METALLOGRAPHY 11, 61-79 (1978) 61 Contrast Phenomena and The Identification of Grain Boundary Ledges L. E. MURR AND ESWARAHALLI VENKATESH Department of Metallurgical and Materials Engineering. New Mexico Institute of Mining and Technology, Socorro. New Mexico 87801 (U.S.A. EDITOR'S NOTE Most metallographers will quickly agree that electron microscopy ts of prime impor- tance to each of us that practice within the field of metallography. This invited paper on the subject of contrast imagery, in electron microscopy comes from the laboratories of Dr. Larry E. Murr, one of America's best electran metallographers. Murr is internationally known for his continuing contributions on structure-property studies that utilize the electron microscope. This invited paper will give the readers of METALLOGRAPHY an interesting insight concerning the typical researches of a ve~ good electron microscopist. This article is part of a series that serve to profile leading world scientists and their metallographic interests via the mechanism t~f invited papers. The bright-field image contrast associated with grain boundary ledges in nickel and type 304 stainless steel as observed in the transmission electron microscope has been studied in the context of existing knowledge of contrast phenomena used in the interpretation of ledge contrast. It is concluded that simple contrast features in the bright-field image such as the fact that ledges appear as parallel black, white, or black-white lines having generally no oscillatory contrast profiles and the fact that large ledges produce observable boundary fringe serra, tions or disturbances (culminating in fringe steps for larger ledges) can be used effectively;, collectively, to identify ledges for quantitative studies of ledge properties. Thermo-mechanical studies were conducted to systematically vary the density of ledges in grain boundaries of nickel and quantitative measurements of ledge density utilizing the contrast criteria outlined indicated an increase in grain boundary ledge density to be correlated with a corresponding increase in the hardness at or near the grain boundary. The prominent contrast features characteristic of grain boundary ledges are discussed as they relate primarily to the bright-field image. Introduction Dislocations unique to the interface separating two crystal grains (a grain boundary) were first recognized by Gleiter and Baro [1, 2], and © Elsevier North-Holland, Inc., 19711