Materials Science Forum Vol. 978

Abstract: The aim of this investigation is to study the influence of temperature on the cyclic plastic deformation behavior of SA333 Gr-6 steel at two loading conditions. Strain-controlled cyclic loading experiments were carried out at ± 0.5% total strain amplitude, 1×10^-3 s^-1 strain rate, and temperature varied from RT to 400°C, whereas stress controlled ratcheting experiments were conducted at fixed mean stress (σ_m) of 50 MPa and stress amplitude (σ_a) of 400 MPa, 115 MPa s^-1 stress rate, and in the temperature range of RT to 350°C. The investigated steel shows cyclic hardening characteristic at DSA temperature regime in both the loading condition. The steel shows lower fatigue lives at 250°C and 300°C temperatures even though plastic strain amplitude is smaller. The ratcheting life of the steel increases and strain accumulation decreases with the increase in temperature up to 300°C and on further increment in temperature ratcheting life get decreased. The steel shows greater cyclic hardening at both the loading conditions at 300°C.

Abstract: In the current study, consequence of ECAP on the toughness characteristics of the Al-Zn-Mg alloys was studied. Three set of Al-Zn-Mg alloys (5, 10 and 15% Zn and 2% Mg) were selected and ECAPed. Also, consequence of zinc on the toughness characteristics of the alloy, before and after ECAP was studied. After ECAP, grain size of the alloys decreased and significant rise in the strength and ductility of the alloys were noticed. Mainly, modulus of toughness of the alloys increased with successive ECAP passes. But, the modulus of toughness of the alloys decreased with rise in the zinc in the material.

Abstract: High entropy alloys (HEAs) generally exhibit either high resistance to deformation or high toughness due to the presence of body-centered or face-centered cubic structure, respectively. To overcome these limitations, new high entropy alloys have been developed in the present study. This investigation aims to synthesis and characterization of novel CoCrFeNi₃Si, CoCrFe₂Ni₂Si, and Co₂CrFeNi₂Si high entropy alloys. The mechanical alloying route is used to synthesize these alloys. Grinding was carried out to 20h and X-ray diffraction (XRD) analysis was done at different time intervals of grinding. The face-centered cubic structure along with the intermetallic compound of Ni-Si was observed after 20h of grinding. Furthermore, a pseudo binary strategy based on the valence electron concentration and mixing enthalpy is also employed to design the high entropy alloys considered in the present study. Carefully analysis of the XRD pattern indicates that from 5 to 20h of mechanical alloying there is a decrement in the initial peaks of elements observed.

Abstract: In the present work, laser weld-brazing experiments were performed to produce aluminum to galvanized steel joints in lap and flange configuration. Tests were carried out using Al-12 % Si eutectic filler wire for joining of AA6082 -T6 with galvanized steel with varying laser power and keeping other parameters (wire feed and laser scan speed) constant. Microstructural characteristics of the laser brazed joints, studied by SEM, revealed cast structure in the brazed zone. Intermetallic formed at the steel interface was non-uniform. From the hardness results, it was noted that the brazed region exhibits lower hardness compared to the base material. The wetting length was improved with increasing filler wire rate, which in turn improved the strength of the brazed joint in both the configuration (lap and flange). At 4 kW laser power, flange configuration sample has failed in AA6082 whereas, in case lap joint, failed in the heat affected zone of AA6082.

Abstract: Bacterial Cellulose (BC) is a biologically derived material having properties that present it as a biomaterial, with potential application in various fields. BC based composites capitalize its properties and enhance its applications. Bacterial cellulose composites were prepared with poly (methyl methacrylate) and polyvinyl alcohol and characterized for optical transmittance, structural properties and tensile test. The transmittance of composites was found to be decreased for higher BC content in composites. Scanning electron micrographs depicts the fibrous structures of bacterial cellulose embedded in PMMA matrix while diffused with PVA matrix and dimension of fibres are in nanometer. Tensile strength of the composites were varying with the change in BC content with maximum strength in BC-PMMA and BC-PVA composites is of 2%BC in PMMA and 25% BC in PVA, respectively. This work is intended to impel research activity for applications of BC composites in area of packaging materials, tissue engineering, and wound dressing materials.

