摘要
To study the effects of La on the microstructure and mechanical properties of refractory high entropy alloys,NbMoTiVSi0.2 alloys with different La contents were prepared.Phase constitution,microstructure evolution,compressive properties and related mechanisms were systematically studied.Results show that the alloys with La addition are composed of BCC solid solution,eutectic structure,MSi2 disilicide phase and La-containing precipitates.Eutectic structure and most of La precipitates are formed at the grain boundaries.Disilicide phase is formed in the grains.La can change the grain morphologies from dendritic structure to near-equiaxed structure,and the average grain size decreases from 180 to 20μm with the increase of La content from 0 to 0.5 at.%.Compressive testing shows that the ultimate strength and the yield strength increase with the increase of La content,which is resulted from the grain boundary strengthening.However,they cannot be greatly improved because of the formation of MSi2 disilicide phase with low strength.The ductility decreases with the increase of La content,which is due to the La precipitates and brittle MSi2 disilicide phase.
为了研究La对难熔高熵合金显微组织与力学性能的影响,制备不同La含量的NbMoTiVSi0.2合金,并对其相组成、显微组织演变、压缩性能及相关机理进行系统分析。结果表明,不同La含量的合金由BCC固溶体、共晶组织、MSi2二硅化物和La析出相组成。共晶组织及大部分La析出相在晶界处形成,而二硅化物相在晶粒内部形成。La的添加使合金晶粒形态由树枝晶转变为近等轴晶,且随着La含量从0增加到0.5 at.%,合金的平均晶粒尺寸由180减小到20μm。压缩性能测试结果表明,由于晶界强化作用,合金的压缩强度和屈服强度均随着La含量的增加而增加;但是由于低强度MSi2相的形成,其提高幅度有限。由于La析出相和脆性MSi2相的形成,因此合金的韧性随着La含量的增加而降低。
基金
The authors are grateful for the financial supports from the National Natural Science Foundation of China(51825401 and 52001114)
the State Key Laboratory of Materials Processing and Die&Mould Technology(P2020-023)
the Guangdong Introducing Innovative and Entrepreneurial Teams,China(2016ZT06G025).
