Method for generating ultra high-temperature / high-pressure cavitation, method for imparting compressive residual stress onto surface of substance, and changing geometric shape, mechanical characteristic and corrosion resistance of surface, and apparatus for generating ultra high-temperature / high-pressure cavitation

Abstract

To provide a method for generating ultra high-temperature / high-pressure cavitation, a method for imparting compressive residual stress onto a surface of a substance, and changing a geometric shape, mechanical characteristics and corrosion resistance of the surface, and an apparatus for generating ultra high-temperature / high-pressure cavitation.SOLUTION: A method for generating ultra high-temperature / high-pressure cavitation includes: irradiating cavitation with an ultrasonic wave U1 and a laser beam in a magnetic field; imparting magnetic energy and laser energy to the cavitation, increasing air bubble energy; and distributing a high temperature reaction field of the cavitation including a high temperature reaction field, which is generated by repeatedly expanding / contracting by irradiation with the ultrasonic wave U1.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for generating ultra-high temperature and pressure cavitation, a method for imparting compressive residual stress to the surface of a material and changing the geometric shape, mechanical properties and corrosion resistance of the surface, and an apparatus for generating ultra-high temperature and pressure cavitation. [Background technology]

[0002] Conventional surface treatment techniques include nitriding, carburizing, laser hardening, high-frequency hardening, shot peening, water jet peening, etc., but these techniques are primarily intended to improve the mechanical strength of the surface. However, each technique has its advantages and disadvantages, such as the lack of compressive residual stress that suppresses crack generation on the surface, the large dimensional change before and after treatment, the thin hardened layer, the formation of an embrittlement layer inside, the occurrence of voids and cracks, and low corrosion resistance and oxidation resistance, and there is a demand for the development of a surface treatment technique that can compensate for these disadvantages in a well-balanced manner.

[0003] Alloy steels for machine structures (low alloy steels, SCM435, SCM440, SNCM430, SNCM630, etc.) are used in a wide variety of industrial equipment and devices, and are essential steel materials for industrial development. However, the environments in which these steel materials are used are becoming harsher every year, and there is a demand for further improvements in fatigue strength, corrosion resistance, high-temperature strength, heat resistance, oxidation resistance, etc. To solve this problem, there is a need for the development and practical application of surface treatment technology.

[0004] Low alloy steel is a steel material that is mainly composed of carbon steel and is combined with several alloying elements, Ni, Cr, and Mo, at less than a few mass percent, often less than 1 mass percent. It is somewhat more expensive than carbon steel, but has high corrosion resistance. There are various types of low alloy steel, such as heat-resistant steel, low-temperature steel, weathering steel, and high-tensile steel, and they are used for various purposes. Low alloy steel is required to have excellent mechanical properties and good weldability, but the additive elements that are effective in improving corrosion resistance are harmful to mechanical properties and weldability. As a result, there is a limit to the amount of additives, and there is a problem that corrosion resistance cannot be further improved.

[0005] In the field of surface modification of alloy steel for machine structures, research and development into imparting compressive residual stress and improving the mechanical strength of the surface by shot peening has been actively conducted for a long time. Currently, it is used in a variety of industrial products, from automobile parts such as springs, gears, conting rods, and crankshafts to aircraft-related parts such as jet engines, wings, and landing gears, and pressure vessels for chemical plants. In recent years, research has also been conducted into modifying metal surfaces using water jet peening as a technology for imparting compressive residual stress (see Patent Document 1).

[0006] Furthermore, a method of generating mechanical and electrochemical cavitation is known as a method for surface modification of carbon steel (see Patent Document 2). In this method, a water jet is ejected from an ejection nozzle immersed in water, and ultrasonic waves are irradiated onto the fluid cavitation generated by the ejection of the water jet, thereby generating cavitation that has both a functional effect and an electrochemical effect.

[0007] In recent years, ultrasonic cavitation (UC) is known to generate hot spots that can promote chemical reactions by generating temperatures of several thousand K, by transmitting ultrasonic vibrations in liquids such as water or organic solvents and using sound pressure changes to isothermally expand and adiabatically compress bubble nuclei of a few μm in size that are originally present in the liquid, thereby raising the temperature inside the bubbles to several thousand degrees. This technology has a wide range of applications, including chemistry, biology, medicine, and cleaning, such as changing molecular structures and cleaning surfaces.

[0008] On the other hand, in water jet cavitation (WJC), the extremely high pressure of tens of thousands of atmospheres generated during the collapse of a microjet near the surface can impart compressive residual stresses to the surface of materials, improving their mechanical strength. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2006-255865 A [Patent Document 2] International Publication No. 2016 / 136656 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the current situation is that the aforementioned UC and WJC are not able to fully utilize the inherent bubble power and potential of bubbles. The reason for this is that the energy concentration within a single bubble and the mutual energy concentration between multiple bubbles are not achieved.

[0011] UC alone does not provide enough energy, limiting its application to the bio and medical fields. One of UC's features is that it can be applied to a wide area for cleaning and other applications, so the processing speed is fast. However, UC alone does not provide enough energy, limiting its application to the bio and medical fields. On the other hand, WJC has been used as a countermeasure against stress corrosion cracking in nuclear power plants. One of WJC's features is that the processing area is limited to the injection position of the injection nozzle, so the processing speed is slow even if the injection nozzle is moved. Also, WJC alone does not provide enough energy, limiting the stress range.

[0012] The present invention aims to provide a method for generating ultra-high temperature and pressure cavitation capable of increasing bubble energy, a method for imparting compressive residual stress to the surface of a material and changing the mechanical properties and corrosion resistance of the surface, and an apparatus for generating ultra-high temperature and pressure cavitation. [Means for solving the problem]

[0013] The invention described in claim 1 is a method for generating ultra-high temperature and high pressure cavitation by irradiating ultrasonic waves and laser light to cavitation in a magnetic field, thereby imparting magnetic energy and laser energy to the cavitation, increasing bubble energy, and distributing the high temperature reaction field of the cavitation including a high temperature reaction field generated by repeated expansion and contraction due to the irradiation of ultrasonic waves.

[0014] The invention described in claim 2 is characterized in that, in claim 1, the cavitation is flow cavitation generated by the ejection of a water jet from an ejection nozzle immersed in water, or bubble nucleus cavitation existing in still water.

[0015] The invention described in claim 3 is a method for generating ultra-high temperature and high pressure cavitation, which comprises spraying a water jet in a magnetic field from an injection nozzle immersed in water, generating flow cavitation in association with the spraying of the water jet, and irradiating the generated flow cavitation or bubble nucleus cavitation present in still water with positrons and laser light to impart magnetic energy, positron energy, and laser energy to the flow cavitation, thereby increasing bubble energy.

[0016] The invention described in claim 4 is characterized in that, in claim 3, ultrasonic waves are irradiated to the fluid cavitation, ultrasonic energy is imparted to the fluid cavitation, bubble energy is increased, and the fluid cavitation including a high-temperature reaction field generated by repeated expansion and contraction due to the irradiation of ultrasonic waves, or the high-temperature reaction field of bubble nucleus cavitation present in still water is distributed.

[0017] The invention described in claim 5 is characterized in that, in claim 2, the nozzle diameter of the injection nozzle is φ0.1 to 2.0 mm, the movement speed of the flow cavitation is 5 m / s or less, and high-pressure water is supplied to the injection nozzle at a pressure of 1 MPa or more and 70 MPa or less and at a flow rate of 0.1 L / min to 100 L / min.

[0018] The invention described in claim 6 is characterized in that in claim 2, the frequency of the ultrasonic waves is 20 kHz or more and 33 kHz or less, and the output of the ultrasonic oscillator that generates the ultrasonic waves is 150 to 2000 W.

[0019] The invention described in claim 7 is a method for imparting compressive residual stress to the surface of a material and changing the geometric shape, mechanical properties, and corrosion resistance of the surface by colliding ultra-high temperature and high pressure cavitation generated by a method for generating ultra-high temperature and high pressure cavitation described in any one of claims 1 to 6 with the material.

[0020] The invention described in claim 8 is characterized in that the substance is made of AZ31B magnesium alloy in claim 7. The invention described in claim 9 is characterized in that the surface potential of the surface of the substance is increased in claim 7.

[0021] The invention described in claim 10 is a device for generating ultra-high temperature and high pressure cavitation, comprising a magnet that generates a magnetic field, imparts magnetic energy to the cavitation, and increases bubble energy; an ultrasonic transducer that irradiates the cavitation in the magnetic field with ultrasound, distributing the high temperature reaction field of the cavitation including a high temperature reaction field generated by repeated expansion and contraction due to the irradiation of the ultrasound; and a laser light irradiation device that irradiates the cavitation in the magnetic field with laser light, imparts laser energy to the cavitation, and increases bubble energy, and distributes the high temperature reaction field of the cavitation including a high temperature reaction field generated by repeated expansion and contraction due to the irradiation of the ultrasound.

[0022] The invention described in claim 11 is characterized in that, in claim 10, it comprises an injection nozzle that is immersed in water and ejects a water jet, and the cavitation is flow cavitation that occurs in conjunction with the ejection of the water jet.

