Effect of alloying elements on the solidification characteristics and microstructure of Al- Si- Cu- Mg- Fe 380 alloy

The effect of varying the major alloying elements within the limits of specification on the solidification behavior, fluidity, and microstructure of a 380 alloy has been studied at two cooling rates. The thermal analysis technique has been used to study the solidification behavior. The alloying elements investigated ranged from 3.22 to 4.09 pct copper, 1.01 to 1.70 pct iron, 0.06 to 0.50 pct magnesium, 1.69 to 3.00 pct zinc, and 0.16 to 0.46 pct manganese. The results show that the solidification behavior of the 380 alloys is complicated, and the cooling curve at 0.4 ‡C/s indicates six reactions taking place during the process of solidification. Cooling curves obtained for each of the alloying element additions, their analysis, and the resultant microstructures are discussed.     

Effect of cooling rate on the solidification behavior of Al-7 Pct Si-SiCp metal-matrix composites

The solidification behavior of two composites based on Al-Si alloy has been investigated as a function of cooling rate. Thermal analysis techniques have been used to establish the relationship between solidification history and the microstructure developed. The results of thermal analysis show that the characteristic parameters are influenced by the cooling rate. A marked difference in these parameters is observed between the reinforced and the unreinforced materials at all cooling rates studied. The cooling rates used in the present study range from 0.3 to 20 K/s. Increasing the cooling rate is shown to affect the undercooling parameters both in the liquidus and eutectic solidification region. The eutectic growth temperature of the composites is observed to be higher than that of the base alloy at all cooling rates. The depression in eutectic temperature ΔT is found to decrease by 27 K for the unreinforced alloy (A356) and by 17 K for the composites (A356 + 10, 20 vol pct SiC) at a higher cooling rate of ≃16 K/s. The presence of SiC reinforcement is observed to suppress the Mg₂Si precipitate formation and decrease the amount of heat liberated during both primary and eutectic phase formation. Dendrite arm spacing (DAS) is correlated to the cooling rate by a relationship of the form DAS =AT ^-n, wheren is found to be of the order of 0.33.     

Growth and adhesion of hot filament chemical vapor deposited diamond coatings on surface modified high speed steel

Diamond coatings were deposited by hot filament chemical vapor deposition on high speed steel substrates. Iron boride diffusion barrier and WC–Co layers were used as interlayers. At high deposition pressure, the quality of the diamond deposits is poor due to the extensive formation of graphitic deposits. At low pressure, diamond films of better quality were obtained, but their adhesion to the substrate was insufficient. A two-step deposition process at low pressure was developed. In a first deposition step performed at high methane percentage, a high nucleation density was achieved. In a second deposition step, the methane percentage was reduced to achieve continuous, dense, and adherent diamond layers on borided or WC–Co coated high speed steel substrates. Adhesion of these diamond layers on the surface modified high speed steel substrates was tested based on reciprocating sliding tests.     

Object-oriented methodology for intersection simulation model under heterogeneous traffic conditions

In developing countries like India, the traffic on roads is highly heterogeneous in nature, with vehicles of widely varying static and dynamic characteristics. In this type of traffic, vehicles do not follow lane discipline and they move freely over the entire width of roadway based on availability of space. To study this type of complex traffic flow and associated vehicular interactions, simulation is considered as an effective tool. An object-oriented methodology (OOM) for heterogeneous traffic simulation is proposed in this paper with focus on mid-block and intersection flow modeling. The paper presents the basics and advanced features of object-oriented programming (OOP) in detail in the context of traffic flow. The sample C++ code is discussed in detail to demonstrate the implementation of OOP features, such as encapsulation, inheritance and polymorphism. The contribution of this research work is the development of software objects for various components such as vehicle, traffic, link and node. This software can be adopted for heterogeneous traffic simulation programs, in general.     

