Study by resonant ultrasound spectroscopy of the elastic constants of the β phase in Cu---Al---Ni shape memory alloys

The evolution with temperature of the elastic constants of the metastable β phase in a Cu-27.96 at.%Al-3.62 at.% Ni shape memory alloy (SMA) has been studied by resonant ultrasound spectroscopy (RUS). The corresponding elastic constants of this cubic phase have been measured near the martensitic transformation temperature in a single crystal. Above the martensitic transformation temperature, an anomalous behavior has been found in the C′elastic constant which shows a softening as the temperature decreases. The internal friction value Q⁻¹ has been obtained in this temperature range from the RUS spectra. The mechanisms associated with the Q⁻¹ increase must be related to {1 1 0} shear.     

用内耗技术研究La0.7Pb0.3MnO3巨磁电阻材料

用低频扭摆法在多功能内耗仪上测量了巨磁电阻材料La_0.7Pb_O.3MnO₃(LPMO)的温度内耗谱和弹性模量.结果表明,内耗峰位与测量频率无关,并且峰高与频率成反比,弹性模量在对应的内耗峰处有明显的转折,内耗峰表现为相变峰的特征.结合电阻和磁化率的测试,解释了内耗和电阻-温度曲线的双峰现象,高温内耗峰和高温电阻峰与居里温度有很好的对应,来源于顺磁半导体向铁磁金属的转变,低温内耗峰和磁化率的单调下降来源于铁磁相分离过程,而较大的低温电阻峰部分来源于相分离过程.     

Anelastic relaxation peak associated with the presence of incoherent θ phase in Al-4wt.%Cu alloy

Internal friction measurements have been made for Al-4wt.%(1.76at.%)Cu alloy aged at various temperatures. A relaxation peak was observed at around 400 °C (ƒ = 1.6 Hz) after the speciment had been aged within the temperature range 330–450 °C. X-ray diffraction analysis showed that the incoherent θ phase is formed after aging within this temperature range and that it grows and becomes coarsened at increasing aging temperatures according to electron microscopy observations. Consequently the 400 °C internal friction peak observed for the first time is associated with the presence of θ phase in the alloy. Examination of the experimental results showed further that this peak is not due to a process occurring inside the θ phase but is associated with the stress-induced relaxation along phase boundaries between the θ particle and the matrix phase.

The activation energy of this peak is found to be 1.0 eV. The relaxation time and the relaxation strength of this peak calculated on the basis of an equivalent inclusion model are in accord with experimental results.     

Internal friction of γ-TiAl-based alloys with different microstructures

A Ti–46.5 at.% Al–4 at.% (Cr, Nb, Ta, B) intermetallic alloy with different microstructures (fine-grained primary annealed (PA) and coarse-grained fully lamellar (FL)) was examined by internal friction experiments. The influence of microstructure on the internal friction properties was studied by high-temperature (300–1270 K) mechanical loss experiments using a low frequency subresonance apparatus (0.01–10 Hz). The mechanical loss spectra show two phenomena: (i) a loss peak of Debye type at about 1000 K (1 Hz) which occurs only in samples with fully lamellar microstructure. The activation enthalpy, determined from the frequency shift, is 3.0 eV. The peak is assigned to thermally activated reversible local movement of dislocations that are part of the mismatch structure of semicoherent lamellar interfaces. (ii) A high-temperature damping background above 1000 K which is controlled by an activation enthalpy of 3.8–3.9 eV. The activation enthalpy agrees well with that of creep and strain rate cycling tests (3.5–3.7 eV) and is in the range of values reported for self-diffusion indicating that both properties (high-temperature background (HTB) and creep) are controlled by volume diffusion assisted climb of dislocations.     

Bimodal Size Distribution and Shape Anisotropy in Ball-Milled Nano-Sized α-Al2O3

-Al₂O₃ prepared by combustion technique was ball-billed in a planetary mill in toluene medium at 300 rpm in ZrO₂ pot with a ball to powder ratio 10:1 for 1, 5, 10, 15, and 20 hours. X-ray diffraction pattern from the milled materials showed super-Lorentzian peak shapes for -Al₂O₃ peak profiles. The super-Lorentzian peak shape has been attributed to the bimodal size distribution of the -Al₂O₃ particles. Rietveld analysis using two different phase fractions of -Al₂O₃ with different microstructural features yielded a low goodness-of-fit of the x-ray data indicating the suitability of the assumed model. The phase fraction of -Al₂O₃ particles with smaller size increases with the milling time. Further the particles shapes were observed to be cylindrical in this case with the cylinder axis along the crystallographic c-axis. The cylinder diameter and the length were obtained to be 86  and 140  respectively after 20 hrs of milling. The -Al₂O₃ particles of larger size are isotropic. It is, thus, proposed that milling induces bimodal size distribution in the initial hours of milling.     

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.     

