Effect of mode of rolling on development of texture and microstructure in two-phase (alpha plus beta) brass

The evolution of microstructure and texture during deformation of two-phase (alpha + beta) brass was studied for different initial microstructure and texture. The deformation processing involved unidirectional and multi-step cross-rolling. The bulk textures were determined by measuring the pole figures and calculating the orientation distribution function ODF for both alpha (fcc) and beta (bcc) phases, while the microstructure and other microstructural parameters were measured through optical microscopy and scanning electron microscopy with electron back scatter diffraction (SEM-EBSD). Results indicate that textures developed after unidirectional rolling and multi-step cross-rolling are significantly different. The variation in initial texture had a pronounced effect on the development of texture in the alpha phase during subsequent deformation. (C) 2010 Elsevier B.V. All rights reserved.

A TEM study on TiB2-20%MoSi2 composite: Microstructure development and densification mechanism

We report the results of transmission electron microscopy (TEM) study, carried out on a hot-pressed TiB2-20 wt.%MoSi2 composite. One of the important microstructural observations includes the detection of crystalline TiSi2 at triple grain junctions. The densification mechanism is discussed, based on experimental observations and thermodynamic analysis

Microstructure related influence on the electrical properties of pulsed laser ablated (Ba, Sr)TiO3 thin films

The microstructural dependence of electrical properties of (Ba, Sr)TiO3(BST) thin films were studied from the viewpoint of dc and ac electrical properties. The films were grown using a pulsed laser deposition technique in a temperature range of 300 to 600 degrees C, inducing changes in grain size, structure, and morphology. Consequently, two different types of films were realized, of which type I, was polycrystalline, multigrained, while type II was [100] oriented possessing a densely packed fibrous microstructure. Leakage current measurements were done at elevated temperatures to provide evidence of the conduction mechanism present in these films. The results revealed a contribution from both electronic and ionic conduction. In the case of type I films, two trapping levels were identified with energies around 0.5 and 2.73 eV, which possibly originate from oxygen vacancies V-O and Ti3+ centers, respectively. These levels act as shallow and deep traps and are reflected in the current-voltage characteristics of the BST thin films. The activation energy associated with oxygen vacancy motion in this case was obtained as 1.28 eV. On the contrary, type II films showed no evidence of deep trap energy levels, while the identified activation energy associated with shallow traps was obtained as 0.38 eV. The activation energy obtained for oxygen vacancy motion in type II films was around 1.02 eV. The dc measurement results were further elucidated through ac impedance analysis, which revealed a grain boundary dominated response in type I in comparison to type II films where grain response is highlighted. A comparison of the mean relaxation time of the two films revealed three orders of magnitude higher relaxation time in the case of type I films. Due to smaller grain size in type I films the grains were considered to be completely depleted giving rise to only grain boundary response for the bulk of the film. The activation energy obtained from conductivity plots agree very well with that of dc measurements giving values 1.3 and 1.07 eV for type I and type II films, respectively. Since oxygen vacancy transport have been identified as the origin of resistance degradation in BST thin films, type I films with their higher value of activation energy for oxygen ion mobility explains the improvement in breakdown characteristics under constant high dc field stress. The role of microstructure in controlling the rate of degradation is found useful in this instance to enhance the film properties under high electric field stresses. (C) 2000 American Institute of Physics. [S0021-8979(00)00418-7].

Microstructure and Properties of the Spray-Formed and Extruded 7075 Al Alloy

In the present investigation, a very good combination of strength and ductility, 630MPa 0.2% proof stress and 14.8% elongation to fracture in tensile test, has been obtained for the 7075 Al alloy after optimizing the processing parameters for spray forming, hot extruding the spray deposit, and peak aging the samples taken from the extruded rod. The spray deposits contained some porosity but it was almost eliminated on hot extrusion. Electron probe microanalysis revealed that even though spray forming was carried out in an open atmosphere, it did not affect the oxygen content and its distribution in the material on spray forming, because the atomizing argon gas provided a protective cover to molten droplets and prevented their oxidation. The chemical composition of the spray-formed material was found to be almost the same as the raw material, and the major alloying elements were found to be uniformly distributed in the extruded rod.

