B改善单晶和多晶Ni＿3Al合金力学性能的微观机制

A MICROMECHANISM FOR B IMPROVING THE MECHANICAL PROPERTIES OF MONO-AND POLYCRYSTALLINE Ni_3Al ALLOYS

通过测量Ｂ含量从０．００至２．２２ａｔ％的单晶和多晶Ｎｉ＿３Ａｌ合金的正电子寿命谱，研究了单晶和多晶Ｎｉ＿３Ａｌ合金中的微观缺陷和电子结构。结果表明，多晶Ｎｉ＿３Ａｌ合金晶界中存在着开空间大于空位的缺陷。晶界缺陷处参与形成Ｎｉ－Ｎｉ和Ｎｉ－Ａｌ键的价电子浓度比基体或位错处的低，晶界是结合力弱化区域。偏聚到Ｎｉ＿３Ａｌ合金缺陷上的Ｂ与缺陷处的Ｎｉ或Ａｌ原子形成强的共价键而增强了这些地方的结合力。以间隙方式固溶到Ｎｉ＿３Ａｌ基体中的Ｂ与它近邻的Ｎｉ或Ａｌ原子交互作用导致了基体中价电子浓度升高，键结合力增强。

The microdefects and electronic structure have been studied by measuring thepositron lifetime spectra of mono- and polycrystalline Ni_3Al alloys with B contentranging from 0.00 to 2.22at%. The experimental results show that the opening spa- ce of the defect on grain boundary is larger than that of a monovacancy in polycry-stalline Ni_3Al alloy.More valence electrons participate in Ni-Ni and Ni-Al bond-ings in bulk corresponding to stronger cohesion,while less valence electrons parti- cipate in those on grain boundaries corresponding to weaker cohesion. When B ato- ms segregate to defects,they form strong covalent bondings with Ni and Al atomsand strengthen the bonding cohesion in those locations.The interaction of B atomswhich occupy interstitial sites,with Ni and Al atoms in bulk leads to the increaseof the density of valence electrons,thus increases the bonding cohesion in the bulk.