D0I:10.13374/i.issn1001-053x.1992.02.008 北京科技大学学报 第14卷第2期 Vo1,14No,2 1992年3月 Journal of University of Science and Technology Beijing March 1992 Evaluation of the Potential of the Ternary Aluminides in Nb-Ti-Al system for Hiyh Temperature Application 元 Chne Guoliang(陈国良)·Sun Zuqing(孙祖庆)·Xie Xishan(谢锡善)· Yao Kefu(姚可夫)·Ren Yunrong(任允蓉)·Yang Wangyue(杨王)" ABSTRACT:Being aimed to developing intermetallic base structural materials to be worked at above 1000C,a systematic investigation has been performed of the fundamental crystallographic structure,phase constitution map,density- composition dependence,oxidation resistance and general mechanical behaviour for the ternary intermetallic alloys in the Nb-Ti-Al system.Promissing resu- Its have been obtained at the initial stage in the current program.The 1100C high temperature strength at the strain rate of 10-2/s and 10-/s for the lernary compound Nb'TiAls (y)base alloys are generally much higher than that of the binary compound TiAl (y),especially in the yi+a2 phase region, it is as high as twice as that of TiAl.The densities are 4.1-4.79g/cm3, depending on relative amount of the intermetallics involved and the density difference between the intermetallics.The oxidation resistance at the tempe- rature of 900-1200C of the compound NbTiAls is relatively low but still acceptable.However,by adjusting the relative amount of constituents and adding a small amount of alloying elements it can be singnificantly improved,The room temperature brittleness remains to be solved. KEY WORDS:aluminide,high temperature alloy,Nb-Ti-Al system,evalution Advanced aero-propulsion design now being considered will require materials with high temperature strength,creep resistance,oxidation resistance and ther- momechanical stability,in excess of the range,where nickel based superalloys 1391一10一21收稿 ·材料系(Dept,of Materials Science and Engineering). 157
第 卷第 期 年 月 北 京 科 技 大 学 学 报 。 口口甲 一 一 心 ” ‘ 陈 国 良 · 。 。 ‘ 孙 祖 庆 ‘ ‘ 谢 锡 善 ’ 翻匕可 夫 ， 。 。 任 允 蓉 ’ 才 夕 杨王 月 ’ 落 ， ， ， ， ， 一 一 。 ℃ 一 一 ‘ ’ 夕 夕 ， 夕、 住 ， 。 一 。 ” ， 一 ℃ 孟 。 ， 。 ， ， 一 一 ， 一 ， 、 ， ， ， 〕 一 一 收稿 · 材料系 DOI ：10．13374／j ．issn1001－053x．1992．02．008
are now being used.The specific properties of ordered intermetallic compounds attract the attention of materials scientists.Various aluminides,such as NisAl, TiAl and TisAl have been studied and tremendous improvement of properties has been achieved.Attention now is also being directed to refractory metal compounds containing Ta,Mo,Nb and Zr,in order to develop structural mate- rials for even higher temperature application. Our present research project is aimed toward serching the possibility of de- veloping a novel intermetallic material to be worked at above 1000C,with emphasis on high melting point,low density and relatively simple crystallogra- phic structure,Unfortunately the melting points for most binary aluminides are lower than 1700C.However it is interesting to note that the melting points of ternary aluminides may be high enough,2.On the other hand,the Ti-Al system offers a rich variety of phase and microstructure,Many of its equili- brium phases are disordered solution with wide compositional range or simple structure based on the ordered solution.In addition,since the third alloying element Nb in Ti-Al alloys enhaces the ductility of TiAl or TisAl,a conside- rable interest has developed in Nb-Ti-Al ternary system.Based on the consi- deration mentioned above.Nb-Ti-Al ternary system was chosen for study. Systematic work was performed of the fundamental crystallographic structure, phase distribution,density-composition dependence,oxidation resistance and general mechanical behaviour.The work is in progress.The resulus obtained in the initial stage are presented in this paper. 1 Experimental Procedure The alloys investigated in the present study were within a wide range of Ti 10 8 B 1380℃1300，C0 1200℃ 50h 60 70h1200℃ 1000℃2h Yom肥50七 2h 10h F.C. 908070 605040302010A1 ,Nb,% Fig.1 Compositions of experimental Fig.2 Homogenizing treatment alloys flow chart 158
