Modeling of Microstructure Evolution in Metallic Multilayers with Immiscible Constituents
- PDF / 577,641 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 69 Downloads / 233 Views
DOI: 10.1007/s11837-012-0547-2 Ó 2013 TMS
Modeling of Microstructure Evolution in Metallic Multilayers with Immiscible Constituents HAIBO WAN,1 YAO SHEN,1,3 XU HE,1 and JIAN WANG2 1.—State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China. 2.—Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. 3.—e-mail: [email protected]
Thermal stabilities of Cu/Nb, Cu/Ag, and Cu/Mo multilayers are studied by a recently developed model for microstructure evolution in multilayers with immiscible constituents, which actually is an extension to the classic grooving theory. The experimentally evidenced zig–zag microstructure is found to form through grooving when grains are staggered in a ‘‘stair-like’’ fashion. Furthermore, stability maps for these systems are developed in terms of the aspect ratio of grain dimensions and the ratio of the distance between two nearest triple junctions to the in-plane grain size. A comparison of stability among the three systems shows that the ratio of the grain boundary energy to the interphase boundary energy is more important than the ratio of the two grain boundary energies in controlling the stability. A simple criterion is also proposed for a quick estimation of the stability. Both maps from the model and from the simple criterion are in good agreement with the experiments for multilayers.
INTRODUCTION Metallic multilayers with immiscible constituents are prone to degrade from their original layered structures by thermal grooving.1–10 Grooves develop at the intersections of grain boundaries with interphase boundaries driven by the reduction of the energies of interphase and grain boundaries. In some cases, the grooves can keep on growing until they penetrate the layers, resulting in layer pinchoff, while in many cases the grooves can finally become stable to preserve the layered structure. Recently, thermal grooving was found to yield a stable zig–zag layered structure,9,10 where the layers are offset by shear at triple junctions with equilibrium groove angles that are aligned in a zig– zag pattern. The zig–zag microstructure is promising in stabilizing multilayers with immiscible constituents, as the zig–zag alignment of triple junction is found to have better ability of anchoring the layered structure.9,10 Generally, the stability of multilayers against pinch-off at high temperatures is dependent on their initial microstructures and thermodynamic properties.5–10 The grain aspect ratio h/l (h is the layer
(Published online January 18, 2013)
thickness and l is the in-plane grain dimension) and the ratio of the grain boundary energy (cGB) to the interphase boundary energy (cPB) cGB/cPB are the two major factors affecting the multilayer stability, as shown in Fig. 1. The ratio cGB/cPB will determine the equilibrium groove half-angle (heq) at the triple junction as heq ¼ cos1 ðcPB =2cGB Þ. When the ratio cGB/cPB is large, heq is small, a
Data Loading...
