2 2 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 consistently staying in solution during etching and storage. Due to the undesirable etch effect, and the fact that optimal colors were already achieved with Klemm’s II, the Klemm’s III testing was discontinued. From all the etchant testing, it was determined that Klemm’s II applied for eight minutes and rinsed with water after polishing with colloidal silica returned the clearest and most colorful micrographs. DESIGN DETAILS After a design was sketched in AutoCAD, the divide function was used to split lines into segments featuring endpoints with 80 to 100 μm spacing. After all entities were cleared, leaving just the segment endpoints, designs were exported as CSV files. The files were then input into the AMH55 automatic hardness testing system, which indented the samples at desired locations. Samples were then recrystallized, polished to a 0.05 μm finish, and etched using Klemm’s II reagent for eight minutes. Images were then taken using the Olympus DSX500 LOM with polarized light/differential interface contrast. Figure 8 is an example of one of the final images created. CONCLUSION Optimized processing conditions to engineer images into the microstructure of C26000 cartridge brass were determined. During annealing, a large grain matrix canvas was created in the microstructure of the brass. The AMH55 were polished to a 0.05 μm finish using a colloidal silica solution on a vibratory polisher for 21 hours. After etching, the samples were only rinsed with water to avoid further scratching from cotton ball cleaning. Figure 7 shows a micrograph etched with Klemm’s II for eight minutes after polishing to a 0.05 μm finish. Figure 7 shows significantly re- duced scratching after etching. After testing, it was decided that Klemm’s III was not optimal as there was a lack of reproducibility during etching. This may be due to Klemm’s III reagent not as well as the lack of contrast between grain boundaries. A common problem among all of the etchants tested was a high density of scratches visible even after the 1 μm polish. To remedy the scratches, samples were polished to a 0.3 μm finish using an alumina solution. Figure 5 exhibits promise for producing the desired result. Figure 6 shows a micrograph etched with Klemm’s II for the fully recommended time of eight minutes after polishing to a 0.3 μm finish. Figure 6 shows that scratches were still visible after the 0.3 μmpolishing. To further remedy the scratches, samples Fig. 7 — Klemm’s II applied for eight minutes after polishing to a 0.05 μm finish. Fig. 8 — Columbine flower with shaded petals, imaged with polarized light. 1 mm 400 μm Fig. 4 — Klemm’s I applied for 90 seconds and imaged with polarized light. Fig. 5 — Klemm’s II applied for four minutes and imaged with polarized light. Fig. 6 — Klemm’s II applied for eight minutes after polishing to a 0.3 μm finish. 400 μm TABLE 2 — ALLOY PROPERTY COMPARISON Process Density, g/cc Hardness, HRC YS 0.2%, ksi UTS, ksi Elongation, % MPIF Standard 35 7.5 38-42 158 172 6 MIM 7.60 41 163.0 179.6 14 Printalloy 7.60 38.5 160.7 180.6 10.3
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