[0023] The invention described in claim 12 is a device for generating ultra-high temperature and high pressure cavitation, comprising: a magnet that generates a magnetic field, imparts magnetic energy to cavitations, and increases bubble energy; a laser light irradiation device that irradiates the cavitations in the magnetic field with laser light, imparting laser energy to the cavitations, and increasing bubble energy; an injection nozzle that is immersed in water and ejects a water jet; and a positron irradiation device that irradiates the cavitations in the magnetic field with positrons, imparting positron energy to the cavitations, and increasing bubble energy, wherein the cavitation is flow cavitation generated by the ejection of the water jet, or bubble nucleus cavitation present in still water, and the device distributes a high-temperature reaction field of the cavitation.

[0024] The invention described in claim 13 is characterized in that, in claim 12, it comprises an ultrasonic transducer that irradiates ultrasonic waves to the cavitation in the magnetic field, thereby distributing the high-temperature reaction field of the cavitation, including the high-temperature reaction field, which is generated by repeated expansion and contraction due to the irradiation of the ultrasonic waves. Effect of the Invention

[0025] According to the present invention, it is possible to provide a method for generating ultra-high temperature and pressure cavitation capable of increasing bubble energy, a method for imparting compressive residual stress to the surface of a material and changing the mechanical properties and corrosion resistance of the surface, and an apparatus for generating ultra-high temperature and pressure cavitation. [Brief description of the drawings]

[0026] [Figure 1] 1 is a diagram showing the overall configuration of an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Diagram 2] 1 is a diagram showing an embodiment of an ultra-high temperature and high pressure cavitation generating device according to the present invention. [Diagram 3] FIG. 2 is a diagram showing the magnetic field distribution in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 4] 4 is a graph showing the emission intensity obtained by a first photon detector in an ultra-high temperature and high pressure cavitation generation device according to an embodiment of the present invention. [Diagram 5] 13 is a graph showing the emission intensity obtained by a second photon detector in an ultra-high temperature and high pressure cavitation generation device according to an embodiment of the present invention. [Figure 6] 1 is a graph showing the emission intensity immediately after pure water is injected and one day later in an ultra-high temperature and high pressure cavitation generation device according to an embodiment of the present invention. [Figure 7] 4 is a graph showing the emission intensity obtained by a first photon detector in an ultra-high temperature and high pressure cavitation generation device according to an embodiment of the present invention. [Figure 8] 13 is a graph showing the emission intensity obtained by a second photon detector in an ultra-high temperature and high pressure cavitation generation device according to an embodiment of the present invention. [Figure 9] 1 is a photograph showing the surface of a workpiece before surface treatment by laser irradiation L in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 10] 1 is a photograph showing the surface of a workpiece after surface treatment by laser irradiation L in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 11] 1 is a photograph showing the surface of a workpiece before surface treatment by LMEI-UC in an ultra-high temperature and high pressure cavitation generating apparatus according to an embodiment of the present invention. [Figure 12] 1 is a photograph showing the surface of a workpiece after surface treatment by LMEI-UC in an ultra-high temperature and high pressure cavitation generating apparatus according to an embodiment of the present invention. [Figure 13] 1 is a photograph showing the surface of a workpiece before surface treatment by EI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 14] 1 is a photograph showing the surface of a workpiece after surface treatment by EI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 15] 1 is a photograph showing the surface of a workpiece before surface treatment by an LEI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 16] 1 is a photograph showing the surface of a workpiece after surface treatment by an LEI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 17] 1 is a photograph showing the surface of a workpiece before surface treatment by MEI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 18] 1 is a photograph showing the surface of a workpiece after surface treatment by MEI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 19] 1 is a photograph showing the surface of a workpiece before surface treatment by an LMEI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 20] 1 is a photograph showing the surface of a workpiece after surface treatment by an LMEI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 21] 1 is an optical microscope photograph showing the surface of a workpiece after surface treatment by EI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 22] 1 is an optical microscope photograph showing the surface of a workpiece after surface treatment by an LEI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Diagram 23] 1 is an optical microscope photograph showing the surface of a workpiece after surface treatment by MEI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 24] 1 is an optical microscope photograph showing the surface of a workpiece after surface treatment by an LMEI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Diagram 25]1 is a photograph obtained by using DFM analysis of the surface of an unprocessed Mg alloy as a workpiece before surface treatment in an ultra-high temperature and high pressure cavitation generating apparatus according to an embodiment of the present invention. [Figure 26] 1 is a photograph obtained using DFM analysis of the surface of a workpiece after surface treatment by LMEI-UC in an ultra-high temperature and high pressure cavitation generating apparatus according to an embodiment of the present invention. [Figure 27] 1 is a photograph obtained using DFM analysis of the surface of a workpiece after surface treatment by MEI-MFC in an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Figure 28] 1 is a photograph obtained using DFM analysis of the surface of a workpiece after surface treatment by an LMEI-MFC in an ultra-high temperature and high pressure cavitation generating apparatus according to an embodiment of the present invention. [Figure 29] 1 is a graph showing the corrosion potential of a test piece surface-treated by the ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Diagram 30] 1 is a graph showing the surface roughness of a test piece that was surface-treated using an ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Diagram 31] 1 is a graph showing the Vickers hardness of a test piece surface-treated by the ultra-high temperature and high pressure cavitation generating device of an embodiment of the present invention. [Diagram 32] 1 is a graph showing compressive residual stress values ​​of test pieces surface-treated by the ultra-high temperature and high pressure cavitation generating device according to an embodiment of the present invention. [Diagram 33] 1 is a graph showing the tensile residual stress value of a Cr-Mo steel test piece surface-treated by LMEI-MFC in an ultra-high temperature and high pressure cavitation generating apparatus according to an embodiment of the present invention. [Diagram 34] 1 is a graph showing the tensile residual stress value of a Cr-Mo steel test piece surface-treated by PLMEI-WJC in an ultra-high temperature and high pressure cavitation generation apparatus according to an embodiment of the present invention. [Diagram 35]1 is a graph showing the tensile residual stress value of a Cr-Mo steel test piece surface-treated by PLMEI-MFC in an ultra-high temperature and high pressure cavitation generator according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, an embodiment of a method for generating ultra-high temperature and pressure cavitation and an apparatus for generating ultra-high temperature and pressure cavitation according to the present invention will be described.

[0028] As shown in Figures 1 and 2, an ultra-high temperature and high pressure cavitation generating device 1 for carrying out a method of generating ultra-high temperature and high pressure cavitation has a reactor 10, an injection nozzle 20, an ultrasonic irradiation element 30, a magnet 40, a laser light irradiation device 50, a photoelectron measuring instrument 60, and a positron irradiation device 70.

[0029] As shown in FIG. 2 and other figures, the reactor 10 has a heptagon in plan view, and is composed of a tapered tank in which the size of the heptagon increases similarly from top to bottom. Each side of the heptagon is composed of five long sides and two short sides. The three long sides are adjacent to each other, and one end of the short side is connected to each end of the three long sides. The remaining two long sides are adjacent to each other, and the other end of the short side is connected to each end of the two long sides. In this way, a space 100 is formed that is surrounded by walls 101 to 105 corresponding to the five long sides of the heptagon in plan view, walls 106 and 107 corresponding to the two short sides, and a bottom wall 108.

[0030] Pure water W1 with a resistivity of 15 MΩ is stored in the space 100 of the reactor 10. The injection nozzle 20 is connected to a container 202 in which the pure water W1 is stored as a high-pressure water supply source via a high-pressure pump 201 (maximum pump pressure 40 MPa, maximum pump flow rate 200 mL, manufactured by L.TEX Co., Ltd., L.TEX8731, whose maximum pump pressure and maximum flow rate have been modified to be larger values; see FIG. 1).

[0031] As shown in FIG. 2, the outlet of the injection nozzle 20 is disposed in the center of the reactor 10 in a plan view, and is immersed in the pure water W1 stored in the reactor 10. The high-pressure water W2, which is composed of the pure water supplied from the outlet to the pure water W1 stored in the reactor 10 by the high-pressure pump 201, has a flow rate of 160 mL / min to 180 mL / min, for example, 180 mL / min, and can be injected / stopped as a high-pressure water jet. The pressure of the high-pressure water W2 is 1 MPa or more and 70 MPa or less, for example, 40 MPa. The pressure of the high-pressure water W2 is monitored by a pressure gauge provided on a pipe member communicating between the injection nozzle 20 and the high-pressure pump 201. In addition, the flow rate of the high-pressure water W2 is monitored by a flow meter provided on the high-pressure pump 201. Water is drained from the space 100 of the reactor 10 through a drain pipe 111 by a pump (not shown) from the top of the reactor 10 at a drainage rate of 400 mL / min.

[0032] If the pressure of the high-pressure water W2 is less than 1 MPa, a water jet with a moderately high pressure cannot be obtained, and the nuclei of ultra-high temperature and high pressure cavitation are difficult to generate, making it impossible to obtain ultra-high temperature and high pressure cavitation appropriately. If the pressure of the high-pressure water W2 exceeds 70 MPa, the water jet pressure is too high and ultra-high temperature and high pressure cavitation cannot be obtained appropriately. In particular, if the pressure is 3 MPa or more, it is possible to spray a water jet that can easily generate ultra-high temperature and high pressure cavitation. Here, "ultra-high temperature and high pressure cavitation" means cavitation that can impart compressive residual stress to Cr-Mo steel, aluminum alloy, magnesium alloy, etc., and can change the geometric shape, mechanical properties, and corrosion resistance of the surface of these materials.

