In-situ measurement method of shear modulus and ductility of metal under extreme high pressure conditions

Abstract

The application relates to an in-situ measurement method of the shear modulus and ductility of metal under an extreme high-pressure condition, which comprises the following steps: S1, sample preparation: preparing a metal film through a radio frequency magnetron sputtering method; S2, sample characterization; S3, sample loading: placing the metal film sample to be measured closely on one side of a diamond table, and placing the sample at the center position of the table and a sample cavity as much as possible; S4, pressure calibration; S5, measurement of compression wave velocity: in pump detection, one path with relatively strong energy is used as pump light, and one path with relatively small energy is used as detection light; the time delay between the two light pulses is used to track and measure the travel time Delta t of the compression wave in the metal film; and S6, derivation of the shear modulus and ductility. The application adopts a symmetric diamond press to obtain a stable test environment under extreme pressure, and provides a complete experimental technical scheme, which is reliable and efficient, and is easy to build and test in an ordinary laboratory.

Description

Technical Field

[0001] This invention relates to the field of material testing under extreme conditions, and more specifically, to an in-situ method for measuring the shear modulus and ductility of metals under extreme high pressure conditions. Background Technology

[0002] Metals are indispensable materials for human societal development. With advancements in science and technology, metallic materials have been widely applied in high-end industrial manufacturing (transportation vehicles, aircraft, weaponry, etc.) and scientific research (materials science, space science, earth science), playing a crucial role. Extending application scenarios or experimental conditions to extreme pressure states significantly shortens the distance between atoms (or molecules) constituting metallic substances, greatly enhances the intermolecular forces, alters bond properties, and leads to a closer arrangement of atoms. These changes profoundly affect the physical and chemical properties of the material. For engineering applications, extreme pressure loading typically causes significant changes in the mechanical properties of metallic materials, such as changes in yield strength or ductility with varying external pressure. However, experimental research on the mechanical properties of metallic materials under extreme high pressure conditions remains challenging. Therefore, developing new high-pressure in-situ measurement techniques is crucial in the research of new metallic materials. Shear modulus is an important mechanical parameter for materials in engineering applications; the yield strength and ductility of a material are directly related to its shear modulus. Typically, in-situ high-pressure measurements of the shear modulus of metals require a multi-faceted press and a piezoelectric transducer. The multi-faceted press generates high pressure by loading the sample, and the piezoelectric transducer excites and probes compression or shear waves within the sample. The wave velocity of the compression or shear wave is then measured by measuring the echo, and the shear modulus of the sample is derived from this. However, this method is limited by the large sample size, typically on the order of millimeters or even centimeters. This results in excessively low experimental pressures, usually not exceeding 10 GPa, which is far from meeting the requirements of certain engineering applications, such as the pressure conditions of structural components in large aircraft or the pressure state of surface coatings on spacecraft under high-speed impacts. The method employed in this invention combines Diamond Anvil Cell-DAC (DAC) technology with ultrafast pump-probe technology to measure the shear modulus of metallic materials in situ under extreme high pressure (100 GPa and above). The shear modulus is then used to determine the change in ductility of the material with pressure, thus providing reliable mechanical parameters for the engineering applications of new materials in special scenarios. It is foreseeable that with the continuous progress of human science and technology, the research on special materials, with a focus on high temperature and high pressure metals, will flourish and be widely applied.

