Materials Science and Engineering, A 163 ( 1993) 81-90 81 Coarsening behavior of L 12 precipitates in melt-spun A1-Ti-V-Zr alloys Hoseok Lee Hyundai Electronics Company, San 136-1,Ami-Ri Bubal-Eub lchon-Kun, Kyoungki-Do 467-860 (South Korea) Seung Zeon Han, Hyuck Mo Lee and Zin-Hyoung Lee Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusung-Dong Yusung-Gu, Taejon 305-701 (South Korea) (Received August 11, 1992; in revised form November 24, 1992) Abstract Aging studies of two melt-spun A1-2at.% (Ti,V, Zr) alloys showed that the would-be metastable L 12 Al3 (Ti,V, Zr) precipi- tates did not transform to stable D02~ ones, and the average radius is 5-7 nm and the interparticle spacing is 20-40 nm at 698 K up to 400 h. The coarsening rate of spherical AI3(Ti0.2V~ 4Zr0.4) precipitates was observed to be five times as fast as that of Al3(Ti01V04Zros) precipitates. The coarsening behavior in both alloys obeyed the Lifshitz-Slyozov-Wagner (LSW) prediction well. Owing to the low coarsening rate and the high thermal stability of the precipitated phase, A1-Ti-V-Zr systems show promise as bases for high-temperature high-strength AI alloys, 1. Introduction Aluminum alloys with adequate strength at elevated temperatures are increasingly in demand in structural applications. So far, several alloy systems designed for high-temperature applications have appeared, of which the rapidly solidified AI-Fe-V-Si systems have received the most attention [1, 2]. While the A1-Fe-V-Si systems appear to be the best, several Al-based systems containing transition metal elements for potential elevated-temperature use were suggested by Adam [3] based on low values of dif- fusivities and solubilities. The equilibrium crYStal struc- tures of Al3Ti, A13V and A13Zr are tetragonal D022, D022 and D023, respectively. At the high temperatures of interest, around 698 K, vanadium and titanium are mutually substitutable in the form of A13(Ti,V) [4]. Much of titanium and vanadium can be substituted for zirconium in the D023-type A13Zr compound, creating A13(Ti,Zr) and A13(V, Zr), respectively [5]. In particular, it has been reported that metastable f.c.c. L 1z-structured AI3M (M=Ti,V, Zr) dispersoids form in the rapidly solidified AI-V-Zr and AI-Ti-Zr systems and both L12- and D0ystructured A13M phases showed slow coarsening kinetics [6-9]. The L 12 precipitates may form as spherical or cellu- lar fan-shaped morphology depending on alloying compositions and aging temperatures [6, 9]. Spherical ones are coherent and coplanar with the aluminum matrix. The D022-type structure is an ordered one derived from the L 12-type structure by introducing an antiphase boundary (APB) with a displacement vector of the type 1/2 [1 10] on every (001) plane. When the 1/2 [110]-type APB is introduced on every other (001) plane in the L 12-type structure, the D023-type structure can be derived. The lattice parameters of tetragonal A13Ti and A13V, a' and c, are very close to a 0 and 2a0, respectively, where a 0 is the lattice parameter of cubic AI and a' is the half diagonal length of the (001) plane in a unit cell of the D022 structure. A13Zr is also tetrag- onal. However, there is a good matching between the a lattice parameters of AI and AI3Zr and between 4a 0 of AI and c of AI3Zr. Thus the D023 phase in this system matches the A1 lattice rather well, and the D023 phase is believed to match the matrix better than the D022 phase does [5, 10]. From this point of view, it was of interest how to design the AI-Ti-V-Zr system and optimize the com- positions of added transition elements to minimize the lattice misfit, and thus interracial energy, and maximize the coarsening resistance and, at the same time, opti- mize the volume fraction of the precipitated stable D023 A13M phase and, therefore, maximize the strengthening effects at high temperatures. In a review article, Froes et al. [ 11 ] showed that the solubility limits (at.%) in binary aluminum alloys under rapid solidifica- tions are, 0.2 to 2 for Ti, 1.4 to 2 for V and 1.2 to 1.5 for Zr. The total amount of added alloying elements to be optimized being fixed to 2 at.%, some work on the alloy design had already been performed along this line 0921-5093/93/$6.(10 © 1993 - Elsevier Sequoia. All rights reserved