안녕 하세요.. 저는 모 대학 재료공학과 2학년에 재학중인 학생입니다... 2학년에 올라가면서 영어 번역 리포트가 나왔는데... 제 잔지식으로는 조금 힘드네요... 책 제목은 INTRODUCTION TO PHYSICAL METALLURGY 입니다.. 여기서 번역하는건데요. Etching The purpose of etching is to make visible the many structural characteristics of the metal or alloy. The process must be such that the various parts of the microstructure may be clearly differentiated. This is accomplished by use of an appropriate reagent which subjects the polished surfase to chemical action. In alloys composed of two or more phases, the components are revealed during etching by a preferential attack of one more of these constituents by the reagent, because of difference in chemical composition of the phases. In uniform single-phase alloys or pure metals, contrast is obtained and grain boundaries are made visible because of differences in the rate at which various grains are attacked by the reagent. This diffrence in the rate of attack is mainly associated with the angle of the different grain sections to the plane of the polished surface. Because of chemical attack by the etching reagent, the grain boundaries will appear as valleys in the polished surface. Light from the microscope, making the grain boundaries appear as dark lines. This is illustrated schematically in Fig.1'11c. The selection of the appropriate etching reagent is determined by the metal or alloy and the specific structure desired for viewing. table 1'3 lists some of the commonetching reagents.
Introduction A nondestructive test is an examination of an object in any manner which will not impair the future usefulness of the object. Although in most cases nondestructive tests do not povide a direct measurement of mechanical properies, they are very valuable in locating material defects that could impair the performance of a machine member when placed in service. Such a test is used to detect faulty material before it is formed or machined into component parts, to detect faulty componenes before as-sembly, to measure the thickness of metal or other materials, to determine level of liquid or solid contents in opaque containers, to identify and sort materials, and to discover defects that may have developed during process-ing or use. Parts may also be examined in service, permitting their re-maval before failure occurs. Nondestructive tests are used to make products more reliable, safe, and economical. Increased reliability improves the public image of the manu-facturer, which leads to greater sales and profits. In addition, manufac-tures use these tests to improve and control manufacturing processes. Before World Wal II, nondestructive testing was not urgent because of the large safety factors that were engineered into almost every product. Service failures did take place, but the role of material imperfactions in such failures was not then fully recognized, and, therefore, little concen-trated effort was made to find them. During, and just after, World Wal II the significance of imperfections to the useful life of a product assumed greater importance. In aircraft design, in nuclear technology, and in space exploration, high hazards and costs have made maximum reliability es-sental. At the same time, there has been extensive growth of all inspection methods in indurstrial and scientific applications. There are five basic elements in any nondestructive test. 1 Source A source which povides some proving medium, namely, a medium that can be used to inspect the item under test. 2 Modification This probing medium must change or be modified as a resulr of the variations or discontinuities within the object being tested. 3 Detection A detector capable of determining the changes in the prob-ing medium 4 Indication A means of indicating or recording the signals from the detector 5 Interpretation A method of interpreting these indications. While there are a large number of proven nondestructive tests in use, this section will concentrate on the most common methods and on one re-cent development. The most common methods of nondestructive testing or inspection are: Radiography Magnetic-particle inspection Fluorescent-penetrant inspection Ultrasonic inspection Eddy current inspection
MOUNTING Specimens that are small or awkwardly shaped should be mounted to facilitate intermediate and final polishing. Wires, small rods, sheet metal specimens, thin sections, etc., must be appropriately mounted in a suitable material or rigidly clamped in a mechanical mount. Synthetic plastic materials applied in a special mounting press will yield mounts of a uniform convenient size (usually 1 in., 1.25 in., or 1.5 in. in diameter) for handling in subsequent polishing operations. These mounts, when properly made, are very resistant to attack by the etching reagents ordinarily used. The most common thermosetting resin for mounting is Bakelite, Fig. 1'9a. Bakelite molding powders are available in a variety of colors, which simplifies the identification of mounted specimens. The specimen and the correct amount of Bakelite powder, or a Bakelite preform, are placed in the cylinder of the mounting press. The temperature is gradu-ally raised to 150, and a molding pressure of about 4,000 psi is applied simultaneously. Since Bakelite is set and cured when this temperature is reached, the specimen mount may be ejected from the molding die while it is still hot. Lucite is the most common thermoplastic resin for mounting. Lucite is completely transparent when properly molded, as shown in fig. 1'9b. This transparency is useful when it is necessary to observe the exact section that is being polished or when it is desirable for any other reason to see the entire specimen in the mount. Unlike the thermosetting plastics, the ther-moplastic resins do not undergo curing at the molding temperature; rather they set on cooling. The specimen and a proper amount of Lucite powder are placed in the mounting press and are subjected to the same temperature and pressure as for Bakelite (150 and 4,000 psi). After this temperature has been reached, the heating coil is removed, and cooling fins are placed around the cylinder to cool the mount to below 75 in about 7 min while the molding pressure is maintained. Then the mount may be ejected from the mold. Ejecting the mount while still hot or allowing it to cool slowly in the molding cylinder to ordinary temperature before ejection will cause the mount to be opaque. Small specimens may be conveniently mounted for metallographic preparation in a laboratory-made clanping device as shown in Fig.1'9c. Thin sheet specimens, when mounted in such a clamping device, are usually alternated with metal "filler" sheets which have approximately the same hardness as the specimens. The use of filler sheets will preserve surface irregularities of the specimen and will prevent, to some extent, the edges of the specimen from becoming rounded during polishing.