Homogenization heat treatment for an additively manufactured precipitation-hardening high-entropy alloy

A precipitation-hardening high-entropy alloy(HEA),(FeCoNi)_(86)Al_(7) Ti_(7),was successfully fabricated using selective laser melting(SLM).Severe segregation of Ti occurred at the boundaries of dislocation cells.Therefore,homogenization heat treatment at 1150℃for 0.5 h was performed to alleviate the microsegregation.After homogenization,almost no dislocation cells were left in the grains,and recrystallization occurred as the average grain size increased from 37 to 54μm.Compared with the initial as-built HEA,the ductility of the HEA increases significantly from 29%to 40%,and the strength decreases slightly from 710 to 606 MPa.For further aging,pre-homogenization can decrease the precipitation of ordered L2_(1) phases.Because void has a high propensity to initiate from the matrix/L2_(1) incoherent interface,pre-homogenization reduced the number of weak points,thus considerably improving the plastic deformation ability of the aged HEA by 36%.In addition,the strengthening mechanism has also been analyzed for the aged HEA.It was revealed that the coherent L1_(2)precipitate contributed the most to the increased strength.

Study on Low Temperature Coefficient Rare-Earth Magnets

The rare-earth hard magnets with lower temperature coefficient, including Nd_2Fe_ 14B/Fe_3B-ferrite compound bonded magnets and Sm_ 0.8RE_ 0.2 (Co_ balFe_ 0.22Cu_ 0.06Zr_ 0.03)_ 7.4(RE=Gd, Er) sintered magnets, were studied. The result shows that the addition, that dope ferrite magnetic powder to double-phase nanocomposite Nd_2Fe_ 14B/Fe_3B magnetic powder, can make β_ jH_c to be obviously decreased. Similarly, the effect of homogeneous heating treatment on magnetic properties was studied. Doping heavy rare earth elements to the 2∶17-type SmCo magnet material powders shows that the sintered magnets obtained lower temperature coefficient, and enhanced magnets temperature stability.