Etching method and etching apparatus

Abstract

To provide: a novel etching treatment method capable of achieving a highly efficient etching treatment of a solid surface in a simple manner; and an etching treatment apparatus used for the etching treatment method.SOLUTION: An etching treatment method is intended for carrying out wet etching using an etchant with respect to a solid surface as a surface to be etched. The etching treatment method includes applying supersonic wave to an etchant holding material in a state where the etchant holding material impregnated with the etchant is in contact with the surface to be etched.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an etching method and an etching apparatus used in wet etching of solid surfaces for the purposes of observing the crystal structure of metal surfaces and treating the surfaces of various materials. [Background technology]

[0002] In general, metals used as structural materials, etc. are polycrystalline bodies in which crystal grains (crystal grains) composed of metal atoms are bonded to each other via crystal grain boundaries, and it is known that the properties such as strength as a structural material vary greatly depending on the type of the metal atoms as well as the form of the metal structure formed by the polycrystalline body. For this reason, as one of the means for evaluating the soundness, etc. of various metallic materials, the crystal structure contained in the metallic material has been observed.

[0003] For example, Non-Patent Document 1 describes a technique for observing the structure of steel materials and the like that constitute various plants, as one of the non-destructive tests. As described in Non-Patent Document 1, when observing the structure of a metal, the surface to be observed is roughly polished and then finished to a mirror finish, and then etched (corroded) using various chemicals to reveal the structure to be observed and enable clear observation of the structure. The above-mentioned etching process is carried out for the purpose of taking advantage of various material differences contained in the surface to be observed, such as between the parent phase and the precipitated phase, between crystal grains and crystal grain boundaries, and differences in crystal grain orientation, and emphasizing the differences by producing irregularities or coloring in accordance with the differences, thereby clarifying and facilitating subsequent observation under a microscope, etc.

[0004] When etching the polished surface of the above metal, an etching solution is generally used, which is made by dissolving a component that produces the desired etching in water or an organic solvent such as alcohol, and the etching solution is brought into contact with the polished surface of the metal under predetermined conditions, causing a chemical reaction between the polished surface of the metal and the etching solution, resulting in the appearance of the desired structure. Therefore, in order to etch the metal surface uniformly, it is necessary to uniformly advance the chemical reaction that occurs between the polished surface of the metal and the etching solution.

[0005] That is, as a method for contacting the polished metal surface with an etching solution as described above, it is possible to contact the polished surface with absorbent cotton soaked in the etching solution, for example, as described in Non-Patent Document 1. On the other hand, for example, in a system in which the progress of etching is strongly influenced by the components of the etching solution in contact with the polished surface, a mechanism for uniformly progressing the chemical reaction that causes the etching phenomenon is required.

[0006] As a means for uniformly progressing the above-mentioned etching, for example, Patent Document 1 describes a technique for propagating ultrasonic waves through the etching solution to separate bubbles generated on the surface of the object to be etched. Patent Document 2 describes a technique for suppressing uneven corrosion caused by etching by including microbubbles in the etching solution in which the sample to be etched is immersed and applying a predetermined ultrasonic wave, and describes that by applying ultrasonic waves in a state in which microbubbles exist in the etching solution, a predetermined resonance state is formed, so that ultrasonic waves are transmitted almost uniformly to the entire etching surface, and hydrogen gas, a reaction product accompanying etching, is absorbed by the microbubbles and smoothly removed.

[0007] Furthermore, Patent Document 3 describes an etching device that agitates the etching liquid around the object to be etched by spraying the circulated etching liquid onto the liquid surface of the etching liquid using a spray nozzle, and describes that this mechanism makes it possible to suppress uneven etching compared to agitating or ejecting the etching liquid from within the etching liquid.

[0008] In addition, in a system in which a solid-phase reaction product is generated due to a chemical reaction between a metal surface and an etching solution, it is known that the reaction product adheres to the metal surface and acts as a mask against etching, impairing the uniformity of the etching. For this reason, as described in Non-Patent Document 1, Patent Document 4, Patent Document 5, etc., a method is known in which the reaction product generated by the etching process is appropriately removed by mechanical action using a buffing cloth or the like, and the etching process is continued.

[0009] Furthermore, the wet etching treatment of a solid surface is not limited to pretreatment for observing the crystal structure of the above-mentioned metal, but is also used for the purpose of smoothing or roughening the surface of metal, glass, etc., as described in, for example, Patent Documents 6 and 7, and in either case, it is expected to efficiently advance the targeted etching. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 60-39174 [Patent Document 2] JP 2012-247382 A [Patent Document 3] JP 2017-168633 A [Patent Document 4] Japanese Patent Application Publication No. 2-141590 [Patent Document 5] Japanese Patent Application Publication No. 62-238380 [Patent Document 6] Japanese Patent Application Publication No. 2-149685 [Patent Document 7] JP 2004-190043 A [Non-patent literature]

