Asit Kumar Khanra

Production of nanocrystalline TiB2 powder through self-propagating high temperature synthesis (SHS) of TiO2–H3BO3–Mg mixture

Abstract Nanocrystalline TiB2 powders are produced through self-propagating high temperature synthesis (SHS) technique by igniting the stoichiometric mixture of titanium oxide (TiO2), boric acid (H3BO3) and magnesium (Mg) powder. Different percentages of NaCl are added to the mixture as SHS diluent in order to control the particle size of the TiB2. The synthesised and purified powder is characterised by X-ray diffraction and electron microscopes respectively. The SEM images show the presence of agglomeration of fine spherical particles. The TEM images reveal the formation of nanocrystalline TiB2 particles. The particle size is found to decrease with the addition of NaCl. The TEM images reveal the presence of crystallographic defects in the powder. In order to find out the reaction mechanism of TiO2–H3BO3–Mg system, the synthesis of TiO2–Mg and H3BO3–Mg mixtures is performed in inert atmosphere and phase analysis of TiO2–Mg and H3BO3–Mg mixtures reveal the reaction mechanism.

Electrical discharge machining studies on reactive sintered FeAl

AbstractbdElectrical discharge machining (EDM) studies on reactive sintered FeAl were carried out with different process parameters. The metal removal rate and tool removal rate were found to increase with the applied pulse on-time. The surface roughness of machined surface also changed with the applied pulse on-time. XRD analysis of machined surface of sintered FeAl showed the formation of Fe3C phase during the EDM process. The debris analysis was used to identify the material removal mechanism occurring during the EDM of sintered FeAl.

Friction Factor Evaluation Using Experimental and Finite Element Methods for Al-4%Cu Preforms

Abstract In this study, ring compression tests and finite element (FE) simulations have been utilized to evaluate the friction factor, m, under different lubricating conditions for powder metallurgical (P/M) Al-4%Cu preforms. A series of ring compression tests were carried out to obtain friction factor (m) for a number of lubricating conditions, including zinc stearate, graphite, molybdenum disulfide powder, and unlubricated condition. FE simulations were used to analyze materials deformation, densification, and geometric changes, and to derive the friction calibration curves. The friction factor has been determined for various initial relative densities and different lubricating conditions, and a proper lubricant for cold forging of P/M Al-4%Cu preforms is found. Studies show that the use of lubricants has reduced the friction. However, increase in the number of pores in the preforms leads to excessive friction. The FE simulation results demonstrate a shift in the neutral plane distance from the axis of ring specimen, which occurred due to variations in the frictional conditions and initial relative densities. The load requirement for deformation, effective stress, and effective strain induced, and bulging phenomena obtained by FE simulations have a good agreement with the experimental data.

Development of Cordierite Based Reticulated Foams with Improved Mechanical Properties for Porous Burner Applications

ABSTRACT Cordierite is a ternary oxide of silica, magnesia and alumina and one of the interesting ceramic materials and a potential material for various thermo-structural applications. The present study is to explore the possibility of enhancing the mechanical properties of cordierite using zirconia as an additive in the range of 0-10 wt% followed by comparative evaluation of properties. Cordierite precursor mix was subjected to calcination to ensure the partial formation of cordierite. A part of calcined cordierite and another two parts were blended with 5 and 10 wt% of zirconia and were planetary ball milled to ensure homogeneity in compositions. The formulations were compacted after granulation. The green compacts were subjected to TG-DSC and XRD investigations were carried out on sintered samples. Mechanical properties such as flexural strength at room and elevated temperatures and thermal expansion behaviour were analyzed for all the samples. Zirconia addition was found to enhance the mechanical properties; however, at higher concentration (10 wt%) segregation of zirconium silicate resulted in the reduction in flexural strength. Reticulated foams of cordierite and cordierite+5 wt% zirconia were fabricated by polymeric sponge replication process and evaluated for their properties. Further, initial trials as a porous combustion media demonstrated the feasibility for burner applications. GRAPHICAL ABSTRACT

Effect of deformation on densification and corrosion behavior of Al-ZrB2 composite

In the present investigation, aluminium based metal matrix composites (MMCs) were produced through powder metallurgical route. Different composites were processed by adding different amount of ZrB 2 (0, 2, 4 and 6 wt. %) at three aspect ratios of 0.35, 0.5, and 0.65, respectively. The powder mixture was compacted and pressureless sintered at 550 °C for 1 h in controlled atmosphere (argon gas). The relative density of the sintered preforms was found to be 90%, approximately. Sintered preforms are used as workpiece materials for deformation study at different temperatures in order to find the effect of temperature on the densification behaviour. Potentio-dynamic polarization studies were performed on the deformed preforms to find the effect of mechanical working. The corrosion rate was found to decrease with increase in deformation.

