Ranjit Bauri

Conventional metal matrix composites (MMCs) suffer from the disadvantage of low ductility. In order to overcome this, reinforcing the metal matrix with metal particles can be taken as an alternative approach. However, processing such composites can pose serious challenges as the metal particles can either go in to solution or form undesirable intermetallics during processing through conventional routes. Friction stir processing (FSP) is emerging as a versatile tool for processing and modification of variety of materials. In the present study, metal particulate reinforced aluminum matrix composite was processed by incorporating nickel particles through friction stir processing (FSP) in one step. The microstructure was characterized by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). SEM observations revealed that particles are uniformly dispersed in the aluminum matrix with excellent interfacial bonding. FSP also lead to grain refinement of the matrix as observed by EBSD and TEM analysis. Moreover, no harmful Al-Ni intermetallics formed in the matrix. The mechanical properties were determined by tensile tests to evaluate the effect of metal particulate reinforcement. The novel feature of the composite is that it exhibits a threefold increase in the yield stress (0.2% proof stress) while appreciable amount of ductility is retained. © 2010 American Institute of Physics.

Samaria doped ceria (SDC) co-doped with Nd2O3 (Nd-SDC) and doubly co-doped with Nd2O3 and Pr 2O3 (Pr-Nd-SDC) was prepared by solution combustion synthesis. X-ray diffraction studies confirmed the nanocrystalline nature of the powder with cubic fluorite phase. Raman spectroscopy showed the characteristic cubic fluorite peak (464 cm-1) of ceria and the vacancy concentration calculated from the peak area ratio (A550/A464) was found to be higher in Pr-Nd-SDC (0.556) compared to Nd-SDC (0.168). The powder was compacted into discs and sintered to obtain dense pellets. The sintering temperature was found to be considerably lower than that required for microcrystalline SDC. The electrical conductivity was obtained by impedance spectroscopy. The doubly co-doped sample (Pr-Nd-SDC) exhibited higher conductivity and lower activation energy compared to the co-doped sample (Nd-SDC). © The Electrochemical Society.

In the present study Ni particles were incorporated in 5083 Al alloy by friction stir processing (FSP) to fabricate metal particle reinforced composite. A conventional cylindrical tool was first used for FSP and several processing parameters (rotational and traverse speeds) were exploredto get a defect free stir zone and uniform distribution of the particles. The effect of tool geometry was also studied by using another tool having special features on the pin and the shoulder. A tool rotation speed of 1200. rpm and traverse speed of 0.4. mm/s were found to be optimum for obtaining a defect free stir zone. However, the distribution of Ni particles was inhomogeneous for all the parameters used with the plain cylindrical tool irrespective of defective or a sound stir zone. The tool with the special features, threads on the pin and spiral grooves on the shoulder, was found to be very effective in both producing a sound stir zone and dispersing the Ni particles. It was also found that ball milled fine particles were dispersed more uniformly in the stir zone compared to the as-received coarse particles. FSP also refined the grain size of the aluminium matrix from 25μm to 3μm. The microstructure was characterised by equiaxed fine grains with a high fraction of high angle grain boundaries and a narrow grain size distribution. The effect of the particle incorporation on the mechanical properties of the alloy was also investigated. The strength increased significantly compared to the base alloy and more importantly a high amount of ductility was also achieved in the composite.