Papers by Keyword: Microstructure

Abstract: The effect of deformation temperature on microstructure, flow stress and corrosion resistance of 2205 duplex stainless steel was investigated at low strain rate of 0.005 s^-1. The flow curve analysis showed that the specimen was mainly characterized with dynamic recovery (DRV) at 850 °C, and the characteristic of dynamic recrystallization (DRX) was enhanced with deformation temperature increasing to 950 and 1050 °C, then flow curves presented steady state with characteristic of DRV at 1150 and 1250 °C. Microstructure analysis exhibited the austenite DRX at deformation temperatures of 1050 and 1150 °C. The specimens deformed at temperatures ranging from 850 to 1250 °C and strain rate of 0.005 s^-1presented active-transpassive behavior, indicating faster corrosion rate compared with the as-received, which can be attributed to more ferrite (δ) and austenite (γ) grain boundaries or δ/γ phase boundaries formation.

Abstract: Master alloys are used in the metals industry to control chemical composition and to help to achieve a particular microstructure or promote growth of desired phases. This study reports on making a Al₃Nb containing aluminium (Al) - niobium (Nb) master alloy by solid-liquid reaction processing, where solid Nb particles are added to the liquid Al. Nb react with Al to form in-situ Al₃Nb. The in-situ formed Al₃Nb particles were facet and polygonal in shape. The three dimensional analysis revealed that the outer surface of the partially reacted Nb was covered with faceted Al₃Nb particles. The different nature and morphologies of the in-situ phases that were produced were determined using SEM, EDX, XRD and extraction techniques. A mechanism for the observed microstructural difference is discussed.

Abstract: Ti₆₀(Ni_xCu_40-x)₄₀ x = 5 - 40 at% ternary alloys were prepared by arc-melting followed by a centrifugal casting into a wedge-shaped copper mould in order to examine glass forming of these compositions. Microstructure of the master alloys and wedge-shaped samples were studied. Among the master alloys, which solidified under non-equilibrium conditions, the sample with 15 at% Ni content displayed clear eutectic structure and its wedge-shaped sample had the finest structure but still crystalline. Microstructure of the other compositions was far from amorphous state.

Abstract: The Cu-Zr-Ag system is characterized by a miscibility gap. The liquid separates into Ag-rich and Cu-Zr rich liquids. Yttrium was added to the Cu-Zr-Ag and Cu-Zr-Ag-Al systems and its influence on liquid immiscibility was studied. This alloying element has been chosen to check the effect of the heat of mixing between silver and the given element. In the case of Ag-Y system it is highly negative (-29 kJ/mol). The liquid becomes immiscible in the Cu-Zr-Ag-Y system. To the effect of Y addition the quaternary liquid decomposed into Ag-Y rich and Cu-Zr rich liquids. The Y addition increased the field of miscibility gap. An amorphous/crystalline composite with 6 mm thickness has been successfully produced by liquid-liquid separation based on preliminary calculation of its composition. The matrix was Cu₃₈Zr₄₈Al₆Ag₈ and the crystalline phases were Ag-Y rich separate spherical droplets.

Abstract: The interaction between Zr addition and intensive melt shearing on grain refinement of commercial purity Mg has been investigated experimentally. It was found that, without intensive melt shearing, the grain structure of Mg is changed from columnar grains to equiaxed grains with the increase in Zr concentration. However, with intensive melt shearing, the grain structure of Mg undergoes a complex change as a function of Zr concentration; for instance, the grain structure showed equiaxed grains at 0.1wt. % Zr concentration, while it was changed to columnar grains at 1wt. % Zr concentration. It was noted that, particularly, under the intensive melt shearing condition, the grain size of Mg with minor addition of Zr (0.1%) was further decreased to 134 ± 4 μm compared with that of Mg without Zr addition (217 ± 15 μm).

Abstract: A numerical model is developed to describe the dendritic growth of multicomponent aluminium alloys, based on a coupled deterministic continuum mechanics heat and species transfer model and a stochastic localized growth model that takes into account the undercooling temperature, curvature, kinetic, and thermodynamic anisotropy. The stochastic model receives temperature and concentration information from the deterministic model and the deterministic heat and species diffusion equations receive the solid fraction information from the stochastic model. The heat and species transfer models are solved on a regular grid by the standard explicit Finite Difference Method (FDM). The dendritic growth model of multicomponent alloy [1,2] is solved by a novel Point Automata (PA) approach [3,4] where the regular cells of the Cellular Automata (CA) method are replaced by the randomly distributed points and neighborhood configuration, similar as appears in meshless methods. The PA method was developed in order to circumvent the mesh anisotropy problem, associated with the classical CA method. The present paper extends our previous developments of Pa method to multicomponent alloys. A comparison of the results, obtained by the PA and CA method is shown for Al-5.3% Zn-2.35% Mg-1.35% Cu-0.5% alloy.

Abstract: Design and characterization of modified Cobalt base alloy for biological applications have been studied and compared. In particular, modification has been realized by addition of Mo, Ti and Zr to better fit the requirements for dental applications. On the samples morphological and surface analysis including residual stress determination have been considered. As a result of this study, a positive effect of Ti addition has been demonstrated. Contrarily, a simultaneous addition of Ti and Zr does not promote any enhancement as microstructure and properties concern.

Abstract: Microstructure evolution of a 3003 sheet cladded with 4004 brazing alloy is investigated during slow heating (1K/min) under secondary vacuum up to isothermal brazing temperature (590°C). Optical and scanning microscopies, EDS chemical analysis and EBSD orientation mapping are used. Experimental results are discussed in the light of thermodynamic calculations using Thermo-Calc. Comparisons show good agreement as long as Mg vaporization does not take place.

Abstract: The present work is aimed at understanding the microstructure evolution in a series of Ti₆₀Fe_40-xCo_x (x= 0, 16, 18, 20, 22, 24) alloys. The ternary alloys are synthesized by arc melting cum suction casting technique under high purity argon atmosphere to obtain alloy cylinders having 3 mm diameter and aspect ratio of 17:1. Detailed X-ray diffractometry and electron microscopic studies are carried out to identify the phases in the investigated alloys. It has been found that the alloys consist of fine scale eutectic matrix between bcc (b-Ti)_ss and Ti(Fe,Co) phases along with the dendritic phase of Ti(Fe,Co), whereas the dendritic phase of Ti₂(Fe,Co) has also been observed for x = 16 and 20. It is also found that ternary Ti₆₀Fe₂₀Co₂₀ alloy shows good combination of compressive strength (~2507 MPa) and plasticity (~16.3 %) among the investigated alloys.

Abstract: The characteristics of Nickel Aluminum Bronze alloy (NAB) after hot deformation were investigated. The NAB alloy have been studied by dilatometer according to study the influence of hot deformation on microstructure of NAB alloy by dilatometer in the temperature range 800 - 950 °C, strain rate 10s^-1 and cooling rate 40 and 100 °C/s. The experimental results showed that peak stress in relation to the involved deformation temperature, peak stresses at a constant strain rate decreased with an increase of deformation temperature. It was found that volume fraction of the β phase significantly increased with increasing temperature and cooling rate. The variation of this phase affected macro hardness of the investigated alloy. By higher temperatures, amount of β phase increased as well as the macro hardness of the NAB alloy.