Combined ultrasonic elastic wave velocity and microtomography measurements at high pressures

Combined ultrasonic and microtomographic measurements were conducted for simultaneous determination of elastic property and density of noncrystalline materials at high pressures. A Paris-Edinburgh anvil cell was placed in a rotation apparatus, which enabled us to take a series of x-ray radiography images under pressure over a 180° angle range and construct accurately the three-dimensional sample volume using microtomography. In addition, ultrasonic elastic wave velocity measurements were carried out simultaneously using the pulse reflection method with a 10° Y-cut LiNbO(3) transducer attached to the end of the lower anvil. Combined ultrasonic and microtomographic measurements were carried out for SiO(2) glass up to 2.6 GPa and room temperature. A decrease in elastic wave velocities of the SiO(2) glass was observed with increasing pressure, in agreement with previous studies. The simultaneous measurements on elastic wave velocities and density allowed us to derive bulk (K(s)) and shear (G) moduli as a function of pressure. K(s) and G of the SiO(2) glass also decreased with increasing pressure. The negative pressure dependence of K(s) is stronger than that of G, and as a result the value of K(s) became similar to G at 2.0-2.6 GPa. There is no reason why we cannot apply this new technique to high temperatures as well. Hence the results demonstrate that the combined ultrasonic and microtomography technique is a powerful tool to derive advanced (accurate) P-V-K(s)-G-(T) equations of state for noncrystalline materials.     

Yield strength of molybdenum at high pressures

In the diamond anvil cell technology, the pressure gradient approach is one of the three major methods in determining the yield strength for various materials at high pressures. In the present work, by in situ measuring the thickness of the sample foil, we have improved the traditional technique in this method. Based on this modification, the yield strength of molybdenum at pressures has been measured. Our main experimental conclusions are as follows: (1) The measured yield strength data for three samples with different initial thickness (100, 250, and 500 microm) are in good agreement above a peak pressure of 10 GPa. (2) The measured yield strength can be fitted into a linear formula Y=0.48(+/-0.19)+0.14(+/-0.01)P (Y and P denote the yield strength and local pressure, respectively, both of them are in gigapascals) in the local pressure range of 8-21 GPa. This result is in good agreement with both Y=0.46+0.13P determined in the pressure range of 5-24 GPa measured by the radial x-ray diffraction technique and the previous shock wave data below 10 GPa. (3) The zero-pressure yield strength of Mo is 0.5 GPa when we extrapolate our experimental data into the ambient pressure. It is close to the tensile strength of 0.7 GPa determined by Bridgman [Phys. Rev. 48, 825 (1934)] previously. The modified method described in this article therefore provides the confidence in determination of the yield strength at high pressures.     

高压下β-Ti的结构稳定性、弹性和电子性能的第一性原理研究

应用第一性原理的方法, 研究了高压下β-Ti在0 K下的结构稳定性、 弹性和电子性能. 吉布斯自由能和电子态密度的研究表明, 随着压力的增加, β-Ti 的结构趋于稳定. β→β 的相变压强为 64.3 GPa, 这一计算结果与其它的理论结果 63.7 GPa 和实验结果 50 GPa相吻合. 弹性常数的计算表明, β-Ti 力学稳定的低压极限约为50 GPa, 该压力下的弹性模量约为30.01 GPa, 接近人体骨骼的弹性模量30 GPa. 另外, 讨论了不同压力下β-Ti体积模量B、 剪切模量G、 杨氏模量E、 泊松比β、 声速和韧性/脆性. 随着压力的增加, B, G, E增加, 但是β减小. B/G 计算表明, β-Ti具有良好的韧性.     

A broadband spectroscopy method for ultrasonic wave velocity measurement under high pressure

A broadband spectroscopy method is proposed to measure the ultrasonic wave phase velocity of Z-cut quartz under high pressure up to 4.7 GPa. The sample is in a hydrostatic circumstance under high pressure, and we can get longitudinal wave and shear wave signals simultaneously in our work. By fast Fourier transform of received signals, the spectrum and phase of the received signals could be obtained. After unwrapping the phase of the received signals, the travel time of ultrasonic wave in the sample could be obtained, and the ultrasonic wave phase velocity could also be resolved after data processing. The elastic constant of measurement under high pressure is also compared with previous studies. This broadband spectroscopy method is a valid method to get ultrasonic wave travel parameters, and it could be applied for elasticity study of materials under high pressure.     