[0011] [Non-Patent Document 1] Journal of the Japan Welding Society, Vol. 79 (2010), No. 8, pp. 760-764 Summary of the Invention [Problem to be solved by the invention]

[0012] As described above, various means are provided for etching metal surfaces that have been polished or the like in accordance with the purpose, such as for observing the structure of the metal, but proposals for new etching methods, etc. are required due to changes in the level of quality required for etching treatments and the desire for improved efficiency, etc. In addition, etching treatments of solid surfaces are also used for the purpose of smoothing or roughening the solid surfaces of various metals, glass materials, etc., and in both cases, it is expected that the intended etching treatments will proceed efficiently. An object of the present invention is to provide a novel etching method that enables simple and highly efficient etching of a solid surface, and an etching processing apparatus for use in said etching method. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides the following means. (1) An etching method for performing wet etching using an etching solution on a solid surface as the surface to be etched, in which ultrasonic waves are applied to an etching solution holding material impregnated with the etching solution while the etching solution holding material is brought into contact with the surface to be etched. (2) The etching method, in which the etching solution holding material is impregnated with the etching solution by being immersed in the etching solution held inside an etching tank. (3) An etching treatment method in which the etching solution holding material contains a material having an official moisture content of 3% or more. (4) The solid is a steel material, and the etching method is aimed at revealing the crystal structure of the steel material. (5) An etching treatment device that performs wet etching using an etching solution on a solid surface as an etching surface, the etching treatment device having an etching solution holding material capable of holding the etching solution inside and an ultrasonic application means capable of applying ultrasonic waves to the etching solution holding material, and capable of applying ultrasonic waves to the etching solution holding material while the etching solution holding material impregnated with the etching solution is in contact with the etching surface. (6) An etching treatment apparatus having an etching tank for holding the etching solution, the etching solution holding material being placed inside the etching tank. (7) The etching treatment device, wherein the etching solution holding material contains a material having an official moisture content of 3% or more. Effect of the Invention

[0014] According to the present invention, efficient etching of solid surfaces becomes possible. In particular, in a system in which a solid-phase reaction product is generated by an etching reaction, it becomes possible to proceed with the etching process while suppressing adhesion of the reaction product to the solid surface, thereby enabling efficient etching. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic diagram showing the mechanism of an etching process according to the present invention. [Diagram 2] 1 is a schematic diagram showing an example of an etching processing apparatus according to the present invention; [Diagram 3] 1 is a schematic diagram showing an example of an etching processing apparatus according to the present invention; [Figure 4] FIG. 1 is a schematic diagram showing an overview of an apparatus used for evaluating an etching process according to the present invention. [Figure 5A] 1 is an optical microscope photograph of the surface of a steel material (S45C) that has been subjected to an etching treatment according to the present invention. [Figure 5B]1 is an optical microscope photograph (comparative example) of a surface of a steel material (S45C) after etching treatment. [Figure 5C] 1 is an optical microscope photograph (comparative example) of a surface of a steel material (S45C) after etching treatment. [Figure 5D] 1 is an optical microscope photograph (comparative example) of a surface of a steel material (S45C) after etching treatment. [Figure 5E] 1 is an optical microscope photograph of the surface of a steel material (S45C) that has been subjected to an etching treatment according to the present invention. [Figure 6A] 1 is an optical microscope photograph of the surface of a steel material (SCr415H) that has been subjected to an etching treatment according to the present invention. [Figure 6B] 1 is an optical microscope photograph (comparative example) of a surface of a steel material (SCr415H) after etching treatment. [Figure 6C] 1 is an optical microscope photograph (comparative example) of a surface of a steel material (SCr415H) after etching treatment. [Figure 7A] 1 is an optical microscope photograph of the surface of a steel material (SCM435) that has been subjected to an etching treatment according to the present invention. [Figure 7B] 1 is an optical microscope photograph of the surface of a steel material (SCM435) that has been subjected to an etching treatment according to the present invention. [Figure 8] 1 is a photograph showing the state of a nonwoven fabric used in an etching treatment according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Etching treatments carried out for the purpose of observing the structure of metals and the like are carried out for the purpose of accentuating various material differences contained in the surface of metals, such as differences between parent phases and precipitated phases, crystal grains and grain boundaries, differences in crystal grain orientation, etc., or of using these differences to impart unique characteristics to the surface of the metal, etc. Etching treatments utilize chemical changes between the surface of the metal, etc. and the etching solution, and the components and concentration of the etching solution, etching temperature, etching time, etc. are adjusted so that chemical changes occur according to the purpose of the etching treatment.

[0017] On the other hand, since the degree of progress of the chemical reaction between the surface of the metal or the like and the etching solution varies depending on, for example, the concentration of each component contained in the etching solution, the concentration of the components involved in the chemical reaction decreases as the chemical reaction progresses, and the concentration of the reaction product of the chemical reaction increases, which inevitably inhibits the progress of the etching process. As a result, if a small amount of etching solution remains on the surface of the metal or the like, it is thought that a phenomenon will occur in which the desired etching reaction does not progress due to the change in the components of the etching solution.

