Reaction Scheme and Liquidus Surface in the Al-Rich Section of the Al-Cr-Ni System

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NTRODUCTION

BECAUSE of the well-known technological importance (for example, the reviews by Stickler,[1] Anton,[2] Decker,[3] and the references quoted therein), the Ni-rich part of the Al-Cr-Ni system early on was subject to experimental investigations[4–6] resulting in quite complete knowledge of the Al-Cr-Ni constitution within the composition range Ni-NiAl-Cr (e.g., Velikanova et al.[7] and Raghavan[8]). For the remaining, more Al-rich part of the system, however, only the exploratory work of Rosell-Laclau et al.[9,10] and the crystal structure determination of the ternary phase j-Al76.2Cr18.0Ni5.8 (space group P63, a = 1.7674 nm, and c = 1.2516 nm by Sato et al.[11]; in the following labeled s1) existed until Grushko et al.[12] reported isothermal sections for 1000 C and 900 C. At both temperatures, the ternary phase f (=s1) exists as single phase over a wide composition range. The melting temperature was measured to be about 1030 C. In the section at 1000 C, another ternary phase was observed in addition. This phase was labeled e, because it was found to have lattice parameters virtually identical to the reportedly binary phase e-CrAl4.[13–15] This phase did not occur at 900 C, but Grushko et al.[12] mentioned the existence of two FRANZ WEITZER, Assistant Professor, and JULIUS C. SCHUSTER, University Professor, are with the Innovative Materials Group, Universitt Wien, A-1090 Wien, Austria. WEI XIONG and SHUHONG LIU, Graduate Students, and YONG DU, University Professor, are with State Key Lab of Powder Metallurgy, Central South University, 410083 Changsha, Hunan, People’s Republic of China. NATALIYA KRENDELSBERGER, Senior Research Fellow, is with the ECHEM Center of Competence in Applied Electrochemistry, A-2700 Wiener Neustadt, Vienna, Austria. Contact e-mail: [email protected] Manuscript submitted March 14, 2008. Article published online July 15, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A

more ternary phases at lower temperatures without giving further details. The present article aims to elucidate the equilibria among these phases at 700 C and to establish the invariant reaction temperatures in this part of the Al-CrNi system. The binary systems Al-Ni and Cr-Ni are accepted as boundary systems as assessed in the literature (References 16 and 17, respectively). The invariant melting temperatures used for the Al-Cr binary system were measured by Chen et al.[18] and are in close agreement with previous literature.[19] A detailed study of the c-phase region of that system is in progress and will be published elsewhere.

II.

EXPERIMENTAL

More than 30 ternary Al-Cr-Ni alloys (about onethird of them three-phase alloys) were prepared by arc melting under high-purity argon atmosphere (from ingots of 99.99 mass pct pure Al, Cr, and Ni; all supplied by Johnson Matthey Alfa Products, Karlsruhe, Germany; or from 99.999 mass pct pure Al wire, 99.98 wt pct pure Cr pieces, and 99.99 mass pct pure Ni plates, all supplied by the Mining Technical Development Center for Non-Ferrous Metals, Beijing, Peop