基于第一性原理的高压下TiAl结构、力学性能及热力学性质研究

采用第一性原理计算方法,研究了压力与温度对TiAl合金结构、力学性能与热力学性质的影响.结果显示,随着外加压力的增加,TiAl体积比降低. 计算了不同压力下TiAl的弹性常数Cij , 所有Cij均力学稳定性判据, 表明不同压力下的模拟结果均满足力学稳定性条件. 通过弹性常数, 计算了体模量与剪切模量, 发现在0 Gpa下的计算值与文献值相吻合,表明计算的准确性. 体模量与剪切模量可以用来反映材料抵抗变形能力, 随着压力的增加, 其数值增加, 表明材料抵抗变形能力得到提升. 由B/G发现, 当压力在10-20 Gpa之间时, TiAl由脆性材料转变为延性材料. 借助准谐德拜模型, 研究了当温度在0-1 000 K、 压力在0-50 Gpa下压力与温度对TiAl体模量、 德拜温度、 线膨胀系数以及热容的影响, 这有助于研究温度与压力对热力学参数的影响. 最后, 研究了不同压力下TiAl的电子结构, 随着压力的增加, 材料的态密度强度降低, Ti原子成键相互作用减弱, Al原子成键相互作用增强, 材料的延性得到提升.     

TiAlN/AlON纳米多层涂层的微观结构和力学性能研究

通过磁控溅射制取一系列不同AlON厚度的TiAlN/AlON纳米多层涂层,并用X射线衍射、扫描电镜、高分辨透射电镜和纳米压痕仪分别对微观结构和力学性能进行表征和测量。研究表明:非晶态的AlON在厚度约小于1 nm时,在TiAlN模板作用下转变为晶体结构,并与TiAlN呈共格外延生长,出现超硬效应,当AlON厚度为0.7 nm时,硬度和弹性模量分别最高可达38.1 GPa和385.6 GPa。当AlON厚度超过1 nm时,逐渐转变为非晶结构并且破坏了多层涂层的共格外延生长,硬度随之降低。因此利用这种机制可以制备出力学性能好、耐高温氧化性的刀具涂层,满足现代切削的需要。     

Energy dissipation of materials at high pressure and high temperature

We report an experimental method to study the anelastic properties of materials at high pressure and high temperature. The multianvil high pressure deformation device, used to apply a cyclic loading force onto the sample, can reach 15 GPa and 2000 K. A synchrotron x-ray radiation source provides time resolved images of the sample and reference material. The images yield stress and strain as a function of time; stresses are derived from the reference material, and strains from the sample. This method has been tested by applying a sinusoidal stress at megahertz to hertz frequency on a San Carlos olivine specimen at 5 GPa and up to 2000 K. Strain as small as 10(-5) can be resolved. We have obtained experimental results which exhibit resolvable attenuation factor (Q(-1)) and shear modulus (M) at deep Earth conditions. These results are in quantitative agreement with previously reported lower pressure data and suggest that temperature and grain size have dominating effect on these properties.     

Measurement of fast-changing low velocities by photonic Doppler velocimetry

Despite the increasing popularity of photonic Doppler velocimetry (PDV) in shock wave experiments, its capability of capturing low particle velocities while changing rapidly is still questionable. The paper discusses the performance of short time Fourier transform (STFT) and continuous wavelet transform (CWT) in processing fringe signals of fast-changing low velocities measured by PDV. Two typical experiments are carried out to evaluate the performance. In the laser shock peening test, the CWT gives a better interpretation to the free surface velocity history, where the elastic precursor, main plastic wave, and elastic release wave can be clearly identified. The velocities of stress waves, Hugoniot elastic limit, and the amplitude of shock pressure induced by laser can be obtained from the measurement. In the Kolsky-bar based tests, both methods show validity of processing the longitudinal velocity signal of incident bar, whereas CWT improperly interprets the radial velocity of the shocked sample at the beginning period, indicating the sensitiveness of the CWT to the background noise. STFT is relatively robust in extracting waveforms of low signal-to-noise ratio. Data processing method greatly affects the temporal resolution and velocity resolution of a given fringe signal, usually CWT demonstrates a better local temporal resolution and velocity resolution, due to its adaptability to the local frequency, also due to the finer time-frequency product according to the uncertainty principle.     

