Influence of powder feedstock characteristics on extrusion-based 3D printing of magnetocaloric structures

Abstract

A significant barrier to the commercialization of magnetic heat pumping is the lack of scalable, low-cost manufacturing techniques that enable shaping brittle magnetocaloric materials into heat exchange structures with porous geometries, controlled chemical gradients, and advantageous anisotropic microstructures. Though direct ink writing additive manufacturing has the potential to expand into a viable net-shaping technology for functional magnetic alloys, it is typically challenging to fabricate dense parts – an observation ascribed to the constraint on powder particle size that inevitably impacts both green density of 3D printed parts and shrinkage during sintering. To this end, we report a comprehensive study on the influence of precursor powder characteristics on the magnetic and structural properties of 3D printed test coupons produced using La0.67Ca0.33MnO3 magnetocaloric particles. Ink formulations comprising powders with nano-scaled, micron-scaled, and bimodal size distributions were printed and sintered. The impact of particle size on part quality and magnetofunctional response was examined, and it was found that test coupon fabricated using nano-scaled powders (~100-200 nm) demonstrated the lowest part porosity (~ 17%) and the highest magnetocaloric response (8 J/kg·K at μ0H=5T). The results presented in this work address critical technical questions about the process feasibility of making magnetic heat pumps with additive manufacturing schemes.