Co, have been studied by mechanical spectroscopy. In this work, the materials are studied up to 0.85T_m of cobalt. A parallel analysis of the materials shows that three domains are characterized by similar internal friction peaks. A region characterized by relaxations in Co, a region characterized by relaxations in the ceramics and a high-temperature region characterized by relaxations at grain boundaries are found. Two peaks are located at high temperatures in both materials. The first located at 1420 K in WC–Co and at 1520 K in TiWCN–Co for 1 Hz is attributed to grain boundary sliding. A very broad and high peak estimated for 1 Hz around 1600 K in WC–Co and above 1700 K in TiWCN–Co has only been directly observed in frequency. It is thermally activated and shows a high, apparent activation energy.     

Mechanical spectroscopy study in commercial grain oriented silicon steel

Mechanical spectroscopy measurements were performed in commercial grain oriented silicon steel to study the outstanding features of modulus and damping spectrum. A relation between the features of the damping and modulus behaviour with the grain boundaries characteristics will be established. It should be pointed out that the elastic modulus shows an anomalous step at around 800 K. The physical mechanism involved in this process will be studied. A cooperative mechanism involving dislocations will be proposed. Besides this, the magnetic characterization of the samples also will be determined.     

Hydriding effects on negative cell electrode

Internal friction (IF) and modulus measurements have been carried out on a composite material taken from the negative electrode of a commercial Ni–metal-hydride (Ni–MH) battery, both in the as-received condition and after in situ gaseous hydrogen exposure, using a sub-resonant torsion pendulum at fixed frequencies between 0.1 and 10 Hz in the temperature range 90–450 K. In both cases the IF spectrum is composed by two peaks: P1 at 190 K and P2 at 290 K, with corresponding modulus variations. The P1 data are detected to be due to a thermally activated process which frequency shift activation energy is (0.175±0.004) eV and fitted to a relaxation peak with a larger wide respect to a Debye peak, being β equal to 2.2. It is interpreted to be due to the movement of misfit dislocations within the AB₅ intermetallic-type alloy particles in the presence of nearby H atoms, acting as a Cottrell atmosphere. Peak P2 is ascribed to the decomposition and formation of hydride phase in the alloy particles upon heating and cooling, respectively. The peak heights are shown to increase in the hydrided samples, supporting the above interpretation. These results are also discussed in connection with previous measurements on an electrode material prepared at the laboratory.     

Internal friction in martensitic, ferritic and bainitic carbon steel; cold work effects

We present the comparative analysis of the temperature dependent internal friction (IF) spectra for 1.23 wt.% carbon steel with martensitic, bainitic or ferritic structure as well as cold-work effects. Samples that have a martensitic structure at room temperature show a characteristic spectrum consisting of five peaks and an exponential background. Tempering at 800 K transforms the sample structure to a completely ferritic one. All peaks are erased upon tempering, except the peak P5 identified as a Snoek–Köster (S-K) relaxation, the amplitude of which is however drastically reduced. The Snoek–Köster peak is also present in the bainitic structure as well as in initial ferrite, but with an amplitude much lower than in martensitic samples. Cold work performed on tempered samples at room temperature either by bending or roll milling is followed by the formation of a very broad double peak between 200 and 300 K. A similar peak is also found in initial ferrite, which has been subjected to heavy machining. A local minimum in the IF spectrum is found at the temperature of cold work and post-aging. This minimum is the effect of dislocation pinning by carbon precipitates.     

Internal friction of Ti–Ni–Cu ternary shape memory alloys

Low frequency internal friction was measured on three specimens of Ti–Ni–Cu ternary alloys, the Cu content varying from 10 to 20 at.%, while Ti content was fixed at 50 at.%. The internal friction spectrum consists mainly of two peaks, a sharper one associated with the B2–B19 transformation and the other one at around 250 K, which is much broader and higher than the former. The peak height of the latter is 0.2 for the specimen containing 20% Cu, which shows that this alloy can be an excellent high damping material. Transformation behavior was studied by electrical resistivity, thermopower and DSC measurements, and was compared with the result of internal friction measurements. Solution treatment at higher temperatures lowers the internal friction peak markedly. Scanning electron microscopy observation reveals that the behaviors of precipitates are different for different solution treatment temperature, suggesting that the precipitation behavior is crucial in the damping properties.     

