ABSTRACT The change in elastic modulus as a function of temperature was investigated for a zircon... more ABSTRACT The change in elastic modulus as a function of temperature was investigated for a zirconium-based bulk metallic glass. High temperature nano-indentation was done over a wide temperature range from room temperature to the glass-transition. At higher temperature, there was a transition from inhomogeneous to homogeneous deformation, with a decrease in serrated flow and an increase in creep displacement. Hardness was found to decrease, whereas elastic modulus was found to increase with temperature. The increase in elastic modulus for metallic glass at higher temperature was explained by diffusive rearrangement of atoms resulting in free volume annihilation. This is in contrast to elastic modulus increase with temperature for silicate glasses due to compaction of its open three dimensional coordinated structure without any atomic diffusion.
Transactions of the Indian Institute of Metals, 2012
ABSTRACT In this study, AZ91 based hybrid nanocomposite was fabricated using mixture of TiC and a... more ABSTRACT In this study, AZ91 based hybrid nanocomposite was fabricated using mixture of TiC and alumina by friction stir processing (FSP). FSP of AZ91 was conducted with as well as without particle addition and under different cooling conditions. Distribution of nano TiC and Al2O3 particles in the Mg matrix was studied using SEM. Grain size analysis of the as-cast and FSP AZ91/(TiC + Al2O3) composite was done using optical microscopy. The performance of the fabricated nanocomposite was investigated using microhardness, bulk hardness and scratch tests. Microhardness testing was done at 50 gf load and bulk hardness at 5 Kgf load. Scratch test was performed at 2 and 5 N normal load values on a universal tribometer using Rockwell indentor. AZ91/(TiC + Al2O3) composite exhibited improved mechanical properties.
ABSTRACT The crystallization behavior and viscosity of an in situ metallic glass composite was in... more ABSTRACT The crystallization behavior and viscosity of an in situ metallic glass composite was investigated using a non-contact electrostatic levitation technique. The width of the supercooled liquid region for the amorphous matrix was found to be 74 K, indicating its excellent stability against crystallization. The viscosity data follows the Vogel–Fulcher–Tammann relation, which was used to determine the fragility of the composite melt. The viscosity of the composite is compared to monolithic metallic glasses in the context of “strong-fragile” liquid behavior.
Transactions of the Indian Institute of Metals, 2012
ABSTRACT Cavitation erosion (CE) of various components in hydroturbines is a critical issue. Seve... more ABSTRACT Cavitation erosion (CE) of various components in hydroturbines is a critical issue. Several attempts have been made in the past to counter CE through various surface modification techniques. In this study, a novel attempt has been made to modify the surface properties of hydroturbine steel with the aid of friction stir processing (FSP). Metallurgical characterization of the processed steel was undertaken with the help of XRD, SEM/EDS, EBSD and optical microscopy. For mechanical characterization micro-hardness and cavitation erosion studies were conducted. EBSD results confirmed the presence of grains in nano range. Processed steel showed gain in hardness of the order of 160 % in comparison to unprocessed steel. XRD results show a significant variation in the type and quantity of various phases in pre- and post processed steel. It was observed that FSPed steel showed a significant improvement in the erosion resistance in contrast to the unprocessed steel.
ABSTRACT Different surface patterns with nanometer length-scales were obtained by electrochemical... more ABSTRACT Different surface patterns with nanometer length-scales were obtained by electrochemical processing of metallic glasses. The wetting behaviour of these surface patterns was studied using sessile drop technique with distilled water droplet. It is demonstrated that the hydrophilic-hydrophobic nature of the metallic glass surface can be controlled through nano topography. The contact angle was found to increase from 70° for the flat metallic glass surface to 112° for the nano-dendritic structure. Atomic force microscopy was utilized to explain the difference in contact angle in term of the surface roughness for different nano-textures.
ABSTRACT Refinement of crystalline dendrites in a metallic glass composite, Zr56.2Ti13.8Nb5.0Cu6.... more ABSTRACT Refinement of crystalline dendrites in a metallic glass composite, Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5, was demonstrated by friction stir processing. The surface hardness of the amorphous matrix as well as the crystalline dendritic phase was found to increase by nearly a factor of two for the processed specimens. Higher hardness for the amorphous matrix was explained by the interaction of shear bands, while that for the crystalline dendrite was explained by grain refinement.
