Development of microstructure and texture in Copper during warm accumulative roll bonding

The evolution of microstructure and texture gradient in warm Accumulative Roll Bonded Cu-Cu multilayer has been studied. Grain size distribution is multimodal and exhibits variation from middle to surface layer. Evolution of texture is largely influenced by shear, in addition to rolling deformation. This leads to the formation of a texture comprising of high fraction of Brass and rolling direction-rotated cube components. Partial recrystallization was observed. Deformed and recrystallized grains were separated using a partition scheme based on grain orientation spread and textures were analyzed for both the partition. Retention of deformation texture components in recrystallized grains suggests the mechanism of recrystallization as continuous recrystallization. Shear deformation plays an important role in grain refinement through continuous recrystallization. (C) 2012 Elsevier Inc. All rights reserved.

Approaching theoretical strengths by synergistic internal and external size refinement

Refinement of the internal grain size leads to strengthening by retarding dislocation motion. There have also been recent reports that a reduction in external diameter enhances the strength of single crystal pillars. Here we show, in a hitherto unexplored domain, a synergistic increase in strength by a combined reduction in internal (0.5 mu m) and external (20-50 mu m) dimensions, with strengths at failure approaching the theoretical value. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Evolution of microstructure and texture in friction stir processed Al-Mg-Mn alloy

Friction stir processing was carried out on the Al-Mg-Mn alloy to achieve ultrafine grained microstructure. The evolution of microstructure and micro-texture was studied in different regions of the deformed sample, namely nugget zone, thermo-mechanically affected zone (TMAZ) and base metal. The average grain sizes of the nugget zone, TMAZ and base metal are 1.5 mu m +/- 0.5 mu m, 15 mu m +/- 8 mu m, and 80 mu m +/- 10 mu m, respectively. The TMAZ exhibits excessive deformation banding structure and sub-grain formation. The orientation gradient within the sub-grain is dependent on grain size, orientation, and distance from nugget zone. The microstructure was partitioned based on the grain orientation spread and grain size values to separate the recrystallized fraction from the deformed region in order to understand the micromechanism of grain refinement. The texture of both deformed and recrystallized regions are similar in nature. Microstructure and texture analysis suggest that the restoration processes are different in different regions of the processed sample. The transition region between nugget zone and TMAZ exhibits large elongated grains surrounded by fine equiaxed grains of different orientation which indicate the process of discontinuous dynamic recrystallization. Within the nugget zone, similar texture between deformed and recrystallized grain fraction suggests that the restoration mechanism is a continuous process.

Microstructural and mechanical behavior study of suction cast Nb-Si binary alloys

The solidification pathways of Nb rich Nb-Si alloys when processed under non-equilibrium conditions require understanding. Continuing with our earlier work on alloying additions in single eutectic composition 1,2], we report a detailed characterization of the microstructures of Nb-Si binary alloys with wide composition range (10-25 at% Si). The alloys are processed using chilled copper mould suction casting. This has allowed us to correlate the evolution of microstructure and phases with different possible solidification pathways. Finally these are correlated with mechanical properties through studies on deformation using mechanical testing under indentation and compressive loads. It is shown that microstructure modification can significantly influence the plasticity of these alloys.

AZ91C magnesium alloy modified by Cd

In the present work, the effect of Cd on the microstructure, mechanical properties and general corrosion behaviour of AZ91C alloys was investigated. Addition of Cd was found not to be efficient in modifying/refining the microstructure or beta-phase. A morphology change in beta-phase from fine continuous precipitates to discontinuous beta-phase upon the addition of Cd was observed. A marginal increment in mechanical properties was observed. General corrosion behaviour was followed with weight loss measurements, potentiostatic polarisation studies and surface studies in 3.5% sodium chloride solution and 3.5% sodium chloride with 2% potassium dichromate solution. Cd addition deteriorated the corrosion behaviour of AZ91C. This behaviour was attributed to the formation of chunks of beta-phase upon the addition of Cd. AZ91C with refined beta-phase distribution, performed rather better in the NaCl solutions. (C) 2013 Elsevier Ltd. All rights reserved.

