Showing papers by "Srinivasa R. Bakshi published in 2009"
TL;DR: In this article, a homogenous dispersion of carbon nanotubes (CNTs) in micron sized aluminum silicon alloy powders was achieved by spray drying, which allowed fabrication of thick composite coatings and hollow cylinders (5 mm thick) containing 5.5 and 10.5 wt.% CNTs by plasma spraying.
Abstract: Homogenous dispersion of carbon nanotubes (CNTs) in micron sized aluminum silicon alloy powders was achieved by spray drying. Excellent flowability of the powders allowed fabrication of thick composite coatings and hollow cylinders (5 mm thick) containing 5 wt.% and 10 wt.% CNT by plasma spraying. Two phase microstructure with matrix having good distribution of CNT and CNT rich clusters was observed. Microstructural evolution has been explained using single splat and the infiltration of CNT clusters by liquid metal. Partial CNT surface damage was observed in case of the 10 wt.% CNT coating due to CNT mesh formation and smaller size of spray dried agglomerate. Increase in the elastic modulus and improvement in the yield strength and elastic recovery properties due to CNT addition was observed by nanoindentation.
179 citations
15 Oct 2009-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the dual role of carbon nanotubes (CNTs) in strengthening roll-bonded aluminum composites has been elucidated, which can be correlated to the degree of dispersion of CNTs in the matrix.
Abstract: The dual role of carbon nanotubes (CNTs) in strengthening roll bonded aluminum composites has been elucidated in this study. An increase in the elastic modulus by 59% has been observed at 2 vol.% CNT addition in aluminum, whereas tensile strength increases by 250% with 9.5 vol.% CNT addition. CNTs play a dual role in the strengthening mechanism in Al–CNT composite foil, which can be correlated to the degree of dispersion of CNTs in the matrix. Better CNT dispersion leads to improvement of elastic properties. In contrast, CNT clusters in the aluminum matrix impede dislocation motion, causing strain hardening and thus improvement in the tensile strength. Dislocation density of the composites has been computed as a function of CNT content to show the effect on strain hardening of the metal matrix–CNT composite.
99 citations
TL;DR: In this paper, a pseudo-phase diagram was generated based on the thermodynamic calculations to predict the type of carbide (Al4C3 or SiC) that would form at the matrix-CNT interface as a function of matrix composition and processing temperature.
93 citations
TL;DR: In this paper, an attempt is made to quantify the quality of distribution of carbon nanotubes in a metal matrix composite by two methods: Dispersion Parameter (DP) and Clustering Parameter(CP).
Abstract: Quantification of the quality of distribution is essential in carbon nanotube (CNT) composites since it reflects the homogeneity of the properties. In this work, an attempt is made to quantify the quality of distribution of carbon nanotubes in a metal matrix composite by two methods. Two parameters have been proposed which are complimentary. The first one called Dispersion Parameter (DP) is based on the image analysis technique and is obtained based on the size of CNT cluster while the second one, named the Clustering Parameter (CP) is based on distances between centers of the nanotubes obtained by Delaunay triangulation. The method is applied to compare the level of distribution of nanotubes in three micrographs of CNT reinforced aluminum composite fabricated by cold spraying. A comparison between two quantification techniques is made. Carbon nanotube distribution obtained by image analysis technique is successfully utilized to correlate and account for experimentally obtained elastic modulus values of the nanocomposite by nanoindentation.
82 citations
TL;DR: In this article, the feasibility of reaction synthesis of Ti3SiC2 phase using plasma spraying of powder mixture of Ti, SiC and graphite was investigated and phase identification and microstructural characterizations of the as-sprayed coatings were conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM), and TEM.
74 citations
TL;DR: In this article, the length to width ratio of the splats was found to be larger for Al particles compared to Al-Si particles, which is explained by the inter-splat delamination mechanism.