。 扭 ， ， 。 ， ， ， “ ℃ ， ， 丫 。 往沮 ， 。 爪 五 〔 ’ ， 〕 。 ， 一 “ 。 了 。 ， 一 ， 一 一 。 一 一 妞 ， ， 一 ， 。 。 “ 红 ， 门 夺 屠 住 气…口 …二 …… 。 盏︺了召 戈心尺 ，叼人自 冲产唱李今七阅 氛以厂、叱 侧刃矫考 面 再 ， 名
compositions among TisAl (aa),TiAl (y),NbTiAla(y1),NbAls()and TiAls (in Nb-Ti-Al ternary system,with Al being from 25at%to 75at%,Nb 0at% to 25at%and Ti (25-75)at%.The actual compositions are shown in Fig.1. The bulk samples for structure study were prepared from 4NAl,2N8Nb and 3NTi by arc melting in a gettered argon atmosphere in a small button of 50g.In excess 5 remelts were performed to ensure mixing of the alloys,The chemical anlysis of the alloy having the NbTiAls composition confirmed the gaseous content was not to be of quantity to significantly influence phase stru- cture(Table 1).The samples for property study were melted by a vacuum induction furnace.The macrosegregation was investigated by a electronprobe at the different location of the ingot,The result showed that the composition from the edge to the centre of the ingot was reasonably homogenous.In orde to eliminate the microsegregation homogenization was performed,The homno- genizing processing flow chat can be seen in Fig.2.Smnall metallographic and Tablel Analysed gaseous content in NbTiAla alloy metho d N,Ppm O,ppm non-comsumablc arc melting <100 65 vacuum induction melting <100 473 mechanical samples were then made by electric spark cutting,Phase identifi- 的 cation was determined by means of microscopy (SEM TEM),microanalysis (EDX),structure analysis (selected area diffraction,microiiffraction,conver- gent beam diffraction and X-ray diffraction).Compessive test was performed on a Gleeble machine at various temperatures up to 1100C.The strain rate was chosen at 10-2/s and 10-5/s (corresponding to the strain rates for hot de- formation and creep respectively).Tensile test was also performed for part of the alloys on a MTS machine.Fracture mode under tcnsile condition was observed by SEM.Static oxidation test and oxidation kinetics measurement were carried out in high temperature furnace in air at from 900 to 1200C 2 Results and Discussion 2,1 Microstructure Studies Limited work has been done on the phase diagram of Nb-Ti-Al ternary system.Relatively little has been concluded on the central area of the phase diagram,especially on the presence of the ternary intermetallic compound NbTiAls.Published reports are subject to controversy1-.Zazharovt2, claimed the existence of NbTiAls having a tetragonal lattice unit of a= 159
脚， 。 。 ， 。 。 个 ， 夕 ， 金 。 夕 ， 。 叮 。 叮 一 一 ， ， 一 写 毯 了 ， 。 皿 几 。 。 几 、 。 ， ， 一 了压 从 ， ， 才护 ， ， ， 一 了 一 。 一 盯 ℃ 。 。 一 “ 、 。 ， 。 、、 ‘‘ 认 了 ‘ ℃ 一 一 。 ， 公 让 〔 一 毛 〕 。 〔 泣 二
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
10 7,5 24 Fig.4 a.TEM morphology of single phasc,b.electron diffraction pattern obtained by Lilling the specimen from +20 to -35 and keeping (421)fized. 161
户沁趁冲 耀骡黝袋蘸戴蒸黝 耀蒸 送宝要肠地里彩旦招轰需鉴凌粱 ‘麟 然赓 老甲令甭定熙呢娜滋否澎斌熊撰篡薰嘿馨髯 鬓罐藻鬓藻暴然撮 鬓馨纂 重蠢夔 誉豪攀 襄封 攀 一 谈 、 一洲 朴滚 套葬 。 。 几 口 。 一 件 一 介爪价扮牛华跳筑旅燕脚份 ， 气七 ， 一 已 红 王母王