ABSTRACT:

Using plastic films and making replicas of microstructures, the scope and usefulness of conventional metallography has been extended to field studies Areas of interest, eg pipelines, boiler tubes, ships and offshore structures which are either inaccessible or difficult to be accessible to the microscope have been thus brought under its scope Replication, however, does not always produce the same high quality micrographs as one obtains with conventional metallography. With this in view, a number of specimens with different microstructures were prepared and observed by both replication and normal metallography It was found that replication is generally well suited for metals having well defined grain boundaries and distinct matrix contrast. For metals where the matrix has a flat contrast (eg fine martensitic matrix), replication leads to somewhat ineffective micrographs Another limitation of replication is that it is not directly suited for submerged structure To overcome this problem a small fixture was designed and fabricated in the laboratory whereby the submerged structures could be readily replicated Laboratory trials showed that the fixture can successfully be used to etch and replicate underwater structures by creating a water-free environment.

INTRODUCTION

Metallography is the study of the structure of materials by examination of specially prepared and etched surfaces. The first stage in metallography is the production of a true and undistorted structure on the surface of the specimen to be examined This usually involves mechanical or electrolytic polishing, followed by-etching. The specimens are then examined under optical microscope for a magnified image of their structure. In recent years the scope and usefulness of conventional metallography has been extended by using plastic film and making replicas of microstructure Replicas may now be made very easily, the techniques for these having been developed primarily for electron microscopy.

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