Improved Plasticity of Fe_(25)Co_(25)Ni_(25)(Si_(0.3)B_(0.7))_(25) High Entropy Bulk Metallic Glass through the Addition of Cu

This work was focused on enhancement in the plasticity of Fe_(25)Co_(25)Ni_(25)(Si_(0.3)B_(0.7))_(25) high entropy bulk metallic glass(HE-BMG)by adding minor Cu(0–1.2,in at.%).It is found that the appropriate addition of Cu can efficiently improve the plasticity of the present HE-BMG while the excessive addition of Cu will deteriorate again the plasticity,and especially,the plastic strain of the present HE-BMG is improved from 0.8%for the Cu-free alloy to 4.7%for the 0.3 at.%Cu-added alloy.The transmission electron microscopy observation shows that there are manyα-Fe(Co,Ni)clusters with sizes of less than 5 nm dispersed in the glassy matrix in the 0.3 and 0.6 at.%Cu-added alloys,which may account for the significant improvement in the plasticity of the two alloys,and further increase in Cu content more than 0.9 at.%leads to the precipitation ofα-Fe(Co,Ni)and Fe(Co,Ni)B compound grains with diameters of tens of nanometers,in which the plasticity of the present HE-BMGs has deteriorated rapidly.