High Strength Al–Ti–Fe Alloys Consisting of Amorphous and fcc-Al Phases Prepared by Rapid Solidification

Coexistent of amorphous and fcc-Al phases were formed in rapidly solidified Al98−xTixFe2 (x=3, 5 and 8 at%) alloys. The structure consists of equiaxed Al grains embedded in the network of an amorphous phase. The grain size of the Al phase is 20 to 30 nm and the interparticle spacing is about 7 nm for the Al93Ti5Fe2 alloy. The volume fraction of the Al phase is evaluated to be 70 to 80%. The mixed structure is presumably formed through the solidification process of liquid→primary fcc-Al+remaining liquid→Al+amorphous phases. The further increase in Ti content to 10 at% causes the formation of an amorphous single phase. The crystallization temperature (Tx) of the amorphous phase increases from 641 to 701 K with increasing Ti content from 3 to 10%. It is to be noticed that the Tx values are much higher than that (\fallingdotseq573 K) for Al–TM–Ln (TM=transition metal, Ln=lanthanide metal) amorphous alloys because of the low diffusivity of Ti. The mixed phase alloys have good bending ductility and exhibit the highest tensile strength (σf) of 1200 MPa for Al93Ti5Fe2. The ductility decreases with further increasing Ti content because of the transition from ductile to brittle nature for the amorphous phase and no high tensile strength exceeding 500 MPa is obtained for the amorphous single phase alloy. The formation of the finely mixed amorphous and Al phases with high σf and Tx values is important for the future development of Al-rich Al–Ti based alloys with high specific strength.