Effects of cold plastic deformation on microstructure and magnetic susceptibility of Au-Pt alloys

Formation of the alloys of paramagnetic gold (Au) and diamagnetic platinum (Pt) holds promise for developing materials with ultra-low magnetic susceptibility. This study investigates the effects of cold plastic deformation on the mechanical properties and magnetic susceptibility of Au-29Pt alloys by microstructure characterization. After cold rolling, the Vickers hardness of the Au-Pt alloy increases from 138.35 HV to 218.28 HV at 80 % deformation. Meanwhile, the volume magnetic susceptibility exhibits a change from −19.10 ppm to −28.60 ppm with minor difference between the results measured from different orientations. The crystal orientation of the Au-29Pt alloys changes but no new phases or no textures are formed. With the increase of the deformation level from 0 % to 60 %, EBSD measurements demonstrates a ∼40-fold increment in average geometric dislocation density. The results indicate the formation of new defects, which are identified as edge dislocations and stacking faults via HRTEM. Consequently, the larger diamagnetic susceptibility at a higher deformation level is mainly correlated with the formation of defects. The results of this study could provide useful guidelines for the design of ultra-low magnetic susceptibility alloys.