Sankaranarayanan Seetharaman

Synthesis and Characterization of Nano Boron Nitride Reinforced Magnesium Composites Produced by the Microwave Sintering Method

In this study, magnesium composites with nano-size boron nitride (BN) particulates of varying contents were synthesized using the powder metallurgy (PM) technique incorporating microwave-assisted two-directional sintering followed by hot extrusion. The effect of nano-BN addition on the microstructural and the mechanical behavior of the developed Mg/BN composites were studied in comparison with pure Mg using the structure-property correlation. Microstructural characterization revealed uniform distribution of nano-BN particulates and marginal grain refinement. The coefficient of thermal expansion (CTE) value of the magnesium matrix was improved with the addition of nano-sized BN particulates. The results of XRD studies indicate basal texture weakening with an increase in nano-BN addition. The composites showed improved mechanical properties measured under micro-indentation, tension and compression loading. While the tensile yield strength improvement was marginal, a significant increase in compressive yield strength was observed. This resulted in the reduction of tension-compression yield asymmetry and can be attributed to the weakening of the strong basal texture.

Synthesis and Properties of Light Weight Magnesium-Cenosphere Composite

Significantly light weight magnesium composite foams are synthesised by addition of fly ash cenosphere particles (waste from coal-fired power plants) in biocompatible pure magnesium using solidification-based disintegrated melt deposition technique. The density of the composite foams synthesised in this study approaches that of plastics- and polymer-based composites. Microstructure development of Mg/cenosphere composite foams was favourable as they exhibited better dimensional stability (reduced coefficient of thermal expansion) and remarkable improvements in tensile strengths, compressive strengths, compressive total strain and microhardness. The present study highlights the processing, microstructure and mechanical properties of Mg/cenosphere composite foams which hold great potential as light weight metal-based green materials for diverse weight critical applications spanning from engineering to biomedical sector.

Enhancing hardness, CTE and compressive response of powder metallurgy magnesium reinforced with metastable Al90Y10 powder particles

In the present study, magnesium composites containing pre-milled metastable Al90Y10 particles were synthesised using powder metallurgy route incorporating microwave-assisted sintering and hot extrusion. The results of X-ray diffraction reveal that the pre-milled powder changed from crystalline structure to metastable structure after 200 hours ball milling and the particle retained its metastable state in all composite samples. Microstructural characterisation shows that metastable particles were fairly distributed in the magnesium matrix and located along the grain boundaries. Further, when the amount of metastable particles increased, microhardness, 0.2%yield compressive strength and ultimate compressive strength increased significantly, coefficient of thermal expansion reduced gradually, while the compressive total strain remained almost the same. Work of fracture that indicates damage tolerance increased up to 66%. The interrelationship between microstructure and properties is discussed. Results suggest that the developed composites exhibit superior strength levels and are promising for compressive strength and damage tolerance-based engineering applications.

Microstructure and damping characteristics of Mg and its composites containing metastable Al85Ti15 particle

This paper reports for the first time the damping behavior of Mg-Al85Ti15 metastable composites synthesized using near dense blend-press-microwave sinter-hot extrusion methodology. Optical microscopy results show that the metastable particles were located along the grain boundaries and the formation of twins within the grains. In addition, scanning electron microscopy reveals reasonable distribution of particles, good matrix-particle interfacial bonding and minimal presence of microvoids. The damping test results show an increment in damping capacity and damping loss rate with the presence and increasing amount of particles. The effect of microstructure on damping characteristics of magnesium and damping mechanisms are discussed.

Microstructure and Mechanical Properties New Magnesium-Zinc-Gadolinium Alloys

Magnesium based materials are effective for structural/component weight reduction in automotive applications. However, their real time applications are limited because of their inadequate mechanical properties, especially the absolute strength and creep resistance. In this regard, the formation of thermally stable ternary compounds is believed to positively influence the properties of Mg-Zn-RE alloys. In this study, new Mg alloys containing Zn and Gd (Mg-2.0Zn-0.5Gd and Mg-3.4Zn-0.8Gd, in at.%) were developed using disintegrated melt deposition technique followed by hot extrusion. The developed alloys were investigated for their microstructural and mechanical properties in hot-extruded conditions. The mechanical properties examined under indentation, tension and compression loads indicated improved mechanical performance due to Zn and Gd addition. The observed mechanical properties are presented using structure-property relationship.