[0033] As shown in Fig. 2, the injection nozzle 20 has an orifice portion 21, a mixing chamber 22, and a horn portion 23. The orifice portion 21 has a cylindrical shape. An upstream end of the orifice portion 21 communicates with a container 202. High-pressure water W2 supplied from the container 202 flows into the orifice portion 21.

[0034] An upstream end of the mixing chamber 22 is connected to a downstream end of the orifice portion 21. The mixing chamber 22 has a slightly larger diameter than the orifice portion 21. High-pressure water W2 flows into the mixing chamber 22 from the orifice portion 21.

[0035] The upstream end of the horn portion 23 is connected to the downstream end of the mixing chamber 22. The horn portion 23 expands in diameter in a tapered manner toward the tip of the horn portion 23 (the outlet of the mixing chamber 22 formed by the downstream end of the horn portion 23). Therefore, the injection nozzle 20 is formed of a horn nozzle. The maximum diameter of the tip of the horn portion 23 is 0.1 mm or more and 2 mm or less, and is 0.1 mm in this embodiment. If the maximum diameter of the tip of the horn portion 23 is less than 0.1 mm, large-sized water jet cavitation cannot be generated. Also, if the maximum diameter of the tip of the horn portion 23 exceeds 2 mm, the flow rate at the outlet portion decreases, and water jet cavitation with a high collapse pressure cannot be obtained. Also, the maximum diameter of the tip of the horn portion 23 is preferably 0.3 mm or less. By making the thickness 0.3 mm or less, water jet cavitation caused by the water jet from the tip of the horn portion 23 can collide with the workpiece, resulting in small peening marks and less surface roughness on the workpiece, thereby enabling surface strengthening to be obtained.

[0036] By setting the maximum diameter of the tip of the horn portion 23 to 0.1 mm, the flow rate can be reduced, making it possible to use pure water instead of tap water. As a result, it is not affected by impurities in tap water and pump noise can be reduced. It is also possible to continue applying ultrasonic energy, magnetic field energy, and laser energy to bubbles for a long period of time. The jet nozzle 20 having the above configuration jets a water jet into the pure water W1 stored in the reactor 10, thereby generating flow cavitation in the pure water W1.

[0037] As shown in FIG. 1, the opening at the lower end of the injection nozzle 20 faces the workpiece (not shown) as a collision object or material placed on the workpiece stage 109 (see FIG. 3) at a distance of 20 mm. The workpiece is, for example, a flat or curved plate having a thickness of 1 mm or more in the vertical direction in FIG. 1 and is made of at least one selected from Cr-Mo steel, Ni-Cr-Mo steel, Ti alloy, Ni-based alloy, aluminum alloy, and magnesium alloy. The water jet ejected vertically downward from the opening at the lower end of the additional nozzle 50 is ejected and collides against the upper surface of the workpiece. As a result, a secondary jet is generated around the upper side of the workpiece, the flow speed of the water by the water jet is weakened, and the flow speed of the flow cavitation is reduced to a predetermined moving speed of 5 m / s or less as described later, and the pressure is reduced.

[0038] The ultrasonic irradiation element 30 is electrically connected to a drive control device 301 (see FIG. 1). The ultrasonic irradiation element 30 can irradiate / stop irradiating ultrasonic waves U1 from a horizontal direction to the water jet that is sprayed vertically downward from the opening at the lower end of the jet nozzle 20, weakening the flow rate and decreasing the dynamic pressure. Specifically, five ultrasonic irradiation elements 30 are arranged, one on each of the inner surfaces of the walls 101 to 105 that correspond to the long sides of the reactor 10, which has a heptagonal shape in a plan view, as described above. By arranging the five ultrasonic irradiation elements 30 in this manner, ultrasonic waves can be irradiated to the entire water jet, increasing energy concentration and improving the processing of the upper surface of the workpiece.

[0039] The ultrasonic wave radiating element 30 radiates ultrasonic waves U1 into the pure water W1 stored in the reactor 10, according to the output from the drive control device 301. The frequency of the radiated ultrasonic waves U1 is not less than 20 kHz and not more than 33 kHz.

[0040] If the frequency of the irradiated ultrasonic wave U1 is less than 20kHz, the frequency is too low to obtain the effect of the ultrasonic wave U1. If the frequency of the irradiated ultrasonic wave U1 exceeds 100kHz, the frequency is too high to obtain the effect of the ultrasonic wave U1. Also, if the frequency exceeds 33kHz, the frequency is far from the resonance radius that easily causes the bubble radius to be isothermally expanded and adiabatically compressed, making it difficult to cause the bubble radius to be isothermally expanded and adiabatically compressed. More preferably, the frequency is around 28kHz.

[0041] In addition, the rated ultrasonic output value of the irradiated ultrasonic waves U1 is 150 W or more and 2000 W or less. If the rated ultrasonic output value of the irradiated ultrasonic waves U1 is less than 150 W, the output of the ultrasonic waves U1 is too weak to sufficiently collapse the cavitation nuclei by expanding and contracting. If the rated ultrasonic output value of the irradiated ultrasonic waves U1 exceeds 2000 W, the output of the ultrasonic waves U1 is strong, but effective expansion of the cavitation nuclei and collapse by contracting them cannot be achieved, so there is no point in increasing the output.

[0042] In other words, the radius that gives the resonant frequency of bubble vibration (vibration to the cavitation nucleus) is called the resonance radius, but if the sound pressure (ultrasonic output) is large, above the resonance radius, the cavitation nucleus does not expand much and does not cause Rayleigh contraction (adiabatic compression). On the other hand, even if the sound pressure is below the bubble radius at which the Blake threshold (sound pressure required for isothermal expansion) is reached, the bubble expansion becomes small. For these reasons, the equilibrium radius of active bubbles that generally cause Rayleigh contraction is between the Blake threshold and the resonance radius.

[0043] The ultrasonic irradiation element 30 is disposed at a position in the pure water W1 stored in the reactor 10, away from the water jet ejected by the ejection nozzle 20 at a distance of 5 wavelengths of the ultrasonic wave U1 emitted from the ultrasonic irradiation element 30 or less. Specifically, when the frequency of the ultrasonic wave U1 emitted is 28 kHz, the ultrasonic irradiation element 30 is disposed at a position of about 54 mm or less away from the water jet ejected by the ejection nozzle 20. If the distance exceeds 5 wavelengths of the ultrasonic wave U1 emitted from the ultrasonic irradiation element 30, the strength of the ultrasonic wave U1 decreases, and the nucleus of the ultra-high temperature and high pressure cavitation does not change from an expanding state to a contracting state, and the effect of surface modification of the material by the ultra-high temperature and high pressure cavitation cannot be obtained sufficiently.

[0044] In addition, the ultrasonic irradiation element 30 irradiates ultrasonic waves U1 to the fluid cavitation at a position away from the injection nozzle 20 where the fluid cavitation can expand and where the flow rate of the fluid cavitation is equal to or lower than a predetermined moving speed. This distributes the high-temperature reaction field of the fluid cavitation including the high-temperature reaction field around the workpiece, which is the object to be impacted, at a position away from the injection nozzle 20. The predetermined moving speed here is 5 m / s, as described in the above-mentioned Patent Document 2 (International Publication No. WO 2016 / 136656). As described above, the ultrasonic irradiation element 30 irradiates ultrasonic waves U1 to the water jet whose flow rate has been weakened and whose pressure has been reduced, thereby generating ultra-high temperature and high pressure cavitation.

[0045] The magnet 40 is, for example, a neodymium permanent magnet (N40 manufactured by Sangyo Supply Co., Ltd.) having a rectangular parallelepiped shape of 20 mm×7 mm×10 mm, 20 mm×10 mm×20 mm, etc. In this embodiment, a neodymium permanent magnet having a rectangular parallelepiped shape of 20 mm×10 mm×20 mm is used.

[0046] As shown in Fig. 3, the magnets 40 are detachably arranged in two rows, 4 magnets per row, on the inside and outside of the lower part of the ultrasonic irradiation element 30 of the wall part 101 to the wall part 105 of the reactor 10 near the bottom wall 108 of the reactor 10. Also, in the upper part of the ultrasonic irradiation element 30 of the wall part 101 to the wall part 105 of the reactor 10 near the discharge port of the injection nozzle 20, the magnets 40 are detachably arranged in two rows, 4 magnets per row, on the inside and outside of the wall part 101 to the wall part 105 of the reactor 10. These magnets 40 are removed when generation of a magnetic field is not required in the space 100 in the reactor 10.

[0047] These 80 magnets 40 are arranged so that the north and south poles of the magnets 40 are non-offset and do not cancel each other out, and the magnetic field generated by the powerful neodymium magnets and their arrangement can be irradiated onto the water jet sprayed from the opening at the lower end of the spray nozzle 20.

