用微合金化和宏合金化改变Ni_3Al合金的晶界结构

Improvement of grain-boundary structure in Ni_3Al alloys by microalloying and macroalloying methods

测量了二元多晶Ｎｉ３Ａｌ．含Ｂ．含Ｚｒ、Ｆｅ和含Ｈｆ、Ｆｅ的Ｎｉ３Ａｌ合金的ｅ＋寿命谱。在Ｎｉ３Ａｌ合金中加入Ｂ，Ｂ原子强烈地偏聚到Ｎｉ３Ａｌ合金的晶界上．使该处的价电子浓度与基体中的相近。含Ｚｒ、Ｆｅ和含Ｈｆ、Ｆｅ的Ｎｉ３Ａｌ合金的τ２都比二元Ｎｉ３Ａｌ的小．且以含Ｚｒ、Ｆｅ的τ２最小．表明在Ｎｉ３Ａｌ合金中加入Ｚｒ、Ｆｅ（或Ｈｆ，Ｆｅ）可增加合金中的金属键成分．使晶界处参与形成金属键的自由电子浓度增加，改善了晶界结构。

Measurements of positron lifetime spectra have been performed for binary Ni3Al,Ni-22.33Al-1.37B,Ni-19.6Al-14.8Fe-0.17Zr and Ni-19.6Al-14.8Fe-0.26Hf alloys.Added to Ni3Al alloy,the B atoms have a strong tendency to segregate at grain boundaries and make the density of valence electrons in grain boundaies similar to that in bulk.Theτ2 values for both Ni-19.6Al-14.8Fe-0.17Zr and Ni-19.6Al-14.8Fe-0.26Hf alloys are smaller than that of binary Ni3Al,which indicates that the addition of metal elements such as Zr(or Had and Fe to Ni3Al alloy can increase the fraction of metallic bonds and density of free electrons participating in metallic bonds in grain boundaries and thus improve the structure of grainboundaries.