Question

define a grain of metal with a schematical explain how grains help to develop a micro structure​

Answer 1

Explanation:

Grain Structure and Topology

Much can be learned about grain structure through optical examination. Sometimes grains are large enough to be seen with the unaided eye; zinc grains on galvanized steel sheet are an example. But usually grain sizes are very small, necessitating viewing with the aid of a microscope. Preparing specimens for optical metallographic observation first requires preparation of a flat, mirrorlike surface through a series of grinding and polishing steps, with care taken to eliminate all scratches. Bulk metals, ceramics, semiconductors, and polymers are opaque and therefore cannot be viewed in transmitted light the way thin biological specimens can. Rather, they must be illuminated from above in a metallurgical microscope as shown in Fig. 3-31. Optical magnifications of ∼1500x are possible. Revealing the grain structure, however, requires that the grain boundaries be delineated by etching with a suitable chemical solution that preferentially attacks them; light impinging at grain boundaries is then scattered, making them appear dark. Beautiful collections of microstructures have been published and reproducing a few of them cannot pretend to be representative. Nevertheless, a number of material structures obtained by optical microscopy are reproduced in Fig. 3-32, immediately revealing their artistic attributes.