TiAl-Cr合金中的β_2相

β_2 PHASE IN TiAl-Cr ALLOYS

在Ｔｉ（４４～４８）Ａｌ（３～６）Ｃｒ（摩尔分数，％）的三元合金中，存在Ｂ２结构的体心立方有序β２相，其形成与含Ｃｒ量有关。β２相铸态成分可表示为：Ｔｉ５５Ａｌ３３Ｃｒ１２。β２相是该合金中显微硬度最高的相，其硬度值随合金中Ｃｒ含量增加而提高。β２相常分布于γ晶界，起阻碍晶粒长大作用。

In the ternary alloys of Ti_(44～48)Al_(3～6)Cr(mole fraction, %), there is an ordered bcc β_2 phase with B2 structure. The formation of this phase is related to the content of Cr. 0.5%(volume fraction) β_2 phase can be precipitated in ascast Ti_44Al_3Cr alloy. The amount of β_2 phase reaches 6%(volume fraction) after long time soaking from 900 ℃ to 1 200 ℃. However, β_2 phase disappears when holding long time above 1 250 ℃. The composition of β_2 phase can be expressed as Ti_55Al_33Cr_12. The microhardness of β_2 phase is the highest among all the phases of the alloy and its microhardness increases with the increase of Cr content in alloys. β_2 phase often distributes at the grain boundaries of γ phase and retards the growth of γ grains. The deformation capability of β_2 phase is the weakest in the phases of the alloy and it inhibits the long distance slip, therefore, β2 phase would make slip dispersive and delay the initiation of cracks.