Hf、B耦合作用对Ti-46Al合金凝固组织演化的影响

Coupling Effects of Hafnium and Boron Additions on Solidification Structure Evolution in Ti46Al Alloy

研究了Ti-46Al-xHf-yB(x=0,3,5,7;y=0,0.2,0.6,1.0)合金的宏观、微观组织特征,探讨了Hf、B耦合作用对凝固组织演化过程的影响。结果表明,在Hf、B耦合作用下,合金的凝固组织由粗大的柱状晶转变为细化的柱状枝晶、等轴枝晶、细小近粒状晶。Hf能促进TiB2的形成,使β-Ti/TiB2共晶线向下平移。当x(Hf)<7%时,合金的初生相为β相,TiB2为共晶相并以卷曲带状形态且主要存在于枝晶间;当x(Hf)=7%且x(B)=1.0%时,合金的初生相为TiB2,以针状存在于粒状组织的心部。

The characteristics of macro-and microstructure of cast Ti-46Al-xHf-yB (x=0, 3,5, 7; y=0, 0.2, 0.6, 1.0) alloys were observed to understand the coupling effects of hafnium and boron additions on the solidification structure evolution in the Ti-46Al alloy. The results reveal that with increasing in Hf and B contents, structure morphology of the alloy is converted from coarse columnar to fine columnar dendrite, then to equiaxed dendrite and further to fine near granular grain. Hafnium content can promote the formation of TiB_2 particles, resulting in the motion-down of β-Ti/TiB_2 eutectic line. With Hf content less than 7%, microstructure of the alloy is composed of primary β phase and eutectic phase TiB_2 with ribbon-like shape mainly existing in the interdendrite, while with 7%Hf and 1% B content, primary phase TiB_2 with needle-like shape existing in near granular grain center can be observed in the microstructure.