快速凝固Cu-Sn合金的组织形态及相结构

Microstructural morphology and phase structure of rapidly solidified Cu-Sn alloy

研究快速凝固Cu-20％Sn亚包晶合金的相结构、晶体生长行为和组织特征，分析冷却速率与组织形成之间的相关规律。结果表明：在急冷快速凝固条件下，合金的包晶转变和共析转变均受到抑制，形成了以亚稳的Cu5.6Sn金属间化合物为主相的快速凝固组织；随着冷却速率的增大，α-Cu相含量减少，Cu5.6Sn相数量显著增多；晶体生长的方向性增强；Cu5.6Sn生长方式由小平面向非小平面生长转变，组织形态由粗大板条状向细密柱状转变。TEM分析表明：在Cu5.6Sn晶内存在大量的位错塞积及孪晶；孪晶之间相互平行，间距约25～80nm；随冷却速率的增大，位错密度增大，孪晶数量增多。

The phase structure, crystal growth behavior and microstructural characteristics of rapidly solidified Cu-20%Sn alloy were investigated and the relationships between the microstructure formation and the cooling rate were analyzed theoretically. The results show that under rapid solidification condition, the peritectic transition and eutectoid transitions of the alloy are all suppressed, which results in the formation of microstructures characterized mainly by metastable Cu5.6Sn metallic compound. With increasing cooling rate, the amount of α-Cu phase decreases, while that of Cu5.6Sn phase increases. Meanwhile, the growth form transforms from faced to non-faced growth and the microstructure exhibits apparent growth orientation. TEM reveals that there exists large quantity of dislocation pile-up and twins in Cu5.6Sn grains. Those twins are parallel to each other with the interspacing about 25～80 nm, and extend to the boundary of Cu5.6Sn branches. The increase of cooling rate results in the increase of dislocation density and twin quantity.