Identifying the character of intrinsic stacking faults in the A15 compoundNb3Al

The character of intrinsic stacking faults on {001} in the A15 intermetalli c compound Nb3Al has been investigated using energy-dispersive X-ray spectr oscopy in a field-emission-gun transmission electron microscope. Line scans were obtained across edge-on faults with an electron beam of approximate d iameter 0.5 nm and it was found that the Al concentration is enhanced at th e fault. Taken in conjunction with crystallographic data obtained previousl y, this implies that a {004} layer composed of Nb atoms only is removed to form these intrinsic stacking faults in Nb3Al. The configuration of these f aults implies that they may form by Nb vacancy coalescence and could act as embryonic nuclei for the precipitation of the D8(b) compound Nb2Al.