[0018] The inventions described in the above Patent Documents 1 and 2 aim to prevent this phenomenon and perform good etching treatment, by stirring and circulating the etching solution by various methods in an environment where a sufficient amount of etching solution is used to complete the etching of the object to be etched, thereby mitigating the degree of change in the composition of the etching solution and non-uniformity, particularly on the surface to be etched, and thereby performing uniform etching.

[0019] In light of the above technical background, the present inventors have investigated etching methods for materials that are difficult to etch, and have unexpectedly found that by using a cloth or the like that can hold an etching solution by being impregnated with the etching solution, and applying ultrasonic waves while the cloth or the like holding the etching solution is in contact with the surface to be etched, the time required for etching can be shortened compared to the case where ultrasonic waves are simply applied to an etching solution, as described in Patent Document 1, for example.

[0020] Furthermore, in particular in systems in which a solid-phase reaction product is produced by the etching process, the reaction product adheres to the surface to be etched, hindering uniform etching, whereas the above-described etching method inhibits the reaction product from adhering to the surface to be etched, making it unnecessary to interrupt the etching process to remove the reaction product, and enabling efficient etching.

[0021] As described above, the etching process according to the present invention enables uniform etching and prevents the adhesion of solid reaction products to the surface to be etched, thereby enabling efficient etching. The mechanism behind this is believed to be as follows.

[0022] Fig. 1 shows a schematic diagram of the state of the vicinity of the surface to be etched when etching is performed by the etching process according to the present invention. For example, when a cloth 3 or the like used for holding an abrasive in buffing is used and the cloth 3 or the like is impregnated with an etching solution 2 and brought into contact with the surface of the object to be etched 1, it is considered that a part of the fiber elements 4 constituting the cloth 3 is in contact with the surface of the object to be etched 1 as shown in Fig. 1. On the other hand, the etching solution 2 impregnated in the cloth 3 or the like is present so as to fill the gaps in the fiber elements 4 constituting the cloth 3, and as a result, it is considered that a state is formed in which both the fiber elements 4 and the etching solution 2 are in contact with the surface of the object to be etched 1.

[0023] In the above state, by applying ultrasonic waves to the cloth 3 and the etching solution 2 using an appropriate means, vibrations are induced inside the etching solution 2 and vibrations 20 are induced in the fiber elements 4. In particular, it is believed that the portions of the fiber elements 4 that come into contact with the surface of the object to be etched 1 generate vibrations of a predetermined amplitude while maintaining contact with the surface of the object to be etched 1.

[0024] It is generally known that at the interface between a solid surface and a fluid, a boundary layer is formed on the fluid side of the interface, where the fluid has difficulty flowing, and if the etching process progresses within this boundary layer and the components of the etching solution change, the progress of the subsequent etching process is considered to be hindered. Since the thickness of the boundary layer is considered to be able to be reduced by increasing the flow rate of the fluid or by cavitation caused by application of ultrasonic waves, the techniques described in the above Patent Documents 1 to 3 are considered to promote the progress of the etching process by reducing the thickness of the boundary layer on the surface of the surface to be etched by stirring the etching solution by various means.

[0025] On the other hand, in the etching process of the present invention, the fiber elements 4 inside the etching solution 2 vibrate while maintaining contact with the surface of the object 1 to be etched, mechanically stirring the area near the surface of the object 1 to be etched, and the boundary layer within the etching solution is continuously destroyed, homogenizing the etching solution, suppressing changes in the components of the etching solution near the surface to be etched, thereby improving the etching efficiency.

[0026] In other words, in the present invention, when wet etching a solid surface with a specified etching solution, an etching solution holding material such as a cloth capable of holding the etching solution inside is used, and the etching solution holding material is impregnated with the etching solution and held in that state and brought into contact with the solid surface to be etched, and ultrasonic waves are applied to the etching solution holding material and the etching solution in that state, thereby performing an etching process on the solid surface.

[0027] 2 and 3 show examples of the configuration when performing the etching treatment according to the present invention. As shown in Fig. 2, the etching according to the present invention can be performed by placing an etching solution holding material 5 capable of holding an etching solution inside in contact with the surface to be etched, impregnating the etching solution holding material 5 with the etching solution 2, and applying ultrasonic waves generated by an ultrasonic generating means 7 to the etching solution holding material 5 and the etching solution 2 via a transducer 6 having appropriate acoustic characteristics. When performing the etching treatment in the form shown in Fig. 2, it is also preferable to provide a wall 9 or the like to prevent leakage of the etching solution.

