Fig.5 TEM morphology and electron diffraction pattern showing the cxistcnc: of yi+y dual phasc region results from the systematic investigation by clectron diffraclion and microana- lysis of thin foil sample indicated that with increasing Nb content the phase having Llo structure and gradually transformed to an phass (denoted as the y phase,,having higher degree of order in terms of selective distribution of Nb atom in a specific location,(101)superlattice spot,which should not appear ◆ in Llo structure can be clearly seea in Fig.5,a micro-diffraction pattern.As a further development of ordering the unit cell of the structure is refitted as y1.The TEM study has proved the existence of the y+y dual phase range. However no evidence has been obtained from X-ray or electron diffraction pattern to indicate the presence of a y+y two phase region.This may su- ggest that the ordering from to be thermodynamic secondary transformation. An estimated parlial phase constitution map was established as shown in Fig.6. The results from rapidly solidified samples further confirmed the existence of NbTiAls phase.Since splat-quenching significantly reduces segregation,TEM clearly shows that,from the foil thinned from the area near surface of the 162…嚷 介热鱿 全江 气 比 二 十 ， 赴 一 幽洲 工 矛 。 ， 一 沮 ， ， 一 夕 了 川 。 夕 一 夕悦 夕， 以 一 ， ， 以 ‘