Friction Stir-Welded Dissimilar Aluminum Alloys: Microstructure, Mechanical Properties, and Physical State

A356 and 6061 aluminum alloys were joined by friction stir welding at constant tool rotational rate with different tool-traversing speeds. Thermomechanical data of welding showed that increment in tool speed reduced the pseudo heat index and temperature at weld nugget (WN). On the other hand, volume of material within extrusion zone, strain rate, and Zenner Hollomon parameter were reduced with decrease in tool speed. Optical microstructure of WN exhibited nearly uniform dispersion of Si-rich particles, fine grain size of 6061 Al alloy, and disappearance of second phase within 6061 Al alloy. With enhancement in welding speed, matrix grain size became finer, yet size of Si-rich particles did not reduce incessantly. Size of Si-rich particles was governed by interaction time between tool and substrate. Mechanical property of WN was evaluated. It has been found that the maximum joint efficiency of 116% with respect to that of 6061 alloy was obtained at an intermediate tool-traversing speed, where matrix grain size was significantly fine and those of Si-rich particles were substantially small.

Microstructural evolution and mechanical properties of Mg composites containing nano-B4C hybridized micro-Ti particulates

In this work, the microstructural evolution and mechanical properties of extruded Mg composites containing micro-Ti particulates hybridized with varying contents of nano-B4C are investigated, and compared with Mg-5.6Ti. Microstructural characterization showed the presence of uniformly distributed micro-Ti particles embedded with nano-B4C particulates that resulted in significant grain refinement. Electron back scattered diffraction (EBSD) analyses of Mg-(5.6Ti + x-B4C)(BM) hybrid composites showed that the addition of hybridized particle resulted in relatively more recrystallized grains, realignment of basal planes and extension of weak basal fibre texture when compared to Mg-5.6Ti. The evaluation of mechanical properties indicated improved strength with ductility retention in Mg-(5.6Ti + x-B4C)(BM) hybrid composites. When compared to Mg-5.6Ti, the superior strength properties of the Mg-(5.6Ti + xB(4)C)(BM) hybrid composites are attributed to the presence of nano-reinforcements, the uniform distribution of the hybridized particles, better interfacial bonding between the matrix and the reinforcement particles and the matrix grain refinement achieved by nano-B4C addition. The ductility enhancement obtained in hybrid composites can be attributed to the fibre texture spread and favourable basal plane orientation achieved due to nano B4C addition. (C) 2013 Elsevier B.V. All rights reserved.

Phase Field Simulation of Equiaxed Microstructure Formation during Semi-solid Processing of A380 Al Alloy

A phase field modelling approach is implemented in the present study towards simulation of microstructure evolution during cooling slope semi solid slurry generation process of A380 Aluminium alloy. First, experiments are performed to evaluate the number of seeds required within the simulation domain to simulate near spherical microstructure formation, occurs during cooling slope processing of the melt. Subsequently, microstructure evolution is studied employing a phase field method. Simulations are performed to understand the effect of cooling rate on the slurry microstructure. Encouraging results are obtained from the simulation studies which are validated by experimental observations. The results obtained from mesoscopic phase field simulations are grain size, grain density, degree of sphericity of the evolving primary Al phase and the amount of solid fraction present within the slurry at different time frames. Effect of grain refinement also has been studied with an aim of improving the slurry microstructure further. Insight into the process has been obtained from the numerical findings, which are found to be useful for process control.

Elastic Properties Of Sulphur And Selenium Doped Ternary PbTe Alloys By First Principles

Lead telluride (PbTe) is an established thermoelectric material which can be alloyed with sulphur and selenium to further enhance the thermoelectric properties. Here, a first principles study of ternary alloys PbSxTe(1-x) and PbSexTe(1-x) (0 <= x <= 1) based on the Virtual Crystal Approximation (VCA) is presented for different ratios of the isoelectronic atoms in each series. Equilibrium lattice parameters and elastic constants have been calculated and compared with the reported data. Anisotropy parameter calculated from the stiffness constants showed a slight improvement in anisotropy of elastic properties of the alloys over undoped PbTe. Furthermore, the alloys satisfied the predicted stability criteria from the elastic constants, showing stable structures, which agreed with the previously reported experimental results.

