| The design concept of high-entropy alloys,bright a new trend and development prospect of structural materials,especially the alloys with high strength,high hardness and excellent properties at both room and elevated temperatures,that they have not only high academic value in the field of scientific research,but also broad prospect in industrial production and engineering application.High-entropy alloys,as a new alloy system,although receiving wide attention and research achievements in recent years by scholars both at home and abroad,the study of high-entropy alloys just began,compared with traditional alloys.Both theoretical research and experimental results a few,rerelatively.The acknowledgement about the alloying mechanism,deformation behavior and the basic scientific problems are limited.In this paper,FeCoNiCrMn alloy with outstanding ductility but low strength was selected as baseline alloy to study the formation of hard phase to strengthen this ductile alloy by adding Si or Nb element into it.The results indicate that there is a phase structure transition from FCC to BCC when adding enough Si into FeCoNiCrMn.The yield strength and hardness increase with increasing the content of Si,due to the formation of hard BCC phase in the ductile FeCoNiCrMn alloy.An example of tailoring the strength and ductility of FeCoNiCrMn Si0.7 high-entropy alloy is demonstrated in this paper.In addition,the FeCoNiCrMn Si0.7 alloy exhibit excellent high-temperature properties,corrosion resistance and oxidation resistance,due to the formation of BCC phase and Si O2 oxide film.The effects of Nb addition on the phase change and mechanical properties of FeCoNiCrMnNbx high-entropy alloy were investigated.The results indicated that there was an evolution of phase structure from FCC to Laves with the increase of Nb content.The Laves was identified to be Nb-rich phase.In the alloys with high amount of Nb,Nb-depleted dendrites and Nb-rich inter-dendrites was observed,due to the positive mixing enthalpy between Nb and other composition elements.The yield strength and hardness increased with increasing Nb content.The yield strength increased from 188.1 MPa for Nb0 to 1101.5 MPa for Nb0.5 alloy.The high strength of FeCoNiCrMnNb0.5 alloy was attributed to the uniformly dispersed Laves precipitates in the matrix,which impeded effectively the dislocation motion during alloy deformation.The Nb-added FeCoNiCrMnNbx alloys also showed excellent strain hardening ability during compression test.The as-cast high-entropy alloys were not always in stable state.Phase structure,phase composition and microstructure would change after aging treatment.the aging alloys FeCoNiCrMn Six and FeCoNiCrMnNbx,precipitated Cr-rich phase,secondenry Laves phase and（Cr Si Mn）0.99（FeCo Ni）1.01phase,respectively.The mechanical properties were improved largely,on account of the second phase strengthening. |