Abstract: In recent years, increasing weld strength along with improved surface properties of the joint during friction stir welding (FSW) has gained noteworthy attention due to increasing applications concerning higher wear resistance and strength related factors. Accordingly, the exploration endures for new materials and ways which will probably increase weld strength along with imparting various improved surface properties to the weld. In spite of several modifications on FSW, its in-situ composite fabrication potential remains quite unfamiliar. In this study, we make available an up to date review of recent in-situ fabricated composites during FSW by using various reinforcements. In particular, the effect of various reinforcements and methodology on the weld strength and surface hardness is reported systematically. Moreover, the strengthening mechanisms accountable for the improvement in weld propeties have been reviewed, and the new potential applications of this new welding strategy are envisaged.

Abstract: The present work deals with the synthesis and characterization of Al-Cu-SiC-Al₂O₃ hybrid metal matrix composite with varying percentage of Al₂O₃. The synthesized hybrid composite samples were conventionally sintered at two different sintering temperatures i.e. 500°C and 600°C for 1 hr each. SEM investigation predicts the uniform distribution of reinforcing particles. The SEM and XRD results of the sintered composites revealed the presence of a new intermetallic alloy CuAl₂ phase along with Al and SiC phases. It is observed that the density and hardness of Al-Cu-SiC-Al₂O₃ hybrid composite increases with increase in wt % of Al₂O₃ and sintering temperature.

Abstract: Research in renewable and clean energy has reached an unprecedented magnitude owing to the growing concerns over environmental hazards caused by the traditional fuels. In this regard, solar, wind and tidal energies are considered to meet large scale energy requirements. Small, stand-alone electronic devices which are growing in numbers in next generation smart cities, can be powered by scavenging energy from sources which would otherwise remain unused, such as mechanical vibrations. The source of mechanical vibration could have diverse origins, ranging from vibrations of machines to flow of wind, motion of automobiles, and human footfall etc. Energy harvesting from the above sources can be achieved through the principle of piezoelectricity. In the present work, piezoelectric ceramic (1-x) Pb (Mg_1/3Nb_2/3O₃)-xPbTiO₃ at x = 0.3 was prepared using conventional solid state method. Lead magnesium niobate and lead titanate (PMN-PT) solid solution within the morphotropic phase boundary composition considerably fulfils the essential piezoelectric characteristics for a high energy density harvester. However, PMN-PT is brittle and thus difficult to assemble directly into an energy harvesting system. Hence flexible piezoelectric composite of 20 wt % PMN-PT and polydimethylsiloxane (PDMS) was fabricated to evaluate its energy harvesting capability. Structural and microstructural characterization of the synthesized composite were performed using x-ray diffraction and optical microscopy. Electrical characterization was carried out using Keithley 6517B high resistance electrometer.

Abstract: Human hair dumped in the waste streams as a waste material in most of the societies which creates many environmental problems, but it has many exceptional physical, mechanical and microstructural properties. The present investigation aims at developing a class of hybrid composite with improved insulation capabilities consisting of epoxy, short hair fibers (SHF), and solid glass microspheres (SGM). Solid glass microspheres (10 wt. %) filled epoxy based hybrid composites are fabricated with four distinct fiber loading (0, 5, 10, 15, 20 wt. %). Density and effective thermal conductivity of these composites are measured experimentally following appropriate ASTM standards. The measured effective thermal conductivities (K_eff) are compared with theoretical values from “Rule of Mixture” model. It is noticed that thermal conductivity of the composite decreases with increase in fiber content. Micro-structural characterization such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) analysis of the composite has been done to know the surface morphology, crystallinity and functional groups present in the composite. It is found that with the incorporation of 20 wt. % hair fiber along with 10 wt. % of SGM the thermal conductivity of the epoxy is reduced by about 27 %.

Abstract: In the current investigation, a large number of experimental data are created for a set of Linz-Donawitz (LD) sludge filled polypropylene composites by fabricating them through compression molding technique and by conducting different tests to find out their physical, mechanical and erosion wear behaviour under controlled laboratory conditions. The erosion wear trials are carried out on the fabricated polypropylene-LD sludge composite samples as per ASTM standard using response surface methodology (RSM). This study discloses that the impact velocity and the filler content are the most predominant factors influencing the erosion rate of the composite. Mechanical characterization of the composites under this investigation reveals that the trends observed in regard to the compressive strengths are quite different from those obtained in the case of tensile strength variations with the filler loading. It is also observed that these LD sludge filled composites show improved micro-hardness and low amount of porosity.