Promotion or Suppression of Eutectic and Peri-Eutectic Growth in Containerlessly Processed Fe–Ni–Ti Alloys

Abstract

The competitive growth mechanisms of ternary eutectic and peri-eutectic transitions of liquid Fe–Ni–Ti alloys were investigated by drop tube technique. As liquid undercooling and cooling rate increased, the microstructure of eutectic Ni40.6Fe36.4Ti23 alloy transformed from the mixture of primary Ni3Ti phase and ternary eutectic into complete ternary eutectic. The predominant growth mode of independently grown Fe2Ti intermetallic phase varied from nonfaceted to faceted growth, while the γ-Fe(Ni) and Ni3Ti phases kept cooperative growth and formed a lamellar structure owing to the coherent interface along \((1 \overline{1}1)_{\gamma }\) and \((0001)_{{{\text{Ni}}_{{\text{3}}} {\text{Ti}}}} \). The peri-eutectic transformation in Fe66.5Ni17.6Ti15.9 alloy was suppressed due to the preferential growth of the primary α′-Fe phase as droplet size decreased. A needle-like Fe2Ti phase precipitated from the supersaturated α′-Fe phase during rapid solidification, and the α-Fe/Fe2Ti interface was characterized as semicoherent. The wear rate and friction coefficient of the ternary eutectic alloy firstly increased and then decreased as controlled by the combined factors of the microstructural transition and grain refinement. For the peri-eutectic alloy, the refinement of microstructure significantly improved the friction performance after rapid solidification. Moreover, the ternary eutectic alloy had a better wear resistance than peri-eutectic alloy, ascribed to the hardening intermetallic phases and the refined microstructure.