August 2025 Volume 7

MATERIALS

The specific heat treat parameters for an Alpha + Beta (Ti 6-4) and Alpha (Ti 6-2-4-2) are shown below: • Ti-6Al-4V: Is either annealed at 691-760°C (1275-1400°F) or solution treated at 955-970°C (1750-1778°F) and quenched in agitated water, followed by aging at 900 to 1150 °F (482 to 621 °C) and air cooled. • Ti-6Al-2Sn-4Zr-2Mo: Is solution treated at 955-980°C (1751-1796°F) and quenched in agitated water, followed by aging at 595°C (1103°F) and cooled in air.

Figure 10: Inclusion Types Monitored by JETQC [15] Forging is one of the most popular methods for forming titanium components and the forging temperature has a critical impact on the microstructure and properties of the forged component. To determine the forging and post-forge thermal cycles, it is important to understand the beta transus temperature. This is the temperature at which titanium undergoes a phase transformation from its low-temperature alpha phase to its high-temperature beta phase. The beta transus temperature varies depending on the specific titanium alloy composition (calculated for each individual heat) but typically ranges between 1700°F and 1850°F (927°C to 1010°C). The forging of titanium alloys is typically divided into two temperature bands by alloy type: • Alpha + Beta Forging (Ti in + β phase): This process occurs below the beta transus temperature, typically between 1500°F and 1750°F (816°C to 954°C). • Beta Forging (Ti in β phase): This process takes place above the beta transus temperature, usually between 1750°F and 2200°F (954°C to 1204°C). Following forging the final properties of titanium alloy forgings are set by the heat treat process. As stated previously, the heat temperatures are determined based on heating below (mill annealing) or above (solution annealing) the Beta transus. The effectiveness of the solution heat treat also depends on the cooling rate from the set temperature. The microstructure can vary widely from a fast (water quench) to a slow (furnace cool) as shown in Figure 10.

Following heat treatment, the forgings are typically surface inspected by both visual (VT) and fluorescent penetrant (PT); and, volumetrically inspected by ultrasonic methods (UT). Conclusions The general design guidelines for selecting a titanium forging are: • Pick titanium alloys when high strength/low weight is required • Consider fabrication requirements – forming/welding/post form or weld heat treat • Avoid halogen containing cleaning solutions (no vapor de-grease), especially for components that have high residual stresses from forming and/or welding • Avoid fluorescent penetrant solutions that contain substantial amounts of chlorine and/or fluorine – should control these elements to low levels • Consider wear/galling/fretting potential for titanium components and specify appropriate coatings where needed Summary • Titanium has been commercially produced since the late 40s/ early 50s • Commercial titanium production is low compared to SST and Aluminum alloys • Major applications outside of aerospace include maritime, medical implants, oil and gas, and chemical.

• Currently aerospace applications account for the largest portion of titanium metal consumption • Current titanium production is limited by the production of titanium sponge • Increasing production of titanium is difficult due to high costs and long return on investments of processing equipment

Figure 11: Microstructure vs. Cooling Medium for Ti Alloys [12]

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