Integrating in situ high pressure small and wide angle synchrotron x-ray scattering for exploiting new physics of nanoparticle supercrystals

Combined small and wide angle synchrotron x-ray scattering (SAXS and WAXS) techniques have been developed for in situ high pressure samples, enabling exploration of the atomic structure and nanoscale superstructure phase relations. These studies can then be used to find connections between nanoparticle surfaces and internal atomic arrangements. We developed a four-axis control system for the detector, which we then employed for the study of two supercrystals assembled from 5 nm Fe(3)O(4) and 10 nm Au nanoparticles. We optimized the x-ray energy and the sample-to-detector distance to facilitate simultaneous collection of both SAXS and WAXS. We further performed in situ high pressure SAXS and WAXS on a cubic supercrystal assembled from 4 nm wurtzite-structure CdSe nanoparticles. While wurtzite-structure CdSe nanoparticles transform into a rocksalt structure at 6.2 GPa, the cubic superstructure develops into a lamellarlike mesostructure at 9.6 GPa. Nanoparticle coupling and interaction could be enhanced, thus reducing the compressibility of the interparticle spacing above ～3?GPa. At ～6.2?GPa, the wurtzite-to-rocksalt phase transformation results in a noticeable drop of interparticle spacing. Above 6.2 GPa, a combined effect from denser CdSe nanoparticle causes the interparticle spacing to expand. These findings could be related to a series of changes including the surface structure, electronic and mechanical properties, and strain distribution of CdSe under pressure. This technique opens the way for exploring the new physics of nanoparticles and self-assembled superlattices.     

Magnetic measurements at pressures above 10 GPa in a miniature ceramic anvil cell for a superconducting quantum interference device magnetometer

A miniature ceramic anvil high pressure cell (mCAC) was earlier designed by us for magnetic measurements at pressures up to 7.6 GPa in a commercial superconducting quantum interference magnetometer [N. Tateiwa et al., Rev. Sci. Instrum. 82, 053906 (2011)]. Here, we describe methods to generate pressures above 10 GPa in the mCAC. The efficiency of the pressure generation is sharply improved when the Cu-Be gasket is sufficiently preindented. The maximum pressure for the 0.6 mm culet anvils is 12.6 GPa when the Cu-Be gasket is preindented from the initial thickness of 300-60 μm. The 0.5 mm culet anvils were also tested with a rhenium gasket. The maximum pressure attainable in the mCAC is about 13 GPa. The present cell was used to study YbCu(2)Si(2) which shows a pressure induced transition from the non-magnetic to magnetic phases at 8 GPa. We confirm a ferromagnetic transition from the dc magnetization measurement at high pressure. The mCAC can detect the ferromagnetic ordered state whose spontaneous magnetic moment is smaller than 1 μ(B) per unit cell. The high sensitivity for magnetic measurements in the mCAC may result from the simplicity of cell structure. The present study shows the availability of the mCAC for precise magnetic measurements at pressures above 10 GPa.     

Density measurements of noncrystalline materials at high pressure with diamond anvil cell

We describe an x-ray absorption method for in situ density measurement of non-crystalline materials in the diamond anvil cell using a monochromatic synchrotron x-ray microbeam. Sample thickness, which is indispensable in the absorption method, can be determined precisely by extrapolating the thickness profile of the gasket obtained by x-ray absorption and diffraction measurements. Diamond deformation across the sample chamber becomes noticeable at high pressures above 10 GPa, which can be monitored with a precision better than 1%, as demonstrated by measurements on crystalline Ag. We have applied the developed method to measure densities of the classic network-forming GeO(2) glass in octahedral form at pressures up to 56 GPa. The fit to the pressure-volume data with the Birch-Murnaghan equation from 13 to 56 GPa gives parameters of V(0)=23.2+/-0.4 cm(3)mol and K=35.8+/-3.0 GPa, assuming that K(')=4. This method could be applicable for in situ determination of the density of liquids and other noncrystalline materials using a diamond anvil cell up to ultrahigh pressures.     