[0048] Specifically, a magnetic field of, for example, 4.48 mT to 6.15 mT or 12.4 mT to 15.2 mT can be formed from the discharge port of the injection nozzle 20 to the developed cavitation cloud. The magnet 40 immersed in the pure water W1 is covered with a waterproof film to prevent the nickel plating on the surface of the magnet 40 from peeling off. In addition, to prevent the photomultiplier tubes built into the first and second detectors from being affected by the magnetic field, two rolls of magnetic shield tape (permalloy tape SB80-40004, manufactured by Taiyo Kanamo Co., Ltd.) are applied.

[0049] The laser light irradiation device 50 is configured by providing a standard collimated laser light source (MXL-BC13-450-80-(D), wavelength 450 nm, maximum emitted light output 42.3 mW, class 3B, manufactured by Kiko Giken Co., Ltd.) to a quartz viewing port ICF flange attached to a through hole formed in the wall portion 106. This allows the laser light irradiation device 50 to irradiate / stop irradiation of laser light to cavitation.

[0050] In addition, a quartz viewing port ICF flange is attached to wall portion 107, and photon counting heads (manufactured by Hamamatsu Photonics K.K.) of the H9319 series (H9319-01 (detection wavelength: 300 to 600 nm; hereafter referred to as "first detector 60-1"), and H9319-02 (detection wavelength: 300 to 800 nm; hereafter referred to as "second detector 60-2") which has higher sensitivity on the higher wavelength side) that constitute photoelectron measuring instrument 60 are provided to perform photon counting, and the results are provided by simply connecting to a PC.

[0051] The H9319 series photon counting head contains a 25mm diameter head-on photomultiplier tube, photon counting circuitry, high voltage power supply circuitry, a counter, and a microprocessor. A single photon striking the photocathode on the head-on photomultiplier tube is converted into a single electron, and the collision of this electron with the first dynode creates an avalanche process involving multiple dynodes. Three dark curtains are used to measure the light emission intensity from various bubbles, and measurements are performed by blocking external light with a triple layer of dark curtains.

[0052] The laser output at a position 40 mm from the laser light source of the viewing port ICF flange of the wall 107 is, for example, 9.51 mW, as measured by a laser power meter (LP10, manufactured by Sanwa Seiki Co., Ltd.), and at the position of the outlet of the injection nozzle 20 at a position 150 mm from the laser light source, it is, for example, 9.40 mW. The optical path of the laser is positioned at a height of 5 mm from the top surface of the sample placed on the workpiece stage 109. The laser light is adjusted so that it passes through the center of the cavitation cloud. This makes it possible to efficiently generate multiphoton excitation in the LMEI-MFC described later.

[0053] The positron irradiation device 70 has a positron source Na-22 and is disposed above the reactor 10. The positron irradiation device 70 is covered with a transparent soft plastic bag to prevent liquid such as pure water W1 from contacting Na-22.

[0054] The positron source Na-22 is a source (NA351) provided by the Japan Radioisotope Association, and is composed of an isotope (disk) sandwiched between Kapton (registered trademark) (polyimide film with a thickness of 7.5 μm). This allows the emission (irradiation) of positrons Na-22 to be stopped / released in approximately 4π directions. This is used in positron annihilation measurements as a vacancy analysis method for materials such as metals. The half-life is 2.6 years, with beta rays at 546 keV and gamma rays at 1.275 MeV. The radioactivity of Na-22 is 1 MBq, a value that does not require any special management under regulations.

[0055] The positron irradiation device 70 is arranged in the magnetic field direction of the magnet 40, and is configured so that the positrons Na-22 fly toward the surface of the degassed deuterated acetone liquid according to Fleming's left-hand rule. As a result, the β+ rays below the magnetic field of the magnet 40, which is at the same height as the positron source Na-22, are bent toward the liquid surface of the pure water W1 and come into contact with the cavitation bubbles rising to the liquid surface. The positrons Na-22 are then captured with a certain probability in the cavitation bubbles rising to the liquid surface of the pure water W1.

[0056] The ultra-high temperature and pressure cavitation generating device 1 having the above-mentioned configuration is used to generate ultra-high temperature and pressure cavitation as follows.

[0057] If necessary, the ultrasonic wave irradiation element 30 irradiates ultrasonic waves U1 to the fluid cavitation that occurs with the ejection of the water jet ejected from the ejection nozzle 20 as necessary. This irradiation causes repeated high and low pressure in the fluid cavitation. Therefore, the generation of nuclei, the diffusion and expansion of the nuclei, the collapse of the nuclei, and the generation of nuclei are repeated. In this repetition, the diffusion and expansion of the nuclei coincide with the generation of nuclei, generating bubbles with a higher temperature and pressure than the conventional UTPC (ultra-high temperature and high pressure cavitation) described in Patent Document 2.

[0058] When the ultra-high temperature and pressure cavitation starts to collapse, it approaches the material of the workpiece. It then causes a volume reduction and generates a high-speed jet (microjet) that penetrates the surface of the material. This high-speed jet (microjet) created by the ultra-high temperature and pressure cavitation collides with the workpiece. This imparts compressive residual stress to the surface of the workpiece, and the microjet performs surface modification, changing the geometric shape, mechanical properties, and corrosion resistance of the surface.

[0059] In this way, the high-temperature reaction field of the flow cavitation, including the high-temperature reaction field generated by expanding and contracting the flow cavitation with ultrasound U1, is distributed ahead of the injection nozzle 20 in the ejection direction of the water jet, because, as described above, the ultrasound irradiation element 30 irradiates ultrasound U1 to the ejection of the water jet.

[0060] Here, in the multifunctional cavitation (MFC) process, which combines the characteristics of both water jet cavitation (WJ) and ultrasonic cavitation (UC), charged bubbles containing ions such as O+, H+, and OH+ are formed by the thermal decomposition of water vapor inside the bubbles. When a magnetic field is applied to these charged bubbles, the Lorentz force acts in the flow direction of the charged bubbles, promoting collisions between the bubbles. These collisions create new bubbles in an avalanche-like manner, increasing the total number of bubbles and improving processing capacity.

[0061] Specifically, metal processing technologies implemented include energy-intensive MFC (EI-MFC) technology, which concentrates ultrasonic irradiation from around the water jet cavitation bubbles, MEI-MFC technology, which adds a magnetic field to this, and laser-assisted high-magnetic field energy-intensive functional cavitation (LMEI-MFC) technology, which irradiates the MFC with laser light to promote multiphoton ionization (photoionization) within the bubbles under a magnetic field, as well as positron and laser-assisted high-magnetic field energy-intensive functional cavitation (PLMEI-MFC) technology, which uses positron irradiation.

[0062] In LMEI-MFC, MFC activated by Coulomb force forms a bell-shaped cavitation jet. Whether or not the laser light promotes ionization within the bubbles is thought to depend on the amount of photons emitted from the bubbles. For large bubbles with a radius of up to several hundred μm, the collapse phenomenon of micro jets becomes dominant, making it possible to perform mechanical processing and electrochemical processing. On the other hand, ultrasonic cavitation and nano-microbubbles with a size of 10 μm or less enable chemical processing and chemical reactions.

[0063] In the PLMEI-MFC, cavitation is activated by irradiating the cavitation bubbles with positrons, and the bubble energy increases. This is the result of the positrons penetrating the bubbles and reacting with the electrons. The mechanism of bubble energy concentration by positron irradiation is as follows.

[0064] When a positron passes through the bubble wall and enters the bubble, it immediately annihilates with an electron, and the mass energy of both is carried away by two gamma ray photons (reaction equation: e + + e -→ 2γ + 1.02 MeV). This reaction energy increases the energy concentration inside the bubbles, and the energy released when the bubbles collapse further improves the degree of processing of the surface of the workpiece. By using the injection nozzle 20 with an extremely fine tip to perform energy-concentrated functional cavitation processing, it becomes possible to perform precision peening, which can impart compressive residual stress while suppressing surface roughness.

[0065] Photoionization is a physical process in which an incident photon causes one or more electrons to be ejected from an atom, ion, or molecule. This is essentially the same process as the photoelectric effect in metals, but the term "photoionization" is more commonly used for gases.

[0066] The emitted electron is called a photoelectron. If the photon energy is less than the electron binding energy, the photon is absorbed or scattered and does not photoionize atoms or ions. Not all photons that collide with atoms or ions contribute to photoionization. The probability of photoionization is related to the photoionization cross section, which depends on the photon energy and the target of photoionization. If the photon energy is below the ionization threshold, the photoionization cross section is almost zero. However, in recent years, it has become possible to create extremely strong (high light intensity or high photon flux density) and uniform coherent light, where a phenomenon called multiphoton ionization (or multiphoton ionization; MPI) occurs.

[0067] Multiple photons that individually have energies below the ionization threshold can actually contribute enough energy to ionize an atom. This is called multiphoton ionization. The probability of this occurring decreases exponentially as the number of photons required increases. However, with the recent development of high-intensity pulsed lasers, multiphoton ionization is becoming feasible.