A comparative dielectric relaxation study of PMN–PT and PMN–PZ ceramics using impedance spectroscopy

AC-impedance spectroscopic studies in the temperature range of 30–400 °C are carried out on solid solutions of lead magnesium niobate (PMN) with lead titanate (PT) and lead zirconate (PZ), both of them in the 65/35 atomic ratio. For PMN–PT this corresponds to the morphotropic phase boundary composition (with normal ferroelectric behaviour), and for PMN–PZ it is near the phase boundary between normal ferroelectric and relaxor ferroelectric compositions. The variation of dielectric permittivity with temperature at different frequencies shows normal ferroelectric and relaxor-like dependence for PMN–PT and PMN–PZ, respectively. Temperature-dependent spectroscopic modulus plots reveal a much broader peak for PMN–PZ compared to that for PMN–PT, which is consistent with the dielectric behaviour. PMN–PT shows nearly ideal Debye behaviour below T_m (the temperature of the permittivity maximum) and the behaviour departs from ideality above T_m, whereas non-ideal Debye behaviour is seen both below and above T_m for PMN–PZ. Complex modulus plots fit well with two depressed semicircles and three depressed semicircles, respectively, for PMN–PT and PMN–PZ. The relaxation observed in the spectroscopic plots around 1 MHz for PMN–PT has been assigned to polarisation relaxation expected for normal-sized domains. No such relaxation could be observed for PMN–PZ around 1 MHz because of the mesoscopic domain sizes.     

Anelastic relaxation in high purity molybdenum single crystals at medium temperatures

The internal friction of deformed molybdenum single crystals with two different orientations has been measured in the 300–1300 K temperature range. After annealing to 950 K, a relaxation peak is seen in the 880–840 K range, with a hysteresis between the warming and cooling runs. For higher annealing temperatures, the peak position change to 970 K for the 1 1 0 and 1040 K for the 1 4 9 sample. The influence of a bias stress on the sample relaxation was studied. Possible mechanisms for this relaxation have been considered, and an interaction of dislocations with vacancy type point defects has been proposed.     

Relaxation peaks associated with the oxygen-ion diffusion in La2−xBixMo2O9 oxide-ion conductors

The effects of bismuth doping on the oxygen-ion diffusion in oxide-ion conductors La_2−xBi_xMo₂O₉ (x=0.05, 0.1, and 0.15) have been studied by both internal friction and dielectric relaxation techniques. Two internal friction peaks of relaxation type (P₁ and P₂ peak) were observed at a measurement frequency of 4 Hz around 380 and 430 K, respectively. As for the dielectric measurement, a prominent dielectric relaxation peak (P_d) was found in all the Bi-doped samples around 700 K at a measurement frequency of 50 kHz, which actually consists of two sub-peaks (denoted as P_d1 and P_d2 peak). With increasing Bi-doping content, two peaks shift to higher temperature and decrease in height, while the activation energy of both peaks increases. The main reason was interpreted as the introduction of the lone-pair electrons of bismuth, which tends to block the diffusion of oxygen ion.     

Thermal shock resistance of SiC fibrerein-forced borosilicate glass and lithium aluminosilicate matrix composites

Thermal shock resistance of an SiC fibre-(Nicalon®) reinforced borosilicate glass (Pyrex) and lithium aluminosilicate (LAS) matrix composite has been investigated experimentally in the temperature range 0–1000 K. Longitudinal Young's modulus and flexure strength of the composites after thermal shock were obtained as a function of thermal shock temperature. The results are discussed with the observed damage of the composite. The borosilicate glass matrix composite showed multiple cracking of the glass matrix perpendicular to the fibre axis when the thermal shock temperature was above 600 K. Decreases in Young's modulus and flexure strength were also recognized after multiple cracking of the matrix was initiated. On the other hand, the LAS matrix composite showed no damage at thermal shock temperatures below 800 K. However, at 800 K and above, microcracking of the matrix along the fibre axis was observed. After thermal shock, no decrease in the flexure strength was recognized, while the Young's modulus decreased due to microcracking of the matrix when the thermal shock temperatures were 800 K and above. It was found that the major advantage of the composite against thermal shock was to retain non-catastrophic failure properties even after the development of thermally induced damage in the composite.     

