“…However, many recent studies have reported the formation of occasional aluminium carbide (Al 4 C 3 ) nanoparticles, especially at the defect sites of nanotubes and along the residual amorphous carbon layers on the surface during multipasses FSP (Izadi & Gerlich, ; Liu et al ., , , ; Lim et al ., ). The same phase transformations were also observed during hot‐pressing of carbon nanotubes in the Al‐matrix at temperatures higher than 793 K (Liu et al ., ). Also, failure of CNTs during other SPD techniques such as MA, ARB and ECAP at room temperature under the repetitive high shear strains have been reported (Salimi et al ., ; Zare et al ., ; Pérez‐Bustamante et al ., ), because CNTs are more fragile when combined axial and radial loading is applied (Shen & Zhang, ).…”