Nanocomposites of carbon nanotubes embedded in a (Ti,Al)N coated film

Titanium aluminum nitride ((Ti,Al)N) thin films are widely used as hard protective coating materials. Due to their remarkable tensile strength and elastic modulus carbon nanotubes (CNTs) are an ideal candidate as reinforcing components in such coatings. In this work (Ti,Al)N thin film were deposited on steel substrate by reactive magnetron sputtering and CNTs were grown on top by chemical vapor deposition (CVD). A second (Ti,Al)N film covered the CNTs in order to achieve a nanocomposite structure similar to reinforced concrete. The chemical evolution of the substrate, structure, morphology and growth of CNTs were analyzed by X-ray photoelectron spectroscopy and scanning electron microscopy. It was possible to achieve homogeneous dispersion of the CNTs within the matrix by adjusting the CVD time. Mechanical testing of the adherence and nanohardness of the (Ti,Al)N/CNT/(Ti,Al)N composite coating were performed by scratch and nanoindentation tests. The improvement of mechanical properties by CNT integration resulted in an increase of the hardness and of Young's modulus. (C) 2012 Elsevier B.V. All rights reserved.

Deposition and characterization of pulsed direct current magnetron sputtered Al95.5Cr2.5Si2 (N1-xOx) thin films

Alireza Karimi, Hossein Najafi

Aluminum rich oxynitride thin films were prepared using pulsed direct current (DC) magnetron sputtering from an Al95.5Cr2.5Si2 (at.%) target. Two series of films were deposited at 400 degrees C and 650 degrees C by changing the O-2/(O-2 + N-2) ratio in the reactive gas from 0% (pure nitrides) to 100% (pure oxides). The films were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and nanoindentation. The results showed the existence of three different regions of microstructure and properties with respect to the oxygen concentration. For the samples deposited at 650 degrees C in the nitrogen rich region (O-2/(O-2+N-2)

2010

Texture change through film thickness and off-axis accommodation of (002) planes

Alireza Karimi, Akshath Raghu Shetty

We present our recent experimental results on the formation of off-axis texture and crystallographic tilting of crystallites that take place in thin film of transition metal nitrides. For this purpose, the microstructural development of TiAlN film was studied, specially the change in texture with film thickness. Fiber texture was measured using theta-2 theta and pole figure X-ray diffraction (XRD), while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the microstructure and changes in texture with thickness. The sin(2)psi method was applied to determine the stresses on (1 1 1) and (0 0 2) plane. With deposition parameters chosen, the growth texture mechanism is discussed in three different stages of film growth. Surface energy minimization at low thickness leads to the development of (0 0 2) orientation. On the other hand, the competitive growth promotes the growth of (1 1 1) planes parallel to film surface at higher thickness. However, contrary to the prediction of growth models, the (0 0 2) grains are not completely overlapped by (1 1 1) grains at higher thickness. Rather the (0 0 2) grains still constitute the surface, but are tilted away from the substrate normal showing substantial in-plane alignment to allow the (1 1 1) planes remain parallel to film surface. Intrinsic stress along (1 1 1) and (0 0 2) shows a strong dependence with preferred orientation. The stress level in (0 0 2) grains which was compressive at low thickness changes to tensile at higher thickness. This change in the nature of stress allows the (0 0 2) planes to tilt away in order to promote the growth of (111) parallel to film normal and to minimize the overall energy of system due to high compressive stress stored in the (1 1 1) grains. The change in surface morphology with thickness was observed using SEM. An increase in surface roughness with film thickness was observed which indicates the development of (1 1 1) texture parallel to film surface. TEM observations support the XRD results regarding texture change. Film hardness was measured by nanoindentation and a correlation between (1 1 1) texture, stress and hardness is obtained. The results indicate that texture development is a complex interplay between thermodynamic and kinetic forces. An attempt is made to understand this phenomenon of off-axis accommodation of (0 0 2) at higher thicknesses, which is a new result not reported previously. (C) 2011 Elsevier B.V. All rights reserved.

2011

Texture change through film thickness and off-axis accommodation of (002) planes

Alireza Karimi, Akshath Raghu Shetty

2011