Microstructure and Tensile Behavior of Ti-Rich Ti-Ni-Cu Melt-Spun Ribbon

Microstructure and mechanical properties of Ti51.5Ni25Cu23.5 ribbon fabricated by melt spinning were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and tensile tests. Some B19 martensite crystalline with (011) compound twin was embedded in the mainly amorphous ribbon, while the ribbon annealed at 450°C for 1 h is at fully martensitic state. Annealing process alter the preferential orientation from (022)-B19 to (111)-B19. Tensile fracture stresses of as-spun ribbon and the annealed ribbon are 1257 MPa and 250 MPa, respectively. The tensile fracture morphology of as-spun ribbon shows typical vein fringe while that of the annealed ribbon reveals fine but depth-inhomogeneous dimples. After tensile deformation, the annealed ribbon exhibits typical martensitic detwinning behavior accompanying with the strain contrast.

Amorphization, Crystallization, and Magnetic Properties of Melt-Spun SmCo7−x(Cr3C2)x Alloys

Effects of Cr3C2 content and wheel surface speed on the amorphous formation ability and magnetic properties have been investigated for melt-spun SmCo7−x(Cr3C2)x (x=0.10-0.25) alloys. Ribbon melt-spun at lower wheel speed (30 m/s) has composite structure composed of mostly SmCo7, a small amount of Sm2Co17, and residual amorphous phases. The grain size of SmCo7 phase decreases with the increase of Cr3C2 content x. When melt spinning at 40 m/s, SmCo7−x(Cr3C2)x alloys can be obtained in the amorphous state for 0.15≤x≤0.25 with intrinsic coercive Hci of the order of 40–70 Oe. DSC analysis reveals that SmCo7 phase first precipitates from the amorphous matrix at 650∘C, followed by the crystallization of Sm2Co17 phase at 770∘C. Optimal coercivity Hci of 7.98 kOe and remanent magnetization Mr of 55.05 emu/g have been realized in SmCo6.8(Cr3C2)0.20 magnet subjected to melt spinning at 40 m/s and annealing at 650∘C for 5 min. The domain structure of the annealed ribbon is composed of interaction domains typically 100–400 nm in size, which indicates the presence of a strong exchange coupling between the grains.

Shape Memory Behavior of Ti-Rich Ti-Ni-Cu Melt-Spun Ribbons

Crystal structures and shape memory properties of Ti-rich Ti52Ni23Cu25 (at.%) ribbon annealed at 450°C for 10 min and 1 h were investigated by X-ray diffraction and dynamic mechanical analyzer. As-spun ribbon was full amorphous and its crystalline peak temperature is 455.4°C. The annealed ribbon is crystallized with strong preferential (110)-B2 orientation. It shows a well-defined shape memory effect and the transformation hysteresis for the annealed ribbon under an external load in the range of 3-9 N is about 38.5°C. With annealing time increasing from 10 min to 1 h, the maximum of transformation strain under the external stress decreases from 1.93% to 1.7%. The temperature dependence of the external stress increases from 0.3 N/°C to 0.43 N/°C. The residual plastic strain is up to about 0.4% at a load of 9 N.

Internal Friction of Ti-Rich Ti-Ni-Cu Melt-Spun Ribbon

Martensitic transformation (MT) and the internal friction (IF) behavior of the initially amorphous Ti-rich Ti-Ni-Cu melt-spun ribbon annealed at 400°C for 10 h were investigated by using DSC and dynamic mechanical analysis (DMA). The annealed ribbon shows B2 structure with strong preferential (110) orientation and exhibits B2↔B19 MT with the temperature hysteresis of 13°C. DMA tests show that the internal friction is frequencies dependence at 1-50 Hz. The tanδ values decrease with the increasing frequency, but it does not meet the 1/f dependence. Isothermal DMA tests show that the tanδ value at a temperature of 15°C in the MT zone increases quickly from 0.005 to 0.045 with the increasing isothermal intervals and keep stable subsequently. The isothermal time to complete the MT can be determined by the DMA tanδ curve directly.

Effect of Binders on the Magnetic Behavior of P/M Processed FeSiBCuNb Alloy

The effect of heat treatment and binder additions on the magnetic behavior of P/M(powder metallurgy) processed Fe73.5Si13.5B9Cu1Nb3 alloy has been investigated. FeSiBCuNb amorphous ribbons produced by plannar flow casting were annealed at temperatures between 480°C and 620°C for 20 to 60 minutes. The annealed specimens were milled using a pin crusher and a hammer mill. The powder was then mixed with mineral or polymer binders to press into a toroidal shape of inductor core at room temperature. Fe73.5Si13.5B9Cu1Nb3 alloy showed maximum permeability when annealed at 540°C for 40 minutes. The microstructure of the annealed ribbon has a ultra-fine α-Fe(Si) grain, ranging from 10 to 20 nm in diameter. Inductor cores produced using a glass binder showed better magnetic properties than polymers or oxide binders. The use of mineral binders in producing nanocrystalline inductor cores significantly improved magnetic properties, compared to a commercial moly-permalloy powder core.