Design and Analysis of Materials and Engineering Structures by Andreas Öchsner Lucas F. M. Silva & Holm Altenbach

Author:Andreas Öchsner, Lucas F. M. Silva & Holm Altenbach
Language: eng
Format: epub
Publisher: Springer Berlin Heidelberg, Berlin, Heidelberg

Fig. 5Experimental EBSD pattern obtained from the lamellar phase indexed as Al4Sr (tetragonal crystal structure), Mean angle of deviation (MAD) = 0.59°, orientation = (151.4, 93.8, 11.5°), spec. plane (-5-10)

3.2 Procedures for Detection of Intermetallic Phases and Grain Boundaries

The selection of the best reagent to reveal the microstructural constituents is an important factor during the development of complex procedures for the quantitative description of the microstructure.

Images of the microstructures after etching in different reagents were registered using the Olympus GX-70 light microscope equipped with a DP70 colour digital camera employing various acquisition techniques. Figure 6 shows examples of microstructures of MRI230D alloy etched with different reagents. The condition for proper detection is a homogeneous grey level from the objects to be measured, which is different from the background level which is not elevated. An initial description of all images obtained during these investigations suggested that this condition could be fulfilled by structural images obtained for unetched samples (Fig. 1). Usage of reagent containing 5–20 ml acetic acid, 80–95 ml H2O (Fig. 6b) also allows the correct detection of intermetallic phases, however, the distinction of the compounds is more difficult than in unetched samples.

Fig. 6Examples of revealed microstructures after etching with different reagents: 25 ml H2O, 75 ml ethylene glycol, 1 ml HNO3 in bright field, low quality for detection of phases (a); 5–20 ml acetic acid, 80–95 ml H2O in bright field, good quality for detection phases (b); 4.2 g picric acid, 10 ml acetic acid, 10 ml H2O, 70 ml ethanol in bright field, very low quality for detection of phases (c); 4.2 g picric acid, 10 ml acetic acid, 10 ml H2O, 70 ml ethanol in polarized field with quarter-wave plate, good quality for detection of grain boundaries (d)

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