1. The School of Mechanical Engineering, Central University of Venezuela, Apartado 49141, Caracas 1042-A, Venezuela
2. The School of Metallurgical Engineering and Materials Science, Central University of Venezuela, Apartado 49141, Caracas 1042-A, Venezuela
3. The Experimental University of Puerto OrdazEstado Bolívar, Venezuela
4. The Electron Microscopy Laboratory of the Technological Institute Dr Federico Rivero’Km 8, Carretera Panamericana, Caracas, Venezuela