Amorphous solid water produced by cryosectioning of crystalline ice at 113 K

Amorphous solid (vitreous) water can be obtained by a number of methods, including quick freezing of a very small volume of pure water, low pressure condensation of water vapour on a cold substrate or transformation of hexagonal ice (the ice which is naturally formed) under very high pressure at liquid nitrogen temperature. Larger volumes can be vitrified if cryoprotectant is added or when samples are frozen under high pressure. We show that a sample of 17.5% dextran solution or mouse brain tissue, respectively, frozen under high pressure (200 MPa) into cubic or hexagonal ice can be transformed into vitreous water by the very process of cryosectioning. The vitreous sections obtained by this procedure differ from cryosections obtained from vitreous samples by the irregular aspect of the sections and by small but significant differences in the electron diffraction patterns. For the growing community of cryo‐ultramicrotomists it is important to know that vitrification can occur at the knife edge. A vitreous sample is considered to show the best possible structural preservation. The sort of vitrification described here, however, can lead to bad structural preservation and is therefore considered to be a pitfall. Furthermore, we compare these sections with other forms of amorphous solid water and find it similar to high density amorphous water produced at very high pressures (about 1 GPa) from hexagonal ice and annealed close to its transformation temperature at 117 K.     

负泊松比曲边内凹蜂窝结构的面内冲击动力学数值研究

利用数值方法研究了具有负泊松比效应的可变弧角曲边内凹蜂窝结构的面内冲击动力学性能,讨论了冲击速度和弧角对曲边内凹蜂窝结构的变形模式与吸能能力的影响。研究结果表明：改变冲击速度和弧角的大小会影响曲边内凹蜂窝结构的变形失效模式;当冲击速度较高时,蜂窝结构内的应力波动范围较大,结构的体能量吸收值随弧角的增大逐渐增大;当冲击速度较低时则不存在上述现象。当弧角大于120°时,曲边内凹蜂窝结构具有负泊松比效应,该结构的吸能能力高于其他弧角所对应的正泊松比蜂窝结构的吸能能力,该现象与冲击速度无关。     

Fabrication and efficiency evaluation of a hybrid NiCrAl pressure cell up to 4 GPa

A hybrid NiCrAl pressure cell was fabricated to measure magnetic quantities under high pressure above 3 GPa. A pressure of 4.0 GPa was achieved and the pressure cell was found to be reusable even after a pressurizing trial up to 4.0 GPa. Pressure was monitored using (63)Cu nuclear quadrupole resonance of Cu(2)O and ruby fluorescence. The pressure efficiency of a fresh cell was maintained at 96%, and no appreciable deformation was observed at pressures below 3 GPa; on the other hand, the efficiency after pressurizing trials decreased gradually and reached 75% at 4 GPa accompanied by a maximum expansion inside the cylinder of 2%.     

An empirical relation for the volume of the crater formed during high velocity oblique impact tests

An empirical equation relating the volume of the crater formed during high velocity oblique impact tests to the velocity and angle of impact and to the target material hardness has been proposed. It is further demonstrated that this equation can predict the volume of the crater formed quite accurately over a wide range of impact velocities (50–350 m s^-1), impact angles (up to 60°) and target hardnesses (1–4 GPa).     

Investigation of SrS under high pressure including the role of temperature

In this paper we focus on the structural and elastic properties of the B1 phase of SrS by using the modified TBP model, including the role of temperature. We have successfully obtained the phase transition pressures and volume changes at different temperatures. In addition elastic constants and anisotropy factor (A) of B1 phase of SrS at different temperatures are discussed. Our results are comparable with the previous ones at high temperatures and pressures. The elastic properties of the B1 phase of SrS have been discussed with various temperature and pressure. More over the thermal properties like Debye temperature, Thermal expansion coefficient (α) and Gruneisen parameter (γ) and anisotropy factor at high temperatures have also been discussed successfully.     

