Question

A Cu-Ni alloy is slowly cooled to 1250°C. Both liquid and solid coexist. If the amount of liquid is 26%, determine the overall composition of the alloy (in wt% Ni). Composition (at% Ni) 0 20 40 1600 TTT 60 80 100 2800 1500 Liquid 1453°C 2600 1400 Liquidus line Solidus line Temperature (°C) 00 Temperature (°F) 1200 2200 1100 2000 1085°C 1000 LL 0 20 80 100 40 60 Composition (wt% Ni) (Cu) (Ni)

Answer 1

A Cu-Ni alloy is slowly cooled to 1250°C. Both liquid and solid coexist. If the amount of liquid is 26%, determine the overall composition of the alloy (in wt% Ni). Composition (at% Ni) 0 20 40 1600 TTT 60 80 100 2800 1500 Liquid 1453°C 2600 1400 Liquidus line Solidus line Temperature (°C) 00 Temperature (°F) 1200 2200 1100 2000 1085°C 1000 L 0 20 80 100 40 60 Composition (wt% Ni) (Cu) (Ni)

Temperature 1250 C (Yellow line) The overall composition will lie on this yellow line anywhere. We know that both solid and liquid coexist. Thus, the overall composition should lie between Point X which is on Liquidus line and Point Y which is on Solidus line. Wt % of liquid Thus, wt% of solid = = 26% 100 - 26 = 74% We want to find point which denotes overall composition. Let this point be represented as B which lies on yellow line and between X and Y Here, Wt Fraction of Ni in liquid phase Wt Fraction of Ni in solid phase (X-ni) = 0.318 (XSni) = 0.444 (31.8 wt%) (44.4 wt %) To find relative amount of each phase, we need to use Lever Rule. Lever Rule states, Amount of Solid phase Amount of Liquid phase Overall Wt Fraction of Ni-Wt Fraction of Ni in liquid phase Wt Fraction of Ni in Solid phase-Overall Wt Fraction of Ni 74 = Overall Wt Fraction of Ni -0.318 0.444- Overall Wt Fraction of Ni On solving above equation, we get, Overall Wt Fraction of Ni = 0.411 Thus, Overall composition of Ni in alloy Overall composition of Cu in alloy = = 0.411 * 100 100 - 41.1 = = 41.1 wt% 58.9 wt%