三元Laves相Cr-Nb-Si(Al)合金的组织演变与强韧化机理

Two series of Laves phase alloys Cr-Nb-Si(Al) were prepared by vacuum non-consumable arc melting, and various techniques including SEM, EDS, a Vickers hardness tester, and a universal mechanical testing machine were conducted to study the microstructures, the mechanical properties, and the underling strengthening and toughening mechanisms of these alloys. The results showed that, the microstructures of alloys Cr-45Nb-xAl(x=0, 7.5, 17.5) evolved from primary Cr₂Nb plus eutectic Cr₂Nb/Nbss to full eutectic Cr₂Nb/Nbss with increasing Al content, whereas the microstructures of alloys Cr-57.5Nb-xSi(x=0, 5, 10) transited from primary Nbss plus eutectic Cr₂Nb/Nbss to dendritic eutectic. The eutectic within the dendrite was Cr₂Nb/Nbss, while transforming to Cr₂Nb/Nb₅Si₃/Nbss at the margin of dendrite. The compression strength and fracture toughness of alloys Cr-45Nb-xAl(x=0, 7.5, 17.5) decreased with increasing Al content, whereas increased firstly and decreased subsequently with increasing Si in the alloys Cr-57.5Nb-xSi(x=0, 5, 10). The compression strength and fracture toughness reached its maximum in the alloy Cr-57.5Nb-5Si and estimated as 2.5 GPa and 15 MPa∙m^1/2, respectively. The excellent combination of strength and toughness of alloy Cr-57.5Nb-5Si originated from the synergistic effects of precipitation strengthening, interface strengthening, solid solution strengthening, second phase toughening and alloying toughening.