The role of carbide additions in the mechanical properties and microstructure of NbTiAl alloys

The mechanical behaviour of Nb₃₅Ti₆Al₅Cr₈V containing different C contents (0, 1, 10 at.%) has been investigated. The deformation microstructures of samples subjected to conventional constant strain rate compression and compressive creep tests have been examined using transmission electron microscopy (TEM). At room temperature all three alloys deform primarily by slip, with some mechanical twinning. Deformation at higher temperatures occurs by a combination of dislocation glide and climb processes, giving more homogeneous microstructures. Most of the dislocations in the matrix of these alloys have Burgers vector b=1/2<111> although some short segments with b=<100> were also observed where two dislocations with b=1/2<111> interact during high temperature deformation. Deformation of carbide at high temperatures occurs primarily by {111}<110> slip. The presence of extensive carbides resulted in a substantial increase in yield strength at room and high temperatures and improved creep resistance but substantially impaired ductility and toughness.