Cu-Containing Fe-Ni Corrosion-Resistant Alloys Designed by a Cluster-Based Stable Solid Solution Model
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I.
INTRODUCTION
THE Fe-Ni alloys are important invar expansion alloys.[1,2] However, they suffer from severe pitting corrosion in high Cl– concentration environment,[3] which needs further surface coating or alloying. Among the many possible alloying elements, Cu is good for resisting Cl– corrosion but can only be used as a minoralloying element due to Cu-Ni spinodal decomposition[4–6] and to Cu-Fe immiscibility.[7] Known industrial alloys are 08Cr18Ni9Cu4 (S30430), 02Cr20Ni18Mo6CuN (S31254), 4J42 (alloy 42), 4J46 (alloy 46), etc., containing Cu contents generally below 4 wt pct. The single fcc solid solution regions at different temperatures in the Fe-Ni-Cu ternary phase diagram are presented in Figure 1, which are readapted from isothermal sections.[8,9] It can be seen that the Cu contents are quite limited, especially on the Fe-rich side, even at high temperatures, and it is important to determine the proper solubility limits of Cu in single-phase Fe-Ni austenite solid solutions that can be reached in normal experimental conditions, i.e., solution treatment plus water quenching. This necessarily requires a quantitative structural model in Fe-rich Fe-Ni-Cu for stable solid solution that easily avoids any solid-state phase transitions
BAOZENG LI, Doctoral Candidate, QING WANG, YINGMIN WANG, and JIANBING QIANG, Associate Professors, CHUNYAN LI, Lecturer, and CHUANG DONG, Professor, are with the Key Lab of Materials Modification by Laser, Ion and Electron Beams (Dalian University of Technology), Ministry of Education, School of Materials Science & Engineering, Dalian University of Technology, Dalian 116024, P.R. China. Contact e-mail: [email protected] CHUNJUN JI, Professor, is with the College of Energy Source and Power, Dalian University of Science and Technology, Dalian, 116024, P.R. China. Manuscript submitted February 24, 2011. Article published online September 30, 2011 544—VOLUME 43A, FEBRUARY 2012
such as Cu precipitation and spinodal decomposition during subsequent cooling.
II.
CLUSTER-PLUS-GLUE-ATOM MODEL
Solid solution alloys and their relevant structure models have been longstanding issues that date back to the Hume– Rothery time.[10] Although considerable efforts were devoted to the description of atomic configurations in solid solution alloys,[11–15] quantitative descriptions of solid solution structures remain unresolved. The cluster-plus-glue-atom model was originally developed for structural analysis and composition design of multicomponent metallic glasses and quasi-crystals.[16,17] This model dissociates an alloy structure into two parts: the cluster part and the glue atom part, where the cluster is the nearest neighbor coordination polyhedron and generally formed in elements with negative enthalpies of mixing (DH < 0), and the glue atoms are those elements having weak DH with the base elements. The alloy composition is then expressed with [cluster](glue)x, with x denoting the number of glue atoms matching one cluster. In the phase diagram, the designed alloy composition is located at a straight
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