Cornell Business and Technology Park, Ithaca, NY 14850 USA Tel: 1-(607)-257-3378
Fax: 1-(607)-257-3201, email: salesinfo@multiwire.com, web: www.multiwire.com
Orienting Nickel Alloy Casting Single Crystals with the MWL110 System Using the Bi-crystal Comparison Tool
The new “Misorientation” routine in the Multiwire NorthStar 5.0 software has been successfully used to quickly calculate the composite misorientation angle about three orthogonal axes of two cubic crystalline grains over a misorientation angular range of 0 to 20 degrees. Typically the routine requires a 5 second data collection time for each x-ray image and a manual clicking on each of the diffraction points (we have an automated version we are now testing in our laboratory).
Step 1 - Mount a single crystal casting sample with a 125 mm film-to-specimen distance. Enter a Collect time of 5 seconds into the Parameters box for integrating a Laue pattern into the computer memory for that duration. For 12 kV operation of a Tungsten x-ray tube, only Miller indices up through 3 are needed in the parameters box. Load indexing file "turbine3.idx" which contains a short table of angles between the following 7 types of planes {100, 110, 111, 210, 211, 311, 331}. These are the only planes that show up at low voltage required to control the strong x-ray fluorescence from the nickel part of the alloy. This makes indexing very simple and reliable.
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Step 2 - Click on menu item "Misorientation" to begin using the bi-crystal routine. A text dialog box appears where you can enter text (letters and numbers) to help keep track of job and sample numbers.
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Step 3 - Either collect a new real-time pattern or call up a prior histogram file from disk. This provides the input for the first of the two comparison images. (Image should be obtained from one side of the boundary line between two different orientations.) Enter two spots that are far apart, then enter the remaining spots in the image. The routine will then index the image as shown.
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| Step 4 - select the input for the image on the other side of boundary and index the pattern. |
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Step 5 - Display the results to screen, printer, or both. Here is the report for the example above: |
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| Two single crystals have zero misorientation if they can be stacked one on top of the other in perfect alignment in their rows of atoms that make up the crystal. If the two crystals are misaligned, then the “Misorientation” routine accurately measures the three angles of misorientation of the two cubic crystals along 3 orthogonal axes of x, y, and z. The nearby (100) planes of the two crystals are compared by breaking down the angular differences along the three axes as Δx, Δy, and Δz. Then the composite misorientation can be written as: misorientation(in degrees)=sqrt(Δx**2 + Δy**2 + Δz**2) (eq. 1) In most cases, the composite misorientation angle needs to be less than some number, say of order of 14 degrees, to be an acceptable part. It takes less than a minute to whiz through a real data collection on both sides of a boundary and determine the misorientation! |
Cornell Business and Technology Park, Ithaca, NY 14850 USA Tel: 1-(607)-257-3378
Fax: 1-(607)-257-3201, email: salesinfo@multiwire.com, web: www.multiwire.com