[0068] In the perturbative regime, the probability P of absorbing N photons is proportional to the Nth power of the laser light intensity I (P ∝ I N ) In resonance-enhanced multiphoton ionization (REMPI), a type of multiphoton ionization, a large number of photons of energy hν are absorbed to obtain energy exceeding the ionization level. The excess energy is then emitted as light.

[0069] In this embodiment, it is possible to carry out the following for cavitation: L, which performs only laser irradiation; EI-UC, which performs only ultrasonic irradiation; LEI-UC, which performs laser irradiation and ultrasonic irradiation; MEI-UC, which performs ultrasonic irradiation in a magnetic field; LMEI-UC, which performs laser irradiation and ultrasonic irradiation in a magnetic field; PMEI-UC, which performs positron irradiation and ultrasonic irradiation in a magnetic field; and PLMEI-UC, which performs positron irradiation, laser irradiation, and ultrasonic irradiation in a magnetic field. These are carried out for the purpose of investigating the activation of bubbles called bubble nuclei, which are several μm in size and exist in pure water as still water.

[0070] In addition, in this embodiment, for water jet cavitation (WJC), it is possible to implement PLM-WJC, which performs positron irradiation and laser irradiation in a magnetic field, L-MFC, which performs laser irradiation and ultrasonic irradiation, MEI-MFC, which performs ultrasonic irradiation in a magnetic field, LMEI-MFC, which performs laser irradiation and ultrasonic irradiation in a magnetic field, PMEI-MFC, which performs positron irradiation and ultrasonic irradiation in a magnetic field, and PLMEI-MFC, which performs positron irradiation, laser irradiation, and ultrasonic irradiation in a magnetic field.

[0071] Next, tests were conducted to verify the effectiveness of a method for generating ultra-high temperature and high pressure cavitation, which is performed by the ultra-high temperature and high pressure cavitation generating device 1 according to this embodiment, in imparting compressive residual stress to the surface of a material and changing the geometric shape, mechanical properties and corrosion resistance of the surface.

[0072] In the test, a Mg alloy rolled plate (AZ31B, manufactured by Osaka Fuji Industrial Co., Ltd.) for machine structural use having the following chemical composition was used as a sample for the workpiece. The units for the chemical composition below are mass%. Al: 3.9 Si:0.90 Mn: 0.37 Si: 0.01 Fe:0.002 Cu: Less than 0.01 Ni: Less than 0.001 Mg:Remainder

[0073] The sample used was the above-mentioned Mg alloy rolled plate cut into a size of 30 mm x 30 mm x 1 mm, and the surface was chemically treated to enhance corrosion resistance (hereinafter referred to as "unprocessed Mg alloy"). Blue marker ink (SG7: manufactured by Sakura Color Products Co., Ltd.) was applied to the sample before processing. The sample as the workpiece was fixed on the workpiece stage 109 with double-sided carbon tape. The standoff distance, which is the distance between the sample and the outlet of the injection nozzle 20, was 20 mm.

[0074] The optical path of the laser was adjusted so that the laser beam passes through the center of the region where the cavitation cloud is formed at a height of 5 mm from the sample surface when the water jet cavitation discharged from the injection nozzle 20 is released. This adjustment is believed to provide the most efficient multiphoton excitation during the LMEI-MFC treatment. In the test, the EI-UC, LEI-UC, MEI-UC, LMEI-UC, EI-MFC, MEI-MFC, LEI-MFC, and LMEI-MFC treatments were each performed for 30 minutes. The test results are shown in Figures 4 to 28.

[0075] The emission intensities detected by the first detector 60-1 are shown in FIG. 4. In the cases of LEI-UC and LMEI-UC, the laser irradiation was performed for 3 minutes, and the photon measurement was started 18 seconds after the laser irradiation was stopped. In this test, a water jet was not used, so bubble nuclei of a few micrometers in size were originally present in the pure water. The results showed that the order of overall emission intensity from lowest to highest was EI-UC, LEI-UC, MEI-UC, and LMEI-UC.

[0076] Specifically, standard ultrasound irradiation generates approximately 150,000 photons / sec, but the LEI-UC, which adds laser irradiation to ultrasound irradiation, irradiates laser light concentrated at the center of the device, so the emission intensity increased to 300,000 to 450,000 photons / sec, as shown in Figure 4. In the MEI-UC, which irradiates ultrasound in a magnetic field instead of laser irradiation, the nuclei of charged bubbles collide with each other due to the Lorentz force during ultrasound irradiation, increasing the number of bubbles. As a result, the MEI-UC showed a higher overall emission intensity than the LEI-UC.

[0077] Furthermore, in LMEI-UC, where laser and ultrasound irradiation were performed under a magnetic field, a higher luminescence intensity was obtained than in MEI-UC, which is believed to be because in LMEI-UC, the Lorentz force under a magnetic field was increased, and laser irradiation was used to induce multiphoton excitation in the bubble nuclei so that the bubble collisions increased, which could activate the bubble nuclei.

[0078] The emission intensities detected by the second detector 60-2 are shown in FIG. 5. As in the case of the first detector 60-1 described above, in the LEI-UC and LMEI-UC, the laser irradiation was performed for 3 minutes, and the photon measurement was started 18 seconds after the laser irradiation was stopped. In the second detector 60-2, which has a high sensitivity in the long wavelength region, the emission intensity values ​​obtained are higher overall than in the case of the first detector 60-1. The results, in which the overall emission intensity is in descending order, are EI-UC, LEI-UC, MEI-UC, and LMEI-UC, which is the same as in the case of the first detector 60-1.

[0079] Next, to examine whether the number of bubble nuclei present in pure water W1 as still water in the reactor 10 decreases by leaving it still, tests were carried out by carrying out L (laser irradiation only) and LEI-UC. Specifically, tests were carried out on the luminescence intensity immediately after the pure water W1 was injected and stored in the reactor 10 (hereinafter referred to as "immediately after injection") and after leaving it for one day (hereinafter referred to as "after leaving it"). The results are shown in FIG. 6.

[0080] Comparing the LEI-UC results immediately after injection and after leaving it, it can be seen that the luminescence decreased and the number of bubble nuclei decreased after leaving it compared to immediately after injection. In contrast, in the case of L, where only laser irradiation was performed without ultrasonic treatment, no particularly remarkable results were obtained. It can be seen that this result was obtained because even if only the bubble nuclei in the laser light path were excited by multiphoton, new bubbles were not generated because ultrasonic waves were not irradiated to this area.

[0081] Next, the emission intensity was evaluated for the EI-MFC, LEI-MFC, MEI-MFC, and LMEI-MFC using the first detector 60-1. For the LEI-MFC and LMEI-MFC that were irradiated with laser, the laser was irradiated for 3 minutes, as in the above test, and photon measurement was started 18 seconds after the laser irradiation was stopped. The results are shown in FIG. 7.

[0082] Overall, the order of decreasing luminescence intensity is EI-MFC, MEI-MFC, LMEI-MFC, and LEI-MFC. Therefore, the luminescence intensities of LMEI-MFC and LEI-MFC are reversed compared to the luminescence intensities of LMEI-UC and LEI-UC shown in Figures 4 and 5.

[0083] As shown in FIG. 4, when there is no magnetic field and no water jet is ejected, the measured emission intensity in the first detector 60-1 is in the range of 250,000 to 550,000 photons / second for a time span of 10 minutes. In contrast, in the case of an energy-intensive process using no magnetic field and ejection of a water jet, the photon count is 2,750,000 to 3,250,000 photons / second, as shown in FIG. 7. That is, compared to the case of no ultrasonic irradiation, the energy-intensive process using ultrasonic irradiation has a result that is 5 to 13 times higher. Furthermore, after 3 minutes of laser light irradiation, a value of 4,000,000 to 5,000,000 photons / second was observed even after the laser light was stopped. This is an increase of 2,000,000 photons / second compared to the case of no laser light irradiation.

[0084] These results indicate that the multiphoton-excited charged bubbles maintained their multivalent state even after being irradiated with a laser beam. It can be seen that in the MEI-MFC, the number of bubbles increased as a result of collisions caused by the Lorentz force due to the magnetic field, and therefore a higher luminescence intensity was obtained than in the EI-MFC. Furthermore, in the LEI-MFC, it can be seen that the multiphoton excitation of bubbles by laser irradiation limits the electrostatic force (Coulomb force) between bubbles of different valences, activating collisions between bubbles and generating a large number of excited bubbles.

[0085] However, in the LMEI-MFC, collisions due to the Lorentz force in the magnetic field were suppressed by collisions due to the Coulomb force. Therefore, it can be seen that the LMEI-MFC is characterized by the generation of high-pressure bubbles, rather than high-temperature bubbles with high luminescence intensity. In the LMEI-UC, energy was concentrated in bubble nuclei with a radius of about several μm that were originally present in pure water, while in the MEI-MFC, EI-MFC, and LMEI-MFC, energy was concentrated in larger water jet cavitation bubbles.

[0086] Furthermore, the number and density of bubbles in the cavitation cloud generated by the outlet of the water jet injection nozzle 20 was significantly increased compared to the values ​​of the bubble nuclei. It can be seen that the multiphoton excitation inside these multiple bubbles increases the charge of the bubbles, resulting in an increase in the emission intensity.

