Enhanced thermal stability of nanocrystalline Cu composites processed by high-pressure torsion: The pinning effect of Al₂O₃, GO, and rGO/Al₂O₃ nanoparticles
Piotr Bazarnik, Maria Emerla, Yi Huang, Anita Wojciechowska, Marta Ciemiorek, Wiktor Bednarczyk, Agnieszka Jastrzębska, M. Lewandowska, Terence G. Langdon
Abstract
Metal matrix composites with improved mechanical properties and thermal stability were produced using mechanical milling, spark plasma sintering (SPS) and high-pressure torsion (HPT). Three types of reinforcing particles were used, i.e., GO, Al 2 O 3 and rGO/Al 2 O 3 . All of the produced composites exhibit higher hardness and tensile strength than pure coper, reaching values of 250 Hv for Cu-GO, 240 Hv for Cu- Al 2 O 3 , 210 Hv for Cu- rGO/Al 2 O 3 and 185 Hv for Cu after HPT. STEM analyses reveal that the HPT significantly refines the grain size of pure copper to ~210 nm, and even more in the Cu-based composites achieving grain sizes as small as ~55-75 nm. Pure Cu after HPT recrystalizes after annealing at 573 K. The Cu- Al₂O₃ composite demonstrated the best thermal stability with a hardness after annealing at 773 K of 220 Hv and a grain size of ~100 nm. The composite of Cu-GO after annealing at 773 K showed slight grain growth up to ~150 nm. The composite Cu-GO/Al 2 O 3 exhibits improved microhardness and tensile strength up to 673 K and annealing of this composite at 773 K which led to a bimodal microstructure. All of the composites annealed at 773 K showed hardness above 180 Hv.