Phase Stability in the Al (6-x) Cu x Zr 2 System for 0 < x < 1.
- PDF / 392,319 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 9 Downloads / 268 Views
PHASE STABILITY IN THE Al( P.
6
-x)CuxZr
2
SYSTEM FOR
0 < x < 1.
B. DESCH*, R. B. SCHWARZ*, AND P. NASH** * Center for Materials Science, Mail Stop K-765, Los Alamos National Laboratory, Los Alamos, NM 87545 ** Metallurgical and Materials Engineering Department, Illinois Institute of Technology, Chicago, IL 60616
ABSTRACT We have determined the structures and thermal stability of AI( 6 x) CuxZr 2 powder (0 : x • 1) powders prepared by mechanically alloying elemental mixtures. In the as mechanically alloyed condition the structure is L1 2 for 0 all x. After heating to 750 C the alloy is single phase D023 for 0 < x < 0.2, is a two-phase mixture of D023 and L1 2 for 0.2 < x < 0.6, and remains in the structure up to Ll phase for 0.6 < x < 1. Al 5 CuZr 2 is stable in the Ll The lattice parameter of the annealed L1 2 phase is Independent of x. 13600C. 1.
INTRODUCTION
Ordered intermetallics offer potential advantages over conventional disordered at high temperatures. The chemical alloys for structural applications ordering increases the elastic moduli and, within a temperature regime, causes In addition, their the flow stress to increase with increasing temperature. relatively low self diffusion rate gives intermetallics good creep resistance Their main disadvantage, however, is and high recrystallization temperatures. fracture. In some intermetallics their low ductility and tendency for brittle (e.g. Ni 3 Al) the lack of ductility has been attributed to grain boundary weakness. In polycrystals of low crystal symmetry (e.g., tetragonal DO 2 and D023 structures) lack of ductility may also result from the number of slip systems being lower than that required to accommodate the plastic deformation of the individual grains. 3
0
and melts at 1580 C, The intermetallic AI 3 Zr has a density of 4.1 g cm" suggesting it may be a good choice for structural applications where Because Al 3 Zr crystallizes in the temperature and density are critical. tetragonal DO2 3 structure, theoretical and experimental research has focused Based on on alloying with the aim of stabilizing the cubic L1 2 structure. band energy calculations, Freeman [1] suggested magnesium and lithium as potential candidates to yield compounds of the type Al 5 XZr 2 which would be Ohashi and Ichikawa [2] observed the formation stable in the L1 2 structure. of metastable Al3Zr precipitates with the L1 2 structure in rapidly cooled Al-5.39 wt% Zr-O.17 wt% Fe. Other minor impurities were copper, silicon, and 0 Upon annealing the alloy at 510 C, the L1 precipitates transformed titanium. Schneibel and Porter f3) reported that arc cast to the stable DO2 3 structure. Al-5.5Fe-25Zr (at.%) was almost single phase L1 2 and measured its mechanical Ternary phase diagram work done on the Al-Cu-Zr system by Markiv properties. and V. V. Burnashova (4] shows a two-phase equilibrium between the L1 2 Al 5 CuZr 2 and D0 2 3 -Al 3 Zr at 5000C. Recently, we measured the structures and thermal stabilities of AI 3 Zr and prepared by mechanically AlsXZr 2 alloy powders (X - Li, Cr
Data Loading...
