How to improve the performance of aviation forgings by controlling temperature and pressure

How to improve the performance of aviation forgings by controlling temperature and pressure

Aviation forgings are key components of the "bones" of aircraft, and they bear the core mission of transmitting loads and withstanding extreme temperatures and stresses. In the harsh service environment of high temperature, high pressure and high stress, these key components have put forward almost stringent requirements on the uniformity of the internal structure, defect-free and performance consistency of the material. Precision forging technology, with its ability to accurately control temperature and pressure parameters, is becoming the core process approach to shaping the excellent performance of aviation forgings.

Precision temperature control: the "baton" of material evolution during forging

Temperature is the core variable that affects the plastic deformation behavior and microstructural evolution of metals. Precision forging technology lays the foundation for material performance optimization through strict temperature control:

Precise deformation temperature window: For different materials (such as titanium alloys, high-temperature alloys, ultra-high strength steels, and aluminum alloys), precision forging sets a specific temperature range. For example, titanium alloys are often forged near or below the β phase transformation point to accurately control the proportion and morphology of the primary α phase, which is crucial to the final strength and fracture toughness. Deviation from the optimal temperature window may lead to insufficient plasticity, cracking or coarsening of the structure.

Mold preheating and constant temperature control: The mold temperature directly affects the surface quality and deformation uniformity of the forging. Precision forging uses precise mold preheating (often up to hundreds of degrees Celsius) and online constant temperature systems (such as induction heating and hot oil circulation) to avoid cracks on the surface of the forging due to contact with the cold mold, and reduce the temperature gradient during deformation to ensure uniformity of the organization.

Gradient heating and cooling strategy: For forgings with complex shapes or large sizes, implement zone heating or gradient cooling strategies. For example, in turbine disk forging, different heating or cooling rates may be used for the rim and hub to coordinate deformation and optimize the grain size and precipitation phase distribution in different areas.

Final forging temperature management: Strictly control the temperature at the end of forging, which affects the degree of dynamic recrystallization, grain size and subsequent heat treatment response. Precision forging optimizes the deformation rate and process step design to ensure that the final forging temperature falls within the target range, creating conditions for obtaining an ideal organization.

Precision pressure control: a "carving knife" for shaping ideal organization and defect-free morphology

Precise control of pressure (strain rate, stress state) directly determines the flow behavior, densification degree and microstructure characteristics of the metal:

Strain rate control: Precision forging equipment (such as servo press, isothermal forging hydraulic press) can accurately control the loading speed and holding time. Lower strain rates (such as isothermal forging) give the material sufficient diffusion and recrystallization time, which is particularly suitable for difficult-to-deform materials (such as nickel-based high-temperature alloys), and can significantly refine the grains, improve organizational uniformity and reduce deformation resistance. High strain rates may be used in specific forming stages.

Multi-directional stress state optimization: Through mold design and multi-directional pressure technology (such as multi-directional die forging), a more favorable stress state is created inside the forging. This can not only effectively close the original tiny pores inside the material (healing looseness), significantly improve density and fatigue performance; it can also promote metal flow in difficult-to-deform areas, achieve precision forming of complex structures (such as aircraft landing gear cylinders with inner cavities), and reduce subsequent machining.

Isostatic near-net-shape forming: Combined with can design and hot isostatic pressing (HIP) technology, the final densification of near-net-shape forgings is achieved under high temperature and high pressure inert gas environment. This can almost completely eliminate internal micro-defects and maximize the material performance potential, and is often used in key rotating parts of engines.

Guarantee of uniform pressure distribution: Precision mold design and finite element simulation optimization ensure that the pressure is evenly distributed in the key areas of the forging during deformation, avoiding local overload leading to folding and cracking, or underload leading to insufficient filling and coarse structure.

Synergistic symphony of temperature control and pressure control: achieving a qualitative leap in performance

The control of temperature and pressure is by no means isolated. The core of precision forging lies in the coordinated optimization of the two:

Thermomechanical coupling effect: Applying precise pressure (strain rate) at a specific temperature can activate specific deformation mechanisms (such as dynamic recrystallization and superplastic flow). For example, precise temperature and pressure controlled forging in the α+β two-phase region of titanium alloy can refine the lamellar α structure or obtain a dual-state structure, greatly improving the comprehensive mechanical properties.

Defect control and microstructure refinement: The optimized temperature field (uniform heating) combined with precise strain rate control and multi-directional pressure can suppress the initiation of voids and cracks to the greatest extent, promote dynamic recrystallization, and obtain ultrafine grained microstructure. For example, the grain size of the high-pressure compressor disc of an aircraft engine can reach ASTM grade 10 or above through precision isothermal forging, significantly improving the high-cycle fatigue strength.

Performance customization: According to the functional requirements of different parts of the forging, the "performance gradient" design is achieved through local temperature and pressure control strategies (such as die zone cooling and local loading). For example, aircraft joint forgings can obtain finer grains and higher strength in high-stress areas, while ensuring good toughness in the connection area.