High Strain Rate Deformation Behavior and Recrystallization of Alloy 718

Abstract

Abstract To study the deformation behavior and recrystallization of alloy 718 in annealed and aged state, compression tests were performed using Split-Hopkinson pressure bar (SHPB) at high strain rates (1000 to 4000 s −1 ), for temperatures between 20 $$^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow/><mml:mo>∘</mml:mo></mml:msup></mml:math> C and 1100 $$^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow/><mml:mo>∘</mml:mo></mml:msup></mml:math> C (293 K to 1373 K). Optical microscope (OM) and electron back-scatter diffraction (EBSD) technique were employed to characterize the microstructural evolution of the alloy. The stress–strain curves show that the flow stress level decreases with increasing temperature and decreasing strain rate. In addition, up to 1000 $$^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow/><mml:mo>∘</mml:mo></mml:msup></mml:math> C, the aged material presents higher strength and is more resistant to deformation than the annealed one, with a yield strength around 400 MPa higher. For both states, dynamic and meta-dynamic recrystallization occurred when the material is deformed at 1000 $$^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow/><mml:mo>∘</mml:mo></mml:msup></mml:math> C and 1100 $$^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow/><mml:mo>∘</mml:mo></mml:msup></mml:math> C, leading to a refinement of the microstructure. As necklace structures were identified, discontinuous recrystallization is considered to be the main recrystallization mechanism. The recrystallization kinetics is faster for higher temperatures, as the fraction of recrystallized grains is higher and the average recrystallized grain size is larger after deformation at 1100 $$^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow/><mml:mo>∘</mml:mo></mml:msup></mml:math> C than after deformation at 1000 $$^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow/><mml:mo>∘</mml:mo></mml:msup></mml:math> C.