Effects of testing temperature and thermal treatments on some mechanical properties of a Si3N4–TiN composite

Strength and fracture toughness of an electroconductive hot-pressed Si₃N₄–35vol.% TiN ceramic composite were evaluated in air as a function of testing temperature up to 1200 °C. The toughness already shows a clear decrease at 800 °C and then remains almost constant, and the flexural strength steadily decreases with increasing testing temperature. At 1200 °C, the strength value is about 40% of that measured at room temperature. After thermal treatments in air (800, 1000 and 1200 °C) and argon (1200 °C) for 100 h, the Young's modulus, hardness, fracture toughness and flexural strength were measured at room temperature and compared to the baseline material. Young's modulus and hardness remain unchanged. The fracture toughness does not show any clear trend with the treatment temperature, while the strength, which is unaffected by the thermal treatment in argon, decreases with increasing treatment temperature in air. The long-term oxidation involves microstructural changes at the surface and in the bulk, such as the formation of a surface oxide layer and a porous sub-layer. In the bulk, the main modification is the partial crystallization of the grain boundary phase.     

Mechanical spectroscopy of polymer-magnetite composites

Mechanical properties of magnetite (Fe₃O₄) filled polypropylene (PP) prepared in an extrusion and injection molding process were investigated. Various grades of magnetite were used. Mechanical spectroscopy was performed in a temperature range from 173 to 428 K with frequencies from 10⁻¹ to 10² Hz, and the crystallinity of test samples was estimated. Damping spectra show an peak of the principal relaxation (285 K) at the glass transition temperature, a relaxation β-peak (220 K) attributed to local motions in the amorphous phase and an ′-peak (365 K) attributed to the relaxation in crystalline parts of the polymer. These peaks correspond to drops of the storage modulus.

The -peak is decreased by the extrusion process while the ′-peak is increased compared to not extruded PP. At high temperatures a drastic increase of the loss factor superposes the ′-peak for higher filler loadings. The crystallinity of the polymer matrices varies between 25 and 37%. At low temperatures the storage modulus increases with an increase in the magnetite fraction. The used particle size distributions show no significant influences on the storage moduli for temperatures from 173 to 285 K, whereas for temperatures above 285 K smaller mean particle sizes lead to higher storage moduli and lower loss factors.     

High-temperature internal friction on TiAl intermetallics

In order to study the microscopic mechanisms controlling the plastic deformation at high temperature of two γ-TiAl alloys with nominal compositions: Ti–46.5Al–4(Cr, Nb, Ta, B) and Ti–45Al–(5–10)Nb (in at.%), internal friction (IF) measurements have been performed. A subresonant torsion pendulum has been used working in two different modes; changing the temperature between 300 and 1200 K at a constant frequency, and varying the frequency between 0.001 and 10 Hz at a fixed temperature. The resulting mechanical spectra show an anelastic relaxation peak at about 1060 K at 1 Hz in one of the alloys and a high-temperature background in both of them. Activation parameters of the loss peak have been calculated and an activation enthalpy of about 3.8 eV is obtained. The characteristics and a possible responsible mechanism for this relaxation peak are discussed.     

Anelastic relaxation due to hydrogen in Ti-35Nb-7Zr-5Ta alloy

Titanium and its alloys are frequently used in the production of prostheses and dental implants due to their properties, such as high corrosion resistance, low elasticity modulus, and high mechanical strength/density relation. Among the Ti-based alloys, Ti-35Nb-7Zr-5Ta (TNZT) is one that presents the smallest elasticity modulus (around 45 GPa), making it an excellent alternative to be used as a biomaterial. In this paper, mechanical spectroscopy measurements were made of TNZT alloys containing several quantities of hydrogen in solid solution. Mechanical spectroscopy measurements were made by using a torsion pendulum, operating at an oscillation frequency in the interval 2-20 Hz, temperature in the range 100-300 K, heating rate of about 1 K/min, and vacuum lower than 10⁻⁵ Torr. A relaxation structure and a reduction in the elasticity modulus were observed for the heat-treated and doped samples. The observed peak was associated with the interaction of hydrogen trapped by oxygen atoms around the titanium atom of the metallic matrix.     