Experimental studies and phase field modeling of microstructure evolution during solidification with electromagnetic stirring

Thixocasting requires manufacturing of billets with non-dendritic microstructure. Aluminum alloy A356 billets were produced by rheocasting in a mould placed inside a linear electromagnetic stirrer. Subsequent heat treatment was used to produce a transition from rosette to globular microstructure. The current and the duration of stirring were explored as control parameters. Simultaneous induction heating of the billet during stirring was quantified using experimentally determined thermal profiles. The effect of processing parameters on the dendrite fragmentation was discussed. Corresponding computational modeling of the process was performed using phase-field modeling of alloy solidification in order to gain insight into the process of morphological changes of a solid during this process. A non-isothermal alloy solidification model was used for simulations. The morphological evolution under such imposed thermal cycles was simulated and compared with experimentally determined one. Suitable scaling using the thermosolutal diffusion distances was used to overcome computational difficulties in quantitative comparison at system scale. The results were interpreted in the light of existing theories of microstructure refinement and globularisation.

Numerical simulation of solidification of liquid aluminum alloy flowing on cooling slope

Preparation of semisolid slurry using a cooling slope is increasingly becoming popular, primarily because of the simplicity in design and ease control of the process. In this process, liquid alloy is poured down an inclined surface which is cooled from underneath. The cooling enables partial solidification and the incline provides the necessary shear for producing semisolid slurry. However, the final microstructure of the ingot depends on several process parameters such as cooling rate, incline angle of the cooling slope, length of the slope and initial melt superheat. In this work, a CFD model using volume of fluid (VOF) method for simulating flow along the cooling slope was presented. Equations for conservation of mass, momentum, energy and species were solved to predict hydrodynamic and thermal behavior, in addition to predicting solid fraction distribution and macrosegregation. Solidification was modeled using an enthalpy approach and a volume averaged technique for the different phases. The mushy region was modeled as a multi-layered porous medium consisting of fixed columnar dendrites and mobile equiaxed/fragmented grains. The alloy chosen for the study was aluminum alloy A356, for which adequate experimental data were available in the literature. The effects of two key process parameters, namely the slope angle and the pouring temperature, on temperature distribution, velocity distribution and macrosegregation were also studied.

Effect of Strain Rate on Evolution of the Deformation Microstructure and Texture in Polycrystalline Copper and Nickel

The evolution of crystallographic texture in polycrystalline copper and nickel has been studied. The deformation texture evolution in these two materials over seven orders of magnitude of strain rate from 3 x 10(-4) to similar to 2.0 x 10(+3) s(-1) show little dependence on the stacking fault energy (SFE) and the amount of deformation. Higher strain rate deformation in nickel leads to weakerh < 101 > texture because of extensive microband formation and grain fragmentation. This behavior, in turn, causes less plastic spin and hence retards texture evolution. Copper maintains the stable end < 101 > component over large strain rates (from 3 x 10(-4) to 10(+2) s(-1)) because of its higher strain-hardening rate that resists formation of deformation heterogeneities. At higher strain rates of the order of 2 x 10(+3) s(-1), the adiabatic temperature rise assists in continuous dynamic recrystallization that leads to an increase in the volume fraction of the < 101 > component. Thus, strain-hardening behavior plays a significant role in the texture evolution of face-centered cubic materials. In addition, factors governing the onset of restoration mechanisms like purity and melting point govern texture evolution at high strain rates. SFE may play a secondary role by governing the propensity of cross slip that in turn helps in the activation of restoration processes.

Influence of microstructure on the wear of grinding media

Owing to the complexity of the wear process, high stress grinding abrasion is quite different from two-body abrasive wear. Reported data on two-body abrasive wear reveal that the wear decreases with an increase in steel hardness. This relationship can be established without having to consider the microstructure of the steel grinding medium. However, it is known that hardness cannot be directly employed to predict the wear of steel balls under three-body grinding abrasion, as occurs during dry grinding of ores in ball mills. The present work suggests that the wear behaviour of grinding balls can be classified according to the microstructural family to which they belong. Thus, in this work on AISI 52100 steel, the separate groups of microstructures were spheroidite—pearlite, bainite, tempered martensite and martensite with retained austenite. It appears that wear behaviour of the first three groups follows the same trend as that observed for two-body wear. The data suggest that an optimum level of retained austenite could improve the wear resistance of microstructures containing martensite.

