Effects of Gd on the microstructure and mechanical properties of GdxCoCrFeNiV0.4 high-entropy alloys

This study investigated the microstructure and mechanical properties of Gd_xCoCrFeNiV_0.4 alloys. Various techniques such as XRD, SEM, EBSD, and TEM were utilized, alongside hardness and compression tests at room temperature. The findings revealed that the high-entropy alloy without Gd element exhibited a single face-centered cubic (FCC) phase. Upon the introduction of Gd element, the phase composition shifted to FCC + hexagonal structure (HS) phases, and further addition of Gd resulted in the presence of FCC + HS + body-centered cubic (BCC) phases. Additionally, the inclusion of Gd element led to the precipitation of Gd-rich particles within the alloy. The Vickers hardness test results revealed a significant increase in alloy hardness as the Gd content rose, from 177.5 HV for Gd0 to 848.4 HV for Gd0.4. This suggests that the presence of the HS phase and BCC phase notably influences alloy hardness. Furthermore, compressive test outcomes demonstrated that the alloy's yield strength rose from 173.74 MPa for Gd0 to 1356.17 MPa for Gd0.3 with increasing Gd content. However, the excessive addition of Gd elements results in significant precipitation of V and Cr elements, leading to grain coarsening, adversely affecting its mechanical properties. The high strength of Gd-containing high-entropy alloys can be attributed to various strengthening mechanisms, such as solid solution strengthening, the presence of the HS phase, the precipitation of a small number of Gd-rich particles, and the grain refinement caused by the addition of Gd.