Colour centres and thermally stimulated luminescence of Na2ZnCl4

Thermally stimulated luminescence (TSL) of Na₂ZnCl₄ single crystals showed three glow peaks having their peak maxima at 343, 425 and 475 K. Optical absorption (OA) data of unirradiated samples revealed an absorption band at 272 nm while X-irradiation caused additional bands at 462 and 723 nm. Growth and room temperature annealing studies of TSL and OA supported the idea of attribution of 425 K glow peak and 462 nm absorption band to F-centres. The 272 nm OA band is due to Zn²⁺ centres whereas the 723 nm absorption band and 475 K glow peak have been assigned to Zn⁺ centres.     

高温后大理岩力学性质及其破坏规律研究

基于大理岩在常温至高温800℃后的力学试验结果,分析了高温后大理岩峰值强度、峰值应变、弹性模量、变形模量以及应力-应变全过程曲线等随温度的变化规律,同时采用岩石声发射仪与扫描电镜试验仪,对高温后大理岩破坏规律进行了探讨。结果表明:高温后大理岩试样高度和直径将变大,质量和密度减小,但在200℃时变化不明显;在常温至高温200℃后,大理岩的力学性质变化不大;高温400℃~800℃,大理岩峰值强度、弹性模量和变形模量随着温度的升高而减小,而峰值应变则变大,并且随着温度的升高,变化越明显;声发射试验得到的振铃计数与应力-时间曲线具有较好地对应关系,充分反映了岩石在不同阶段内的破裂演化规律;温度对大理岩的破坏规律有着显著影响,温度升高使大理岩由脆性破坏向延性破坏的方向发展。     

Mechanical relaxation in simple molecular liquids from the liquid to the supercooled state

Attenuation and velocity of acoustic waves have been revealed at ultrasonic frequencies (2, 5 and 10 MHz) in some glass-forming liquids. The mechanical response has been studied following continuously the materials from the liquid to the supercooled state, using an experimental set-up developed to this purpose. A peak in the attenuation of longitudinal acoustic waves has been observed in a temperature region in which the liquids are supercooled. Correspondingly, the sound velocity shows a dispersion, increasing from liquid-like to solid-like values for decreasing temperatures. Both features develop above the calorimetric glass transition temperature (T_g). In the deeply supercooled liquids, nearly 10 K above their calorimetric T_g, also the propagation of transverse wave sound (which is a characteristic behaviour of solid-like materials) has been experimentally detected. Shear and longitudinal relaxation times are not decoupled in the time–temperature region investigated. Compared to the mechanical one, the dielectric relaxation studied as a function of temperature at the same frequency of the ultrasonic experiments shows a loss peak centred at the same temperature. Depending on the liquid investigated, the mechanical relaxation spectrum can be broader than the dielectric one, specially in the low temperature flank, suggesting that some dissipative processes at lower energies can contribute to the mechanical loss, even though they do not couple to the electric probe field.     

Interactions of hydrogen in copper studied by internal friction technique

Internal friction (IF) in electrochemically hydrogen-charged copper was studied in the temperature range of 80–500 K. A distinct peak of relaxation caused by hydrogen was observed in the vicinity of 130 K at the frequency of about 1 Hz. The observed peak has an enthalpy and pre-exponential factor of relaxation 0.28 eV and 4.6×10⁻¹³ s, respectively. Effects of copper microstructure and oxygen content on the hydrogen internal friction peak in copper were studied and discussed.     

Variations of internal friction in YBa2Cu3Ox superconductors

The internal friction (Q ^–1) spectrum of YBa₂Cu₃O_x superconducting ceramic exhibits several peaks. It has been confirmed that the high-temperature peak (around 240 K) depends on structural changes and varies during subsequent cycles of cooling and heating.Q ^–1 conductivity, X-ray spectra and the shielding effect have been measured on several samples having different superconducting properties obtained by various thermal treatments. Splitting is a characteristic feature of the high-temperature internal friction peak of the sample which exhibits good superconducting properties. In the case of the specimen exhibiting the worst properties the peaks decrease and overlap. In both cases an increase can be observed of this peak with the number of thermal cycles. After ageing at 470 K, the high-temperature peak disappears. Subsequent thermal cycles slightly recover it. Hysteresis of the Young modulus is also observed. The results are interpreted as transition of the 04 oxygen atom between two energy minima in the O4-Cu-O4 chain.