Pramoda K. Nayak

Processing and Characterization of Alumina/ Chromium Carbide Ceramic Nanocomposite

Materials with nano-scale components as reinforcement phase are adding new dimensions to composite materials, thereby fascilating major improvement in functional and structural properties. Ceramic nanocomposites are the blends of different ceramic matrices with nanometer sized functional particles. The advantages of these nanocomposites include: improved mechanical properties, surface properties, decreased permeability to gases, water and hydrocarbons, higher thermal stability and heat distortion temperature, higher chemical resistance, smoother surface appearance and higher thermal conductivity. The incorporation of only a few percent of nano-sized particles makes great property changes and formerly unachievable property combinations possible. The ceramic nanocomposites can be devided into into three types; intragranular composite, intergranular composite and nano/nano composite (Niihara, 1991) according to their microstructures. In intra and intergranular nano-composite, the nano-sized particles are dispersed mainly within the matrix grains or at the grain boundaries of the matrix, respectively. The aim of these composites is to improve the mechanical properties such as hardness, facture strength, toughness and also high temperature mechanical properties such as hardness, strength, creep and fatigue facture resistances. On the other hand, nano/nano composites are composed of the dispersoids and matrix grains within the nanometer size. The primary purpose of this type of nano-composite is to add new functions such as machinability and super plasticity like metals to ceramics.

Strengthening alumina ceramic matrix nanocomposites using spark plasma sintering

The strengthening of Al 2 O 3 –Cr 2 O 3 /Cr 3 C 2 nanocomposites has been investigated using nano-indentation technique. These composites are fabricated by metal organic chemical vapor deposition (MOCVD) using Cr(CO) 6 as a precursor and Al 2 O 3 as the matrix followed by spark plasma sintering (SPS). The nanocomposites have a higher elastic modulus and are able to endure higher plastic deformation than monolithic alumina. The microstructures of the dislocation, transgranular and stepwise fracture surfaces are observed. Moreover, Al 2 O 3 –Cr 2 O 3 /Cr 3 C 2 nanocomposites have high hardness, fracture toughness and facture strength due to strengthening by second phase Cr 3 C 2 particles and the solid solution of Al 2 O 3 –Cr 2 O 3 .

Growth of single crystal silicon carbide by liquid phase epitaxy using samarium/cobalt as unique solvent

An approach for synthesizing single crystal silicon carbide at low temperature using liquid phase epitaxy is proposed. A mixture of samarium and cobalt (Sm:Co = 64:36 at.%) was used as a unique solvent in this synthesis process. Electron microscopy indicates the epitaxial growth of single crystal silicon carbide with a thickness of 4 µm over a silicon wafer followed by the formation of polycrystalline silicon carbide and silicon carbide whiskers. Some growth mechanisms are proposed to explain the formation of silicon carbide. It is hypothesized that the single crystal silicon carbide grew from the liquid phase, whereas polycrystalline silicon carbide whiskers grew via the vapor–liquid–solid process.

Effect of Nano-TiN on Mechanical Behavior of Si3N4 Based Nanocomposites by Spark Plasma Sintering (SPS)

Ceramic nanocomposites are often defined as a ceramic matrix reinforced with submicron/ nano sized particles of a secondary phase. The advantages of these nanocomposites include: improved mechanical properties, surface properties, high thermal stability and superior thermal conductivity. It is very fascinating/interesting for the researchers to synthesize these composites as the incorporation of few percent nanosized particles changes the materials property substantially. Niihara et al.,[35], [36] have reported that the mechanical properties of ceramics can be improved significantly by dispersing nanometer-sized ceramic particles into ceramic matrix grains or grain boundaries. According to their observation, 5 vol% of sil‐ icon carbide nanoparticles into alumina matrix increases the room temperature strength from 350 MPa to approximately 1 GPa. Other strength improvements through similar ap‐ proaches have been observed in alumina-silicon nitride, magnesia-silicon carbide, and sili‐ con nitride-silicon carbide composite systems.