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Mechanisms of Simultaneously Improving the Strength and Ductility of an In-Situ Tib 2/Al-Zn-Mg-Cu Composite by Elliptical Cross-Section Torsion Extrusion

This work conducts an integrated experimental and simulation research on the multiple mechanisms of performance improvement of a metal matrix composite via a new severe plastic deformation method, i.e., elliptical cross-section torsion extrusion (E-TE). Results evidence that the E-TE efficiently homogenizes the particle distribution and refines the composite’s microstructure, thus yields a simultaneous improvement of the strength and ductility. The microstructure refinement is dominated by mechanical deformation and processing temperature and mainly attributed to the joint effect of three mechanisms: (1) fragmenting of large grains and smashing of particle bands/clusters due to extensive shear deformation of the E-TE; (2) higher driving force and more nucleation sites provided by fine precipitation and reinforced particles for dynamic recrystallization (DRX) through accelerating dislocation generation and pinning dislocation movement, as well as additional DRX by coarse particles via particle stimulated nucleation; (3) the impeding of grain growth by dispersed particles. Moreover, increasing processing temperature results in the successive coarsening and dissolution of precipitations; the precipitation dissolution deteriorates the grain refinement and weakens the strength of the particle/matrix interface. Full-field crystal plasticity simulations reveal that the strength improvement of the E-TE processed composite is mainly attributed to grain boundary strengthening, while reinforced particles sustain high stress and strengthen the matrix as well, and these contributions increase with the decrease of the matrix’s grain size. The grain refinement and particle homogenization also improve the fracture toughness and ductility of the composite by retarding the generation of damages and impeding the crack propagation.