Equal channel angular extrusion for bulk processing of Fe-Co-2V soft magnetic alloys, part I: Processing and mechanical properties

The soft magnetic alloy Fe-Co-2V, also known as Permendur-2V or Hiperco (R) 50A, was subjected to equal channel angular extrusion (ECAE) at 750-850 degrees C using two processing routes. Hiperco is a trade name of Carpenter Technology Corporation. ECAE, which is a severe plastic deformation process, refined the grain size to about 1.5-3 mu m, compared to 25-70 mu m for the conventional Hiperco (R) bar. The fine-grain microstructure is homogenous throughout the ECAE material, from center to edge, due to the simple-shear ECAE process. Fine-grained Hiperco (R) has previously only been obtainable in the sheet form. ECAE resulted in yield and tensile strengths of 650-700 MPa and 900-1400 MPa, respectively, representing a 2-3-fold strength increase compared to the conventional bar. The yield strength was demonstrated to fit well to the Hall-Petch relationship established using previous reports on the strength of conventional bar and sheet materials. High ductility, up to 18%, was obtained in the ECAE processed billets and attributed primarily to the partially disordered bcc crystal structure upon quenching from ECAE.