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High temperature flow behavior of Al-6.65Si-0.44Mg (all in wt%) (A356) alloy and A356+5 wt% B4C composite were investigated by compression test at temperatures 470, 500, 530 and 570 degrees C and strain rates 10(-3), 10(-2), 10(-1) and 1 s(-1). Constitutive relationship was established by the prediction of materials constants alpha, beta n, Q and InA. The variations in stable and instable regions of processing map were investigated in A356 alloy and A356+5 wt% B4C composite. It was found that the existence of instability domain for A356 alloy, over the range of temperatures similar to 510-570 degrees C and strain rates similar to 1- 4 x 10(-2) s(-1), was extended to regime of temperatures similar to 470-570 degrees C over the same strain rates upon 5% B4C reinforcement. The microstructural evolutions by stable and instable regions were studied in scanning electron microscope (SEM) and by the electron backscatter diffraction (EBSD) technique. (C) 2016 Elsevier B.V. All rights reserved.

High temperature tensile flow behavior of aluminum-boron carbide (Al-B4C) composites of 0, 5 and 15% B4C, hot rolled to similar to 88% with intermediate annealing at 350 degrees C, was investigated by constant initial strain rate (CIS) ((epsilon) over dot = 1 x 10(-2)s(-1)) test technique at 500 degrees C and strain rate jump ((epsilon) over dot = 5 x 10(-5) - 1 x 10(-2)s(-1)) test technique over the temperature range of 400-500 degrees C. In the as-cast condition, the flow stresses obtained between CIS and strain rate jump test techniques were found to be significantly different at 500 degrees C. The strain rate sensitivity index (m) was found to be similar to 0.1 over (epsilon) over dot = 1 x 10(-4) - 1 x 10(-2)s(-1) for all the composites in both as-cast as well as hot rolled condition. Tensile elongations were found to be 0.36 in both as-cast and hot rolled aluminum, whereas the same reduced in Al-5% B4C composite to 0.35 and 0.27, respectively. The values of activation energy (Q) for deformation of rolled aluminum and Al-5% B4C composite were determined to be 194.2 and 73.4 kJ/mol, respectively. The microstructural examination, using SEM and EBSD techniques, revealed cavitation in aluminum upon differential strain rate test, and grain refinement upon rolling, which increased later during tensile test.

Differential strain rate compression tests were conducted to study flow behavior of hot rolled Al-5 wt% B4C composite as a function of sample orientation (longitudinal and transverse) over the temperature and strain rate ranges of 25-500 degrees C and 10 (4) to 1 s (1), respectively. The longitudinal samples are found to show lower flow stress than that shown by the transverse samples in the temperature range of 25200 degrees C. The reverse becomes true at higher temperatures of 300-500 degrees C. The values of stress exponent (n) and activation energy for deformation (Q), based on applied stress, ranged from 10 to 46 and 307416 kJ/mol, respectively. However, by considering effective stress, these values were reduced to n = 8 and Q = 126-190 kJ/mol. This stress exponent ofn = 8 is further reduced to n = 5 by considering substructural evolution, which suggests the dislocation climb creep mechanism to be favorable for deformation. (C) 2013 Elsevier Ltd. All rights reserved.

Multipass friction stir processing of brittle as-cast hypereutectic Al-Si alloy resulted in bimodal distribution of ultrafine silicon particles in nano-size aluminum matrix. As compared to the as-cast material, the stress-strain curves revealed simultaneous increase in strength by four times and in ductility by 14 times after three overlap multipass FSP. The transformation from brittle cleavage fracture to completely ductile fracture is confirmed by the fractographs of tensile samples taken before and after the friction stir processing. (C) 2015 Elsevier B.V. All rights reserved.

The present paper describes a cost effective route to produce Al alloy-10 wt % TiB2 metal matrix composites by in-situ molten flux assisted reaction synthesis. Now a days main focus is given to aluminium alloy as a matrix material due to its unique combination of good corrosion resistance, low density, superior mechanical properties, good vibration damping, higher wear resistance due to which alloy finds extensive applications in naval applications. With TiB2 as particulate addition in Al-Alloy (Al-5Mg) matrix properties of alloy can greatly be improved.

