2 1 A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 2 2 However, the spacing of 150 μm was still not close enough to produce a continuous line. Figure 2 shows a continuous line of recrystallized grains created by indentations at a spacing of ~75 μm at the 1 kgf load. Unlike the 150 μm spacing, the 75 μm spacing shows grain overlap. These grains, however, were deemed to be too clustered. For this reason, the optimal indentation spacing was determined to be between 80 and 100 μm. To test if this process could produce clean designs, the word “hi,” a square, and a smiley face were created using the optimal load of 1 kgf and optimal spacing of between 80 and 100 μm. Figure 3 shows the desired recrystallized grain continuity and density. The etchants as described in the procedure above were used, and some of the images showing the etchant colors are included in this article. All images were taken with polarized light using the Olympus DSX500 LOM with polarized light/differential interface contrast. Samples were polished to 1 μm finish before being etched. According to the ASM Handbook, the three Klemm’s reagents can be etched for a variety of times. Figures 4 and 5 show the images acquired after applying the selected etchants to the brass samples at half the maximum time for each reagent (90 seconds for Klemm’s I, and four minutes for Klemm’s II), then cleaned with soap and a cotton ball. As seen in Fig. 4, Klemm’s I did not produce the desired vibrant colors. Klemm’s I was thereby eliminated due to the lack of colors produced Fig. 2 — Recrystallization of 75 μm spacing at 1 kgf load. Fig. 3 — Annealed samples showing successful results with 1 kgf and 80-100 µm spacings after completed process: (a) “Hi,” (b) square, and (c) smiley face. 400 μm 150 μm 150 μm 150 μm so no further hardening work was required to provide activation energy for recrystallization. With the canvas prepared, the researchers set out to create localized areas of deformation. They programmed a LECO AMH55 microhardness indenter to enable coordinates to be imported from an AutoCAD converted image and a pattern of localized deformation to be created. Several iterations were required to determine the optimal load and spacing for the pattern. Figure 1 shows some results of iterating through indentation loads to produce sufficient cold work to initiate recrystallization. As seen in Fig. 1, not every indentation produced significant recrystal- lization after annealing. Both the 200 and 300 gf loads resulted in insufficient recrystallization after annealing. Figure 1c shows indentations made with equal spacing of ~150 μm with a 500 gf load. While all indentations at 500 gf produced recrystallized grains, the grains that were produced did not overlap, so the optimal spacing was not achieved when a spacing of 150 μm was used. The recrystallization for 500 gf could also be considered slightly less than optimal because the grain clusters are slightly smaller than desired. Fig- ure 1d shows indentations at a spacing of ~150 μm with a 1 kgf load. At the 1 kgf load, the recrystallized grains were observed to be an optimal size, indicating the best force to use in later designs. tassium metabisulfite)[4,5]. The optimal etch was determined to be eight minutes in Klemm’s II. Images were obtained with an Olympus DSX500 LOM with polarized light/differential interface contrast. RESULTS AND DISCUSSION The goal of this project was to create an artistic design using microstructural transformations with no photographic digital manipulation, with results that would be pleasing to the viewer and to leave them wondering, “How did they do that?” The team’s choice of C26000 cartridge brass was based on a large supply of the material, over 10 years of recrystallization and grain growth data generated by lab classes at the Colorado School of Mines, and the beauty in the microstructure of recrystallized brass. The authors obtained their “canvas” by growing very large grains on the order of 800 µm using an annealing treatment of 850°C for 45 minutes. The as-received material was fully hard cold-worked brass sheet, (a) (c) (b)
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