a factor of about 10 at 1200c for 100h.The representive results are shown in Table 2.Al2Oa and TiAl2 were generally detected but without the oxide of Nb,except where the content of Nb is high. Various alloying elements such as Cr,Y,Si,Co,Ce etc.were added at different level to investigate the possibility of improving the oxidation resis- tance.The results indicated that some of the alloying elements greatly redu- ced the weight gain,which could be as low as 7.2mg/cm3 at 1200C for 100h. 2.4 General mechnical behaviour The flow stress at 1100'C at the strain rate of 10-2/s are summarised in Fig.10a,with classified according to the strength level and the representive data in Table 3.It can be scen that the high temperature strength of the alloys based on yi+n or y,+a2 phases are higher than those for y-base alloys. 0.2 of 450MPa is obtained in y,+az region,the strength of the alloys within the y+n phase field reaches up to approximately 320MPa.The lowest stre- ngth area is around binary TiAl,being 190MPa,which is about 43%of that of NbTiAs.By combining the data of the measured strength and density it can be obtained that the specific strength of NbTiAls is 97MPa/(g/cm3),in A330~450Pa A 60~100MPa B200~330MPa B 39~60MPa 0 c100~200HPa C 28~39MPa 20304050607080 0 50 50 60 405060 0 20 10 V 5 b90807060504030 201rA1 Nb ,908070605040302010 b,5 Nb,% A Traasgranular B Intergranular C Mixed trasyraanular and Intergra- nular Fig.10 Compressive strength map at 1100C,a.with strain rate of 10-2/s,b.with strain ratc of 10-5/s. contrast,for TiAl that is only 50MPa/(g/cm3). Fig,10b shows the at 1100c at the strain rate of 10-5/s,claasified by 165℃ 。 五 声 ， 五 ， ， ， ， ， 。 ℃ 。 ’ 一 ， 。 夕、 叮 夕 ， 夕 一 ，。 。 夕 ， 夕 呼 又 。 ， ， 。 “ ， 于 多 介 矛 ， 日 多 乡 一 尸 么 户 多 咯 份 仑︸ 八·， 会了沁 勺资。 夸 ’ ，入，， 勺 毋 孕 今 八护刀 材夸 严 马 、﹄松 入 丁云 石 今 八 入匕，。 。 匕 ， 红 尹 ， 住 盆 ℃ ， 一 ‘ 。 一 亡 访巴︺ ，基 ， · 一 卜 “ 。 工 ℃ 大 扭 耳 一 ‘