(Ag2Se)1-x(Bi2Se3)x的热电性能研究

具有本征低晶格热导率的I-V-VI₂族三元硫属化合物在热电领域引起了广泛关注。AgBiSe₂作为这类化合物中少有的n型半导体, 成为一种有潜力的热电材料。本工作系统研究了AgBiSe₂的热电性能。基于Ag₂Se-Bi₂Se二元相图, 单相的(Ag₂Se)_1-x(Bi₂Se₃)_x的成分在x=0.4~0.62范围可调, 使得该材料载流子浓度具有可调性。结果表明, 通过组分调控获得了较宽范围的载体浓度1.0×10¹⁹~5.7×10¹⁹ cm^-3, 并基于声学声子散射的单一抛物带模型对其电传输性能进行了综合评估。本研究获得的最高载流子浓度接近理论最优值, 在700 K实现了最高ZT值0.5。本研究有助于深入理解AgBiSe₂的传输特性和决定热电性能的基本物理参数。     

Hydrogen chemisorption on the Si(1 1 1)√3 × √3R30 °-Al, -Ga, -B surfaces: An ab initio HF/DFT molecular orbital modelling using atomic clusters

A comprehensive study of atomic hydrogen chemisorption on the Si(1 1 1) √3 × √3R30 ° -Al, -Ga and -B cluster modelled surfaces is presented using Hartree-Fock/density functional theory methods. Extrapolation of the results to the extended (1 1 1) silicon surface is also discussed. It is found that the chemisorption of hydrogen on the Al and Ga terminated surfaces induces a transition from the √3 × √3 structure to a local 1 × 1: H-like reconstruction with a stable SiAl (or SiGa) sites. The subsurface boron induced √3 × √3 reconstruction is also lifted by hydrogen chemisorption but, in this case, boron adatoms are likely to be segregated on the surface, predominantly as BH or/and BH₂.     

Correlation of electrical properties and internal friction in mixed conduction glasses containing ionic and electronic conduction (1) Fe2O3-Na2O-P2O5 glasses

The electrical properties and internal friction in (40–x)Fe₂O₃·xNa₂0.60P₂O₅ glasses were measured. Two or three peak on internal friction were observed in the temperature range of –100 to 300° C at a frequency of about 1 Hz. The peak area of internal friction could be explained quantitatively by the additivity law of diffusion of Na⁺ ion and hopping of electrons which are carriers similar to those of dielectric loss. Activation energy, peak temperature of dielectric loss and internal friction showed almost the same value. Both relaxation phenomena have the same mechanism which is due to the diffusion of Na⁺ion and the hopping of electrons between Fe²⁺ Fe³⁺. The high-temperature peak is assumed to result from the interaction between protons or alkali ions and non-bridging oxygen.     

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.     

用内耗技术研究La0.7Pb0.3MnO3巨磁电阻材料

用低频扭摆法在多功能内耗仪上测量了巨磁电阻材料La0.7Pb0.3MnO3(LPMO)的温度内耗谱和弹性模量。结果表明，内耗峰位与测量频率无关，并且峰高与频率成反比，弹性模量在对应的内耗峰处有明显的转折，内耗峰表现为相变峰的特征，结合电阻和磁化率的测试，解释了内耗和电阻-温度曲线的双峰现象，高温内耗峰和高温电阻峰与居里温度有很好的对应，来源于顺磁半导体向铁磁金属的转变，低温内耗峰和磁化率的单调下降来源于铁磁相分离过程。而较大的低温电阻峰部分来源于相分离过程。     

The low frequency internal friction and electric magnetic properties in La0.7Pb0.3MnO3 bulk materials

The polycrystalline samples of La_0.7Pb_0.3MnO₃ synthesized by the sol–gel method were studied by the low frequency internal friction measurements and the resistance and ac susceptibility measurements. There are two internal friction peaks at 258 and 198 K, respectively, the peak positions of which do not shift with frequency but the peak heights of which decrease with increasing frequencies. The modulus softening is evident at the corresponding temperatures. Corresponding to the two internal friction peaks, there are two resistance peaks, and a sharp rise and a following continuous decrease of ac susceptibility. It is suggested that the high temperature peaks correspond to the paramagnetic (PM) to ferromagnetic (FM) transition, while the low temperature peaks originate from the process of an anti-ferromagnetic phase (AFM) separating from the ferromagnetic matrix (phase separation) in polycrystalline materials. The peak positions of internal friction and resistance will move towards higher temperature when the sample was annealed in flowing oxygen, and the low temperature peaks become smaller.     

两种不同界面结合强度碳/铝复合材料的内耗特性

本文研究了两种不同界面结合强度的碳/铝复合材料经不同次数加载热循环处理后的内耗值及内耗机制。弱界面结合的C/L2复合材料的内耗值变化主要由界面脱粘引起,而强界面结合的C/LD2复合材料的内耗值变化主要由位错运动所致。     

Inclusion Complexes of Tolnaftate with β-Cyclodextrin and Hydroxypropyl β-Cyclodextrin

