Mechanical Behavior of Multilayered Nanoscale Metal‐Ceramic Composites

Abstract

Single and multilayered structures at nano‐length scale are very attractive materials due to their high strength, toughness, and wear resistance relative to conventional laminated composites. In this study, single layered Al, SiC, and multilayered Al/SiC composites were synthesized by DC/RF magnetron sputtering. The microstructure of the multilayered structures was characterized by scanning electron microscopy (SEM). The elastic and plastic behavior of single and multilayered materials was investigated by nanoindentation and tensile testing. For nanoindentation, an analytical model was employed to subtract the contribution of the Si substrate, in order to extract the true modulus of the films. Finite element simulations were employed to confirm the analytical predictions and to investigate the anisotropic elastic behavior of the multilayered composite. It was concluded that while indentation provides reasonable Young's modulus and hardness values in monolithic layers, it does not provide the true modulus of the multilayered materials because of their inherent anisotropy.

High temperature micropillar compression of Al/SiC nanolaminates

“…The difference, although very small, is very probably caused by the elastic anisotropy of Al/SiC laminates due to the layer orientation, as discussed in Ref. [2], While the transverse elastic modulus is measured directly during micropillar compression, nanoindentation tests perpendicular to the layers are influenced by both the transverse and the longitudinal elastic moduli, because of the multiaxial stress state. Thus, when loading perpendicular to the layers, in nanoindentation one would expect a slightly higher modulus because of the contribution from loading parallel to the layers.…”

“…The sample holder was continuously rotated during sputtering to obtain uniform layer thicknesses. The deposition rates were ^7.5 nm min -1 for A1 and 3.9 nm min -1 for SiC [2,19,31,32], A total of 40 layers (20 A1 and 20 SiC) were deposited. The individual layer thickness of A1 and SiC were targeted to be ~60 nm.…”

“…Nanolaminated composites (also referred to as nanolayered or nanoscale multilayers) with individual layer thicknesses <100 nm have been the topic of many recent experimental and theoretical studies [1,2]. In particular, metal-ceramic multilayers show an attractive combination of electrical [3,4], magnetic [5][6][7], optical [8][9][10] and mechanical [11] properties, which are appealing for a number of engineering applications.…”

Indentation-Induced Shear Band Formation in Thin-Film Multilayers

“…The stress-strain curves extracted from micro-tensile experiments of Al and Al/SiC multilayer films show that, while independent Al layers experience an expected work hardening leading to perfect plasticity, the Al/SiC multilayer film as a whole exhibits work softening (Deng et al, 2005a). This implies that the SiC layers themselves have a strain softening behavior.…”

“…This phenomenon has not surfaced in the previous finite element models associated with elastic-perfect-plasticity. However, from the micro-tension tests of Deng et al (2005a), it is inferred that the SiC film actually exhibits strain softening after yielding. The present exploratory work thus focuses on attempting shear band initiation in finite element models by incorporating strain softening of the SiC layers.…”