Tertiary creep and creep fracture in mechanically alloyed Al-C-O alloys

The tertiary creep and creep fracture of a set of four mechanically alloyed aluminium alloys with different contents of oxygen and carbon were studied at 623 and 723 K. At low applied stress, the strain to fracture is low, the time to fracture is power-law dependent upon the applied stress, and the specimens fail by intergranular fracture. At high applied stress, the development of a pronounced tertiary stage is observed, the elongation to fracture is increased, the time to fracture is exponentially dependent upon the applied stress, and the fracture appearance is transgranular. The transition stress decreases with increasing temperature and volume fraction of the secondary phases. Analysis of the tertiary creep in the high-stress region leads to the conclusion that the necessary condition for fracture is given by the achievement of a critical fraction of damaged area. (C) 1998 Chapman & Hall.