材料期刊网

以高纯Nb和Si粉末为原料, 通过机械球磨+真空热压烧结制备了高致密度的Nb-16Si难熔合金. 利用SEM和XRD分析了球磨后复合粉末的形貌变化以及热压烧结后材料的显微组织和相组成. 机械球磨后粉末颗粒获得细化, Si固溶于Nb形成间隙固溶体, 烧结后材料由铌基固溶体(Nb_ss), Nb₅Si₃, Nb₃Si及少量高Si含量的铌基固溶体(Nb_ssI)组成, 平均晶粒尺寸约为2 μm, 呈等轴状. 烧结材料呈现典型的穿晶断裂模式及韧性相增韧. 测定了材料的Vickers硬度及各相的纳米硬度, 利用单边切口直通梁法(SENB)测定其室温断裂韧性. 利用烧结-锻造技术成形了Nb-16Si难熔合金推力室模拟件, 其微观组织与热压烧结材料相似, 力学性能较烧结材料有所降低, 与金属间化合物的大小有关.

Nb--16Si refractory alloy was prepared by mechanical milling and hot--press sintering from high--purity Nb and Si powders. The milling process was carried out in a planetary ball mill for 24 h. The milled powders were consolidated by hot pressing in the argon atmosphere at 30 MPa and 1500 ℃ for 1 h. The powders ball--milled and material hot--pressed were characterized by XRD and SEM. The size of milled particles was refined and the Si atoms were dissolved into the Nb lattice to form interstitial solid solution. The results reveal that Nb--16Si refractory alloy consists of Nb solid solution (Nb_ss), Nb₅Si₃, Nb₃Si and another Nb solid solution (Nb_ssI) with high Si content. The average grain size is about 2 μm and the grains are nearly equiaxed. The predominant fracture mode is transgranular fracture with river patterns in Nb_ss and relatively flat cleavage planes in silicides. Nano-hardness values of Nb₅Si₃, Nb₃Si and Nb_ss determined by nano--indentation are 13.9, 12.7 and 4 GPa, respectively. The fracture toughness of the alloy reaches 10.98 MPa?m^1/2, indicating ductile phase toughening plays a positive role in improving the fracture toughness. A model of trust chamber was fabricated by sinter--forging and its microstructure is similar to the hot--pressed material.