May 2025 Volume 7

MATERIALS

ADVANCED MATERIALS & FORGING Working with Titanium and Superalloys By FIA Staff

Forging of Superalloys Superalloys are high-performance metals recognized for their superior mechanical strength, resistance to thermal creep, and oxidation resistance under extreme temperatures. These characteristics make them indispensable in applications such as jet engines, power plants, and chemical processing. However, the forging process for superalloys is complex due to their intricate compositions and high resistance to deformation. Characteristics of Superalloys Superalloys stand apart from standard stainless steels and carbon steels due to their extensive alloying and complex composition. Their composition includes multiple elements that contribute to solid solution and precipitation strengthening. While these mechanisms enhance their high-temperature durability, they also reduce plasticity, making forging more challenging. As forging occurs at high temperatures, solid solution and precipitation strengthening continue, further diminishing plasticity. Thus, precise temperature regulation and specialized techniques are required to prevent material defects and achieve proper shaping. For precipitation-strengthened superalloys, forging should be executed above the precipitation phase solution temperature to improve plasticity and workability. Forging Techniques for Superalloys • Preheating: Gradual heating is necessary to prevent thermal shock and cracking. A controlled heating rate ensures uniform temperature distribution.

• Controlled Forging Temperature: Proper temperature maintenance is crucial. Low temperatures can cause cracking, while excessively high temperatures can lead to grain growth and reduced mechanical properties. • Multiple Forging Steps: Due to limited plasticity, superalloys typically require multiple forging stages, interspersed with annealing treatments to restore ductility and relieve internal stresses. • High-Pressure Forging: Superalloys necessitate high compressive forces due to their strength and deformation resistance. High-tonnage presses and specialized dies help achieve the desired shape. • Post-Forging Heat Treatment: Heat treatments such as solution annealing and aging are applied post-forging to optimize mechanical properties and restore lost strength. Forging of Titanium Alloys Titanium alloys are widely used in industries requiring high strength-to-weight ratios, corrosion resistance, and biocompatibility. Titanium forging follows similar principles to superalloy forging but poses unique challenges due to the metal's reactivity and temperature sensitivity. Industries such as aerospace, marine shipbuilding, and military/ defense depend on titanium forging for high-performance applications. The high strength to-density ratio and corrosion resistance of titanium make it an optimal choice for various demanding environments. Forged titanium components offer precision and customization, ensuring their efficacy in specialized applications.

FIERF Research: Microstructure Evolution in INCOLOY® 945 During Hot Deformation Hot deformation processing of superalloys is one of the first steps in controlling the microstructure. Specifically, the grain size is directly impacted by hot deformation temperatures, strain rates, hold times, and cooling rates. Furthermore, carbide precipitation upon subsequent processing steps can be influenced by the hot deformation conditions. In this project, the effects of hot deformation at 1150 °C in compression and torsion on microstructural evolution were assessed on INCOLOY® 945, which is used for downhole oil and gas service applications. The hot compression and hot torsion specimens exhibited similar deformation behavior when their effective stress versus effective strain behavior was compared. Moderate differences are attributed to the non-uniform strain and strain rate through the diameter of the torsion specimen during deformation. The grain size during hold times after hot deformation increased linearly with the square root of hold time and was larger for lower deformation strain rates. Carbide precipitation did not occur after the hot deformation processing, likely because the deformation temperature was sufficiently high to put all of the carbon into solution. Significant carbide precipitate did occur after the lower temperature aging treatments. There was no difference in the carbide morphology between the hot compression and torsion conditions. Source: https://www.forging.org/content/technical-library/Non_Ferrous/Microstructure_Evolution_in_INCOLOY__945_During_Hot_Deformation.aspx

FIA MAGAZINE | MAY 2025 44