ABSTRACT The change in elastic modulus as a function of temperature was investigated for a zircon... more ABSTRACT The change in elastic modulus as a function of temperature was investigated for a zirconium-based bulk metallic glass. High temperature nano-indentation was done over a wide temperature range from room temperature to the glass-transition. At higher temperature, there was a transition from inhomogeneous to homogeneous deformation, with a decrease in serrated flow and an increase in creep displacement. Hardness was found to decrease, whereas elastic modulus was found to increase with temperature. The increase in elastic modulus for metallic glass at higher temperature was explained by diffusive rearrangement of atoms resulting in free volume annihilation. This is in contrast to elastic modulus increase with temperature for silicate glasses due to compaction of its open three dimensional coordinated structure without any atomic diffusion.
Transactions of the Indian Institute of Metals, 2012
ABSTRACT In this study, AZ91 based hybrid nanocomposite was fabricated using mixture of TiC and a... more ABSTRACT In this study, AZ91 based hybrid nanocomposite was fabricated using mixture of TiC and alumina by friction stir processing (FSP). FSP of AZ91 was conducted with as well as without particle addition and under different cooling conditions. Distribution of nano TiC and Al2O3 particles in the Mg matrix was studied using SEM. Grain size analysis of the as-cast and FSP AZ91/(TiC + Al2O3) composite was done using optical microscopy. The performance of the fabricated nanocomposite was investigated using microhardness, bulk hardness and scratch tests. Microhardness testing was done at 50 gf load and bulk hardness at 5 Kgf load. Scratch test was performed at 2 and 5 N normal load values on a universal tribometer using Rockwell indentor. AZ91/(TiC + Al2O3) composite exhibited improved mechanical properties.
ABSTRACT The crystallization behavior and viscosity of an in situ metallic glass composite was in... more ABSTRACT The crystallization behavior and viscosity of an in situ metallic glass composite was investigated using a non-contact electrostatic levitation technique. The width of the supercooled liquid region for the amorphous matrix was found to be 74 K, indicating its excellent stability against crystallization. The viscosity data follows the Vogel–Fulcher–Tammann relation, which was used to determine the fragility of the composite melt. The viscosity of the composite is compared to monolithic metallic glasses in the context of “strong-fragile” liquid behavior.
Transactions of the Indian Institute of Metals, 2012
ABSTRACT Cavitation erosion (CE) of various components in hydroturbines is a critical issue. Seve... more ABSTRACT Cavitation erosion (CE) of various components in hydroturbines is a critical issue. Several attempts have been made in the past to counter CE through various surface modification techniques. In this study, a novel attempt has been made to modify the surface properties of hydroturbine steel with the aid of friction stir processing (FSP). Metallurgical characterization of the processed steel was undertaken with the help of XRD, SEM/EDS, EBSD and optical microscopy. For mechanical characterization micro-hardness and cavitation erosion studies were conducted. EBSD results confirmed the presence of grains in nano range. Processed steel showed gain in hardness of the order of 160 % in comparison to unprocessed steel. XRD results show a significant variation in the type and quantity of various phases in pre- and post processed steel. It was observed that FSPed steel showed a significant improvement in the erosion resistance in contrast to the unprocessed steel.
ABSTRACT Different surface patterns with nanometer length-scales were obtained by electrochemical... more ABSTRACT Different surface patterns with nanometer length-scales were obtained by electrochemical processing of metallic glasses. The wetting behaviour of these surface patterns was studied using sessile drop technique with distilled water droplet. It is demonstrated that the hydrophilic-hydrophobic nature of the metallic glass surface can be controlled through nano topography. The contact angle was found to increase from 70° for the flat metallic glass surface to 112° for the nano-dendritic structure. Atomic force microscopy was utilized to explain the difference in contact angle in term of the surface roughness for different nano-textures.
ABSTRACT Refinement of crystalline dendrites in a metallic glass composite, Zr56.2Ti13.8Nb5.0Cu6.... more ABSTRACT Refinement of crystalline dendrites in a metallic glass composite, Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5, was demonstrated by friction stir processing. The surface hardness of the amorphous matrix as well as the crystalline dendritic phase was found to increase by nearly a factor of two for the processed specimens. Higher hardness for the amorphous matrix was explained by the interaction of shear bands, while that for the crystalline dendrite was explained by grain refinement.
Uploads
Papers by Harpreet Arora