Rheocasting refers to a process in which a liquid metal is vigorously agitated during initial stage of solidification to produce globular semisolid slurry which remains highly fluid. This slurry is directly fed into any shaping operation to obtain SSM parts. Rheocasting is an energy saving as well as cost saving, good surface finish and negligible porosity for a specialized casting, in which heating step of thixocasting is completely eliminated. Rheocasting also offers shot size flexibility and amenable for processing of wrought alloys and metal matrix composites, which are otherwise difficult to process by thixocasting route. A slurry with globular shape of the solid phase particles and hence injected directly into the die. In the present development, Al base thin wall components for electronic packaging applications were produced by rheocasting process. The paper presents the die designing aspects, optimization of rheocasting process parameters to achieve the sound casting and mechanical property. Thin walled Al-Alloy components lot was realized by the novel processing technology, meeting dimensional accuracy, desired microstructure, mechanical property, value for high integrity component needed for space applications.

Flow properties of aluminum and aluminum-boron carbide (Al-B4C) composites, containing 5, 10 and 15 wt% B4C, were investigated by compression tests at strain rates of 10−4, 10−3 and 10−2 s−1 over the temperature range 25 to 500℃. The nature of stress–strain curves as a function of reinforcement, temperature and strain rate revealed that (1) flow stress initially increases as the reinforcement increases, but it decreases for Al-15% B4C composite, (2) flow stress increases with the increase in strain rate, with the strain rate sensitivity index varying from 0.01 for aluminum at 200℃ to 0.30 for Al-5% B4C composite. The activation energy for deformation is found to vary from 124 to 187 kJ/mol for Al-15% B4C and Al-5% B4C composites, respectively.

This article presents an economical and attractive fabrication technique to produce aluminum (6061) boron carbide functionally gradient material (FGM). Aluminum (6061) boron carbide FGM was produced by flux assisted reaction synthesis followed by centrifugal casting. Optical and analytical microscopy examination of FGM reveals the gradient of boron carbide particulate in aluminum matrix. As the density difference of boron carbide and molten aluminum are very close, the effect of centrifugal force ‘G’ during centrifugal casting on boron carbide distribution and hardness was also studied. The microstructure of material so produced exhibits a gradual change of hardness from 55 Hv in aluminum to 150 Hv in boron carbide region.

This paper presents a novel technique to synthesize TiC-reinforced iron base (Fe-TiC) functionally graded materials (FGM) using SHS reaction followed by centrifugal casting. The in-situ reinforced Fe-TiC steel composites were prepared by aluminothermic SHS reactions using metal oxides and elemental powders. Ferritic as well as austenitic matrix Fe-TiC composites were obtained by judicious thermite charge composition. FGM microstructure was characterized in terms of TiC area fraction, particle size, and chemical analysis using optical and analytical electron microscopy. The results reveal a gradient of TiC particles across the thickness in the inner face and a particle-free region in the outer surface. Hardness profiles have shown an increasing trend from outer surface to TiC-rich inner surface. Wear studies indicated better wear performance of TiC-rich inner face as compared to particle-free outer surface of ferritic or austenitic steel matrices.

Observations pertaining to the erosive–corrosive wear behaviour of samples of En31 steel hardfaced separately with Fe–TiC and a commercial cobalt based material are reported in the present investigation. Erosion–corrosion tests were carried out by the sample rotation technique in 3·5%NaCl solution for varying test durations of 8–32 h (corresponding traversal distances 136–544 km) at a fixed traversal speed of 4·71 m s−1. The effect of the hardfaced layer on the wear behaviour was assessed through testing one set of each of the hardfaced and substrate steel samples under identical test conditions. The wear rate increased initially with traversal distance, attained the maximum and decreased thereafter. In the case of the steel substrate, the wear rate increased once again towards the final stage of testing. Hardfaced layers exhibited substantially decreasing wear rate compared with the substrate. Moreover, the performance of the Fe–TiC composite layer was intermediate between those of the cobalt bas...

TiC-reinforced austenitic steel composites have been prepared by self-propagating high temperature synthesis (SHS). The in situ reinforcement of a Fe-Mn-based austenitic steel matrix with TiC was achieved upon aluminothermic reduction of iron oxide (Fe2O3), manganese dioxide (MnO2) and titanium dioxide (TiO2) powders in the presence of carbon (C). This highly exothermic thermite reaction was found to produce in situ the Fe-Mn-TiC austenitic steel composites. The reaction kinetics, recovery of Mn and TiC, yield of metal, and composite microstructure were found to strongly depend on the process parameters, such as green composition, blending sequence, and average particle size of Al powder used as a reducing agent.