[0003] With the development of high-temperature and high-pressure technology, humans have been able to study the properties of materials under extreme conditions. Currently, it is mainly divided into two categories: dynamic high pressure and static high pressure. Dynamic high pressure technology is an experimental technique that uses pulse loading to generate ultra-high pressure, transiently creating a high-pressure and high-temperature environment through explosions, high-speed impacts, or powerful lasers. Compared to dynamic high pressure, static high pressure devices can provide a stable in-situ measurement environment for quasi-hydrostatic pressure. Previously, methods for measuring the elastic wave velocity or elastic modulus of materials under static high pressure mainly included ultrasonic echo technology based on large-cavity presses, inelastic X-ray scattering based on DAC, Brillouin scattering, and pulse-excited scattering. However, all of these techniques have limitations: 1) Inability to separate temperature effects: During dynamic high-pressure impact loading, pressure and temperature effects are coupled, making it difficult to directly obtain the effects caused by either pressure or temperature alone. 2) Low experimental pressure: Due to limitations in experimental equipment and sample volume, ultrasonic echo technology results in relatively low experimental pressures, typically not exceeding 10 GPa. 3) High energy and time consumption limitations: Inelastic X-ray scattering requires the use of a synchrotron radiation source, is time-consuming, and is only applicable to samples containing elements with atomic numbers between 30 and 50. 4) Cannot measure opaque samples: Brillouin scattering and pulsed excitation scattering both require optically transparent samples, thus they cannot be used to measure metallic materials. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide an in-situ measurement method for the shear modulus and ductility of metals under extreme high pressure conditions. This method can accurately measure the shear modulus of metal materials in situ under static high pressure loading, and then determine the pressure dependence of the metal's ductility. It has the characteristics of all-optical measurement, non-destructive testing, high pressure, high precision, and short experimental time. It is currently the ideal solution for measuring the elastic mechanical properties of metals under ultra-high pressure.

[0005] The technical solution adopted by this invention to solve its technical problem is: to construct an in-situ measurement method for the shear modulus and ductility of metals under extreme high pressure conditions, comprising the following steps:

[0006] S1. Sample preparation: Metal thin films are prepared by radio frequency magnetron sputtering;

[0007] S2. Characterizing the sample: The metal thin film prepared by sputtering method is placed under a scanning electron microscope for observation to check the sputtering uniformity of the film surface, so as to determine whether the sample surface is smooth and whether there are obvious pores; the initial thickness of the metal thin film is determined by scanning the cross section with a scanning electron microscope or by measuring the thickness of the metal step with a profilometer, combined with the known compression wave velocity of the metal material at room temperature and pressure and the travel time of the system measured echo.

[0008] S3. Sample loading: Place the metal film sample to be tested close to one side of the diamond stage, and place it as close as possible to the center of the stage and the sample chamber;

[0009] S4. Calibration pressure: Pressure calibration is performed using two methods: ruby ​​fluorescence peak and diamond Raman scattering signal.

[0010] S5. Measuring the velocity of the compression wave: In the pump detection, the one with stronger energy is used as the pump light and the one with less energy is used as the probe light. By tracking and measuring the travel time Δt of the compression wave in the metal thin film through the time delay between the two light pulses, the wave velocity is obtained according to the sample thickness.

[0011] S6. Derive the shear modulus and ductility.

[0012] According to the above scheme, in step S1, the radio frequency magnetron sputtering method specifically involves: using a metal thin film coating material as the target cathode, bombarding the target material with argon ions to generate cathode sputtering, and sputtering the grains in the target material onto the substrate.

[0013] According to the above scheme, in step S2, the diffraction peaks matching the standard are observed by X-ray diffraction, or the diffraction rings are observed by synchrotron radiation X-ray diffraction. Uniform diffraction rings prove that the sample is in an ideal isotropic state.

[0014] According to the above scheme, in step S3, in order to prevent the sample from slipping and deforming due to asynchronous deformation between the metal film and the substrate under high pressure, the metal film is peeled off from the substrate.

[0015] According to the above scheme, in step S4, the specific method of using ruby ​​for pressure calibration is as follows: several ruby ​​particles are arranged close to the sample as pressure calibration particles, and they are distributed as symmetrically and at as much intervals as possible. The laser is focused on the ruby ​​particles to ensure that the pressure can be accurately measured when there is a pressure gradient. When using diamond as pressure calibration, the laser is focused on the center of the diamond anvil to obtain the Raman scattering signal of diamond under high pressure, and then the pressure is calibrated by combining it with the pressure calibration formula.

[0016] According to the above scheme, in step S5, the compression wave velocity measurement device includes a pump optical path, a detection optical path, a sample assembly device, and a signal processing and acquisition device.

