高铬 Nb Si金属间化合物基复合材料的定向凝固组织

采用液态金属冷却定向凝固技术制备了高铬 Nb-Si金属间化合物基复合材料, 分析了不同熔化温度和凝固速度下复合材料的相组成及组织特征。结果表明: Nb-22Ti-17Cr-16Si-2Al-2Hf(原子分数)合金相组成为Nb_ss、 α-Nb₅Si₃、 Laves相NbCr₂和少量的(Nb_ss+ Nb₅Si₃)共晶, 定向凝固没有改变复合材料的相组成。熔化温度为1550 ℃时, Nb_ss相呈颗粒状, Nb₅Si₃相呈随机分布的块状或短板条状; 随着熔化温度的提高, Nb_ss转变为枝晶状且沿轴向定向生长, Nb₅Si₃相转变为有一定定向效果的长板条状。随着凝固速度的增大, 组织明显细化且定向效果增强, 凝固速度为18 mm/min时, Nb₅Si₃呈定向效果良好的细长条状。 

Microstructurs analysis of directionally solidified Nb-Si based composite with a high content of Cr

An advanced ultrahigh temperature Nb-Si based composite with a high content of Cr was prepared by directional solidification. The microstructure and phases were investigated under the condition of different melting temperatures or different solidification rates. The results reveal that the microstructure is composed of Nb_ss, α-Nb₅Si₃, NbCr₂ phases and a small amount of (Nb_ss+ Nb₅Si₃) eutectic. The composites phase composition has not been changed by directional solidification. The Nb_ss phase appears like grain and the Nb₅Si₃ phase is randomly distributed in the block or short lath at 1550 ℃. With the increase of the melting temperature, the Nb_ss phase changes from large grains to dendrites, while the Nb₅Si₃ phase undergoes an evolution from block to batten morphologies. The composite microstructure is fined obviously and the directional effects enhance as the increase of the solidification rates. The excellent directionally solidified microstructure is obtained when the solidifying rate is 18 mm/min, and the Nb₅Si₃ phase is column shape with good orientation.