Attempt to ductilize a lightweight intermetallic compound by controlling crystal structure and microstructure

本文试图通过改变晶体结构和显微组织来改善轻质、耐高温氧化的三铝化钛（Al_3Ti）基金属间化合物的低室温延展性这一严重缺陷。采用氩弧熔炼法制备Al_3 （Ti_<1-y>， X）锭，其中X=Sc， Er或Lu， y=0.25,0.5和0.75。x射线衍射结果表明，各钢锭在y=0.25时均由l12相和d0 <22>相组成。通过压缩试验，与D0_<22>单相制备的Al_3Ti单片复合材料进行了塑性试验。结果表明，Sc的加入使合金的塑性提高到3%左右，而添加Er和Lu的合金的塑性几乎为零，与Al_3Ti相同。当Sc添加量y=0.5和y=0.75时，塑性进一步提高，分别达到6%和11%。为了消除凝固缺陷和凝固偏析，采用了在三铝化物基合金中很少采用的热加工方法。在约10^<-3> Pa的真空条件下，在1175°C / 55%的温度下，成功地对Al_<74> Ti_<26>和Al_<65> Cr_9 Ti_<26>合金进行了热等温自由锻造，获得了完全再结晶的组织，几乎没有因凝固而产生的不均匀性。该锻件使铬改性合金的塑性从4%提高到9%。为进一步减轻Al_3 Ti的重量，用锂代替一半的钛原子，采用感应熔炼法制备了Al_6 TiLi锭，发现其不含l12相，且具有与Al_3 Ti二元化合物相同的D0_<22>晶格。

An attempt has been made by modifying crystal structure and microstructure to improve the low room temperature ductility, a serious drawback, of titanium trialuminide (Al_3Ti) base intermetallics which are lightweight and have excellent resistance to high temperature oxidation. Ingots of Al_3 (Ti_<1-y>, X) was produced by argon arc melting, where X=Sc, Er or Lu, and y=0.25,0.5 and 0.75. Each ingot was found to consist of L1_2 and D0_<22> phases at y=0.25 by X-ray diffraction. The ductility (plasticity) of these ingots was assessed by compression test in comparison with that of monolithic Al_3Ti compound composed of D0_<22> single phase and produced in the same way. The results showed that the Sc addition raise the plasticity to about 3% while Er and Lu added alloys have virtually nil plasticity, being the same as the Al_3Ti. The increase in the Sc addition, y=0.5 and y=0.75, brought about further increase in the plasticity to 6% and 11%, respectively. To eliminate the solidification defects and solidification segregation, hot working was applied which had rarely carried out in trialuminide base alloys. Hot isothermal free forging at 1175ﾟC by 55% in a vacuum of about 10^<-3> Pa was found to be made successfully for Al_<74> Ti_<26> and Al_<65> Cr_9 Ti_<26> alloys resulting in a completely recrystallized structure with practically no inhomogeneity arising from solidification. This forging increased the plasticity of the chromium modified alloy from 4% to 9%. An Al_6 TiLi ingot, which was produced by induction melting in an attempt for further reduction in the weight of Al_3 Ti by replacing half of titanium atoms by lithium, was found to contain no L1_2 phase and to have the same tetragonality of the D0_<22> lattice as the Al_3 Ti binary compound.