[0017] According to the above scheme, in step S6, the compression wave velocity V P Determined by formula (1):

[0018] V P = 2d / Δt (1)

[0019] Where Δt is the time interval between two adjacent echoes, and d is the sample thickness;

[0020] The thickness of the metal thin film under high pressure is determined by formula (2):

[0021] d / d0 = (V / V0) 1 / 3 (2)

[0022] Where d0 is the initial thickness of the sample, V is the cell volume of the sample under high pressure, and V0 is the cell volume under normal pressure. The change in volume V follows the equation of state of metals under high pressure.

[0023] Based on the known equation of state, the density ρ and bulk modulus B of the metal under different pressures are obtained. Based on formulas (3) and (4), the shear modulus G and shear wave velocity of the metal material under high pressure are derived.

[0024] G=3(ρV P 2 -B) / 4 (3)

[0025] V S =(G / ρ) 1 / 2 (4).

[0026] The in-situ measurement method for the shear modulus and ductility of metals under extreme high pressure conditions according to the present invention has the following beneficial effects:

[0027] 1. The experimental technique of diamond pressure cavity combined with ultrafast pump detection used in this invention can directly obtain ultra-high time resolution compression wave signals in samples with extremely small size. By analyzing the echo signals in the ultra-short time window, the wave velocity information in the medium in the extremely small spatial region can be determined.

[0028] 2. High measurement accuracy of the present invention: The measurement method of the present invention can perform high-precision measurements on metal thin film samples in DAC, and the wave velocity measurement time resolution can reach 10. -12 On the order of s, with a spatial resolution of 10 -8 On the order of m;

[0029] 3. The experimental pressure of this invention is high: the pressure range measured by this invention is extended by an order of magnitude (reaching 100 GPa and above) compared to traditional methods. Combined with high-precision ultrafast pump detection, the compression wave velocity of metal samples under corresponding pressure conditions can be obtained, and their shear modulus can be derived.

[0030] 4. The present invention has high measurement efficiency: the wave velocity measurement of a pressure point can be completed in just a few minutes, which is far more efficient than the traditional testing method that often takes several hours;

[0031] 5. The measurement cost of this invention is low and it is safe and pollution-free: This measurement method does not require additional experimental consumables or high-power experimental equipment, will not pose a safety threat to experimental personnel and laboratories, and will not generate experimental waste that pollutes the environment.

[0032] 6. The invention has strong anti-interference ability: The invention uses a fully optical method for testing, which has the advantages of being suitable for extreme environments (high temperature, high pressure), resisting electromagnetic radiation, and causing no damage to the surface of metal thin films;

[0033] 7. The invention has a wide range of applications: it can be applied to fields that require in-situ measurement of the elastic properties of metallic materials under high temperature and high pressure, such as high-end industrial manufacturing (vehicles, aircraft, weapons and equipment, etc.) and scientific research (materials science, space science, earth science). Attached Figure Description

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0035] Figure 1 This is an exemplary method for measuring the pressure dependence of the shear modulus and ductility of metals under high pressure according to the present invention;

[0036] Figure 2 This is a schematic diagram of the assembly of the metal thin film sample after the substrate has been peeled off by pressing down according to the present invention;

[0037] Figure 3 This is a schematic diagram of the assembly of a metal thin film sample under high pressure without the substrate being peeled off, according to the present invention.

[0038] Figure 4 This invention uses a pressure calibration method based on the ruby ​​fluorescence peak.

[0039] Figure 5 This invention relates to a pressure calibration method for diamond Raman scattering signals.

[0040] Figure 6 This is a schematic diagram of the system for in-situ high-pressure experiments using ultrafast pump detection combined with a diamond anvil cell, as described in this invention. Detailed Implementation

[0041] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0042] like Figure 1-6 As shown, the in-situ measurement method for the shear modulus and ductility of metals under extreme high pressure conditions of the present invention involves a complete experimental process, including metal sample preparation, sample assembly in a DAC (Digital Acoustic Deposition Unit), integration of the ultrafast pump detection system and the DAC device, measurement of elastic wave velocity, derivation of shear modulus, and analysis of ductility. The corresponding flowchart includes the following steps:

[0043] S1. Sample preparation:

[0044] The sample used in this invention is a metal thin film prepared by radio frequency magnetron sputtering. The metal thin film coating material is used as the target cathode, and argon ions bombard the target to generate cathode sputtering, sputtering the grains in the target material onto the substrate. Depending on the different physical properties of the metal, such as acoustic impedance, single-crystal silicon, silicon dioxide, magnesium oxide, or sapphire can be selected as the substrate. The surface of the substrate to be coated needs to be polished.

