添加Nb对LI_2型Al_3Ti-8Mn基合金的相组成影响

Effect of Nb Additions on Phase Formation in Ll_2 Type Al_3Ti-8Mn-based Alloys

在单相Ll2结构Al67Mn8Ti25金属间化合物中加入少量Nb（0．5at％～4．0at％），并相应调整Al，Ti含量后，其组织变化显著。在邻近Al－Ti－Nb-8Mn四元系Al3Ti－8Mn区域设计了32种实验合金，随Nb加入量的变化，其结构除单相Ll2外，尚有Ll2＋A12Ti，L12＋DO22，LI2＋LI0，Ll2＋Al2Ti＋DO22和Ll2＋Al2Ti＋Ll0等5种复相或多相组织。Nb含量一定，随Al／Ti比的降低，会导致片状或网纹状Al2Ti组织析出，Nb含量较高时会进一步促使波纹或针片状Ll0TiAl相的形成。初步制定了Al－Ti－Nb-8Mn四元系邻近Al3Ti-8Mn区域的室温相组成图。

The microstructure of a monolithic Ll2Al67Mn8Ti25, compound changes significantly when modified with a small amount ofNb (0. 2~4. 0at%) and with corresponding adjustments to the Ti and Al contents. In 32 experimental alloys near the Al3Ti-8Mncomposition region of the Al-Ti-8Mn-Nb quaternary system, five multiphase regions. Ll2+Al2Ti, Ll2+DO22, Ll2+Ll0, Ll2,+Al2Ti+DO22 and Ll2+Al2Ti+Ll0 formed adjacent to the original Ll2 single phase. When Nb content keeps constant, the plate-like or nettyAl2Ti phase precipitates appear with the decrease of Al/Ti ratio. The ripple-like Ll0 AlTi phase may appear in the alloys containedhigher Nb c0ntents. A room temperature constitutional diagram near the Al3Ti-8Mn region of Al-Ti-Nb-8Mn quaternary system hasbeen determined.