合金元素韧化或脆化FeAl金属间化合物的微观机制

通过测量二元FeAl以及含B，Zr或Si的FeAl合金的正电子寿命谱参数，计算合金基体和缺陷处的价电子密度.结果表明，当Al原子和Fe原子结合形成FeAl合金时，Al原子提供价电子与Fe原子的3d电子形成局域的共价键.FeAl合金基体的价电子密度很低，FeAl合金中金属键和共价键共存.FeAl合金晶界缺陷的开空间大于Fe空位或Al空位的开空间，FeAl合金晶界处的金属键合力很弱.在FeAl合金中加入少量的B，一部分B原子以间隙方式固溶到FeAl基体中，增加基体的价电子密度；另一部分B原子偏聚到FeAl合金的晶界上，也增加了晶界处的价电子密度.在FeAl合金中加入Zr，增加了合金中的金属键成分，使基体中的价电子密度增加，增强了基体中金属键合力.Zr原子的加入还降低了FeAl合金的有序度，使合金晶界容易弛豫，晶界缺陷的开空间变小.Zr原子在晶界附近出现，还增加了晶界处的价电子密度.在FeAl中加入B或Zr有利于提高合金的韧性.在FeAl合金中加入Si，晶界处的Si原子与邻近的原子形成强的共价键，使得在晶界处参与形成金属键的价电子密度降低.在FeAl中加入Si使合金更脆.关键词：

THE MICROSCOPIC MECHANISM OF ALLOYING ELEMENTS AFFECTING THE DUCTILITY OR BRITTLENESS OF FeAl INTERMETALLICS

The valence electron densities of bulk and microdefects in binary FeAl, and FeAl doping with B,Zr or Si have been calculated by using the positron lifetime parameters of the alloys. The density of valence electron is low in the bulk of FeAl alloy. It indicates that, in Fe atom the 3d electrons have well-localized properties and tend to form covalent bonds with Al atoms, thus the bonding nature in FeAl is a mixture of metallic and covalent. The large-open-volume defects occur in grain boundaries in FeAl and the cohesion of the grain boundaries is weak due to the low density of valence electron there. When a small amount of B atoms is added into FeAl alloy, some of B atoms segregate to the grain boundaries and increase the valence electron density; this will strengthen the bonding cohesion in the grain boundaries. The other B atoms are dissolved interstitially into the bulk, they interact with Fe and Al, increase the density of valence electrons and thus the bonding cohesion in the bulk. The addition of Zr into FeAl results in the increase of the density of valence electrons in the bulk and grain boundary. Whereas, if FeAl is alloyed with Si, the density of valence electrons in the grain boundary will decrease. B and Zr are found to be beneficial elements for improving the brittleness of FeAl alloy, while Si exhibits an opposite effect.