[0045] S2. Sample characterization:

[0046] The thickness of the metal thin film varies from tens to hundreds of nanometers. The sputtered metal thin film is observed under a scanning electron microscope to examine the sputtering uniformity of the film surface, determining whether the sample surface is smooth and free of obvious pores. The initial thickness of the metal thin film is determined by scanning the cross-section with a scanning electron microscope or by measuring the thickness of the metal step using a profilometer, combined with the known compression wave velocity of the metal material at room temperature and pressure and the travel time of the system's measured echo. Diffraction peaks matching the standard are observed by X-ray diffraction, or diffraction rings can be observed using synchrotron radiation X-ray diffraction; uniform diffraction rings indicate that the sample is in an ideal isotropic state.

[0047] S3. Sample loading:

[0048] Figure 2 and Figure 3 This diagram illustrates the assembly of a metal thin film sample and the excitation and detection of ultrasonic signals during ultrafast pumping in a DAC. A and A' are a pair of diamond anvils, B is a metal gasket (made of stainless steel or rhenium), C is the sample chamber, D is the pressure-transmitting medium, E is the metal thin film placed within it (some metal needs to be plated onto the substrate material), F is the ruby ​​pressure calibration, G is the detection pulse, H is the pump pulse, and I is the substrate material. The two opposing diamond anvils A and A' are fixed within the pressure chamber of the device. A pre-pressurized and perforated metal gasket B is placed between the diamond anvils, together forming a sealed sample chamber C.

[0049] The metal thin film sample E to be tested is placed against one side of the diamond mesa, and preferably centered between the mesa and the sample cavity. To prevent slippage and deformation of the sample due to asynchronous deformation of the metal thin film and the substrate (difference in material compressibility coefficients) under high pressure, the metal thin film can be peeled off from the substrate, thereby better ensuring experimental accuracy. Therefore, this invention provides two different high-pressure assembly methods. Figure 2 This is a schematic diagram of the assembly of a metal thin film sample after it has been peeled off from its substrate under high pressure, which helps to better avoid interference caused by slippage and deformation of the sample. Figure 3This is a schematic diagram of the assembly of a metal thin film sample under high pressure without the substrate being removed. The substrate material can better support the metal thin film.

[0050] S4. Pressure Calibration:

[0051] Accurate pressure calibration is a crucial prerequisite for high-pressure experiments. Figure 4 and Figure 5 Two pressure calibration methods, one based on ruby ​​fluorescence peaks and the other on diamond Raman scattering signals, were demonstrated. Figure 4 The diagram illustrates a pressure calibration method using ruby. Several ruby ​​particles (at least two) are arranged close to the sample as pressure calibrators, spaced as far apart and symmetrically as possible. The laser is focused onto the ruby ​​particles to ensure accurate pressure measurement even in the presence of a pressure gradient. Typically, ruby ​​corresponds to two Raman fluorescence peaks for a 532nm laser. By obtaining the center wavelength of the R1 peak (usually the stronger main peak), and combining it with the pressure calibration formula P(GPa) = 248.4[(Δλ / λ0+1)], the pressure is calibrated. 7.665 -1] is used to determine the pressure value. Where λ0 is the wavelength corresponding to the R1 peak under normal pressure, and Δλ is the wavelength shift of the R1 peak under high pressure.

