JPH0381638A - Method for obtaining replica of metallic structure - Google Patents

Abstract

PURPOSE:To allow the sampling and microscopic inspection of a change in metallic structure and metal defect even in the corner positions where materials form perpendicularity or curvature by applying a prescribed mixture consisting of cellulose acetate and the balance an org. solvent on the surface of a specimen corroded by an etching soln. after grinding. CONSTITUTION:The surface of the section where the specimens intersect with each other at the curvature is buffed, cleaned and dried and thereafter, the surface is corroded by the liquid mixture composed of 3 to 7wt.% cellulose acetate clay and the balance acetone. The voids 2 by the creep damages of the specimens, the precipitation of carbides 3, and extremely slight flaws are then distinctly produced and even the section which is heretofore impossible to be microscopically inspected is easily microscopically inspectable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a metallographic replica collection method that allows relatively easy and non-destructive detection of aging deterioration (metal defects) in a specimen.

(Prior art) An inspection hole is drilled in the center of the rotating body of a large electric motor such as a steam turbine or a generator to inspect the material, and this inspection hole can be used to perform, for example, magnetic particle inspection. Non-destructive tests such as ultrasonic flaw detection and penetrant testing are used depending on the situation and are performed along with visual inspection.

For example, in the center hole of a steam turbine rotor, during long-term use at high temperatures, carbides become coarse and voids occur due to creep damage, which causes material deterioration.

For this reason, advanced quality control has recently been required, and for large rotating bodies, in addition to the above-mentioned inspection methods, every corner of the rotating body is inspected for metal structures or metal defects, and the materials are used for long periods of time. A method is used to accurately grasp the tendency of subsequent deterioration over time.

One of them is to collect a part of the specimen using an electron microscope.
There is a method of predicting aging of the material by observing changes in the metal structure or metal defects from the test piece.

However, this method does not allow for examining the metallographic structure and metal defects using scrap materials; however, it is possible to collect the material used in the actual machine and use it as a test piece to examine changes in the accurate metallographic structure and metal defects. Although this is the most preferable in this respect, it is not preferable in that it causes a decrease in the strength of the actual machine and may even lead to damage to the actual machine.

(Problem to be solved by the invention) Recently, the replica method has been developed as a method to easily examine changes in metal structure and metal defects using the actual material without taking it as a test piece. It is used in the field of seeds.

In this method, after polishing and etching the surface of the specimen, an organic solvent is applied, an acetyl cellulose film is applied to the surface of the specimen, and the metal structure and metal defects are transferred to the coated film. It is removed from the subject and examined under an electron microscope.

Although this method allows for easy sampling and microscopic examination of changes in metal structure and metal defects, it is not always possible to sample and microscopically examine the complex shape of the specimen.

That is, it is not suitable for corner areas where two materials form a right angle or a curvature corner. Even if an organic solvent is applied to this area, the transfer film may not adhere to the surface to be inspected, wrinkles may occur in the film itself, or bubbles may form in the film in some cases, so that a desirable film cannot be formed.

Therefore, the present invention provides a metal mould, which makes it possible to easily and preferably sample and examine changes in metal structure and metal defects even in corner areas where two materials form a right angle or a curvature corner.
ix replica collection method.

[Structure of the invention]

(Means for Solving the Problems) In accordance with the above object, in the present invention, after polishing, 3.0 to 7.0% by weight of acetic acid cotton is applied to the surface of the specimen corroded with a corrosive solution or the like.
This is a metallographic replica collection method in which a mixed flux consisting of a residual organic solvent is applied to the specimen to form a transfer film.

(Function) With the above configuration, a transfer film can be easily formed even in a corner region where the objects to be examined intersect with each other at a right angle or with a curvature, or in a region with a complicated shape.

Further, the acetic acid cotton content is 3.0 to 7.0% by weight, but if it is less than 3.0% by weight, the thickness of the transfer film will be insufficient and deformation will occur when the film is peeled off.

If the amount of cotton acetate is 7.0% by weight or more, the organic solvent of the blending agent tends to evaporate and a large amount of cotton acetate is applied, causing bubbles and making it impossible to obtain a transfer film of uniform thickness.

Furthermore, the optimum range of the blending agent that satisfies the above conditions is 3.
The amount is 0 to 7.0% by weight, and if it exceeds this range, an optimal transfer film cannot be obtained.

(Example) Next, as an example of the present invention, a mixed agent consisting of 5.0% by weight of acetic acid cotton and 95.0% by weight of an organic solvent was applied to a part where the specimens intersect with a curvature (3R). Let's talk about.

The blending agent is acetic acid cotton (cellulose acetate) clay (L-3
0) 5.0% by weight and organic solvent acetone 95.0% by weight
It is a mixed melt consisting of. Even in areas where the object to be examined intersects with such a mixture with a curvature, the mixture can form a film up to the corners, enhancing the transfer effect.

The following steps are taken to transfer a metal structure or metal defect from a portion where the specimen intersects with curvature using the transfer agent having the above configuration.

First, the surface of the area where the specimen intersects with curvature is polished with a puff, washed, dried, and then corroded with a corrosive solution such as Nital (a mixture of nitric acid and alcohol).

In this way, voids due to creep damage to the test object,
Carbide precipitation and minute scratches clearly appear.

Next, spray the mixture for 3 to 5 seconds on the curved area of the subject or
~ 30~40% when applied 5 times. The transfer film is about 2-3
Formed in minutes. When the formed transfer film is peeled off and examined under an electron microscope, the metal structure and metal defects are revealed as shown in the drawing. Based on these results, the degree of aging deterioration can be predicted.
Estimate its lifespan.

By the way, although this invention has been explained by using a transfer agent having the above composition to transfer the metal structure and metal defects, the present invention is not limited to this embodiment.
) It is also possible to form a film using a high-grade polymer (7) (L-40, 50°70).

〔Effect of the invention〕

As explained above, this invention uses acetic acid cotton 3.0 as a transfer agent.
~7.0% by weight, the remainder being an organic solvent, and using this transfer agent, it can be applied to the corners of the subject - a much simpler product, and by adopting this invention, it can be applied to areas that could not be examined with a microscope until now. It is also possible to easily examine changes in the metal structure using a microscope, and the transfer rate is also high, making the transferred image clearer.

[Brief explanation of drawings]

The drawing shows an electronic microscope photograph of a metal structure replica transferred to a specimen having a corner portion with a radius of curvature of 31II11 using a mixed solution of 5.0% by weight of acetic acid cotton and 95.0% by weight of acetone. 1...Grain boundary 2...Void 3...Carbide

Claims (2)

[Claims] (1) A metallographic replica collection method characterized by applying a mixed agent consisting of 3.0 to 7.0% by weight of acetic acid cotton and the balance organic solvent to the surface of the specimen whose surface has been corroded after polishing. . (2) The method for collecting a metallographic replica according to claim 1, wherein the mixed flux contains a liquefied gas.