[0028] The etching method according to the present invention can also be carried out by placing the object 1 to be etched in an etching tank 8 holding an etching solution 2 so that the surface to be etched is in contact with an etching solution holding material 5, and applying ultrasonic waves to the etching tank 8 by an ultrasonic wave generating means 7 or the like, as shown in Fig. 3. In this case, as shown in Fig. 3(a), the surface to be etched may be placed on the upper surface of the etching solution holding material 5, so that the etching solution holding material 5 and the surface to be etched are brought into contact with each other by the weight of the object 1 to be etched, or as shown in Fig. 3(b), the etching solution holding material 5 may be placed on the upper surface of the surface to be etched, and a weighted body 11 may be further used to bring the etching solution holding material 5 and the surface to be etched into contact with each other.

[0029] The etching solution holding material 5 can be any material that has a structure capable of holding the etching solution by the action of the surface tension of the etching solution due to the presence of minute voids, such as woven fabrics, knitted fabrics, nonwoven fabrics, raised fabrics, paper-like materials, cotton-like materials (fiber masses), etc., made up of various fiber elements 4, as well as porous substances such as sponges made up of sea sponges or synthetic polymers, and the like, and can be used as the etching solution holding material 5 without any particular limitations.

[0030] As the fiber elements 4 constituting the etching solution holding material 5, there can be used cellulose fibers derived from plants such as cotton thread, regenerated cellulose fibers made from cellulose, fibers made of polylactic acid, natural fibers made of proteins such as wool and silk thread, and fibers made of synthetic polymers such as polyester and PET resin. When using an aqueous solution in which various reactive components are dissolved as the etching solution, it is preferable to use an etching solution holding material 5 made of a material such as cellulose fibers, regenerated cellulose fibers, or synthetic polymer fibers that exhibit high hydrophilicity by hydrating with water, in order to improve the retention of the etching solution.

[0031] The affinity of fibers and the like for water can be evaluated, for example, by the degree of weight change (moisture content) exhibited by various fibers due to moisture absorption in a room temperature atmosphere. In the present invention, when an etching solution retention material is described as being hydrophilic, this means that the material constituting the etching solution retention material has an official moisture content of 3% or more under standard conditions (20°C, humidity 65%), and in particular, by being composed of a material with a moisture content of 5% or more or 10% or more, the etching solution retention material can well retain a water-based etching solution.

[0032] From the standpoint of moisture content, for example, by using an etching solution holding material containing natural fibers such as wool (standard moisture content: approximately 16%), silk, linen (approximately 9%), and cotton (approximately 7%), or regenerated cellulose fibers such as rayon and cupra (approximately 13%), the aqueous etching solution in particular is held well in the voids within the etching solution holding material, and both the fiber elements constituting the etching solution holding material and the etching solution can be brought into contact with the surface to be etched.

[0033] In addition, in the case of the regenerated cellulose fibers such as rayon and cupra, the fiber diameter can be freely set during spinning, and it is possible to make fine fibers with a fiber diameter of about 10 μm or less, particularly 20 μm or less, and even 10 μm or less, and it is possible to form an etching solution holding material that exhibits high water retention by effectively acting on the surface tension of the etching solution. Furthermore, by making the fibers constituting the etching solution holding material fine, it is possible to reduce the average distance between adjacent fiber elements, and even when ultrasonic waves with a high frequency and limited amplitude are applied, it is possible to suppress unevenness that occurs when the fiber elements come into contact with the etching surface and sweep it.

[0034] In addition, the etching liquid holding material can be constructed from multiple types of materials, and can have a structure suited to its purpose, for example, a structure that combines a part that mainly comes into contact with the surface to be etched and contributes to the flow of the etching liquid near the surface to be etched, and a part that mainly contributes to holding the etching liquid.

[0035] On the other hand, since friction occurs between the etching solution holding material 5 and the object to be etched due to ultrasonic vibration during the etching process, it is desirable to use an etching solution holding material 5 made of a material whose hardness is sufficiently lower than that of the object to be etched in order to prevent the surface to be etched from being damaged, particularly when the etching method of the present invention is used as a pretreatment for metal structure observation.

[0036] For example, as shown in FIG. 3, when performing an etching process inside an etching tank 8 holding an etching solution 2, since there is no risk of the etching solution leaking from the etching solution holding material 5, it is possible to select the etching solution holding material 5 mainly from the viewpoints of ease of use and availability, and for example, it is possible to perform the etching process using absorbent cotton or nonwoven fabric made of regenerated cellulose fibers.

[0037] On the other hand, when etching is performed mainly using an etching solution impregnated in the etching solution holding material 5 in the form shown in FIG. 2, by using an etching solution holding material 5 that is made of a material that exhibits good hydrophilicity, such as fine regenerated cellulose fibers having a fiber diameter of about 10 μm or less, preferably 10 μm or less, and that exhibits high water retention, it is possible to perform etching on, for example, a surface to be etched that is not horizontal.

[0038] As described above, in the etching process according to the present invention, the boundary layer formed in the etching liquid is disturbed by stirring the vicinity of the surface to be etched using the fiber elements 4 and the like that make up the etching liquid holding material 5, thereby enabling efficient etching to be performed. It is preferable to use an etching liquid holding material 5 that is flexible overall and can easily come into uniform contact with the surface to be etched.

