Mechanical Properties of Ni embedded Alumina Nanocomposite Thin Films N. Sudhir, D. Kumar, S. Yarmolenko, and J. Sankar Center for Advanced Materials and Smart Structures Department of Mechanical Engineering North Carolina A & T State University, Greensboro, NC 27411 ABSTRACT There is a wide spread interest in metal-ceramic nanocomposites due to their enhanced mechanical and magnetic properties when the size of metal particles is reduced to nano-scale. This paper presents results from our study of thin film ceramic-metal nanocomposites created by embedding nano-sized Ni metal particles in amorphous alumina matrix using pulsed laser deposition technique. Micro structural study of nanocomposites using high resolution transmission electron microscopy and scanning transmission electron microscopy with atomic number (Z) contrast (STEM- Z) have shown that nanocrystals of Ni are well separated from each other in alumina matrix. The size of nanoparticles is controlled by parameters of pulsed laser deposition method (deposition time and substrate temperature). Size of Ni nanoparticles is found to be 5 – 15 nm. Mechanical properties like hardness, elastic modulus and fracture toughness of samples having different particle size are investigated using nanoindentation continuous stiffness measurement (CSM) technique. Our results indicate that particle size has significant (up to 20 %) effect on hardness of thin film composites. Fracture toughness of these nanocomposites has been studied using Li-Bhushan method and a method relating fracture toughness and residual stress. INTRODUCTION Nanocomposites, formed by dispersion of metallic nano clusters into ceramic matrix, have been an alternative to innovative structures in recent days. It has been noticed that there is a significant improvement in strength when the particle size is reduced to nanoscale. Thin film nanocomposites formed by embedding metallic nanocrystallites can be engineered by proper selection of the metal and matrix. Magnetic nanoparticles introduced into ceramic matrix yielded in higher remanence compared to those in isotropic microcrystalline magnets [1]. Properties like coercivity and blocking temperature are also improved due to reduction of particle size to few nanometers [2]. Ni hardness is found to be increased significantly when its particle size was reduced from 10 μm to 10 nm [3]. Some of the applications of nanoparticles include dispersions and coatings, functional nanostructures, consolidated materials and biological systems [4]. Nanocomposites broad application is limited due to unavailability of suitable production technique that has control over the size, distribution and shape of the nanocrystals. Several deposition techniques like sol-gel processes, ion implantation, spray pyrolsis and gas condensation are employed successfully to some extent [5]. In recent years pulsed laser deposition (PLD) process is found to be ideal technique for synthesis of nanocrystallites [6]. Ceramics are well known for their high hardness, high melting temperatures, excellent wear resistance and chemical stability. But the application of these ceramics at wide spread scale is being limited by their brittleness. Previous studies indicated that dispersion of ductile metal particles usually nanoclusters into the ceramic matrix results in a composite with significant improvement in toughness as well as hardness The addition of second phase ductile inclusions can influence the crack propagation and thus fracture toughness[7]. Increase in toughness can be attributed to the plastic work done in deforming the ductile inclusions [8]. Al 2 O 3 ceramic has high hardness, chemical stability and refractory properties. Considerable amount of research has been done in Al 2 O 3 -based nanocomposites with metal and sometimes ceramic nano 28th International Conference on Advanced Ceramics and Composites B: Ceramics Engineering and Science Proceedings. Vol 25, Issue 4, 2004. John Wiley & Sons, Inc