[0052] Furthermore, since the uncertainty of the ruby ​​fluorescence peak increases when the pressure exceeds 50 GPa, it is necessary to obtain pressure information by measuring the Raman scattering signal of diamond. Figure 5 The method shown uses diamond as the pressure calibration point. A 532nm laser is focused at the center of the diamond anvil to obtain the Raman scattering signal of diamond under high pressure. This signal is then combined with the pressure calibration formula P(GPa)=66.9-0.5281ν+3.585x10 -4 ν 2 The calibration pressure is used. Here, ν is the wave value (cm) corresponding to the high-frequency edge of the diamond Raman peak under high pressure. -1 Finally, the experimental pressure is determined by combining the pressure with the fluorescence peak of the ruby. It is worth noting that because pressure gradients at different locations within the diamond can cause variations in Raman scattering signals, the beam must be focused on the same location within the diamond during each pressure calibration. The remaining space in the sample cavity is filled with a transparent pressure-transmitting medium D, maintaining a quasi-hydrostatic pressure state within the sample cavity. For pressures below 50 GPa, transparent solid pressure-transmitting media with low yield strength, such as NaCl or KBr, are used. As the pressure increases, pressure-transmitting media like NaCl can cause a significant increase in the pressure gradient within the sample cavity, leading to an imbalance in the hydrostatic pressure conditions. Therefore, for tests above 50 GPa, it is recommended to use inert gases such as Ar, He, or Ne as the pressure-transmitting medium when filling the sample, instead of NaCl or KBr.

[0053] S5. Compression wave velocity measurement:

[0054] Figure 6 This is a schematic diagram of an experimental system combining ultrafast pump-probe and DAC, mainly composed of a pump optical path, a probe optical path, a sample assembly device, and a signal processing and acquisition device. Specifically, it includes: a femtosecond pulsed laser source 1, half-wave plates 2-1 and 2-2, a quarter-wave plate 2-3, polarization beam-splitting crystals 3-1 and 3-2, plane mirrors 4-1, 4-2, 4-3, and 4-4 mounted on a controllable stepper motor rail for delaying the optical path, a dichroic mirror 5, an acousto-optic modulator 6, a barium borate crystal 7, a long-focal-length objective lens 8, a DAC device 9, a photodetector 10, a lock-in amplifier 11, and a computer 12. The laser emitted by the femtosecond laser is split into two mutually perpendicular beams by the half-wave plate 2-1 and the polarization beam-splitting crystal 3-1 with different energy ratios. The stronger beam is used as the pump light, and the weaker beam as the probe light. The travel time Δt of the compressed wave in the metal thin film is tracked and measured by the time delay between the two optical pulses.

[0055] S6. Derivation of shear modulus and ductility:

[0056] Ultrafast pump-probe technology can measure the compression wave velocity V with ultra-high spatial resolution. P It can be determined using formula (1):

[0057] V P = 2d / Δt (1)

[0058] Where Δt is the time interval between two adjacent echoes, and d is the sample thickness. If within the elastic range, i.e., the sample does not undergo plastic deformation, the thickness of the metal film under high pressure can be determined by formula (2):

[0059] d / d0 = (V / V0) 1 / 3 (2)

[0060] d0 is the initial thickness of the sample, V is the cell volume of the sample under high pressure, and V0 is the cell volume under normal pressure. The change in volume V follows the equation of state for metals under high pressure. Based on the known equation of state, the density ρ and bulk modulus B of the metal under different pressures are obtained. According to formulas (3) and (4), the shear modulus G and shear wave velocity of the metal material under high pressure can be derived.

[0061] G=3(ρV P 2 -B) / 4 (3)

[0062] V S =(G / ρ) 1 / 2 (4)

[0063] Shear modulus is closely related to the mechanical properties of materials, and the ratio of bulk modulus to shear modulus (B / G) can be used to determine the ductility of metals. Pugh proposed a minimum critical value of approximately 1.75 for judging the ductility / brittleness of solid materials; the higher the B / G ratio, the better the ductility. Generally, in engineering applications, the stronger the ductility of metals, the better, as they are more suitable for various extreme pressure environments and can provide excellent candidate materials for scientific research and equipment manufacturing. Furthermore, extrapolating the linear relationship between compression wave velocity and density based on Birch's theorem allows for the determination of wave velocities at higher pressures, providing support for research on materials in higher pressure ranges.

