0.8418nm and c=0,4538nm.In contrast,Jewett et alt 4)disproved the above rcsult,Their published Nb-Ti-Al phase diagram at 1200C indicated that the alloy with nominal composition of NbTiAls was located within the dual-phase ficld y+n.In order to resolve the apparent conflict between the previous studies,the phase structure and morphology of the sample having NbTiAls com- position,annealed,water quenched from 1200,900,600C and splat quenched respectively,were investigated.The results from X-ray diffraction were some- time ambiquous indeed,the diffraction pattern may be indexed by two phases e+n.Optical and electronic microscopy revealed the existence of a needle-like morphology.However,EDX analysis clearly showed that the compositions of the matrix and the needle-like area were essentially the same,the needle-like mor- phology may be caused by twinning or a diffusionless transformation in solid state at intermedium temperature range (Fig.3).Importantly,indexing the electron di- ffraction patterns from the matrix undoubtly proved to be presence of NbTiAls ternary compound.Fig.4 shows a series of EDP obtained by tilting the thin foil sample from 20 to -35.Using the lattice pararmeter of a=0.8383nm and c=0.4673nm of tetragonal lattice unit,the reciprocal lattice spacing and iheir mutual angles were calculated.It was found that all the patterns could be indexed by the calculated spacings and angles within very small deviation.The Fig.3 Back scallered clectron micrograph of the alloy having stoichiomctric composition of NbTiAl3, microanalysis confirmed the composition range of the phase as 15-20 at%Nb, 20-25at%Ti and 56-62at%Al roughly.Based on the analysis by electron diffra- ction the X-ray diffraction peaks can also be indexed by same crystallogra- phic parameters as the above within a reasonable measuring error,except one or two weak peaks of n phase,which may be caused by a minor segregation.Our work on the electron channel enhaneing analysis [s)show- ed that the addition of Nb occupied the site of Ti sublattice in TiAl.The 160仑 ， 〔 盛 ’ 。 〔 一 一 ℃ 一 。 夕 ， ， ， ， ， ， ℃ 注 ， 一 ， 。 叩 一 ， 一 、 ， 一 。 ， 一 。 ， 谬 豹公滁群燃撇 粥 长、 甘韶 屯 洲扮 徽撰簇瀚燕 拼 林 葬 推拼林奎 龚父 卜 人 伙挤 一 丁 一 丫 启 囊攀 粼级 漱 拜象黔 “ ， ， 一 ， 一 一 写 一 ， 叩 ， 。 孟 ” 〕 。 万