Atomic force microscopy of slip lines in FeAl
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Atomic force microscopy of slip lines in FeAl J. H. Schneibel Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6115
L. Martinez Instituto de Fisica, Laboratorio de Cuernavaca, UNAM, P.O. Box 139-B, C.P. 62210, Cuernavaca, Morelos, Mexico (Received 12 December 1994; accepted 15 May 1995)
Fe-40 at. % Al-0.1 at. % B specimens were polished flat, strained at room temperature, and examined in an atomic force microscope. The angles of height contours perpendicular to the slip lines were interpreted as shear strains and were statistically evaluated. The frequency distributions of these shear strains correlated well with the macroscopic strains. The maximum shear strains found were not much larger than the macroscopic strains. In particular, no steep slip steps corresponding to large local shears were found.
The slip lines formed on the surfaces of deformed crystalline solids are often employed to assess the prevalent slip systems.1 Any further characterization of slip is usually performed qualitatively by optical microscopy. Typically, slip is classified into categories such as fine, coarse, planar, wavy, diffuse, or uniform. The plaucity of quantitative descriptions of slip character suggests that its accurate description is difficult. On the other hand, the character of slip is often thought to have a bearing on fracture behavior. For example, coarse and planar slip may lead to particularly high stress concentrations if blocked by grain boundaries. This suggests that our understanding of fracture might benefit from more quantitative studies of slip. Another issue of interest is the measurement of the plastic strain of a material by quantifying its slip line appearance. One might in this way be able to assess the history of a material without the use of strain gages or other measuring devices. This would be particularly useful in the case of thin films, the deformation behavior of which might be unduly influenced by strain probes. In recent year, atomic force microscopy (AFM) has gained increasing importance as a tool for the precise geometric assessment of surfaces. For example, Fries et al.2 have examined the topography and roughness of stressed surfaces by studying areas on the order of 100 X 100 fira. Harvey et al.3 quantitatively characterized the surfaces of fatigued titanium and a high strength-low alloy (HSLA) steel. The present work considers monotonic deformation, and the slip lines formed during room temperature deformation of a B2 iron aluminide will be quantitatively assessed. J. Mater. Res., Vol. 10, No. 9, Sep 1995 http://journals.cambridge.org
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An iron aluminide alloy with the nominal composition Fe-40 at. % Al-0.1 at. % B was arc-cast in argon from elemental constituents with typical purities of 99.9%. The casting, which had a diameter and a length of 25 and 120 mm, respectively, was extruded in a mild steel can at 1173 K with an area reduction of 9 : 1 . Tensile specimens with a gage section of approximately 1 X 3 X 13 mm
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