On characterization of deformation microstructure in Boron modified Ti-6Al-4V alloy

Addition of boron in small quantities to various titanium alloys have shown significant improvement in mechanical behavior of materials. In the present study, electron back-scatter diffraction (EBSD) techniques have been applied to investigate the deformation microstructure evolution in boron modified two-phase titanium alloy Ti-6Al-4V. The alloy was hot compressed at 750 degrees C up to 50% height reduction at two different strain rates (10(-3) s(-1) and 1 s(-1)). The EBSD analyses indicated significant differences in deformed microstructure of the base alloy and the alloy containing boron. A strong subgrain formation tendency was observed along with inhomogeneous distribution of dislocations inside large a colonies of Ti64. In contrast, a colonies were relatively strain free for Ti64 + B, with more uniform dislocation density distribution. The observed difference is attributed to microstructural modifications viz, grain size refinement and presence of TiB particles at grain boundary produced due to boron addition. (C) 2010 Elsevier B.V. All rights reserved.

Precursor Dependent Microstructure Evolution and Nonstoichiometry in Nanostructured Cerium Oxide Coatings Using the Solution Precursor Plasma Spray Technique

A solution precursor plasma spray (SPPS) technique has been used for direct deposition of cerium oxide nanoparticles (CNPs) from various cerium salt solutions as precursors. Solution precursors were injected into the hot zone of a plasma plume to deposit CNP coatings. A numerical study of the droplet injection model has been employed for microstructure development during SPPS. The decomposition of each precursor to cerium oxide was analyzed by thermogravimetric-differential thermal analysis and validated by thermodynamic calculations. The presence of the cerium oxide phase in the coatings was confirmed by X-ray diffraction studies. Transmission electron microscopy studies confirmed nanocrystalline (grain size <14 nm) characteristic of the coatings. X-ray photoelectron spectroscopy studies indicated the presence of a high concentration of Ce3+ (up to 0.32) in the coating prepared by SPPS. The processing and microstructure evolution of cerium oxide coatings with high nonstoichiometry are reported.

Wide Ranged La Modification in CCTO Ceramics Through Sol-Gel: Effect on Microstructure and Dielectric Properties

Sol-Gel method was employed to synthesize pure and wide ranged La-modified CaCu3Ti4O12 ceramics using mixed acetate-nitrate-alcoxide individual metal-ion precursors. SEM pictures revealed that grain size monotonously decreases with the extent of La incorporation. All the prepared ceramics manifested dielectric constant in the range similar to 10(3)-10(4). Dielectric loss was found to decrease with La incorporation and got optimized for 20% La3+ while retaining its high dielectric constant which may be industrially important. Room temperature Impedance spectroscopy suggested that decrease in grain resistance is responsible for reduction in dielectric loss according to Internal Barrier Layer Capacitor (IBLC) model.

Local texture and microstructure in cube-oriented nickel single crystal deformed by equal channel angular extrusion

Local texture and microstructure was investigated to study the deformation mechanisms during equal channel angular extrusion of a high purity nickel single crystal of initial cube orientation. A detailed texture and microstructure analysis by various diffraction techniques revealed the complexity of the deformation patterns in different locations of the billet. A modeling approach, taking into account slip system activity, was used to interpret the development of this heterogeneous deformation.

Effect Of Electroslag Refining On Microstructure And Mechanical-Properties Of Is-7670 Alloy

The electroslag refining technique is one of the modern tools which is capable of imparting superior mechanical and chemical properties to metals and alloys. Refining usually results in the elimination of a number of casting or solidification defects, such as shrinkage porosity, gas porosity, pipe, micro- and macro segregation. Remelting also imparts a directional grain structure apart from refining the size of the inclusions, grains and precipitates. This technique has over the years been used widely and successfully to improve the mechanical and chemical properties of steels and alloy steels which are used in the nuclear, missile, aerospace and marine industries for certain critical applications. But the application of ESR to aluminium and its alloys is only recent. This paper investigates the response of an aluminium alloy (corresponding to the Indian Specification IS: 7670) to ESR. Based on theoretical considerations and microstructural evidence it elucidates how ESR of aluminium alloys differs from that of ferrous alloys. The improvement achieved in mechanical properties of the alloy is correlated with the microstructure.

Deformation processing map for control of microstructure in Al---4Mg alloy

The compression test flow stress data of Al-4Mg alloy at different temperatures and strain rates are analysed using a dynamic materials model which considers the workpiece material as a dissipator of power causing microstructural changes. A processing map representing the efficiency of power dissipation as a function of temperature and strain rate has been established and optimum processing conditions for the alloy are determined. The features of the map correlate well with the microstructure and mechanical properties.