654877bd_erials_Science_and_Engineering__Significance
[Date] 1890 [Candidate Moment] Adolf Martens examines the microstructure of a hard steel alloy and finds that, unlike many inferior steels that show little coherent patterning, this steel had many varieties of patterns, especially banded regions of differently oriented microcrystals. [Significance] 
Initiates the use of microscopy to identify the crystal structures in metals and correlate these observations to the physical properties of the material.
Greatest Moments in Materials Science and Engineering
Significance