Preparation And Characterization Of LPBF In-situ Alloyed Fe-Cr-Co Permanent Magnet Alloy

Laser Powder Bed Fusion（LPBF）in-situ alloying technology is an additive manufacturing technique that utilizes heterogeneous powders as raw materials and achieves alloying during the printing process.By controlling the alloy element ratios in the raw powder,the desired alloy microstructure and properties can be directly formed in the printed part,thereby expanding the application scope of additive manufacturing technology.LPBF in-situ alloying technology has vast application prospects in the field of permanent magnetic materials.This technology allows for quantitative adjustment of component compositions,facilitating the preparation of alloys with different compositions and potentially accelerating the development and application of novel permanent magnetic materials.Furthermore,LPBF in-situ alloying technology not only meets the requirements for manufacturing permanent magnetic materials with complex shapes and structures,but also enables control of alloy element ratios and microstructures to adjust the magnetic and mechanical properties of permanent magnetic materials,thereby optimizing performance and customization,and offering new possibilities for manufacturing high-performance permanent magnetic devices.This paper focuses on the Fe-Cr-Co permanent magnetic alloy system.Based on a heterogeneous powder laser in-situ alloying equipment system,we first explored the influence of LPBF in-situ alloying process on the formability of Fe-25Cr-15Co（wt.%）permanent magnetic alloy.Comparative studies were conducted with the same composition alloy produced by vacuum melting to analyze the microstructure,magnetic properties,and mechanical properties of LPBF in-situ alloyed samples,aiming to validate the feasibility of using LPBF in-situ alloying technology for preparing Fe-Cr-Co permanent magnetic alloys.Subsequently,to enhance the performance of magnets,Cu element was introduced,and（60-x）Fe-25Cr-15Co-x Cu（x=0-6 wt.%）alloys were efficiently prepared using LPBF in-situ alloying technology.The effects of Cu content on alloy phase composition,microstructure,magnetic properties,and mechanical properties were investigated.Finally,typical alloys of LPBF in-situ alloying were subjected to a heat treatment process with the introduction of static magnetic fields of 2 T,4 T,and 8 T to study the influence of magnetic field intensity on the microstructure and properties of LPBF in-situ alloyed magnets.The following are the main results and conclusions:（1）By optimizing the LPBF in-situ alloying process,we successfully fabricated crack-free,homogeneous,and highly dense Fe-Cr-Co alloys.The microstructure and properties of LPBF in-situ alloyed Fe-25Cr-15Co（wt.%）alloy exhibited anisotropy on both the horizontal and vertical planes of the specimen.In the preferred orientation,its performance was comparable to that of the same composition vacuum-melted samples.This validates the feasibility of utilizing LPBF in-situ alloying technology for preparing Fe-Cr-Co permanent magnetic materials.Additionally,it provides a reference for understanding the anisotropic properties of permanent magnetic materials fabricated by LPBF.（2）The Cu content significantly influences the performance of Fe-Cr-Co alloys.The study found that when the addition of Cu is 2 wt.%,the Fe-25Cr-15Co-2Cu（wt.%）alloy exhibits optimal magnetic properties,with coercivity(_（8）,remanence(),and maximum energy product(（）₈（6）)values of 27.3 k A/m,0.89 T,and 10.21 k J/m³,respectively.Compared to the Fe-25Cr-15Co（wt.%）alloy,the₍（8） and（）₈（6）of the Fe-25Cr-15Co-2Cu（wt.%）alloy increased by 19.4%and 27.9%,respectively.The experimental results combined with first-principles calculations analyzed the mechanism of Cu content on the alloy’s magnetic properties.Additionally,the increase in Cu content significantly improves the material’s mechanical properties.The yield strength of the Fe-25Cr-15Co-2Cu（wt.%）alloy is 908 MPa,which is approximately 6.9%higher than that of the Fe-25Cr-15Co（wt.%）alloy.（3）After heat treatment at a magnetic field intensity of 4 T,theα₁ phase particles in the spinodal decomposition structure of the LPBF in-situ alloyed magnet exhibit a certain aspect ratio and show clear orientation in the direction of the external magnetic field.Additionally,the magnetic domains of the alloy present a strip-like structure and grow along the direction of the heat treatment magnetic field,thereby enhancing the alloy’s magnetic properties.The₍（8）,,and（）₈（6）of the Fe-25Cr-15Co-2Cu（wt.%）alloy are 35.62 k A/m,1.24 T,and26.15 k J/m³,respectively.The Curie temperature of the alloy is 641℃.Furthermore,under the mechanisms of dislocation strengthening and spinodal decomposition strengthening,the yield strength of the alloy is 1268 MPa.Magnetic field heat treatment significantly improves both the magnetic and mechanical properties of the alloy.In this paper,the feasibility of LPBF in-situ alloying technology for the preparation of permanent magnet materials is verified,and Fe-Cr-Co-Cu permanent magnet alloys with gradient variation of Cu content are efficiently prepared using the advantages of this technology.This method can be further extended to other component systems to provide an efficient solution for the development of high-performance novel permanent magnet alloys.Additionally,by adjusting the gradient composition,versatile magnetic circuit characteristics can be realized,potentially bringing about significant changes in the design and application of permanent magnetic materials.