Concentration behavior of liquidus temperatures and undercooling of Al-Cu-Co at normal pressure

TL;DR

This study investigates the liquidus temperatures and undercooling behavior of Al-Cu-Co alloys during slow cooling, revealing how phase formation and chemical order influence crystallization in this system.

Contribution

It provides detailed analysis of phase formation and liquidus extrema in Al-Cu-Co alloys, highlighting the role of chemical short-range order during crystallization.

Findings

Extrema observed on liquidus lines at phase boundaries.

Undercooling depends on concentration and chemical order.

Phase formation varies with alloy composition.

Abstract

Differential thermal analysis has been conducted for the Al-Cu-Co alloys with the composition range of 15 at.% Co and 10 to 30 at.% Cu, and 25 at.% Co and 2.5 to 20 at.% Co. The features of the formation of solid phases have been studied during the crystallization in a crucible in the conditions of slow cooling (rate of cooling to 1 K s-1) at normal pressure. On the state diagram of the Al-Cu-Co system with 15 at.% Co and 25 at.% Cu the concentration sections have been built, which allows to determine the concentration ranges from which different phases are formed during the first stage of crystallization. Along the boundaries of different phase regions, extrema are observed on the liquidus line. The observed extrema on the liquidus lines and concentration dependences of undercooling are associated with change in the chemical short-range order at the considered concentrations both in the liquid and solid states.