M. Krishna

A study on damping behaviour of aluminite particulate reinforced ZA-27 alloy metal matrix composites

Abstract ZA-27 based metal matrix composites (MMCs) have been prepared with 1, 2, 3, and 4% of reinforcement by the compocasting method. Sample specimens of dimensions 70×10×2 mm were machined from prepared ingots. The damping behavior and dynamic Young’s modulus of base alloy and the particulate reinforced composites were studied over a temperature range of 30–300°C using a dynamic mechanical analyzer. The damping capacity of the materials was observed to increase with the increase in temperature whereas the dynamic modulus was found to decrease with the increase in temperature. The damping capacity at lower temperature may be attributed to the coefficient of thermal expansion (CTE) mismatch induced dislocations and intrinsic damping of the matrix alloy, whereas damping capacity at higher temperature may be attributed to the matrix–reinforcement interface and thermoelastic damping.

Corrosion behaviour of garnet particulate reinforced LM13 Al alloy MMCs

Abstract This paper describes a study of the corrosion characteristics of LM13 Al alloy-based composites reinforced with various amounts of garnet particulates. The weight loss method was used and the corrodent was 1 M HCl solution at room temperature. The durations of the tests ranged from 24 to 96 h. Corrosion tests were performed on the unreinforced matrix alloy as well as on the various composites in both heat-treated and as-cast conditions. In each test, the corrosion rates of the unreinforced matrix alloy and the composites were found to decrease with duration of exposure to the corrodent. Solution heat treatment at 525°C followed by artificial aging at 175°C was found to improve the corrosion resistance of every specimen tested. Corrosion resistance was also found to improve with increase in garnet content. An attempt is made in the paper to explain these phenomena.

Seawater Durability of Epoxy / Vinyl Ester Reinforced With Glass / Carbon Composites

Seawater aging response was investigated in marine-grade glass/epoxy, glass/vinyl ester, carbon/epoxy and carbon/vinyl ester composites with respect to water uptake, interlaminar shear strength, flexural strength, tensile strength, and tensile fracture surface observations. The reduction of mechanical properties was found to be higher in the initial stages which showed saturation in the longer durations of seawater immersion. The flexural strength and ultimate tensile strength (UTS) dropped by about 35% and 27% for glass/epoxy, 22% and 15% for glass/vinyl ester, 48% and 34% for carbon/epoxy 28%, and 21% carbon/vinyl ester composites respectively. The water uptake behavior of epoxy-based composites was inferior to that of the vinyl system.

Study of mechanical properties of epoxy/glass/nanoclay hybrid composites

The objective of this research was to study the mechanical properties of epoxy/glass/nanoclay hybrid composites. Nanomer 1.30E nanoclay (0—6 wt%) was initially dispersed into epoxy using ultrasonication and the hybrid nanocomposite was fabricated using hand lay-up technique. Mechanical properties such as ultimate tensile strength, Young’s modulus, flexural strength, flexural modulus, interlaminar shear strength, and microhardness of the hybrid composites increased with increase in nanoclay loading up to 5 wt%. Glass transition temperature increased marginally at 2 wt% nanoclay loading and the same decreased for further addition of the filler. The tensile-fractured specimens were studied to examine the mode of failure using scanning electron microscope.

The Processing and Characterization of MWCNT/Epoxy and CB/Epoxy Nanocomposites Using Twin Screw Extrusion

This paper presents results of the processing of nanocomposites based on epoxy and nanofillers, namely multiwalled carbon nanotubes (up to 10 wt%) and carbon black (up to 15 wt%). The twin screw extruded nanocomposites showed increases in electrical and thermal conductivities, tensile strength, microhardness and glass transition temperature. Electrical conductivity increased on the order of 1011 at 10 wt% of nanotubes loading and at 15 wt% of carbon black. Greater increases in thermal and mechanical properties were observed in cases of nanotube-dispersed composites more so than others. SEM and AFM were used to examine the dispersion of the fillers.