[0039] In the etching process according to the present invention, in order to bring the etching solution holding material 5 into good contact with the surface to be etched, it is desirable to place the two in a form in which they are pressed against each other. By appropriately setting the pressing force, it is possible to prevent the etching solution holding material from not contacting a part of the surface to be etched due to the tension of the etching solution holding material or the unevenness of the surface to be etched, and to perform a uniform etching process. On the other hand, if the pressing force is excessive, the part of the etching solution holding material that contacts the surface to be etched is prevented from being displaced between the etching solution holding material and the surface to be etched, and the boundary layer may not be sufficiently disturbed.

[0040] The pressure with which the etching solution holding material 5 is pressed against the surface to be etched is, for example, 0.1 to 10 g / cm when the surface to be etched is flat. 2 or 0.5~3g / cm 2 By adjusting the pressure within this range, it is possible to adjust the density at which the fiber elements 4 and the like constituting the etching solution holding material 5 contact the surface to be etched and the pressure at the contact point.

[0041] In order to press the etching solution holding material 5 against the surface to be etched, for example, when performing the etching process in the form shown in Fig. 2, an oscillator 6 having a predetermined mass can be used, or a force can be applied from the outside to the oscillator 6. Furthermore, when performing the etching process in the form shown in Fig. 3, the object 1 to be etched can be placed on the etching solution holding material 5, so that the weight of the object 1 to be etched brings the etching solution holding material 5 into contact with the surface to be etched, and further, weight can be applied to the back surface of the object 1 to be etched to bring the etching solution holding material 5 into strong contact.

[0042] The thickness of the etching solution holding material 5 when performing the etching treatment according to the present invention can be appropriately determined depending on the type of the etching treatment and the like. For example, as shown in Fig. 3, when etching a flat surface to be etched by immersing the etching solution holding material 5 in an etching solution, a cloth-like etching solution holding material having a thickness of about 0.1 to 5 mm or 0.5 to 2 mm can be used to bring the etching solution holding material into contact with the surface to be etched. When etching a curved or uneven surface to be etched, a sponge-like etching solution holding material that can absorb the unevenness and come into contact with the entire surface can be used, and an appropriate weight can be applied to the back surface of the object to be etched as necessary, thereby achieving a good etching process.

[0043] On the other hand, when performing an etching process using an etching solution held in an etching solution holding material 5 in contact with a surface to be etched in the form shown in Fig. 2, it is desirable to use an etching solution holding material 5 having a thickness sufficient to hold an amount of etching solution sufficient for the etching process. In addition, when performing an etching process in the form shown in Fig. 2, it is also effective to supply an etching solution to the etching solution holding material 5 from the outside as necessary.

[0044] In the etching process according to the present invention, the etching solution 2 and the fiber elements 4 constituting the etching solution holding material 5 are mixed in the space to which ultrasonic waves are applied, and the etching process is performed in a state where both are in contact with the surface to be etched at the same time. In this state, the propagation speed of ultrasonic waves in the fiber elements 4 and the etching solution 2 is different, so that the form of ultrasonic propagation becomes complex, and the generation of standing waves in the vicinity of the surface to be etched is suppressed. In particular, even when the power density of the applied ultrasonic waves is increased, erosion of the material to be etched due to localization of ultrasonic energy can be suppressed.

[0045] In particular, when etching a system that generates solid-phase reaction products by chemical reactions associated with etching is performed by the etching process according to the present invention, it has been observed that the reaction products are unlikely to adhere to the etched surface. For example, as described in Patent Documents 4 and 5, in particular in etching processes for iron-based materials, a phenomenon occurs in which solid-phase reaction products precipitate and adhere to the etched surface due to chemical reactions with the etching solution, which hinders uniform etching, and therefore it has been necessary to remove the solid-phase reaction products by mechanical polishing such as buffing during the etching process.

[0046] On the other hand, according to the etching method of the present invention, adhesion of reaction products to the surface to be etched is suppressed, so that the etching process can be completed without interruption, enabling efficient processing. As described above, the mechanism by which the etching method of the present invention suppresses adhesion of reaction products to the surface to be etched is not clear. However, it is believed that the stirring effect of the etching solution holding material 5 as described above suppresses changes in the composition of the etching solution near the surface to be etched, thereby preventing a local increase in the concentration of reaction products and suppressing the amount of precipitation.

[0047] Furthermore, after performing the etching process of the above system with the etching solution holding material 5 in contact, solid phase precipitates may be observed inside the etching solution holding material 5. This suggests the existence of a mechanism in which the precipitates are removed from the etched surface by mechanical action due to contact with the etching solution holding material 5 in the early stages of precipitation of the reaction products, or the presence of the etching solution holding material as a solid phase near the etched surface causes nucleation and precipitation of the reaction products on the surface of the etching solution holding material.