[0064] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. An in-situ measurement method for the shear modulus and ductility of metals under extreme high pressure conditions, characterized in that, Includes the following steps: S1. Sample preparation: Metal thin films are prepared by radio frequency magnetron sputtering; S2. Characterizing the sample: The metal thin film prepared by sputtering method is placed under a scanning electron microscope for observation to check the sputtering uniformity of the film surface, so as to determine whether the sample surface is smooth and whether there are obvious pores; the initial thickness of the metal thin film is determined by scanning the cross section with a scanning electron microscope or by measuring the thickness of the metal step with a profilometer, combined with the known compression wave velocity of the metal material at room temperature and pressure and the travel time of the system measured echo. S3. Sample loading: Place the metal film sample to be tested close to one side of the diamond stage, and place it as close as possible to the center of the stage and the sample chamber; S4. Calibration pressure: Pressure calibration is performed using two methods: ruby ​​fluorescence peak and diamond Raman scattering signal. The specific method for using ruby ​​for pressure calibration is as follows: several ruby ​​particles are arranged close to the sample as pressure calibration particles, and they are spaced apart and symmetrically distributed. The laser is focused on the ruby ​​particles to ensure that the pressure can be accurately measured in the presence of a pressure gradient. Alternatively, diamond is used as the method for pressure calibration. The laser is focused on the center of the diamond anvil to obtain the Raman scattering signal of the diamond under high pressure, and then the pressure is calibrated by combining it with the pressure calibration formula. S5. Measuring the velocity of the compression wave: In the pump detection, the one with stronger energy is used as the pump light and the one with less energy is used as the probe light. By tracking and measuring the travel time Δt of the compression wave in the metal thin film through the time delay between the two light pulses, the wave velocity is obtained according to the sample thickness. S6. Derive the shear modulus and ductility.

2. The in-situ measurement method for the shear modulus and ductility of metals under extreme high pressure conditions according to claim 1, characterized in that, In step S1, the radio frequency magnetron sputtering method specifically involves using a metal thin film coating material as the target cathode, bombarding the target material with argon ions to generate cathode sputtering, and sputtering the grains in the target material onto the substrate.

3. The in-situ measurement method for the shear modulus and ductility of metals under extreme high pressure conditions according to claim 1, characterized in that, In step S2, the diffraction peaks matching the standard are observed by X-ray diffraction, or the diffraction rings are observed by synchrotron X-ray diffraction. Uniform diffraction rings prove that the sample is in an ideal isotropic state.

4. The in-situ measurement method for the shear modulus and ductility of metals under extreme high pressure conditions according to claim 1, characterized in that, In step S3, to prevent slippage and deformation of the sample due to asynchronous deformation between the metal film and the substrate under high pressure, the metal film is peeled off from the substrate.

5. The in-situ measurement method for the shear modulus and ductility of metals under extreme high pressure conditions according to claim 1, characterized in that, In step S5, the compression wave velocity measurement device includes a pump optical path, a probe optical path, a sample assembly device, and a signal processing and acquisition device.

6. The in-situ measurement method for the shear modulus and ductility of metals under extreme high pressure conditions according to claim 1, characterized in that, In step S6, the compression wave velocity V P Determined by formula (1): V P = 2 d / D t (1) Where, Δ t The time interval between two adjacent echoes. d For sample thickness; The thickness of the metal thin film under high pressure is determined by formula (2): d / d 0 = ( V / V 0) 1 / 3 (2) in, d 0 represents the initial thickness of the sample. V This represents the unit cell volume of the sample under high pressure. V 0 represents the volume of the unit cell under normal pressure. V The changes in ______ follow the equation of state for metals under high pressure; Based on the known equation of state, obtain the density of the metal under different pressures. ρ bulk modulus B Based on formulas (3) and (4), the shear modulus of metallic materials under high pressure is derived. G and shear wave velocity parameters: G =3( ρV P 2 - B ) / 4(3) V S =( G / ρ ) 1 / 2 (4)。

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