Experiment_01-Crystal_Structure_X_-_Ray_Diffraction -...

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ME 3701, Materials of Engineering, LSU 1 Experiment: Crystal Structure Analysis in Engineering Materials Safety Caution: Check the X-ray caution sign in the lab. Observe how the instructor performs the experiment. Avoid contact with X-ray. Objective The purpose of this experiment is to introduce students to the use of X-ray diffraction techniques for investigating various types of crystal structure encountered in metallic materials. Abstract The X-Ray diffraction technique is used to determine the crystal structure and interatomic spacing of crystalline samples through constructive interference of reflected x-ray beams. Bragg's Law and X-Ray diffraction data, in combination with the expressions for interatomic spacing in terms of the lattice parameter and Miller indices for a crystal, can be utilized to identify crystal structures, determine lattice constants, and locate defects within a structure. X-Ray diffraction data has been collected for a FCC aluminum sample and a BCC steel sample; the data will be analyzed to determine the lattice parameter and preferred orientations for these materials. Background Metallic and ceramic materials utilized in mechanical engineering applications have crystalline microstructures; many material properties are related to the atomic arrangement on various planes within the structures. Three basic crystal structures encountered in metallic materials are the Body-Centered Cubic (BCC), Face-Centered Cubic (FCC) and Hexagonal Close-Packed (HCP) as illustrated in Figure 1. (a) (b) (c) Figure 1 - Atomic arrangement in common metallic crystal structures: a.) Face-Centered Cubic (FCC), b.) Body-Centered Cubic (BCC), c.) Hexagonal Close-Packed (HCP). [Shackelford, 1996] Engineering metals are commonly composed of substitutional solid solutions. Steels, which often contain carbon interstitially, are alloyed with Manganese, Chromium, Nickel, Molybdenum, etc. substitutionally to enhance performance in both its FCC and BCC structural phases; BCC ferrite is quite important. Aluminum, Titanium, and Copper alloys such as brass, generally contain substitutional atoms in their FCC structures. Titanium alloys have HCP and/or BCC structures. X-ray diffraction techniques can be utilized to identify the structure of various materials; this investigation will focus on the use of X-ray diffraction methods applied to basic metallic materials with BCC, FCC and/or HCP structures. The atoms are arranged on the densest packed planes on the {1 1 1} family of planes in FCC structures. There are four sets of non-parallel planar stacks in each FCC crystal or grain, and on each plane there are three non- parallel close packed <1 1 0> directions (two example planes are shown in Figure 2). Slip, which is the main phenomenon in plastic deformation, generally occurs on the most densely packed planes along the most densely packed directions. Since slip can occur along any one slip plane along any one direction on it, there are altogether 12 possible slip directions that can occur in FCC crystals. As a result, there are 12 slip systems in FCC materials
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This note was uploaded on 03/08/2011 for the course ME 3701 taught by Professor Moldovan during the Spring '11 term at LSU.

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Experiment_01-Crystal_Structure_X_-_Ray_Diffraction -...

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