Microstructural Evolution and Ultrafine-Grain Formation During Flow Forming of Thick-Walled Cu-Ni Alloy Tubes

Area of Science:

• Materials Science
• Metallurgy
• Manufacturing Engineering

Background:

• Flow forming is a key technique for manufacturing thick-walled tubes, especially those with gradient microstructures.
• Understanding microstructure evolution and ultrafine-grain formation mechanisms is crucial for optimizing this process.

Purpose of the Study:

• To investigate the microstructure evolution during the flow forming of BFe10-1-1 thick-walled tubes.
• To elucidate the mechanisms responsible for ultrafine-grain formation under flow forming conditions.

Main Methods:

• Flow forming experiments were conducted on BFe10-1-1 thick-walled tubes.
• Finite element (FE) simulations and electron backscatter diffraction (EBSD) were used for characterization.
• A coupled finite element analysis-cellular automaton (FEA-CA) model incorporating local plastic strain gradients was developed.

Main Results:

• Microstructural transformation follows a continuous dynamic recrystallization pathway with high-angle boundary development.
• A significant through-thickness gradient in grain size was observed, with the outer layer showing accelerated refinement.
• An ultrafine-grained structure (approx. 0.39 μm) formed on the outer surface due to high strain and strain-gradient effects.

Conclusions:

• The mechanism of ultrafine-grain formation is pass-dependent, with distinct stages of substructure establishment, grain refinement, and saturation.
• Flow forming effectively produces gradient microstructures in thick-walled Cu-Ni alloy tubes.
• The developed FEA-CA model accurately captures microstructure evolution during flow forming.