Development of Directionally Solidified TiAl/Ti3Al Alloys

定向凝固TiAl/Ti3Al合金的研制

基本信息

批准号：
06555203
负责人：
YAMAGUCHI Masaharu
金额：
$ 11.07万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

Directionally solidified ingots containing only one lamellar orientation for the complete ingot can be produced. Unfortunately, the lamellar microstructure in these ingots was perpendicular to the growth direction. However, since only one orientation was observed, microstructural control may be achievable by using a seed crystal during directional solidification. There are two requirements that must be met if the orientation of the lamellar microstructure is to be controlled by using a seed crystal. The first is that the alpha phase must nucleate first from the liquid. The basic idea is to control the orientation of the alpha phase upon nucleation. Since the lamellar microstructure forms with the (111) gamma// (0001) alpha orientation relationship, once the orientation of the alpha phase is determined, the orientation of the lamellar microstructure is also determined. Secondly, upon heating or cooling, either the alpha phase or the alpha-2 phase must be thermodynamically stable. That is, upon heating or cooling, the alloy must not pass through the gamma single-phase region since recrystallization may occur. These two requirements are met in the TiAl-Si system. Within the composition range of 40-50 at%Al, the addition of Si to TiAl shifts the primary alpha region towards much lower Al content. At a composition of Ti-43Al-35Si, either alpha or alpha-2 is stable from the melting temperature to room temperature and the orientation of the lamellar microstructure can be controlled using a seed material. The room temperature mechanical properties were determined by tensile tests and by three point bend tests. From bend specimens oriented with the notch parallel to the lamellar microstructure, the Ti-43Al-3Si alloy was found to have a greater fracture toughness than a TiAl-PST crystal of the same orientation.

可以生产仅包含一种层状取向的完整铸锭的定向凝固铸锭。不幸的是，这些锭中的层状微观结构垂直于生长方向。然而，由于仅观察到一种取向，因此可以通过在定向凝固过程中使用晶种来实现微观结构控制。如果要通过使用晶种来控制层状微观结构的取向，则必须满足两个要求。首先是α相必须首先从液体中成核。基本思想是控制成核时α相的取向。由于层状组织以(111)γ//(0001)α取向关系形成，因此一旦确定了α相的取向，则层状组织的取向也就确定了。其次，在加热或冷却时，α相或α-2相必须是热力学稳定的。也就是说，在加热或冷却时，合金不得穿过γ单相区，因为可能发生再结晶。 TiAl-Si 系统满足了这两个要求。在 40-50 at% Al 的成分范围内，向 TiAl 中添加 Si 会使初生 α 区向低得多的 Al 含量移动。在 Ti-43Al-35Si 成分下，α 或 α-2 从熔化温度到室温都是稳定的，并且可以使用晶种材料控制层状微观结构的取向。室温机械性能通过拉伸试验和三点弯曲试验测定。从切口平行于层状微观结构取向的弯曲样品中，发现 Ti-43Al-3Si 合金比相同取向的 TiAl-PST 晶体具有更高的断裂韧性。