Effect of Zr on the Microstructure of Second- and Third-Generation BCC HEAs

The possible effect of Zr on the microstructural evolution of second- and third-generation body-centered cubic high-entropy alloys with increasing temperature was investigated by comparing two pairs of alloys differing from one another only by the presence of Zr in one of them. The experimental procedure comprised alloying in an arc furnace with subsequent thermal treatments at 1000 degrees C and 1300 degrees C, followed by water quenching. We found that Zr tended to segregate as the temperature was increased, through formation of various intermetallic compounds owing to its highly electropositive nature. In the third-generation matrix, however, this segregation trend was somewhat mitigated by redissolution of much of the Zr in a NbTiZr-based solid solution which formed in the as-cast product. Without Zr, this third-generation matrix displayed severe Ti segregation.