[0087] Next, the emission intensities of the EI-MFC, LEI-MFC, MEI-MFC, and LMEI-MFC were evaluated using the second detector 60-2 in the same manner as in the case of the first detector 60-1 described above. The results are shown in FIG. 8. Compared to the case of the first detector 60-1 described above, the emission intensities of all of them were lower. This result shows that the maximum value of the emission intensity shifted to the ultraviolet region as the bubble temperature increased.

[0088] As shown in FIG. 8, the second detector 60-2 obtained an emission intensity of 2,000,000 to 3,500,000 photons / second, which indicates that the energy-intensive process using ultrasonic irradiation produces results that are 5 to 35 times higher than when ultrasonic irradiation is not performed.

[0089] In the wavelength range detected by the second detector 60-2, the emission intensity of the MEI-MFC was not as strong as that of the EI-MFC. Furthermore, no significant difference in emission intensity was detected between the LMEI-MFC and the LEI-MFC. These results show that the emission intensity in the detection wavelength range of the first detector 60-1 is stronger than that in the detection wavelength range of the second detector 60-2.

[0090] Next, the samples were subjected to L (laser irradiation only), LMEI-UC, EI-MFC, LEI-MFC, MEI-MFC, and LMEI-MFC for 30 minutes each. The results of the surface condition of the samples after the tests are shown in the photographs in Figures 9 to 20.

[0091] Comparing the photographs before and after L (laser irradiation only) shown in Fig. 9 and Fig. 10, respectively, it can be seen that there is almost no change in the ink coating. Even if a bubble nucleus with a diameter of several micrometers is originally present in the pure water and is excited by multiphoton irradiation, the bubble is not irradiated with ultrasonic waves. This shows that isothermal expansion or adiabatic compression of the high-temperature bubble does not occur.

[0092] Comparing the photographs before and after LMEI-UC shown in Fig. 11 and Fig. 12, respectively, with LMEI-UC, ink peeling occurred in the area irradiated by the laser light, regardless of the water jet nozzle discharge position. This peeling effect is the result of multiphoton excitation of small bubble nuclei of a few micrometers that were originally present in the pure water W1. The collision of these charged bubbles promotes ink peeling. It can be seen that the width of the ink separation zone in the direction of the applied magnetic field is wider because the collision of the charged bubbles is promoted by the Lorentz force. This result shows that while the processing area is limited to the position of the water jet jet in LMEI-MFC, LMEI-UC, which uses bubble nuclei cavitation that are widely present, can process a wide area.

[0093] In contrast, when EI-MFC was performed, comparing the before-treatment photograph shown in FIG. 13 with the after-treatment photograph shown in FIG. 14, slight peeling occurred in the center of the test piece in the after-treatment photograph. No dents were observed in the peening area. Also, unlike LMEI-UC, the water jet cavitation jet impinges on the injection center, and the impinging jet flows at high speed along the surface of the Mg alloy sample, so ink separation does not occur along the impact area of ​​the laser light. It can be seen that the ink did not peel off because the surface of the sample was covered by the water jet. It can be expected that the rapid movement of small-sized cavitation bubbles generated from the injection nozzle 20 composed of a narrow nozzle will suppress isothermal expansion and adiabatic compression because the break pressure threshold required for expansion increases.

[0094] The water jet cavitation bubbles generated from the outlet of the 0.1 mm jet nozzle 20 are small and do not spread easily. However, in the case of LMEI-UC, the ultrasonic radiation was concentrated on the bubble nucleus because there was no flow. Therefore, although the bubbles were small, many bubble nuclei were able to detach the ink by undergoing isothermal expansion and adiabatic compression.

[0095] Comparing the before photograph in Fig. 15 and the after photograph in Fig. 16, when performing LEI-MFC, a thin delamination region was generated from the center to the upper left of the sample in LEI-MFC. In LEI-MFC, the delamination region expanded because the laser light was irradiated from the lower right to the upper left. This indicates that in MFC, activation of charged bubbles by multiphoton excitation in response to the laser light is included.

[0096] In addition, when the MEI-MFC was performed, the ink peeling area was significantly enlarged when comparing the photograph before the MEI-MFC performed (Fig. 17) with the photograph after the MEI-MFC performed (Fig. 18). This area was circular and large in the UTPC, but was flat in the horizontal direction in the MEI-MFC. This is thought to be due to the influence of the magnetic field (NS) from right to left.

[0097] In addition, when LMEI-MFC is performed, the ink peeling area is significantly enlarged when comparing the photograph before the procedure shown in Fig. 19 with the photograph after the procedure shown in Fig. 20. It can be seen that the area contains more activation of charged bubbles due to multiphoton excitation in response to the laser light.

[0098] Optical microscope photographs of the surfaces of samples made with EI-MFC, LEI-MFC, MEI-MFC, and LMEI-MFC are shown in Figures 21 to 24. Localized ink peeling can be seen in Figures 21 and 22, which show optical microscope photographs of the surfaces of samples made with EI-MFC and LEI-MFC, respectively. In contrast, the peeled area has increased in Figures 23 and 24, which show optical microscope photographs of the surfaces of samples made with MEI-MFC and LMEI-MFC, respectively. Furthermore, the processing marks made with LMEI-MFC are flattened, and cracks perpendicular to the rolling scratches have occurred.

[0099] These results show that the LMEI-MFC is highly functional. The cracks are generated by the collapse of many bubbles, which causes high stress on the metal surface with minimal heat, resulting in insufficient rise in surface temperature. Therefore, it is necessary to optimize the conditions by lowering the water jet injection pressure or the laser light intensity.

[0100] Photographs of the unprocessed Mg alloy, LMEI-UC, MEI-MFC, and LMEI-MFC constituting the samples, taken using dynamic force mode (DFM) analysis, are shown in Figures 25 to 28. As shown in Figure 25, the unprocessed Mg alloy has lap-shaped scratches partially accompanied by linear peeling on the surface.

[0101] In contrast, in the LMEI-UC, the unevenness of the rolling scratches is reduced, as shown in Figure 26. This shows that, although the typical UC (energy concentration by ultrasonic waves) bubble temperature is very high and the collapse pressure is low, a certain degree of high temperature and high pressure treatment is achieved by concentrating the energy. In the MEI-MFC, the rolling scratches completely disappeared, and both flattened and non-flattened areas were observed, as shown in Figure 27. In the LMEI-MFC, some areas were completely flattened, and the rolling scratches were reduced uniformly overall, as shown in Figure 28.

[0102] When this is estimated using the graph of emission intensity shown in FIG. 7, it can be seen that the collapse temperature was higher than that obtained by MEI-MFC. This is due to the higher temperature and pressure during the process, which is achieved by the Lorentz force in the magnetic field. The DFM analysis also shows that there is no significant peening mark on the metal surface with MEI-MFC or LMEI-MFC. And from the above results, it can be seen that the surface strengthening can be obtained by obtaining small peening mark and less surface roughness due to the outlet diameter of the injection nozzle 20 being 0.1 mm.

[0103] The results of KFM (Kelvin Force Microscope: Surface Potential Microscope) analysis of the same unprocessed Mg alloy (unprocessed, conversion treatment) as the sample, LMEI-UC, MEI-MFC, and LMEI-MFC are shown in Fig. 29. The error bars in the graph shown in Fig. 29 indicate a standard deviation of plus / minus 1. The higher the corrosion potential (Surface potential) corresponding to the increase in surface potential in the KFM analysis results, the better the corrosion resistance.

[0104] The KFM analysis results showed a slight decrease in potential for the LMEI-UC (1080 mV) compared to 1155 mV for the unprocessed Mg alloy. However, there was a large variation in the potential for the treated samples, with some local areas exceeding 1500 mV and others below 745 mV. For the MEI-MFC, the corrosion potential decreased to about 745 mV, whereas for the LMEI-MFC it was as high as 917 mV.

[0105] These results are believed to be due to the chemical treatment applied to the surface of the untreated material to improve its corrosion resistance. Nevertheless, in the LMEI-UC, the protective film from this chemical treatment could be removed in some areas, creating areas with high and low corrosion potentials. In the MEI-MFC, the protective film was completely removed, but in the LMEI-MFC, a protective film was created and the corrosion potential was improved.

[0106] The arithmetic mean surface roughness Ra values ​​of the same unprocessed Mg alloy (unprocessed, conversion treatment) as the sample, LMEI-UC, MEI-MFC, and LMEI-MFC are shown in FIG. 30. As shown in the graph in FIG. 30, in LMEI-UC, part of the conversion coating that existed on the Mg alloy remained, and the surface roughness also changed significantly. In LMEI-MFC, the coating completely peeled off, and the workability was better than that of MEI-MFC. The surface roughness increased with LMEI-MFC.

[0107] The Vickers hardness values ​​of the same unprocessed Mg alloy (unprocessed, conversion treatment), LMEI-UC, MEI-MFC, and LMEI-MFC are shown in Figure 31. In LMEI-UC, the bubbles that first underwent isothermal expansion and adiabatic compression act as nuclei to promote hardening, and the highest value is shown. Even if the bubbles are small and have the smallest heat capacity, it can be seen that the treatment temperature and pressure increase according to the number of bubbles by applying various types of energy. The surface treatment temperature is determined by the balance of the amount of heat transferred to the material surface by the microjet, the amount of heat released into the water, and the amount of heat transferred from the material surface to the inside.

