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In the present work,crystal structure and formation mechanism of the secondary phase in Heusler NiMn-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_(44.1)Mn_(35.1)Sn_(10.8)Co_(10) as-cast bulk alloy and melt-spun ribbon,possessing a face-centered cubic(fcc) Ni_(17)Sn_3-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.
In the present work, crystal structure and formation mechanism of the secondary phase in Heusler NiMn-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 (44) Mn_ (35.1) Sn_ (10.8) Co_ (10) as-cast bulk alloy and melt-spun ribbon, possessing a face-centered cubic (fcc) Ni_ (17) Sn_3-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. Host 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 illustrated partial amorphous state due to high local cooling rate.