This investigation deals with the influence of hardfacing En31 steel separately with Fe–TiC composite and commercial cobalt base (stellite 6) material on their sliding wear behaviour at 2.94 m/s speed and varying applied pressures. Wear response of the samples was substantiated through the scanning electron microscopic studies of the wear surfaces, subsurface regions and debris particles. The hardfaced samples revealed superior wear performance than that of the substrate. Further, the steel hardfaced with cobalt-based stellite offered higher wear resistance over the one overlayed with Fe–TiC composite. The applied pressure controlled the wear behaviour (rate) in a complex manner and its influence was dependent on material composition/microconstituents and test conditions. The friction coefficient got reduced with pressure except in the case of the Fe–TiC composite overlay beyond 2 MPa. The hardfaced samples were noted to be better suited for more severe conditions. Microcracking was quite frequently observed on wear surfaces of the hardfaced material especially under mild wear conditions. Sticking of fine debris particles on to the specimen surface was also observed.

Ultrafine grain (UFG) microstructure of Al-30Si alloy formed by friction stir processing (FSP), was correlated with its corrosion property. Electrochemical impedance spectroscopy and anodic polarization studies of FSPed Al-30Si alloy in 3.5 wt.% NaCI solution showed nobler corrosion and pitting potential as well as reduction of corrosion current density with increasing number of FSP passes. The homogenization of UFG microstructure with refined primary silicon particles changed the semi-conducting nature of passive film formed on Al-30Si alloy from n to p type resulting in improved corrosion resistance. Correlation of grain and silicon particle size on corrosion properties reveals Hall-Petch type relationship. (C) 2014 Elsevier Ltd. All rights reserved.

Flow behavior of aluminum-5 wt.% boron carbide (Al-B4C) composite was investigated by carrying out compression tests over a range of strain rates (10(-4)-10(0) s(-1)) and temperatures (200-500 A degrees C). The flow stress data obtained from these tests at true strain 0.5 were used to develop processing map. The stable and instable flow regimes in the map were characterized by the microstructural examination using Scanning Electron Microscopy and Electron Backscattered Diffraction. The optimum condition for processing of Al-5%B4C composite was found to lie between 425 and 475 A degrees C at the strain rate of around 10(-4) s(-1). A strain-compensated Sellars-McG Tegart constitutive equation was established to model high-temperature deformation behavior of the material.

Hypereutectic Al-30 wt.% Si alloy was subjected to friction stir processing (FSP) to modify the cast microstructure. FSP reduces the size of undesirable coarse silicon particles, eliminates porosities, and homogenizes and refines the cast microstructure. This paper demonstrates the effect of two pass overlap friction stir processing on microstructural refinement of Al-30Si alloy, which delineates significant reduction in size and aspect ratio of silicon particles from average 200 to 2 mu m and 4.93 to 1.75 mu m respectively. The stir zone of two pass overlap FSP exhibits relatively homogeneous Si particle distribution. Increase in frequency of silicon particles less than 1 mu m was also observed in two pass FSP stir zones. Hardness in stir zones was measured to be 75 Hv after first pass and the same changed to 85 Hv respectively after second pass. Further uniform microhardness was observed in the FSP stir zone which was not the case in as-cast Al-30Si microstructure. (C) 2009

Microstructural evolution and related dynamic recrystallization phenomena were investigated in overlapping multipass friction stir processing (FSP) of hypereutectic Al-30 pct Si alloy. FSP resulted in the elimination of porosities along with the refinement of primary silicon particles and alpha aluminum grains. These alpha aluminum grains predominantly exhibit high angle boundaries with various degrees of recovered substructure and dislocation densities. The substructure and grain formation during FSP take place primarily by annihilation and reorganization of dislocations in the grain interior and at low angle grain boundary. During multipass overlap FSP, small second phase particles were observed to form, which are accountable for pinning the grain boundaries and thus restricting their growth. During the multipass overlap FSP, the microstructure undergoes continuous dynamic recrystallization by formation of the subgrain boundary and subgrain growth to the grain structure comprising of mostly high angle grain boundaries.

The present investigation discusses observations pertaining to the synthesis of Cu-based composites containing TiC particles in the range of 45–50 volume % by self-propagating high temperature synthesis (SHS) process. A composite with 11–13 volume % TiC dispersion was also synthesized through remelting and dilution. The composites were observed to contain a copper matrix together with a Cu–Ti intermetallic compound, TiC dispersoid particles and partially reacted graphite. The regions showing partially reacted graphite (carbon) became less prominent in the diluted composites. Al addition led to the refinement of TiC particles, higher hardness, reduced density and improved degree of formation and better homogeneity of the distribution of TiC particles. Dilution caused reduced hardness, while the density followed a reverse trend.