[0048] In the etching process according to the present invention, etching solutions generally used can be used depending on the material to be etched. For example, in the etching process of steel materials, an aqueous solution of ferric chloride, an ethanol solution of nitric acid, an aqueous solution of picric acid, an ethyl ether solution, etc. can be used. In addition, in the etching process of titanium alloys, a mixed acid aqueous solution of hydrofluoric acid and nitric acid can be used, for aluminum alloys, a mixed acid aqueous solution of hydrofluoric acid, hydrochloric acid, nitric acid, etc., an aqueous caustic soda solution can be used, and for copper alloys, an ethanol solution of hydrochloric acid or an aqueous solution of ammonium persulfate can be used. In addition, for materials to be etched other than metals, for example, for glass, etc., an aqueous hydrofluoric acid solution can be used for etching.

[0049] In the etching process according to the present invention, the ultrasonic application means for applying ultrasonic waves to the etching solution holding material impregnated with the etching solution can be any ultrasonic application means that can excite vibrations at a frequency of about 20 to 200 kHz with a predetermined output without any particular limitation.

[0050] For example, when performing an etching process by placing an etching solution holding material 5 impregnated with an etching solution in contact with a surface to be etched as shown in FIG. 2, ultrasonic waves can be applied to the etching solution holding material 5 and the etching solution held in the etching solution holding material 5 by exciting ultrasonic waves to a transducer 6 arranged on the back surface of the etching solution holding material 5 using an ultrasonic generating means sold under the name of, for example, an ultrasonic cutter.

[0051] Furthermore, when performing an etching process by immersing the surface to be etched in an etching solution as shown in FIG. 3, for example, an apparatus for applying ultrasonic waves to liquid, such as an ultrasonic cleaner, can be used to place the etching solution and an etching solution holding material inside a tank to which ultrasonic waves can be applied, and the object to be etched is placed so that the surface to be etched is in contact with the etching solution holding material, thereby applying ultrasonic waves to the etching solution and the etching solution holding material 5.

[0052] The etching process according to the present invention can be carried out by contacting an etching solution holding material for holding the etching solution with the surface to be etched, which is a conventional etching process in which a solid surface is wet-etched using an etching solution to which ultrasonic waves are applied, and by applying the present invention to various etching processes for solid surfaces of metals, inorganic materials, etc., it is possible to shorten the etching process time and to prevent the etching process from being interrupted by suppressing adhesion of reaction products, etc.

[0053] The etching treatment according to the present invention can be preferably applied to a system in which the concentrations of various components in the etching solution are kept low or etching treatment at a low temperature is required for the purpose of increasing the selectivity of the etching reaction on the surface to be etched, and etching takes a long time.

[0054] Furthermore, by applying the etching process according to the present invention to a system in which a solid-phase reaction product is generated by an etching reaction and adheres to the surface to be etched, such as an etching process for observing the structure of an iron-based material, the adhesion of the solid-phase reaction product to the surface to be etched is suppressed, making it possible to efficiently perform etching with high precision.

[0055] Furthermore, in addition to the wet etching treatment as a pretreatment for observing the crystal structure of the above-mentioned metal, the etching treatment according to the present invention can be applied to etching treatments aimed at smoothing or roughening the surface of metals, glass, etc., and can be preferably used in systems in which the etching reaction causes significant consumption of the etching solution, systems in which the acceptable range of the composition of the etching solution when causing the target etching reaction is narrow, and systems in which the etching reaction produces solid-phase reaction products that inhibit the desired etching treatment.

[0056] Hereinafter, the etching treatment according to the present invention will be described in more detail using as an example the appearance of prior austenite grain boundaries observed in a steel material that has been subjected to a quenching treatment by the etching treatment. However, the present invention should not be construed as being limited to these examples. EXAMPLES

[0057] The steel materials used as samples for the etching treatment according to the present invention and their heat treatment conditions are shown in Table 1. All of the steel materials used in the evaluation had a thermal history of a so-called quenching treatment, in which a martensite structure having high hardness etc. is introduced by a non-diffusion phase transformation by heating to a temperature range where an austenite structure is formed and then rapidly cooled, and the crystal structure has prior austenite grain boundaries, which are the crystal grain boundaries of the austenite structure.

[0058] [Table 1]

[0059] In steel materials that have been quenched, mechanical properties such as strength, toughness, and corrosion resistance change depending on the size of the crystal grains when the steel is austenitized, and therefore prior austenite grain boundaries are observed for the purpose of controlling the material quality, etc. On the other hand, as described in Patent Document 5, for example, an etching process for revealing prior austenite grain boundaries in various quenched steel materials is accompanied by various problems, and measures to avoid these problems have been proposed, making this an etching process with a high degree of difficulty.

[0060] The apparatus used to evaluate the etching process according to the present invention is shown in Fig. 4. The samples used were each steel material cut into a cube with a side of about 1 cm, embedded in epoxy resin with a diameter of φ30 mm and a height of about 25 mm so that one face of the cube was exposed, and used as the etched object (sample) 1. The exposed face of the steel material was mirror-polished using emery paper and buff polishing, and this face was used as the etched face for the following etching process.

