Reobservations of Recrystallization and its Eeffect on Mechanical and Magnetic Properties in a Severely Cold-Rolled Ni-Based Soft Magnetic Alloy

Despite of extensive researches for decades, there are many unclear aspects for recrystallization phenomenon in the cold rolled Ni-based alloys. Hence, different thermal cycles were conducted in order to determine microstructural evolutions and its effect on the magnetic and mechanical properties of a 90% cold-rolled thin sheet of a Ni-Fe-Cu-Mo alloy (~80 μm). The obtained results revealed that the recrystallization was started at a temperature of 550°C and was completed after 4 hours. An increase in the number of annealing twins was observed with an increase in annealing temperature, which was due to a bulging and long-range migration of grain boundaries during the discontinuous recrystallization. Ordering transformation occurred in the temperature range of 400-600°C and as a result, hardness, yield strength, and UTS were increased, while with an increase in the annealing temperature these mechanical properties were decreased. Maximum toughness was obtained by annealing at 550°C for 4 hours, while the highest elongation was obtained after annealing at 1050°C, where other mechanical properties including toughness, hardness, yield strength, and UTS were decreased due to the grain growth and secondary recrystallization. Moreover, coercivity and remanence magnetization were decreased from 4.5 Oe and 3.8 emu/g for the cold rolled sample to below 0.5 Oe and 0.15 emu/g for the sample annealed at 950°C, respectively.