Crystal structure and formation mechanism of the secondary phase in Heusler Ni-Mn-Sn-Co materials

Abstract

In the present work, crystal structure and formation mechanism of the secondary phase in Heusler Ni-Mn-Sn-Co materials were investigated using X-ray diffraction, scanning/transmission electron microscopy and selected-area electron diffraction techniques. Experimental results showed that the secondary phase presented in both Ni_44.1Mn_35.1Sn_10.8Co₁₀ as-cast bulk alloy and melt-spun ribbon, possessing a face-centered cubic (fcc) Ni₁₇Sn₃-type structure. The secondary phase in the as-cast bulk alloy was resulted from a eutectic reaction after the formation of a primary dendritic β phase during cooling. However in the melt-spun rapidly solidified ribbon, the secondary phase was largely suppressed as nano-precipitates distributed along the grain boundaries, which was attributed to a divorced eutectic reaction. The secondary phase exhibited partial amorphous state due to high local cooling rate.

Keywords

Heusler Ni-Mn-Sn-Co materials / Secondary phase / Melt spinning / Divorced eutectic reaction / Microstructure