[0108] The initial bubble size obtained by MEI-MFC and LMEI-MFC is larger than that generated by *-UC (where "*" is MEI or LMEI). Therefore, the bubble temperature in the reactor 10 increased due to repeated isothermal expansion and adiabatic compression in the former. As a result, the heat input to the metal surface increased and exceeded the recrystallization temperature of the alloy. This removed the accumulated deformation and replaced it with undistorted crystalline grains, decreasing the hardness of the alloy.

[0109] The compressive residual stress values ​​of the same unprocessed Mg alloy (unprocessed, conversion treatment) as the sample, LMEI-UC, MEI-MFC, and LMEI-MFC are shown in Figure 32. The residual stress values ​​were measured using an X-ray device (PULSTEC μ-X360s) with a measurement area diameter of Φ2 mm.

[0110] From the graph shown in Figure 32, it is clear that a larger stress was applied by MEI-MFC and LMEI-MFC than by unprocessed Mg alloy. The surface of the sample by LMEI-MFC, which is considered to have the highest workability, has cracks on its surface as shown in Figure 24, so the compressive residual stress value of the sample by LMEI-MFC is clearly lower. This is due to the release of compressive residual stress by the cracks.

[0111] It is also clear that LMEI-MFC using a fine nozzle can impart various effects to the material surface, such as improving compressive residual stress and hardness, and improving corrosion resistance. The collapse of small cavitation bubbles generated from a fine nozzle suppresses the depth of the peening mark and reduces surface roughness, enabling precision peening of small machine parts.

[0112] Also, the LMEI-MFC allows for higher energy photon output, for example using a 400 nm laser beam. Instead of placing the magnet 40 on the walls 101-107 of the reactor 10, it can be placed near the outlet of the injection nozzle 20 to increase the magnetic field near the water jet and promote bubble collision. Furthermore, the LMEI-MFC can be performed on small flat specimens used for bending fatigue testing of materials such as aluminum alloys and steels to improve fatigue strength and fatigue life.

[0113] The tensile residual stress values ​​of the unprocessed Cr-Mo steel sample (milled surface, test piece thickness 1 mm) and the LMEI-MFC are shown in Figure 33. The tensile residual stress of the Cr-Mo steel sample (milled surface, test piece thickness 1 mm) before LMEI-MFC (before processing) was 400 MPa, whereas after processing it was -420 MPa, resulting in a high stress improvement of 820 MPa. This is evident from the fact that the flow rate was high at 180 mL / min, and numerous ultra-high temperature and high pressure cavitations with concentrated energy processed the surface of the sample.

[0114] The tensile residual stress values ​​of the unprocessed Cr-Mo steel sample (milled surface, test piece thickness 1 mm) and the PLM-WJC sample in which laser irradiation and positron irradiation were performed on water jet cavitation (WJC) without concentrated ultrasonic irradiation in a magnetic field are shown in Figure 34.

[0115] The tensile residual stress of the Cr-Mo steel sample (milled surface, test piece thickness 1 mm) before PLM-WJC (before processing) was 434 MPa, whereas after processing it was -451 MPa, and the amount of stress improvement was a high value of 885 MPa. This indicates that the energy of positron irradiation has a high effect on bubbles.

[0116] The tensile residual stress values ​​of the unprocessed Cr-Mo steel (milled surface, test piece thickness 1 mm) as a sample and the PLMEI-MFC in which focused ultrasonic irradiation, laser irradiation, and positron irradiation were performed in a magnetic field in response to water jet cavitation (WJC) are shown in Figure 35.

[0117] The tensile residual stress of a Cr-Mo steel sample (milled surface, test piece thickness 1 mm) before PLMEI-MFC (before processing) was 690 MPa, whereas after processing it was -473 MPa, and a high stress improvement of 1,163 MPa was obtained. This indicates that the energy of positron irradiation has a high effect on bubbles. This value exceeds the improvement in water jet cavitation and functional cavitation using conventional large-diameter nozzles.

[0118] When a positron enters the bubble, it immediately annihilates with an electron, and the mass energy of both is carried away by two gamma ray photons. That is, e + + e -→ It can be seen that the reaction energy of 2γ + 1.02 MeV increased the cavitation energy to the ultimate level. The execution time (processing time) was limited to 10 minutes. This is because processing for more than 10 minutes would cause the pure water W1 in the reactor 10 to become wavy on the surface, and there was a risk of cavitation overflowing from the tank.

[0119] According to the method for generating ultra-high temperature and high pressure cavitation and the device for generating ultra-high temperature and high pressure cavitation of the above-mentioned embodiment, the following effects are achieved. As described above, the ultra-high temperature and high pressure cavitation generating device 1 comprises a magnet 40 that generates a magnetic field, imparts magnetic energy to the cavitation, and increases bubble energy, an ultrasound irradiation element 30 having an ultrasound transducer that irradiates ultrasound U1 to the cavitation in the magnetic field, distributing a high-temperature reaction field of the cavitation including a high-temperature reaction field generated by repeated expansion and contraction due to the irradiation of ultrasound U1, and a laser light irradiation device 50 that irradiates laser light to the cavitation in the magnetic field, imparts laser energy to the cavitation, and increases bubble energy, distributing a high-temperature reaction field of the cavitation including a high-temperature reaction field generated by repeated expansion and contraction due to the irradiation of ultrasound U1.

[0120] As described above, in the method of generating ultra-high temperature and high pressure cavitation, ultrasonic waves U1 and laser light are irradiated onto the cavitation in a magnetic field, magnetic energy and laser energy are imparted to the cavitation, increasing its energy, and distributing high temperature reaction fields of the cavitation including high temperature reaction fields generated by repeated expansion and contraction due to irradiation of ultrasonic waves U1.

[0121] This can activate bubble nuclei because the Lorentz force under the magnetic field is increased and laser irradiation is used to induce multiphoton excitation within the bubble nuclei so that bubble collisions are increased.

[0122] The ultra-high temperature and high pressure cavitation generating device 1 also includes a magnet 40 that generates a magnetic field, imparts magnetic energy to the cavitations, and increases bubble energy, a laser light irradiation device 50 that irradiates the cavitations in the magnetic field with laser light, imparting laser energy to the cavitations and increasing bubble energy, an injection nozzle 20 that is immersed in water and ejects a water jet, and a positron irradiation device 70 that irradiates the cavitations in the magnetic field with positrons, imparting positron energy to the cavitations and increasing bubble energy. The cavitation is flow cavitation that occurs with the ejection of the water jet, and distributes a high temperature reaction field of the cavitation.

[0123] In the method of generating ultra-high temperature and high pressure cavitation, a water jet is sprayed in a magnetic field from an injection nozzle immersed in water, and flow cavitation is generated as the water jet is sprayed. The generated flow cavitation is irradiated with positrons and laser light, imparting magnetic energy, positron energy, and laser energy to the flow cavitation, thereby increasing bubble energy.

[0124] As a result, when a positron passes through the bubble wall and enters the bubble, it immediately annihilates with an electron, and the mass energy of both is carried away by two gamma ray photons (reaction equation: e + +e - → 2γ + 1.02 MeV). This reaction energy increases the energy concentration inside the bubbles, and the energy released when the bubbles collapse can further improve the degree of processing of the surface of the workpiece.

[0125] The apparatus also includes an ultrasonic irradiation element 30 having an ultrasonic transducer that irradiates ultrasonic waves U1 to cavitation in a magnetic field, distributing a high-temperature reaction field of cavitation including a high-temperature reaction field that is generated by repeated expansion and contraction due to the irradiation of ultrasonic waves U1.

[0126] Then, ultrasonic waves U1 are irradiated to the fluid cavitation, ultrasonic energy is imparted to the fluid cavitation, the bubble energy is increased, and the high-temperature reaction field of the cavitation, including the high-temperature reaction field generated by repeated expansion and contraction due to the irradiation of ultrasonic waves U1, is distributed. By carrying out this on a sample as a workpiece, it is possible to increase the amount of stress improvement of the tensile residual stress value in the workpiece.

[0127] The cavitation is composed of fluid cavitation generated by the injection of a water jet injected from the injection nozzle 20 immersed in water. As a result, when the nuclei of fluid cavitation are diffused and expanded by the irradiation of ultrasonic waves U1, the nuclei contract and collapse, causing a volume reduction, generating a high-speed jet that penetrates the solid surface of the workpiece as a sample, and promoting the surface modification of the workpiece. At this time, it is possible to increase the size of the cavitation bubbles and increase the number of bubbles to increase the bubble temperature and pressure to the limit, so that a high compressive residual stress can be imparted to the outermost surface of the workpiece. In addition, a hardened layer can be formed on the outermost surface of the workpiece, and a high-toughness layer can be formed immediately below it. In addition, it is possible to prevent the occurrence of cracks immediately below the surface hardened layer of the workpiece.

