Samir Chandra Roy

Comparative study of the role of the nucleation stage on the final crystalline quality of (111) and (100) silicon carbide films deposited on silicon substrates.

We study the impact of the nucleation step on the final crystalline quality of 3C-SiC heteroepitaxial films grown on (111) and (100) oriented silicon substrates by low pressure chemical vapor deposition. The evolution of both the structural and morphological properties of 3C-SiC epilayers in dependence on the only nucleation parameters (propane flow rate and duration of the process) are investigated by means of x-ray diffraction, scanning electron, atomic force, and optical microscopies. At first, we show how the formation of interfacial voids is controlled by the experimental parameters, as previously reported, and we correlate the density of voids with the substrate sealing by using an analytical model developed by V. Cimalla et al. [Mater. Sci. Eng., B 46, 190 (1997)]. We show that the nucleation stage produces a more dense buffer layer in case of (111) substrates. Further, we investigate the impact of the nucleation parameters on the crystalline quality of 3C-SiC epilayers. Within our experimental set...

Transmission electron microscopy investigation of microtwins and double positioning domains in (111) 3C-SiC in relation with the carbonization conditions

In this work, transmission electron microscopy is used to investigate the influence of the carbonization conditions on the formation of crystal defects in 3C-SiC layers deposited on (111) silicon. We focus on two kinds of defects; (1) the stacking faults and microtwins lying in the (1¯1¯1) planes, and (2) the double positioning domains. While the density of the stacking faults and microtwins is found independent on the carbonization conditions, the size of the double positioning domains is strongly influenced by the propane flow rate and can be related to the substrate sealing at the early stage of carbonization.

Cavitation erosion: Using the target material as a pressure sensor

Numerical prediction of mass loss due to cavitation erosion requires the knowledge of the hydrodynamic impact loads generated by cavitation bubble collapses. Experimental measurements of such impact loads using conventional pressure sensors are not reliable (if not impossible) due to the micron size and the very small duration of the loading. In this paper, a new method to estimate these loading conditions is proposed based on cavitation pitting tests and an iterative inverse finite element modeling. The principle of the method is as follows. First, numerous pits corresponding to localized plastically deformed regions are identified from a cavitation test performed in a dedicated tunnel. Then each pit is numerically reproduced by finite element simulations of the material response to a representative Gaussian pressure field supposed to mimic a single bubble collapse. This gives the size and pressure distribution of the bubble impacts. The prime objective of this study is to find out if the target material...

Towards numerical prediction of cavitation erosion

This paper is intended to provide a potential basis for a numerical prediction of cavitation erosion damage. The proposed method can be divided into two steps. The first step consists in determining the loading conditions due to cavitation bubble collapses. It is shown that individual pits observed on highly polished metallic samples exposed to cavitation for a relatively small time can be considered as the signature of bubble collapse. By combining pitting tests with an inverse finite-element modelling (FEM) of the material response to a representative impact load, loading conditions can be derived for each individual bubble collapse in terms of stress amplitude (in gigapascals) and radial extent (in micrometres). This step requires characterizing as accurately as possible the properties of the material exposed to cavitation. This characterization should include the effect of strain rate, which is known to be high in cavitation erosion (typically of the order of several thousands s−1). Nanoindentation techniques as well as compressive tests at high strain rate using, for example, a split Hopkinson pressure bar test system may be used. The second step consists in developing an FEM approach to simulate the material response to the repetitive impact loads determined in step 1. This includes a detailed analysis of the hardening process (isotropic versus kinematic) in order to properly account for fatigue as well as the development of a suitable model of material damage and failure to account for mass loss. Although the whole method is not yet fully operational, promising results are presented that show that such a numerical method might be, in the long term, an alternative to correlative techniques used so far for cavitation erosion prediction.