Observation of magnetically hard grain boundaries in double-perovskite Sr2FeMoO6

Unusual low-temperature magneto-resistance (MR) of ferromagnetic Sr2FeMoO6 polycrystals has been attributed to magnetically hard grain boundaries which act as spin valves. We detected the different magnetic hysteresis curves for the grains and the grain boundaries of polycrystalline Sr2FeMoO6 by utilizing the different probing depths of the different detection modes of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD), namely, the total electron yield (TEY) mode (probing depth similar to 5 nm) and the total fluorescence yield (TFY) mode (probing depth similar to 100 nm). At 20 K, the magnetic coercivity detected in the TEY mode (H-c,H- TEY) was several times larger than that in the TFY mode (H-c,H- TFY), indicating harder ferromagnetism of the grain boundaries than that of the grains. At room temperature, the grain boundary magnetism became soft and H-c,H- TEY and H-c,H- TFY were nearly the same. From the line-shape analysis of the XAS and XMCD spectra, we found that in the grain boundary region the ferromagnetic component is dominated by Fe2+ or well-screened signals, while the non-magnetic component is dominated by Fe3+ or poorly screened signals. Copyright (C) EPLA, 2014

Correlation of microstructure and creep behaviour of MRI230D Mg alloy developed by two different casting technologies

The relationship between the as-cast microstructure and creep behaviour of the heat-resistant MRI230D Mg alloy produced by two different casting technologies is investigated. The alloy in both ingot-casting (IC) and high pressure die-casting (HPDC) conditions consists of alpha-Mg, 06 ((Mg,AI)(2)Ca), Al-Mn and Sn-Mg-Ca rich phases. However, the HPDC alloy resulted in relatively finer grain size and higher volume fraction of finer, denser network of eutectic C36 phase in the as-cast microstructure as compared to that of the IC alloy. The superior creep resistance exhibited by the HPDC alloy at all the stress levels and temperatures employed in the present investigation was attributed to the more effective dispersion strengthening effect caused by the presence of finer and denser network of the C36 phase. The increased amount of the eutectic C36 phase was the only change observed in the microstructures of both alloys following creep tests. (C) 2015 Elsevier B.V. All rights reserved.

Analysis of Microstructure and Texture Evolution in Mg-3Al-1Zn Alloy Processed Through Groove Rolling

The mechanism of grain refinement in a AZ31 Mg alloy subjected to hot groove rolling is investigated up to large strain (epsilon(t) similar to 2.5). The alloy shows enhanced yield strength without compromising ductility. The change in strain path during rolling has resulted in significant weakening of basal texture. The microstructure analyses show that dynamic recrystallization (DRX) contributed significantly to grain refinement and hence to the observed mechanical properties. The combined effects of DRX and texture evolution on mechanical properties have been addressed.

Evolution of annealing texture in cryo-rolled copper

The present study addresses the evolution of texture and microstructure during annealing in a cryorolled copper. Transition from copper to brass texture during the cryo-rolling has been illustrated. Twinning and interaction between twins and shear bands have been found to play the important role in grain refinement and strengthening. The low temperature vacancy clustering and its effect on the recrystallization have been experimentally demonstrated. Fine scale twinning, and grain refinement have been attributed to the higher yield strength found in the case of samples subjected to cryo-rolling. (C) 2015 Elsevier B.V. All rights reserved.

Wear Behavior of Cooling Slope Rheocast A356 Al Alloy

In the present study, the dry sliding wear behavior of rheocast A356 Al alloys, cast using a cooling slope, as well as gravity cast A356 Al alloy have been investigated at a low sliding speed of 1ms(-1), against a hardened EN 31 disk at different loads. The wear mechanism involves microcutting-abrasion and adhesion at lower load for all of the alloys studied in the present work. On the other hand, at higher load, mainly adhesive wear along with oxide formation is observed for gravity cast A356 Al alloy and rheocast A356 Al alloy, cast using a 45 degrees slope angle. Unlike other alloys, 60 degrees slope rheocast A356 Al alloy is found to undergo mainly abrasive wear at higher load. Accordingly, the rheocast sample, cast using a 60 degrees cooling slope, exhibits a remarkably lower wear rate at higher load compared to gravity cast and 45 degrees slope rheocast samples. This is attributed to the dominance of abrasive wear at higher load in the case of rheocast A356 Al alloy cast using a 60 degrees slope. The presence of finer and more spherical primary Al grain morphology is found to resist adhesive wear in case of 60 degrees cooling slope processed rheocast alloy and thereby delay the transition of the wear regime from normal wear to severe wear.

Organic alloys of room temperature liquids thiophenol and selenophenol

The first examples of organic alloys of two room temperature liquids, obtained and characterized via in situ cryo-crystallography, are presented. Thiophenol and selenophenol, which exhibit isostructurality and similar modes of S center dot center dot center dot S and Se center dot center dot center dot Se homo-chalcogen interactions along with weak and rare S-H center dot center dot center dot S and Se-H center dot center dot center dot Se hydrogen bonds, are shown to form solid solutions exhibiting Veggard's law-like trends.