[0128] The nozzle diameter of the injection nozzle is φ0.1 to 2.0 mm, the moving speed of the fluid cavitation is 5 m / s or less, and high-pressure water is supplied to the injection nozzle at a pressure of 1 MPa to 70 MPa and a flow rate of 0.1 L / min to 100 L / min. This makes it possible to efficiently enlarge the cavitation bubbles and increase the number of bubbles to maximize the bubble temperature and pressure. When energy-intensive functional cavitation processing is performed using the injection nozzle 20 with an extremely fine tip, it becomes possible to perform precision peening processing that can impart compressive residual stress while suppressing surface roughness.

[0129] The frequency of the ultrasonic wave U1 is 20 kHz or more and 33 kHz or less, and the output of the ultrasonic generator that generates the ultrasonic wave U1 is 150 to 2000 W. This allows the ultrasonic wave U1, which has a frequency similar to the resonance frequency of bubbles of 300 μm or more, which is the size of water jet cavitation, to be irradiated with strong output to the cavitation. As a result, it becomes possible to easily expand the nucleus of the cavitation. This allows the method of generating mechanical and electrochemical cavitation MFC to be carried out using any frequency in the frequency band of the ultrasonic wave U1.

[0130] In addition, in the method of changing the geometric shape, mechanical properties, and corrosion resistance of a surface, ultra-high temperature and high pressure cavitation generated by the method of generating ultra-high temperature and high pressure cavitation is collided with a material to impart compressive residual stress to the surface of the material. This makes it possible to impart a high compressive residual stress not previously seen to the surface of the workpiece as a material. Also, a hardened layer can be formed on the outermost surface of the workpiece, and a high toughness layer can be formed immediately below it. It is also possible to prevent the occurrence of voids and cracks immediately below the surface hardened layer of the workpiece, and a layer with high toughness can be formed. It is also possible to increase the surface potential of the surface, making it possible to suppress the occurrence of rust and improve corrosion resistance.

[0131] The workpieces constituting the material samples are made of AZ31B magnesium alloy and SCM440 Cr-Mo steel, which makes it possible to increase the surface potential of the surfaces of the AZ31B magnesium alloy and SCM4440 Cr-Mo steel.

[0132] The method for generating ultra-high temperature and pressure cavitation, the method for imparting compressive residual stress to the surface of a material and changing the geometric shape, mechanical properties and corrosion resistance of the surface, and the device for generating ultra-high temperature and pressure cavitation according to the present invention are not limited to the contents of the above-mentioned embodiments, but various modifications and variations are possible, as shown below.

[0133] For example, the configuration of the device used in the method of generating ultra-high temperature and high pressure cavitation is not limited to the configuration of the device in the above-mentioned embodiment. For example, in this embodiment, L, EI-UC, LEI-UC, MEI-UC, LMEI-UC, PLMEI-UC, PLM-WJC, EI-MFC, LEI-MFC, MEI-MFC, LMEI-MFC, etc. are implemented, but are not limited to these. At least one of the following may be performed: water jet from the injection nozzle 20, ultrasonic irradiation from the ultrasonic irradiation element 30, magnetic field formation from the magnet 40, laser light irradiation from the laser light irradiation device 50, and positron irradiation from the positron irradiation device 70.

[0134] In addition, the injection nozzle 20 is configured by a horn nozzle, but is not limited thereto. For example, it may be configured by a nozzle having another shape. In addition, for example, the ultrasonic wave irradiation element 30 irradiates ultrasonic waves U1 to the water jet from a horizontal direction with respect to the water jet injected vertically downward, but is not limited to this configuration. For example, the ultrasonic waves U1 may be irradiated from a direction close to parallel to the water jet. In addition, in this embodiment, pure water W1 is used, but is not limited thereto. For example, when it is necessary to prevent reaction with impurity elements such as sodium hypochlorite in the water, ultrapure water or the like may be used. In addition, the workpiece is configured by AZ31B magnesium alloy or SCM440 Cr-Mo steel, but is not limited thereto. [Industrial Applicability]

[0135] The present invention can be used in fields that utilize the high-temperature reaction field of fluid cavitation, and can be widely applied, for example, in fields in which compressive residual stress is imparted to the surface of a material and the geometric shape, mechanical properties, and corrosion resistance of the surface are changed. [Explanation of symbols]

[0136] 1. Ultra-high temperature and pressure cavitation generation device 20 Injection nozzle 30 Ultrasonic irradiation element 40 Magnet 50 Laser light irradiation device 70 positron irradiation device U1 Ultrasonic W1 Pure water

Claims

1. A method for generating ultra-high temperature and high pressure cavitation by irradiating cavitation with ultrasound and laser light in a magnetic field, thereby imparting magnetic energy and laser energy to the cavitation, increasing bubble energy, and distributing high temperature reaction fields of the cavitation including a high temperature reaction field generated by repeated expansion and contraction due to the irradiation of ultrasound.

2. 2. The method for generating ultra-high temperature and pressure cavitation according to claim 1, wherein the cavitation is flow cavitation generated in association with the ejection of a water jet from an ejection nozzle immersed in water, or bubble nuclei present in still water.

3. 3. The method for generating ultra-high temperature and high pressure cavitation according to claim 2, wherein the nozzle diameter of the injection nozzle is φ0.1 to 2.0 mm, the moving speed of the fluid cavitation is 5 m / s or less, and high pressure water is supplied to the injection nozzle at a pressure of 1 MPa or more and 70 MPa or less and a flow rate of 0.1 L / min to 100 L / min.

4. A method for generating ultra-high temperature and high pressure cavitation by spraying a water jet in a magnetic field from an injection nozzle immersed in water and generating flow cavitation in association with the spraying of the water jet into the water, and irradiating the generated flow cavitation or bubble nuclei present in still water with positrons and laser light to impart magnetic energy, positron energy, and laser energy to the flow cavitation and increase bubble energy.

5. 5. A method for generating ultra-high temperature and high pressure cavitation as described in claim 4, which comprises irradiating the fluid cavitation or the bubble nuclei with ultrasound to impart ultrasonic energy to the fluid cavitation or the bubble nuclei, increasing bubble energy, and distributing the high temperature reaction field of the fluid cavitation including a high temperature reaction field generated by repeated expansion and contraction due to the irradiation of the ultrasound.

6. 5. The method for generating ultra-high temperature and high pressure cavitation according to claim 4, wherein the nozzle diameter of the injection nozzle is φ0.1 to 2.0 mm, the moving speed of the fluid cavitation is 5 m / s or less, and high pressure water is supplied to the injection nozzle at a pressure of 1 MPa or more and 70 MPa or less and at a flow rate of 0.1 L / min to 100 L / min.

7. A method for imparting compressive residual stress to a surface of a material and changing the geometric shape, mechanical properties and corrosion resistance of the surface by colliding ultra-high temperature and high pressure cavitation generated by the method for generating ultra-high temperature and high pressure cavitation according to any one of claims 1 to 6 with the material.

8. 8. A method for imparting compressive residual stress to a surface of a material and altering the surface geometry, mechanical properties and corrosion resistance of the material as set forth in claim 7, wherein the material is comprised of AZ31B magnesium alloy.

9. 8. The method for imparting compressive residual stress to the surface of a material and changing the geometric shape, mechanical properties and corrosion resistance of the surface as claimed in claim 7, further comprising increasing the surface potential of the surface of the material.

10. A magnet that generates a magnetic field, imparts magnetic energy to the cavitation, and increases bubble energy; An ultrasonic transducer that irradiates ultrasonic waves to the cavitation in the magnetic field, and distributes the high-temperature reaction field of the cavitation including a high-temperature reaction field that is generated by repeating expansion and contraction due to the irradiation of the ultrasonic waves; A laser light irradiation device that irradiates the cavitation in the magnetic field with laser light to impart laser energy to the cavitation and increase bubble energy, An apparatus for generating ultra-high temperature and high pressure cavitation, which distributes the high temperature reaction field of the cavitation including a high temperature reaction field generated by repeated expansion and contraction due to the irradiation of the ultrasonic wave.

11. A jet nozzle is provided which is immersed in water and jets a water jet, The ultra-high temperature and high pressure cavitation generating device according to claim 10, wherein the cavitation is fluid cavitation that occurs in association with the ejection of the water jet.

12. A magnet that generates a magnetic field, imparts magnetic energy to the cavitation, and increases bubble energy; A laser light irradiation device that irradiates the cavitation in the magnetic field with a laser light to impart laser energy to the cavitation and increase bubble energy; a jet nozzle that is immersed in water and jets a water jet; a positron irradiation device that irradiates the cavitation in the magnetic field with positrons to impart positron energy to the cavitation and increase bubble energy; The cavitation is either fluid cavitation caused by the ejection of the water jet or bubble nucleus cavitation present in still water, A device for generating ultra-high temperature and high pressure cavitation that distributes the high temperature reaction field of the cavitation.

13. 13. An apparatus for generating ultra-high temperature and high pressure cavitation as described in claim 12, comprising an ultrasonic transducer that distributes the high temperature reaction field of the cavitation, including the high temperature reaction field, generated by irradiating ultrasonic waves to the cavitation in the magnetic field and causing repeated expansion and contraction due to the irradiation of the ultrasonic waves.

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