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 | A P R I L 2 0 2 1 2 1 testing on samples in the longitudinal direction was performed according to ASTM E8[7], and optical microscopy was performed using a Keyence digital Fig. 6 — Deviation from the nominal planned dimensions on the T-profile. Note that the near net extruded profile exhibits consistent dimensions with minimal variation along the full length of the extrusion, much less than the permissible limits per AMS 2245. Fig. 7 — Deviation from the nominal planned dimensions on NNS-3. Note that the near net extruded profile exhibits consistent dimensions with minimal variation along the full length of the extrusion, much less than the permissible limits per AMS 2245. TABLE 1 — AVERAGE TOLERANCES ON KEY CHARACTERISTICS OF NEAR NET EXTRUSIONS Product type Location Flatness, in. Max. bow, in. Max. twist, deg. T-profile North 0.013 0.055 0.3 South 0.008 NNS-3 North 0.000 0.010 0.7 South 0.000 microscope. As observed in Table 2, mechanical testing results are in full compliance with the strength requirements of AMS 4935 for both geometric profiles. In addition, optical micrographs present a microstructure resulting from beta processed Ti-64, with colony alpha along the recrystallized beta grain boundaries (Fig. 8). Average grain size, measured according to ASTM E112[8], was found to be 100 µm. Longitudinal and transverse surface roughness was also measured using a standard profilometer that resulted in a range of 80-130 Ra for both profiles. Buy-To-Fly. Each preform process such as forging, casting, and plate stock incurs a considerable loss of material during machining due to the excessive material envelope built around the finished product. Extrusions considerably reduce the buy-to-fly ratio and provide advantages not offered by alternative preform processes. With the development of near net shape extrusions, the buy-to-fly ratio is further reduced, thus decreasing the costs associated with machining. It must be stated that the original standard extrusion for a T-profile was already an improvement over its previous preform (plate). Table 3 presents further reduction in the buy-to-fly ratio. Fig. 8 — Optical micrographs from the near net shape extrusions: T-profile (top) and NNS-3 (bottom) indicate colony alpha along the recrystallized beta grains. Samples were etched with Kroll’s reagent after polishing.
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