Papers by Author: Roman Nowak

Abstract: A small titanium-decorated fullerene cluster (C60[TiH2]6)7 was studied by MD simulation over a wide range of energy, from the solid state to the vaporization of the nanosystem. The low energy, solid state structure of the cluster was obtained as a deformed pentagonal bipyramid. Several physical characteristics: the radial distribution function, the mean square displacement, the translational velocity autocorrelation function, translational diffusion coefficient, Lindemann index, etc., were calculated for a wide range of energy in the system.

Abstract: The nanosystem composed of only as few as seven endohedral fullerene K+@C60 molecules was simulated using the MD method. The interaction was taken to be the full site-site pairwise additive Lennard-Jones (LJ) potential, which generates both translational and anisotropic rotational motions of each endohedral fullerene. The atomically detailed MD simulations allow the dynamics of the motion of K+@C60 molecule inside the cluster to be analysed. The radial distribution function, the mean square displacement, the translational velocity correlation functions and the Lindemann index of endohedral fullerene have been calculated for several energies of the nanosystem. The solid/liquid phase transition and the existence of the liquid phase in the endohedral potassium ion fullerene cluster was found.

Abstract: The present paper reports molecular dynamics study of the elastic deformation of zinc- blende GaAs crystal by spherical diamond indenter acting on the (001) plane. The atomic displacements under field of elastic deformation result in generation of characteristic atomic structure with arms located along <110> directions. The phase transformation from zinc-blende to rock-salt GaAs structure was recognized in thin volume under indenter.

Abstract: Ceramic nanocomposites became nowadays an important ingredient of many structural and electronic ceramics, as well as ceramic coatings. The same applies to chemically processed and environmental related ceramics. The performance and characteristics of ceramic components are considerably influenced by the characteristics of precursor powder. The outstanding properties possessed by advanced nanoceramics are achieved through exceptional composition and microstructure that require very careful control throughout the successive stages of the applied processing.

Abstract: Special mechanical properties have widely been demonstrated with bulk nanocrystalline materials. An increasing effort has been made to transfer such improvements also into thermal sprayed ceramic coatings. This paper focuses on such efforts in alumina-based ceramic coatings. The optimization of process conditions and effect of different process parameters on the mechanical performance of high velocity oxy-fuel (HVOF) sprayed ceramic coatings is discussed.

Abstract: HVOF thermal spraying has been developed to deposit dense Al2O3-coatings for improved protective properties. As compared to generally used plasma sprayed coatings HVOF coatings can be prepared much denser and thus are better suited for applications where protective properties of the coating are needed. In this paper we describe the development of HVOF spraying technologies for nanocrystalline Al2O3- and Al2O3-Ni-coatings. The microstructure and the mechanical properties of these novel coatings are reported and compared to a conventionally processed Al2O3-coating.

Abstract: The present paper is based on the contribution by Niihara and his co-workers devoted to indentation testing of ceramic materials, while it provides new observations of peculiarities registered during nanoindentation of sapphire, GaAs and InGaNAs deposited by MBE-technique. Exploiting previous studies of the spherical indentation in sapphire, the present authors recognized different causes that result in the apparently similar pop-in phenomenon for sapphire and GaAs-based semiconductors. The finite element modeling of the quasi-plastic nanoindentation of the ( 1 1 20) plane of sapphire with the elastically deformable tip confirmed that the deformation of sapphire is governed by twinning which causes pop-in phenomenon, as suggested earlier by Niihara et al. The singularities registered for GaAs-based crystals are associated with dislocation movement within {111} slip bands, which is in contrast to the case of sapphire.