[0061] The etching solution 2 is generally used for revealing prior austenite grain boundaries, and is prepared by dissolving 2 g of picric acid, 0.15 g of sodium chloride, 0.07 g of sodium sulfate, and 5 g of a surfactant in 100 g of water. Each sample was immersed in a glass beaker (capacity: 500 ml) as an etching tank 8 containing about 250 ml of the etching solution in a room temperature atmosphere for a predetermined period of time to perform an etching process.

[0062] In the etching process, when the etching solution holding material 5 was brought into contact with the surface to be etched, a nonwoven fabric (Bencotto (registered trademark)) made of regenerated cellulose fiber (Cupra) with an average line diameter of about 10 μm was laid on the bottom of the beaker as the etching solution holding material 5 (thickness in a dry state: about 1 mm), and the surface to be etched of the sample was placed on the etching solution holding material with the surface to be etched facing downward, and the surface to be etched and the etching solution holding material were brought into contact with each other by the weight of the sample. In addition, under conditions in which the etching solution holding material 5 was not used, the surface to be etched of the sample was immersed in the etching solution with the surface to be etched facing upward.

[0063] In the process of applying ultrasonic waves during etching, the etching tank 8 with the sample immersed therein was immediately placed in an ultrasonic cleaner 12 (Bransonic 1210J type: Emerson Japan, Ltd.) filled with tap water as a vibration transmitter 11, and ultrasonic waves were applied at room temperature for a predetermined time. In the process of not applying ultrasonic waves during etching, the etching tank 8 with the sample immersed therein was left stationary for a predetermined time to perform the etching process. After etching for a specified time, the samples were removed and washed with water. If necessary, inclusions adhering to the etched surface were washed off with absorbent cotton soaked in diluted neutral detergent and running water, and then the samples were dried with a blower and observed under an optical microscope.

[0064] 5A to 5D show optical microscope photographs of the etched surface of the S45C material after etching under various conditions. In Fig. 5A to 5D, the surface to be etched is indicated as "US" when ultrasonic waves were applied during the etching process, and "BF" when the surface to be etched was brought into contact with the etching solution holding material, and the immersion time in the etching solution is also indicated.

[0065] As shown in Figure 5A, in the sample where ultrasonic waves were applied while the etching surface was in contact with the etching solution holder, a contrast that is thought to be a prior austenite grain boundary that separates prior crystal grains of about several tens of μm was obtained after 5 minutes of etching treatment. In addition, no scratches that were thought to be caused by the etching solution holder that was in contact with the surface of the sample during etching were observed.

[0066] On the other hand, in the sample to which ultrasonic waves were applied without using an etching solution holder (Fig. 5B), contrast derived from crystalline structures such as prior austenite grain boundaries was not obtained after 5 minutes of etching. In addition, in the sample that was left in a state where the etched surface was in contact with the etching solution holder (Fig. 5C), contrast derived from crystalline structures was not obtained after 5 minutes of etching. Furthermore, in the sample that was treated by immersing in the etching solution for 30 minutes (Fig. 5D), contrast derived from crystalline structures was not obtained.

[0067] Furthermore, in the sample to which ultrasound was applied for 10 minutes while the etched surface was in contact with an etching solution holder (Fig. 5E), contrast was observed mainly within the crystal grains compared to the sample etched for 5 minutes (Fig. 5A). It was inferred that etching for about 5 minutes was sufficient to reveal the prior austenite grain boundaries.

[0068] From the above results, it was shown that by applying ultrasonic waves to the etching surface while the etching solution holding material impregnated with the etching solution is in contact with the etching surface, it is possible to reveal clear prior austenite grain boundaries in a short time. This result was presumably due to the fact that by applying ultrasonic waves while the etching solution holding material is in contact with the etching surface, the boundary layer of the etching solution generated near the surface of the etching surface is effectively stirred, the change in the composition of the etching solution near the surface of the etching surface is suppressed, and the chemical reaction between the etching surface and the etching solution continues to progress.

[0069] 6A to 6C show optical microscope photographs of the etched surface of the above-mentioned SCr415H material after etching under various conditions. The notations "US", "BF", immersion time in the etching solution, etc. in Fig. 6A to C are the same as those in Fig. 1.

[0070] As shown in Fig. 6A, by the etching process according to the present invention, in which ultrasonic waves are applied while an etching solution holding material is in contact with the etching surface, a contrast believed to be a prior austenite grain boundary dividing grain sizes of about several tens of µm was obtained even in the SCr415H material by a 5-minute etching process. On the other hand, in the sample to which ultrasonic waves were applied without using an etching solution holding material (Fig. 6B) and the sample that was left stationary while in contact with the etching solution holding material (Fig. 6C), contrast believed to be a prior austenite grain boundary was observed in some places, but it was observed that the clarity was not as good as that in Fig. 6A.

