Starink, M.J. and Wang, S.C.
The thermodynamics of and strengthening due to co-clusters: general theory and application to the case of Al-Cu-Mg alloys.
Acta Materialia, 57, . (doi:10.1016/j.actamat.2009.01.021).
Co-clusters in ternary or higher order metallic alloys are metastable structures involving two or more distinct alloying atoms that retain the structure of the host lattice. A thermodynamic model based on a single interaction energy of dissimilar nearest neighbour alloying elements is presented, and a model for the strengthening due to these co-cluster dimers is derived. The model includes a new treatment of (short-) order strengthening relevant to these co-clusters and further encompasses modulus hardening and chemical hardening. The models are tested against data on a wide range of Al-Cu-Mg alloys treated at temperatures between 20 and 220ºC. Both quantitative calorimetry data on the enthalpy change due to co-cluster formation and strengthening due to co-clusters is predicted well. It is shown that in general (short-range) order strengthening will be the main strengthening mechanism.
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The following people are gratefully acknowledged: Ms. A. Dion, and Drs. J.L. Yan, Z. Zhu and N. Gao for performing selected DSC experiments, Dr. N. Gao for performing tensile tests on a 2024 alloy, Dr. G. Mahon for thermomechanical processing of Alloy 2b, Drs. G. Mahon, S. Court and L. Kovarik for discussions on low Cu Al–Mg–Cu–Mn alloys. QinetiQ (Farnborough, UK), Alcan (former Banbury Labs), Airbus UK and Prof M.J. Mills and Dr. L. Kovarik are gratefully acknowledged for providing alloys.
||co-clusters, cosegregation, calorimetry, enthalpy, entropy, free energy, strengthening, modulus hardening, chemical hardening, guinier-preston, GPB, 2024, Al-Cu-Mg, Al-Mg-Si, co-segregation
||T Technology > TN Mining engineering. Metallurgy
||University Structure - Pre August 2011 > School of Engineering Sciences > Engineering Materials & Surface Engineering
||07 Nov 2008
||06 Aug 2015 02:51
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