摘要
采用非晶晶化法制备由？-TiAl相组成、晶粒尺寸为0.15？m的粉末冶金Ti-50%Al（原子分数）合金。首先对Ti、Al元素混合粉末进行高能球磨，制备Ti-50%Al非晶粉末；再通过1000℃/1 h热压，得到致密度为96%的Ti-50%Al合金。采用X射线衍射研究制备过程中的结构演变；利用透射电镜对非晶粉末和致密TiAl合金的微观形貌进行观察。结果表明，Ti-50%Al混合粉末经过100 h高能球磨后转化为无序的非晶相，其结构演变过程为：Ti＋ Al？Ti（Al）过饱和固溶体（h.c.p）？非晶相。Ti-50%Al 非晶粉末在随后的热压过程中发生晶化，晶化温度为660~750℃，晶化过程为：非晶相？无序？相（h.c.p）？？-TiAl相（＋？2-Ti3Al相），非晶晶化后化学成分基本保持不变。Ti-50%Al非晶的晶化过程与具有高过冷度的过冷液体的形核过程类似，？相晶体以非晶结构中存在的h.c.p.晶体团簇或以二十面体簇转变的h.c.p.晶体团簇为核心而形核和长大。
A powder metallurgical titanium aluminide alloy Ti-50%Al with mean grain size of about 0.15？m, composing entirely of？-TiAl phase was prepared by amorphous crystallization method using amorphous Ti-50%Al （atom fraction） powders as raw materials. The amorphous Ti-50%Al powders were fabricated by mechanically alloying in a planetary ball milling system using Ti and Al powders as raw materials, and then the amorphous Ti-50%Al powders were hot pressed at 1 000℃for 1h to obtain the titanium aluminide alloy, whose relative density is about 96%. X-ray diffraction （XRD） was used to characterize the structure evolution during the mechanically alloying and the process of crystallization;and transmission electron microscope （TEM） was used to characterize the morphologies of the amorphous powders and the titanium aluminide alloy. The results show that, after 100 h milling, the blended powders change into an amorphous phase completely, the process of structural transformation can be described as： Ti＋Al？Ti（Al） h.c.p？amorphous. Crystallization occurs at a suitable process during hot pressing in the temperate range of 660~750℃, the process can be described as： amorphous？disordered α phase （H.C.P）？ordered ？-TiAl phase （＋ordered ？2-Ti3Al phase）, in which the disordered？phase is a metastable phase. During crystallization, it is observed that the chemical compositions maintain invariant, it is supposed that the transformation may be similar to the process of nucleation of undercooling liquid, in which the disordered ？ phase may nucleate and grow at the basic of the h.c.p crystalline clusters which is in the amorphous structure or has changed by icosahedral clusters existing in the amorphous structure.
出处
《粉末冶金材料科学与工程》
EI
北大核心
2013年第5期687-692,共6页
Materials Science and Engineering of Powder Metallurgy
基金
国家高技术研究发展计划(863计划)资助项目(715-005-0040)
