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NbMoTiVSix refractory high entropy alloys strengthened by forming BCC phase and silicide eutectic structure
Journal of Materials Science & Technology ( IF 10.9 ) Pub Date : 2020-06-25 , DOI: 10.1016/j.jmst.2020.04.050
Qin Xu , Dezhi Chen , Chongyang Tan , Xiaoqin Bi , Qi Wang , Hongzhi Cui , Shuyan Zhang , Ruirun Chen

In order to improve mechanical properties of refractory high entropy alloys, silicide was introduced and NbMoTiVSix (x = 0, 0.1, 0.2, 0.3, and 0.4, molar ratio) refractory high entropy alloys are prepared by vacuum arc melting. Phase composition, microstructure evolution and mechanical properties were systematically studied. Results show that the silicide phase is formed in the alloys with addition of silicon, and the volume fraction of silicide increases from 0 to 8.3 % with increasing of silicon. Microstructure observation shows that the morphology of dendrite changes from columnar to near equiaxed, eutectic structure is formed at grain boundaries and composed of secondary BCC phase and silicide phase. The average length of the primary and second dendrites decreases with the increasing of silicon. Whereas, the ratio of eutectic structure increases from 0 to 19.8 % with the increment of silicon. The refinement of microstructure is caused by heterogeneous nucleation from the silicide. Compressive tests show that the yield and ultimate strength of the alloys increases from 1141.5 MPa to 2093.1 MPa and from 1700.1 MPa to 2374.7 MPa with increasing silicon content. The fracture strain decreases from 24.7 % –11.0 %. Fracture mechanism is changed from ductile fracture to ductile and brittle mixed fracture. The improvement of the strength is caused by grain boundary strengthening, which includes more boundaries around primary BCC phase and eutectic structure in grain boundary, both of them is resulted from the formation of silicide.



中文翻译:

通过形成BCC相和硅化物共晶结构增强NbMoTiVSi x难熔高熵合金

为了改善难熔高熵合金的力学性能,引入了硅化物和NbMoTiVSi xx通过真空电弧熔化制备耐火的高熵合金,即(摩尔比= 0、0.1、0.2、0.3和0.4)。系统地研究了相组成,微观组织演变和力学性能。结果表明,随着硅的加入,合金中形成了硅化物相,随着硅含量的增加,硅化物的体积分数从0增加到8.3%。显微组织观察表明,枝晶的形态从柱状转变为近等轴,在晶界形成共晶组织,由次生BCC相和硅化物相组成。第一和第二树枝状晶体的平均长度随着硅的增加而减小。而随着硅的增加,共晶结构的比例从0增加到19.8%。微观结构的细化是由于硅化物的异质形核引起的。压缩试验表明,随着硅含量的增加,合金的屈服强度和极限强度从1141.5 MPa增加到2093.1 MPa,从1700.1 MPa增加到2374.7 MPa。断裂应变从24.7%–11.0%降低。断裂机理从韧性断裂转变为韧性脆性混合断裂。强度的提高是由晶界强化引起的,晶界强化包括BCC初生相周围的更多晶界和晶界中的共晶结构,这两者都是硅化物的形成所致。断裂应变从24.7%–11.0%降低。断裂机理从韧性断裂转变为韧性脆性混合断裂。强度的提高是由晶界强化引起的,晶界强化包括BCC初生相周围的更多晶界和晶界中的共晶结构,这两者都是硅化物的形成所致。断裂应变从24.7%–11.0%降低。断裂机理从韧性断裂转变为韧性脆性混合断裂。强度的提高是由晶界强化引起的,晶界强化包括BCC初生相周围的更多晶界和晶界中的共晶结构,这两者都是硅化物的形成所致。

更新日期:2020-06-25
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