Tolnaftate, an antifungal agent, was found to form inclusion complexes with both β-cyclodextrin (β-CD) and hydroxypropyl β-cyclodextrins (HPBCDs) with two different degrees of substitution [HPBCD(A)-8% and HPBCD(B)-3%]. Complex formation in the solution state was studied using phase solubility and spectral shift methods. Solid complexes were prepared by the coprecipitation method. Solubilities and dissolution rates were determined for each solid complex, its corresponding physical mixture, and free drug. The increase in solubility of tolnaftate with added HPBCD was found to be significantly greater than with added β-CD. For both HPBCD(A) and HPBCD(B), over the concentration range 0-0.05 M. 1:1 complexes with stability constants of 1460 ± 139 M^-1 and 1860 ± 165 M^-1 were observed, respectively. Over the β-CD concentration range 0-0.02 M, a 1:1 complex with a stability constant of 1190 ± 105 M^-1 was observed. At higher HPBCD concentrations, the increase in solubility was observed to show a positive deviation from linearity (type A_p phase diagram). Using the spectral method, in a 2 5% v/v methanol in water system, the stability constants were determined to be 1020 ± 150 M^-1 1110 ± 120 M^-1 and 1100 ± 260 M^-1 for HPBCD(A), HPBCD(B) and β-CD, respectively. The solid complexes prepared showed improved dissolution over physical mixtures and free drug.     

High temperature creep of modified α + β brasses

Good machinability and formability of technical brasses α + β have to be preserved when alternative modifications are developed instead of alloying with toxic lead. Several model brasses of this type, which exhibit satisfactory machinability, are creep tested at 780 °C to compare their high temperature formability. The observed stationary creep rate and local ductility may highly differ for various alloy types. To characterize the impact of individual additions, superposition laws for the respective quantities are proposed and applied to the measured values. The strong effect of even small amounts of some additions on the creep rate and the boundary component of ductility is suggested to be due to segregation phenomenon. Rigid particles, such as phosphides, enhance significantly the creep resistance of the material, though restrict the macroscopic stability of plastic flow. On the other hand, the contribution of liquid particles to the creep damage may be effectively obstructed by phosphides.     

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 of hydrogen-doped metallic glasses of high glass forming ability

Seven multi-component metallic glasses of high glass forming ability (four Zr-based, a Mg-based, a Pd-based and a La-based glasses) have been hydrogenized electrolytically and internal friction has been measured at temperatures between 80 and 400 K. Hydrogen damping has been observed in every alloy; the internal friction peak is quite broad, where the peak value increases and then decreases and the peak temperature decreases with increasing hydrogen content. Compared with the results of the hydrogen damping in binary metallic glasses so far reported, the peak height versus peak temperature relation is generally shifted to higher temperature side in multi-component glasses, the origin of which has been discussed.     

Temperature dependent damping studies of Ni-Mn-Ga polymer composites

Mechanical properties of ferromagnetic shape memory alloy (FSMA) polyurethane (PU) polymer composites are studied using dynamic mechanical analysis (DMA) at different temperatures. The sample used in the study is Ni-Mn-Ga/PU polymer composite. DMA studies reveal that the mechanical modulus decreases, when the temperature increases. The peak in internal friction (tanδ) appears twice due to martensite transformation of the reinforced particles and glass transition of the polymer matrix. The strain is due to the motion of twin boundaries rather than the phase transformations. Twin boundary motion is found to be the root cause for the martensite-austenite transformation and vice versa, and leads to enhanced damping mechanism. Speculations on twin boundaries of this sample to show concrete evidence on change in internal friction (tanδ) are still underway. This paper proposes that Ni-Mn-Ga/PU polymer composites can be used as efficient dampers.     

Quantitative determination of the volume fraction of intergranular amorphous phase in sintered silicon nitride

In this paper, a commercial liquid phase sintered silicon nitride with Y₂O₃ and Al₂O₃ additives is investigated. The material is characterised by a large, and stable, internal friction peak near 1150 °C. The peak is linked with the glass transition in intergranular amorphous volumes, whose presence is confirmed with transmission electron microscopy. An estimate of the volume fraction of the amorphous phase is calculated from the difference in stiffness below and above the glass transition temperature. The procedure relies on accurate Young’s modulus data, which were obtained with the impulse excitation technique (IET). The amount of amorphous pocket phase was estimated at 12.4 vol.%. For the first time, microstructural evidence supporting this estimate is obtained, using analysis of scanning electron microscopy (SEM) images. The rather large amount of amorphous matter explains the limited high temperature potential of the material, which was primarily and successfully developed for wear applications.     

Mechanical spectroscopy of hydrogen-absorbing quasicrystals

The H-induced damping peak in icosahedral quasicrystals, generally attributed to a Snoek-type reorientation mechanism, was studied in comparison between Zr_69.5Cu₁₂Ni₁₁Al_7.5 and Ti₅₃Zr₂₇Ni₂₀ using the vibrating-reed technique. Whereas the peak in Zr_69.5Cu₁₂Ni₁₁Al_7.5 is practically the same as in the amorphous phase (in accordance with icosahedral short-range order in metallic glasses), significant differences in shape and position of the peak are found between the two quasicrystalline alloys. These might possibly be used as a probe to distinguish between icosahedral structure types. Another interesting result is a higher intrinsic damping of quasicrystalline Zr_69.5Cu₁₂Ni₁₁Al_7.5, compared to the amorphous phase, between 450 and 650 K.