Determining the equation of state of amorphous solids at high pressure using optical microscopy

A method to determine the volumetric equation of state of amorphous solids using optical microscopy in a diamond anvil cell is described. The method relies on two- dimensional image acquisition and analysis to quantify changes in the projected image area with compression. The area analysis methods prove to be robust against improper focusing and lighting conditions while providing the accuracy necessary to deduce small area changes, which correspond to small volume changes in an isotropic material. The image capture, area analysis method is used to determine the compression of cubic crystals, yielding results in good agreement with diffraction and volumetric measurements. As a proof of concept, the equation of state of amorphous red phosphorus is measured up to 12 GPa under hydrostatic conditions where the quantified volume change between the red and black phases is approximately ΔV/V(0) ≈ 0.05 after a reduction of volume nearing 35% at 8 GPa. A large hysteresis is present during decompression and eventually results in a 15% permanent densification relative to the starting volume, which is attributed to a pressure induced crystallization from red to black phosphorus. The robustness of the technique is also demonstrated by measuring the equation of state of GeSe(2) glasses for semi transparent samples and As(2)O(3) in which gold coating is used as a contrasting aid.     

Studying single nanocrystals under high pressure using an x-ray nanoprobe

In this report, we demonstrate the feasibility of applying a 250-nm focused x-ray beam to study a single crystalline NbSe(3) nanobelt under high-pressure conditions in a diamond anvil cell. With such a small probe, we not only resolved the distribution and morphology of each individual nanobelt in the x-ray fluorescence maps but also obtained the diffraction patterns from individual crystalline nanobelts with thicknesses of less than 50 nm. Single crystalline diffraction measurements on NbSe(3) nanobelts were performed at pressures up to 20 GPa.     

Separation of the reservoir and wave pressure and velocity from measurements at an arbitrary location in arteries

Previous studies based on measurements made in the ascending aorta have demonstrated that it can be useful to separate the arterial pressure P into a reservoir pressure P* generated by the windkessel effect and a wave pressure p generated by the arterial waves: P = P*+p. The separation in these studies was relatively straightforward since the flow into the arterial system was measured. In this study the idea is extended to measurements of pressure and velocity at sites distal to the aortic root where flow into the arterial system is not known. P* is calculated from P at an arbitrary location in a large artery by fitting the pressure fall-off in diastole to an exponential function and assuming that p is proportional to the flow into the arterial system. A local reservoir velocity U* that is proportional to P* is also defined. The separation algorithm is applied to in vivo human and canine data and to numerical data generated using a one-dimensional model of pulse wave propagation in the larger conduit arteries. The results show that the proposed algorithm is reasonably robust, allowing for the separation of the measured pressure and velocity into reservoir and wave pressures and velocities. Application to data measured simultaneously in the aorta of the dog shows that the reservoir pressure is fairly uniform along the aorta, a test of self-consistency of the assumptions leading to the algorithm. Application to data generated with a validated numerical model indicates that the parameters derived by fitting the pressure data are close to the known values which were used to generate the numerical data. Finally, application to data measured in the human thoracic aorta indicates the potential usefulness of the separation.     

The compact capacitor bank CQ-1.5 employed in magnetically driven isentropic compression and high velocity flyer plate experiments

Based on the low inductance capacitor, the parallel-plate transmission line, and the explosive network closing switch, a compact pulsed power generator CQ-1.5 has been developed at the Institute of Fluid Physics and is capable to deliver a current of peak of 1.5 MA within rise time of 500-570 ns into a 2-3 nH inductive load. The work is motivated to do isentropic compression experiments (ICEs) on metals up to 30-50 GPa and to launch flyer plates at velocities over 8 kms. The experiments were conducted with the diagnostics of both Doppler pin system and velocity interferometer system for any reflectors, and the measured free surface velocity histories of ICE samples were treated with a backward integration code. The results show that the isentropes of Cu and Al samples under 35 GPa are close to their Hugoniots within a deviation of 3%. The LY12 aluminum flyer plates were accelerated to a velocity over 8.96 kms.