Analysis of the evolution of microcreep during physical aging and mechanical deformation in poly(methyl methacrylate) using a microstructural model

The evolution of poly(methyl methacrylate) (PMMA) during physical aging at 90°C is followed by torsional microcreep tests. On the aged specimen a longitudinal stress is applied which induces a strain of 5 percent after 30 days of creep. The torsional microcreep tests are performed during the longitudinal creep in order to compare the structure evolution of PMMA caused by straining with its evolution measured during aging. The microcreep, for the first 800s, follows a reversible logarithmic law. In this stage the mobile defects achieve their activated form which is perfectly reversible when unloaded. The physical aging reduces this logarithmic part of microcreep. This is due to the decrease of either the number or the volume of the mobile defects. Beyond a critical elongation ? = 1 percent, the longitudinal straining has just the opposite influence, i.e., the logarithmic part of microcreep increases. This critical elongation ? = 1 percent corresponds to the beginning of the steady state longitudinal creep. The transient that precedes this steady state has no detectable influence on the structure of the specimen.     

Study on vital static properties of fine blanking of GFRP composites with that of conventional drilling

Among the high performance engineering materials, fiber-reinforced plastics play an important role. The present work is concerned with the comparison of vital static strength properties of fine blanking with conventional drilling on hand lay-up made glass fiber-reinforced plastic (GFRP) laminates of four different reinforcement lay-up sequences such as unidirectional [0/0]_n, angle ply [0?±?45]_ns, quasi-isotropic [0/45/90]_ns, and cross-ply [0/90]_n. Observation includes tensile and flexural bending strengths of the specimens without hole and with hole by conventional drilling and fine blanking. In this work, an endeavor has been made to simulate the service conditions to determine their effect on the response of composite laminates. Detailed studies on GFRP composites when subjected to different loading environments such as static loading, particularly tensile loading, and low frequency high amplitude (fatigue) loading were carried out. The response of the composite laminates to these service environments has been evaluated in terms of flexural strength and modulus. From the tensile study, it was observed that by inserting a hole at center by drilling, the strength was reduced to one third, and by inserting a hole at center by fine blanking, the strength was increased nearly 20% than that of drilling. Apart from this, the flexural test conducted on polymeric composite specimens showed that an exposure to low frequency and high amplitude loading enhances the flexural strength up to certain duration of exposure, beyond which, due to accumulation of damage within the composites, the flexural strength reduces with number of cycles. This can be attributed to possible strain-induced stiffening of fibers and interface.     

Tailoring C60 for Efficient Inorganic CsPbI2Br Perovskite Solar Cells and Modules

Although inorganic perovskite solar cells (PSCs) are promising in thermal stability, their large open-circuit voltage (V_OC) deficit and difficulty in large-area preparation still limit their development toward commercialization. The present work tailors C₆₀ via a codoping strategy to construct an efficient electron-transporting layer (ETL), leading to a significant improvement in V_OC of the inverted inorganic CsPbI₂Br PSC. Specifically, tris(pentafluorophenyl)borane (TPFPB) is introduced as a dopant to lower the lowest unoccupied molecular orbital (LUMO) level of the C₆₀ layer by forming a Lewis acidic adduct. The enlarged free energy difference provides a favorable enhancement in electron injection and thereby reduces charge recombination. Subsequently, a nonhygroscopic lithium salt (LiClO₄) is added to increase electron mobility and conductivity of the film, leading to a reduction in the device hysteresis and facilitating the fabrication of a large-area device. Finally, the as-optimized inorganic CsPbI₂Br PSCs gain a champion power conversion efficiency (PCE) of 15.19%, with a stabilized power output (SPO) of 14.21% (0.09 cm²). More importantly, this work also demonstrates a record PCE of 14.44% for large-area inorganic CsPbI₂Br PSCs (1.0 cm²) and reports the first inorganic perovskite solar module with the excellent efficiency exceeding 12% (10.92 cm²) by a self-developed quasi-curved heating method.     

An Integrated Trust Assisted Energy Efficient Greedy Data Aggregation for Wireless Sensor Networks

Wireless Personal Communications - Wireless sensor networks (WSN) gathers information pertaining to sensitive data. As because the sensor nodes in WSN are remote and unattended for a longer period...