A series of alloys was prepared to investigate the crystallization of Co-rich HiTPerm-type alloys ͓͑Co 1−x Fe x ͒ 88 Zr 7 B 4 Cu 1 ͔ with Fe:Co ratios within or near the two-phase ͑bcc+ fcc͒ region of the binary phase diagram. The goal of this work is to better understand the phase evolution and crystallization of alloys in which the Fe-Co binary phase diagram predicts more than one transition metal rich primary crystalline phase to be present in equilibrium at the primary crystallization temperature. X-ray diffraction, transmission electron microscopy, and high-temperature vibrating-sample magnetometry have been performed to identify the first phase to crystallize and to follow the evolution of phases during crystallization. The bcc phase appears to be the primary crystalline phase that forms first after annealing at 450°C for 1 h, in agreement with previous work on Co-rich nanocomposite alloys. We observe that as the Co concentration is increased, the fcc crystalline phase forms at lower annealing temperatures and its volume fraction increases for a given annealing temperature.

The magnetic properties observed after various thermal-magnetic treatments for a ͑Co 0.85 Fe 0.15 ͒ 83.6 Ni 4.4 Zr 7 B 4 Cu 1 alloy are compared with those for a ͑Co 0.88 Fe 0.12 ͒ 79.4 Nb 2.6 Si 9 B 9 alloy of similar Co:Fe ratio which exhibited a large field induced anisotropy in previous work. The qualitative conclusions arrived at here also apply to the ͑Co 0.85 Fe 0.15 ͒ 88 Zr 7 B 4 Cu 1 alloy without Ni. For the transverse magnetic field annealed ͑Co 0.85 Fe 0.15 ͒ 83.6 Ni 4.4 Zr 7 B 4 Cu 1 alloy, the highest anisotropy fields H K ͑H K ϳ 35-40 Oe͒, field induced anisotropies K U ͑K U ϳ 1700-2000 J / m 3 ͒, and lowest coercivities H C ͑H C ϳ 0.5-1.5 Oe at f = 3 kHz͒ were observed for field annealed amorphous ribbons as compared to field crystallized ribbons. For the ͑Co 0.88 Fe 0.12 ͒ 79.4 Nb 2.6 Si 9 B 9 alloy, the field induced anisotropy is a maximum for field crystallized ribbons ͑H K ϳ 28-45 Oe, K U ϳ 800-1800 J / m 3 ͒ and the increase in dynamic coercivity ͑H C ϳ 0.5-1 Oe at f = 3 kHz͒ observed upon crystallization is much less dramatic. The field annealed amorphous alloy of composition ͑Co 0.85 Fe 0.15 ͒ 83.6 Ni 4.4 Zr 7 B 4 Cu 1 exhibited field induced anisotropies and dynamic coercivities that are competitive with the field crystallized alloys of composition ͑Co 0.88 Fe 0.12 ͒ 79.4 Nb 2.6 Si 9 B 9 .