Synthesis and characterization of nano silicon and titanium nitride powders using atmospheric microwave plasma technique

AbstractWe have demonstrated a simple, scalable and inexpensive method based on microwave plasma for synthesizing 5 to 10 g/h of nanomaterials. Luminescent nano silicon particles were synthesized by homogenous nucleation of silicon vapour produced by the radial injection of silicon tetrachloride vapour and nano titanium nitride was synthesized by using liquid titanium tetrachloride as the precursor. The synthesized nano silicon and titanium nitride powders were characterized by XRD, XPS, TEM, SEM and BET. The characterization techniques indicated that the synthesized powders were indeed crystalline nanomaterials. Graphical AbstractA simple, scalable and inexpensive method based on microwave plasma was developed for synthesizing 5 to 10 g/h of silicon and titanium nitride nanopowders. Silicon was synthesized by homogenous nucleation of silicon vapour while titanium nitride was synthesized by using liquid titanium tetrachloride as the precursor.

A Study of Mechanical Properties and Fractography of ZA-27/Titanium-Dioxide Metal Matrix Composites

This paper reports an investigation of the mechanical properties and the fracture mechanism of ZA-27 alloy composites containing titanium-dioxide (TiO2) particles 30–50 µm in size and in contents ranging from 0–6 wt.% in steps of 2 wt.%. The composites were fabricated by the compocasting technique. The results of the study revealed improvements in mechanical properties such as Young’s modulus, ultimate tensile strength, yield strength and hardness of the composites, but at the cost of ductility. The fracture behavior of the composites was influenced significantly by the presence of titanium dioxide particles. Crack propagation through the matrix and the reinforcing particles resulted in the final fracture. Scanning electron micrscopy (SEM) analyses were carried out to furnish suitable explanations for the observed phenomena.

Effect of aging parameters on the micro structure and properties of ZA-27/aluminite metal matrix composites

The effect of heat treatment and aging at various temperatures for different intervals of time on the microstructure of ZA-27 matrix alloy and aluminite particulate reinforced ZA-27 alloy metal matrix composites (MMCs) has been studied using micro hardness, electrical resistivity, X-ray diffraction and differential scanning calorimetry (DSC) data. The composite samples were aged at 32, 80, 180, and 250 °C after solutionizing at 320 °C for 3 h followed by cold water quenching. The micro hardness values showed an initial increase reaching a peak value which was followed by a reduction in hardness values with increase in aging time. The trend followed by electrical resistivity was very similar to that of hardness. Further, the time to reach peak hardness decreased with increase in the weight percentage of the reinforcement. These results indicated that the aging and precipitation kinetics in the matrix alloy are significantly accelerated due to the presence of particulate reinforcement. Changes in the properties of the composites during aging are explained on the basis of micro structural alterations caused by the heat treatment.

Development and Characterization of Electrocodeposited Nickel-Based Composites Coatings

The objective of the article is to study the development and characterization of composite coatings using nickel-tungsten carbide (Ni-WC), nickel-silicon carbide (Ni-SiC), nickel-carbon black (Ni-CB), and nickel-carbon nanotube (Ni-CNT) materials using electrocodeposition technique by varying the composition of reinforcements. The electrochemical parameters such as current density, bath temperature, and pH of the solution were maintained at constant levels for all the coating configurations. The composition of the coating and its proportion were studied using x-ray diffraction and energy dispersive x-ray spectroscopy, respectively. Mechanical properties such as ultimate tensile strength and microhardness were studied. Morphology of the coatings and fracture surfaces were studied using scanning electron microscope. Improvement in mechanical properties of composite coatings was found due to the reduction in crystalline size of the composites coatings. Although loading of carbon nanotube was the least, it also shows good mechanical properties along with Ni-WC composite coatings.

Fatigue studies of polyurethane sandwich structures

The fatigue characteristics of polyurethane foam-cored (PUF) composite sandwich structures were investigated using three-point bending tests carried out according to ASTM C 393. Three types of specimens (epoxy/glass-PUF-epoxy/glass, polyester/glass-PUF-polyester/glass, and epoxy/glass-PUF-polyester/glass) were considered for investigation. Experimental results indicate that degradation of stiffness occurs due to debonding and sliding between the skin and the foam during fatigue cycles. Epoxy/glass-PUF-epoxy/glass sandwich structures exhibit higher bending strength along with higher stiffness degradation than the other two types of sandwich panels, due to higher initial fatigue loading. The lowest fatigue properties have been obtained for the polyester/glass-PUF-polyester/glass sandwich panel specimens. Better performance of the epoxy/glass-PUF-epoxy/glass sandwich panels is most likely due to the superior properties of the outer thin skins. Most of the specimens fail within the foam region and not at the skin level. This situation is possibly due to debonding between the foam and the skin. The fatigue damage development in the foam and skin has been investigated using scanning electron microscopy.