Rapid acquisition of a unique combination of strength and ductility in La-Fe-Co-Si magnetocaloric alloy: Eutectic interface construction by selective laser melting

In this work, La,Cu,Si-rich eutectic interfaces consisting of the refined α-Fe and LaCuSi phases are primarily constructed via adding Cu by selective laser melting to rapidly acquire a combination of strength and ductility in La-Fe-Co-Si alloy. As a result, the ingot exhibits a decreased porosity from 2.52 vol% to 1.84 vol%. It is also the lowest porosity that has been reported among the La-Fe-Si-based ingots fabricated by laser additive manufacturing until now compared to those without eutectic interfaces， so these as-built ingots exhibit the enhanced hardness. More importantly, due to the ductility of α-Fe and LaCuSi phases, the ductility of the ingot is significantly increased to 6 % and a yield stage is first discovered with a yield strength 549.43 MPa and ductility 6 % in the as-built ingot. Simultaneously, the compression strength is as large as 583.88 MPa. After a short annealing process at 1323 K for 12 h, large amounts of the refined magnetocaloric La(Fe,Co,Si)₁₃ phases are formed. The interfacial phases are transformed to LaCu₂ phases semi-coherent to La(Fe,Co,Si)₁₃ phases and ductile LaCuSi phases. It causes an extra 36 % enhancement of compression strength to 918.98 MPa without any ductility sacrifice thanks to the combined impact of the refinement and second-phase strengthening. It is the highest strength that has ever been reported in this material. Simultaneously, a wide working temperature interval 300 K–340 K with high magnetocaloric cyclicity is obtained.