[0071] 7A and 7B show optical microscope photographs of the etched surface of the SCM435 material after the etching process according to the present invention. The notations "US", "BF", and immersion time in the etching solution in Fig. 7A and B are the same as those in Fig. 5. In particular, as shown in FIG. 7A, by subjecting SCM435 material to the etching process according to the present invention, it was observed that a contrast believed to be a prior austenite grain boundary appeared clearly even after a short etching time of about 2 minutes.

[0072] It is believed that the appearance of prior austenite grain boundaries, etc. by etching treatment is affected by the individual structure of the grain boundaries, and in particular, the ease of appearance of prior austenite grain boundaries changes depending on the alloy components present as precipitates at the grain boundaries, and the etching selectivity with respect to the grain interior changes, etc. From this, it was presumed that the degree of appearance of prior austenite grain boundaries, etc. changes depending on the alloy components contained in the steel material and the heat treatment history, etc., and that the degree of effect of the etching treatment according to the present invention changes depending on the steel material used as a sample.

[0073] On the other hand, as described above, the etching treatment according to the present invention makes it possible to reveal prior austenite grain boundaries even in materials in which the prior austenite grain boundaries are difficult to reveal, and it has been shown that the prior austenite grain boundaries and the like can be clearly revealed by a short-time etching treatment.

[0074] 8 shows a photograph of the etching solution holding material (nonwoven fabric) after a sample containing the S45C material was etched for 5 minutes using the etching solution by applying ultrasonic waves while the etching solution holding material was in contact with the etching surface. After etching of steel materials such as the S45C material by the etching process according to the present invention, it was observed that black stains, as shown in FIG. 8, were attached to the etching solution holding material (nonwoven fabric) immersed in an etching bath 8 at all points in contact with the etching surface of the sample.

[0075] As described in Non-Patent Document 5, etc., it is known that when steel materials are etched using an etching solution containing picric acid or the like, reaction products adhere to the sample surface, and therefore the products must be removed mechanically in a timely manner in order to achieve a uniform etching process. On the other hand, in the etching process according to the present invention, it was observed that the adhesion of reaction products to the sample surface after etching was significantly reduced.

[0076] From the above, it is presumed that the stains attached to the nonwoven fabric shown in Figure 8 are the result of products that precipitated on the sample surface during etching being mechanically removed by the nonwoven fabric used as an etching solution retention material, or that the products precipitated on the fiber elements that make up the nonwoven fabric.

[0077] For this reason, the etching process according to the present invention can suppress the adhesion of reaction products generated by the etching process to the surface to be etched, and can suppress the reaction products from acting as a mask and causing the etching process to become non-uniform, thereby enabling a high-quality etching process. Furthermore, even in an etching process that generates a large amount of reaction products, the adhesion of the reaction products to the surface to be etched can be suppressed, enabling a continuous etching process and making the process more efficient. [Industrial Applicability]

[0078] According to the present invention, efficient etching treatment of solid surfaces becomes possible, and by applying the present invention to quality control, surface treatment, etc. of various metal structures for which etching treatment has traditionally been used, it is possible to improve the efficiency and quality of these treatments. [Explanation of symbols]

[0079] 1. Object to be etched 2. Etching solution 3 cloth 4. Fiber elements 5 Etching solution holding material 6 Transducers 7 Ultrasonic generating means 8 Etching tank 9. Etching solution leakage prevention wall 10 Weighted body 11 Vibration transmitter (water) 12 Ultrasonic cleaner 20 Vibrations

Claims

1. 1. An etching method for performing wet etching using an etching solution on a solid surface as an etching target surface to reveal a crystal structure of the etching target surface, comprising the steps of: An etching method comprising applying ultrasonic waves to an etching solution holding material impregnated with an etching solution while the etching solution holding material is in contact with the surface to be etched.

2. 2. The etching method according to claim 1, wherein the etching solution holding material is impregnated with the etching solution by being immersed in the etching solution held inside an etching tank.

3. 3. The etching method according to claim 1, wherein the etching solution holding material contains a material having an official moisture content of 3% or more.

4. 4. The etching method according to claim 1, wherein the solid is a steel material, and the etching method is aimed at revealing the crystal structure of the steel material.

5. An etching processing apparatus that performs wet etching using an etching solution on a solid surface as an etching target surface to reveal a crystal structure of the etching target surface, An etching solution holding material capable of holding an etching solution therein; an ultrasonic wave applying means capable of applying ultrasonic waves to the etching solution holding material; 1. An etching treatment apparatus, characterized in that ultrasonic waves can be applied to an etching solution holding material impregnated with an etching solution while the etching solution holding material is in contact with a surface to be etched.

6. An etching tank for holding the etching solution, 6. The etching processing apparatus according to claim 5, wherein the etching solution holding member is disposed inside the etching tank.

7. 7. The etching processing apparatus according to claim 5, wherein the etching solution holding material contains a material having an official moisture content of 3% or more.

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