AES study of Cu and S surface segregation in a ternary Ni-Cu(S) alloy in combination with a linear heating method

Abstract

Surface segregation of Cu and S in a Ni-18.7 at.%Cu alloy with 0.0007 at.%S was studied by means of Auger electron spectroscopy. A linear temperature programmed heating method was employed to in-situ heat the sample in the temperature range from 423 K to 1121 K at a constant rate of 0.02 K/s. It was found that the Cu started to segregate at 560 K and reached the maximum surface coverage values of 41.4 at.% at 896 K. Once the Cu reached the maximum surface coverage, it started to desegregate until Cu was replaced by S. At that moment, S segregation reached the maximum surface coverage values of 17.1 at.%. The modified Darken model simulations for both the kinetic and equilibrium in a ternary system were compared with the measured surface segregation profile results yielding the segregation parameters. The segregation parameters for both Cu and S in Ni-Cu(S) ternary alloy, namely the segregation energy (ΔG0), the interaction parameter (Ω) and the diffusion parameters (pre-exponential factor (Do) and the activation energy (Q)) were determined as: ΔGCu0 = −36.0 kJ/mol, ΔGS0 = −136.0 kJ/mol, ΩCu-Ni = 7.6 kJ/mol, ΩS-Ni = 28.1 kJ/mol and ΩCu-S = −10.3 kJ/mol, DCu in Ni = 8.6 × 10−14exp(-145.2 kJ/RT) m2/s and DS in Ni = 9.2 × 10−2exp(-224.0 kJ/RT) m2/s.