Accelerated development of soft magnetic alloys

Abstract

The accelerated development of new soft magnetic materials is urgently required to address the challenges of next generation high frequency rotating electrical machines. We used high-throughput experimental and characterization techniques as well as thermodynamic modeling and machine learning (ML) to develop novel soft magnetic materials based on the Fe-Co-Ni alloy system. The experimental methods include (i) Direct energy deposition based additive manufacturing of compositionally graded bulk materials, (ii) Magnetic thin films with a range of compositions, (iii) Chemical flow synthesis of magnetic nanoparticles, (iv) Spark plasma sintered compositionally graded magnetic alloys. The structural, magnetic, mechanical, and electrical properties were determined. The feasibility of our strategy to develop new soft magnetic alloys has been demonstrated.Introduction: Soft magnetic materials are the key component for various applications such as electric motors and generators, magnetic shielding, robotics, electromagnets, sensors, etc[1, 2]. Such systems utilize a significant fraction of the total energy consumption of the world, hence increasing their efficiency will have a significant impact on the urgent need for energy conservation. High frequency rotating electrical machines require magnetic materials with a balance of magnetic, mechanical, and electrical properties. The traditional methods of developing such materials are costly and time consuming, limiting the opportunity to discover new excellent materials. Hence, high throughput methods are of high demand for accelerated discovery of novel materials and to improve the properties of existing materials. We present experimental and computational high throughput approaches to design new magnetic materials.Methods: Compositionally graded Fe-xNi[3], Fe-xCo, Fe-xNi-yMo, Fe-xCo-yNi samples were prepared by a DED process. High purity spherical Fe, Co, Ni, Mo powders with sizes ranging from 50 to 150 mm were employed. Thin film libraries of Fe-Co-Ni were prepared by co-sputtering of Ni-21Fe and Co targets using magnetron sputtering at a base pressure of 10-8 torr. Thermodynamic modeling was found to be very helpful to identify the heat treatment conditions [4]. The following characterization methods were employed: XRD for crystal structure and phase fraction, EPMA-WBS and EDX for composition, PPMS and magnetic field assisted TGA for magnetic properties, four-point probe for electrical resistivities, and nono(micro)-indentation for mechanical properties. A neural network model was trained on the data to predict the magnetic, mechanical and electric properties. Figure 1 shows the methods and the properties of our interest.Results and discussion: Additive manufacturing was utilized to explore a range of compositions. Iron rich ternary Fe-Co-Ni (Fe> 75%, Co<20%, Ni<25%) alloys exhibit saturation magnetization (Ms), coercivity (Hc), Curie temperature (Tc) and hardness values ranging from 167 to 218.4 emu/g, 19.6 to 10.2 Oe, 534 to 940 °C, 185 to 359 Hv, respectively. Fe-8Co-9.1Ni and Fe-7.4Co-11.3Ni were found to have optimum magnetic and mechanical properties with Ms of 218.4 and 217 emu/g, Hc of 10.2 and 13 Oe, Tc of 765 and 741 °C, hardness of 334 and 359 Hv, respectively.In spark plasma sintered compositionally graded Ni-21Fe-xCo alloys, the largest Ms, Hc, Tc and HV were observed in Co rich samples while the resistivity was found to be larger in Ni rich samples. As an example, the compositions along the diameter of 7.6 cm sample of a co-sputtered thin film is shown in figure 2. Thus, the feasibility to accelerate the development of novel soft magnets has been demonstrated in the Fe-Co-Ni system.Acknowledgement: This work is supported by the AME Programmatic Fund by the Agency for Science, Technology and Research, Singapore under Grant No. A1898b0043. **