Abstract: Composite coatings containing aluminum and aluminum–11.6 wt.% silicon eutectic alloy phases of varying compositions were fabricated using cold spraying. Coating contained a uniform distribution of the two phases. The hardness of the coatings increased as the volume fraction of Al–Si in the coating increased. The length to width ratio of the splats was found to be larger for Al particles compared to Al–Si particles. Dry sliding ball-on-plate wear tests indicated that the wear volume loss was similar for the Al and Al/Al–Si composite coatings in spite of the increase in microhardness. This discrepancy is explained by the inter-splat delamination mechanism. The coefficient of friction of aluminum coating reduced on Al–Si addition.
53 citations
TL;DR: In this article, the interaction of carbon nanotubes (CNTs) with the flame/energy sources during different thermal spray processes was compared, and the retention of CNT structure was attributed to micron size metal/ceramic powder which acts as a carrier and thermal shield against high heat in plasma spraying (PS) and high-velocity oxy fuel spraying (HVOF).
Abstract: This study compares the interaction of carbon nanotubes (CNTs) with the flame/energy sources during different thermal spray processes viz. plasma spraying (PS), high-velocity oxy fuel spraying (HVOF), cold spraying (CS), and plasma spraying of liquid precursor (PSLP). CNTs were successfully retained as reinforcement in metal and ceramic composite coatings in all thermal spray processes except PSLP. The retention of CNT structure is attributed to micron size metal/ceramic powder which acts as a carrier and thermal shield against high heat in plasma spraying (PS) and high-velocity oxy fuel spraying (HVOF). However, vaporization of CNTs occurred in PSLP under the intense heat of the plasma which is attributed to phase transformation in unshielded CNTs.
44 citations
TL;DR: In this article, the authors synthesized a HA reinforced with sub-micrometer Al2O3 and carbon nanotubes (CNTs) as a coating on the Ti-6Al-4V substrate via plasma spraying.
Abstract: Hydroxyapatite (HA) reinforced with sub-micrometer Al2O3 and carbon nanotubes (CNTs) has been synthesized as a coating on the Ti-6Al-4V substrate via plasma spraying. The addition of Al2O3 and CNTs to HA has shown improvement in the hardness and elastic modulus by 65% and 50%, respectively, when compared to HA. Consequently, HA-Al2O3-CNT coatings have been nano-scratched to understand their wear performance. Reinforcement of HA by Al2O3 shows a decrease in the wear volume by more than 13 times, whereas HA-Al2O3-CNT coating demonstrated further wear volume reduction of five times compared to that of HA-Al2O3 coating.
33 citations
TL;DR: This study computes the friction force during splat sliding in the plasma-sprayed Al-Si coating based on the instrumented depth-sensing nanoindentation and microindentations experiments.
Abstract: This study computes the friction force during splat sliding in the plasma-sprayed Al−Si coating based on the instrumented depth-sensing nanoindentation and microindentation experiments. A small intersplat friction force (∼10−4 N) contributes to the occurrence of the splat sliding. As compared with nanoindentation, more and more splat sliding occurs during microindentation because of the increase in the applied load, which accounts for the ∼26% loss of the elastic modulus.
19 citations
TL;DR: In this paper, the elastic modulus of PZT and lead zirconate titanate (PZT) was investigated using nanoindentation technique and the results showed that the porosity increases by evaporation of PbO phase during plasma spraying.
Abstract: Nanomechanical properties of the plasma sprayed lead zirconate titanate (PZT) coating have been investigated using nanoindentation technique. PZT coating processed at higher plasma power of 32 kW exhibited lower elastic modulus E of 98 GPa compared with the modulus (113 GPa) of the coating processed at plasma power of 20 kW. The variation in the elastic modulus is attributed to the fine porosity of the PZT coating, which is formed during plasma spraying. Porosity increases by evaporation of PbO phase during plasma spraying. Overall effective elastic modulus of both coatings is computed using micromechanics models and compared with the experimentally obtained values. Hashin–Shtrikman and rule of mixtures models predict values that closely match with nanoindentation values.
15 citations