Institute of Fundamental Technological Research

Electron back-scattered diffraction (EBSD) studies carried out for the Cu/α−Al2O3 composites manufactured by pulsed laser deposition method and by the powder metallurgy enable to uncover a set of orientation relationships characteristic for materials of this type. The identified interfaces are categorized according to the bonding strength. Additionally, their microstructure is reproduced by molecular dynamic (MD) simulations. The obtained classification of the phase boundaries constitutes key information for effective composite design.

EBSD, Cu/α−Al2O3 composites, PLD, bonding strength, molecular dynamics simulation

A Nd:YAG laser operating at a wavelength of 266 or 355 nm is used to deposit a thin layer of copper on the (0 0 0 1)α-Al2O3 surface. The formation process is precisely controlled by identification of time distribution of two characteristics: energy and flux density of particles incident on the substrate. For this purpose, the Cu-plasma expansion is described by means of an analytical hydrodynamic model whose self-similar solutions are fitted to the experimental plasma images and time-of-flight spectra. The obtained nanocomposite is examined by the aberration-corrected high-resolution transmission electron microscopy (Cs-HRTEM) method. The results reveal that copper crystals assume one main orientation relative to the substrate (1 1 1)[2 −1 −1]Cu∥ (0 0 0 1)[−1 −1 2 0]α–Al2O3 and the formed interface has a specific microstructure. To reconstruct the phase boundary region, molecular dynamic (MD) and static (MS) simulations are carried out. The results show that strong bonding between copper and sapphire induces structural changes in the (1 1 1) Cu layer nearest the substrate and leads to formation of the system of partially dissociated dislocations in the next layer. In consequence, the Cu/α–Al2O3 interface becomes the semicoherent system. The lattice matching regions of the individual Cu layers are significantly lowered, which results in strong deformations along the closed packed planes. The reconstructed interface is used for Cs-HRTEM image simulation. A good accordance with the experimental results indicates that the MD model correctly maps the microstructure at the phase boundary of the synthesized nanocomposite.

Recent investigations reveal that interface bonding strength is dependent on the relative orientation of crystallites of the both phases [2]. The experimental, theoretical and computational investigations confirm this observation in the case of Cu/Al2O3 system, [3], [4]. It is shown that the statistical distribution of the values of interface strength for different relative orientations of bonded phases should be included in the phenomenological model of the damage initiation in nanocomposites. The novelty of the presented study is the combination of different experimental techniques: HRTEM, EBSD and molecular dynamics simulations with phenomenological theory of damage development in nanocomposites due to debonding at the interphase boundary [5], [6], [7]. A class of new models with the yield condition determined by one of quadric surfaces, in particular paraboloid or ellipsoid one is considered and the comparison with popular Gurson approach is discussed, [8].

nanocompistes, strength, interface, bonding, HRTEM, EBSD, molecular dynamics

The composition of metal with ceramics is applied to many devices, structural elements of machines as well as their equipment. Therefore, evaluating the strength of interfaces of this type becomes an important scientific issue of fundamental character. Numerous attempts are made to solve the posed problem, both experimental and theoretical ones. The presented approach enables local, more precise determining the mechanical properties of interfaces. The basis of conducted calculations is the geometry of the interface strongly preferred by the considered system of materials. It is defined by the mutual orientation of crystallites of two phases and the position of the plane boundary. The combination of two advanced research methods: electron back-scatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM) enables identification of this crucial characteristics. The second of them additionally reveals a representative microstructure of the interface in the form of a projection. We reconstruct it in three dimensions by means of molecular dynamics (MD) simulations. In this way, we identify deformation mechanisms that enable the formation of the bonding between the metallic phase and ceramic one.

nanocomposites, deformation in interface, HRTEM