Improvement of mechanical properties and fracture toughness of low SFE Cu-Al alloy through microstructural modification by multiaxial cryoforging

摘要

Aim of the present study is to investigate mechanical properties and fracture toughness of low SFE ultrafine grained (UFG) Cu-4.5 wt%~1 Al alloy processed through multiaxial cryoforging followed by short-annealing. The homogenized annealed samples (800 °C, 4 h) were cryoforged for 5, 9 and 11 cycles. The 11-cycles cryoforged sample showed more than 10 times improvement in the yield strength (YS) (818 MPa) as compared to that of the homogenized annealed sample (76 MPa). However, the ductility decreased to 10.1% elonagtion due to suppression of dynamic recovery and recrystallization during cryoforging. Cryoforging followed by short-annealing (225-300 °C for 20 min) was found to enhance the ductility without affecting its YS. Fracture toughness study has been carried out through analysis of apparent fracture toughness (K_Q) using linear elastic fracture mechanics, equivalent energy fracture toughness (K_(ee)) and J-integral values using elastic plastic fracture mechanics from 3-point bend test data. The improvement of the YS with significant ductility as well as fracture toughness is ascribed to the formation of ultrafine grains & rhombic blocks (due to the intersection of nanotwins close to 90°), mutual crossing & misorientation of microshear bands and multisystem deformation twins. The low SFE of the alloy is found to play the pivotal role to develop such microstructural features.