Mechanical Behavior of Alumina based Reticulated Foams Encapsulated and Infiltrated with Polymer under Quasistatic and Dynamic Conditions

ABSTRACT Cellular ceramic structures, due to their unique combination of thermal, structural and mechanical properties, are widely explored for the wide range of thermo-structural applications. However, the ceramic based structures have not been well explored for energy absorption properties due to their inherent brittleness. In the present study, alumina based ceramic foams were fabricated by polymeric sponge replication process and further these foams were encapsulated and infiltrated respectively in epoxy resin. All the three foams – bare, encapsulated and infiltrated were evaluated comparatively under quasistatic compression and dynamic impact conditions. The study revealed that the energy absorption properties can be significantly enhanced through encapsulation and infiltration of bare foam with epoxy resin. Extent of enhancement in energy absorption in case of infiltration was superior in comparison to encapsulation in both static and dynamic test conditions. The study demonstrated the possibility of exploring the potential of encapsulated and infiltrated ceramic foams in various shock attenuating applications. GRAPHICAL ABSTRACT

Microstructural Analysis and Simulation Studies of Semi-solid Extruded Al–Cu–Mg Powder Metallurgy Alloys

Semi-solid extrusion of Al–Cu–Mg Powder Metallurgy (P/M) alloys had simulated under three different temperatures and extrusion angles in the present investigation. Al, Cu, and Mg powders were taken in different ratios in order to produce strong and light weight P/M alloys. Billets were prepared with an aspect ratio of one (φ 15 × 15 mm) to get good deformation results. Al–4Cu–0.5Mg alloy composition was optimized to do semi-solid extrusion after considering density, hardness, and strength as best parameters to optimize. Alloys were sintered at 550 °C and prepared samples with Initial Relative Density (IRD) of 90% for densification and deformation studies. The working temperature range for semi-solid extrusion test was derived from TG/DTA analysis. Extrusion tests were performed on a hydraulic press under different deformation temperatures (550, 575 and 600 °C) and different solid fractions (0.93, 0.76, and 0.56) respectively. All the extrusion tests were performed with a low extrusion ratio of 1.44, die approach angles of 30°, 45°, and 60° and strain rate of 0.1 s−1. High density (>95%) and high hardness (>1000 MPa) extruded Al alloys were produced with good microstructures. Microstructural analyses were done for all Al alloys and found uniform distribution of grains at different temperatures. Dynamic recrystallization of grains was found with increasing liquid fraction during extrusion experiments. For an accurate prediction of microstructure evolution the strain rate, strain and temperature have to be considered and these can be calculated by FEM simulation. Simulation studies had been performed at three selected temperatures using Deform-2D software. Simulation and experimental results have been shown good agreement between them.

Hot Deformation Studies of Al–Cu–Mg Powder Metallurgy Alloy Composite

High-performance requirements of materials in automobile industry gave the scope of alloying of monolithic metal powders which plays a significant role in the enhancement of properties. In the present study, monolithic powder matrix aluminum is alloyed with respective proportions of copper and magnesium by mechanical alloying. With 4 wt% of Cu as constant, different wt% (0.25, 0.5, 0.75, and 1) of Mg are added to form various powder alloy preforms. The alloy preforms are triaxially compacted in a tool steel die and sintered at 550 °C for 1 hour in continuous flow high pure argon gas atmosphere. The sintered alloy preforms are subjected to uniaxial deformation at two different temperatures, (400 and 500 °C). The hardness and the relative density increases with the extent of deformation. Potentiodynamic polarization is performed on deformed preforms to evaluate the effect of deformation. Corrosion rates and hardness of the alloy preforms were correlated with the relative densities. The extent of deformation and compositional variations on all the properties were analyzed.

Processing and properties of sintered submicron IR transparent alumina derived through sol–gel method

AbstractFor the first time, sintered alumina with high transparency in mid infrared region, composed of submicron grains, has been fabricated using sol–gel processing. Commercially available boehmite powder was used to prepare the stable sol. The sol was mixed with appropriate amount of sintering aids and alumina seeds. The sol was further gelled, dried, and heat treated at 1000 °C for producing alumina powder. The powder was further shaped into pellets by compaction and sintered at temperatures between 1200 and 1400 °C in air. Sintered samples were further pressed hot isostatically to produce sintered submicron transparent alumina. The synthesized powder was characterized for its morphology and phase. The sintered and hot isostatically pressed samples were characterized for their physical, mechanical, and optical properties. The present method produced transparent alumina with transparency upto 87% in mid-wave infrared region. These transparency values were at par with the transparency of single crystal sapphire in the mid-wave infrared region and the hardness values were even superior than sapphire.