MICROSTRUCTURE OF DUPLEX LAMELLAR PHASES IN AN FE-37.3WT-PERCENT NI-3.58WT-PERCENT TI-0.2WT-PERCENT-C

A mode of grain boundary precipitation in Fe-37.3wt.%Ni-3.58wt.%Al-3.3 wt.%Ti-0.2wt.%C alloy aged at 823K has been investigated by transmissi on electron microscopy. Fine gamma' particles of Ll(2)-type ordering f irstly precipitated within the gamma matrix during ageing treatment at 823K. The aged matrix phases (gamma and gamma') were later encroached on by the grain boundary lamellar phases. Quite uniquely, these duple x fine lamellae are composed of alternately aligned ferrite and gamma' platelets. These two phase constituents in the lamellae are separated by the interface arallel to both {110}(alpha) and {111}(gamma') plane s.