Crystopher Brito

Steady and unsteady state peritectic solidification

Abstract In the present study, Pb–Bi as a model of alloys from peritectic systems was directionally solidified under transient heat flow conditions, which is the class of heat flow encompassing the majority of industrial solidification processes. Some experiments were also carried out in a vertical tube furnace under cooling rates closer to equilibrium during solidification in order to broaden the range of solidification parameters. Thermal parameters such as the tip growth rate (VL) and the cooling rate were experimentally determined and correlated with the primary (λ1) and secondary (λ2) dendrite arm spacings by experimental growth laws. It is shown that the proposed growth laws are able to encompass also the growth of dendritic branches during steady state growth from the melt.

Characterization of Dendritic Microstructure, Intermetallic Phases, and Hardness of Directionally Solidified Al-Mg and Al-Mg-Si Alloys

THE authors regret that numerical errors were identified in Figures 10(a, right graph) and (b, right graph) and 12. In the calculation of the growth rate of the Al-3.0 wt pct Ni alloy, a mistake has been found. The corrected figures and their respective legends are reproduced below. The error does not change the main discussions and conclusions of the work. In addition, a sentence containing the discussion associated with Figure 12 has been rewritten as follows. As can be observed in Figure 12, the BKmodel roughly matches the experimental tendency of evolution of the secondary dendrite arm spacing with the growth rate.

Electrochemical Behavior of an Al-Fe-Ni Alloy Affected by Nano-Sized Intermetallic Particles

The aim of this study is to determine the effect of the resulting microstructural array of an as-cast Al-1 wt% Fe-1 wt% Ni alloy on its electrochemical corrosion behavior in a stagnant and naturally aerated 0.5 M NaCl solution at room temperature. Electrochemical impedance spectroscopy (EIS) plots, potentio-dynamic polarization curves, and equivalent circuits are used to evaluate the corrosion response. It was found that nano-sized Al9FeNi intermetallic (IMC) particles have an important role on the corrosion resistance, which significantly affect the anode/cathode area ratio and as consequence, the examined electrochemical parameters. A mixture of interconnected spheroids and fiber-like IMC particles induces a drastic and rapid increase in the current density, while intermittent IMC particles reduce the corrosion action.

Influência na microestrutura e na microdureza decorrente da adição de 4%Ag na liga Al-4%Cu solidificada unidirecionalmente

Al-Cu alloys are used in several industrial applications, such as automotive and aerospace manufacturing, which demand mechanical strength and toughness performances. The Al-Cu-Ag ternary alloy system has been investigated to obtain a better understanding on ternary eutectic alloys besides its inherent applications. However, studies concerning the effects on microstructure and hardness due to Ag addition on Al-Cu alloys solidified under transient conditions, are not found in literature. In this sense, the main objective of this work consists in investigating the solidification parameters such as growth (VL) and cooling (Ṫ) rate, microstructure and microhardness regarding the effects of adding 4wt% Ag on a Al-4wt%Cu alloy

Length scale of the dendritic microstructure affecting tensile properties of Al–(Ag)–(Cu) alloys

The dependence of tensile properties on the length scale of the dendritic morphology of Al–Cu, Al–Ag and Al–Ag–Cu alloys is experimentally investigated. These alloys were directionally solidified (DS) under a wide range of cooling rates (Ṫ), permitting extensive microstructural scales to be examined. Experimental growth laws are proposed relating the primary dendritic arm spacing, λ1 to Ṫ and tensile properties to λ1. It is shown that the most significant effect of the scale of λ1 on the tensile properties is that of the ternary alloy, which is attributed to the more homogeneous distribution of the eutectic mixture for smaller λ1 and by the combined reinforcement roles of the intermetallics present in the ternary eutectic: Al2Cu and nonequilibrium Ag3Al.

Microstructure and Tensile/Corrosion Properties Relationships of Directionally Solidified Al–Cu–Ni Alloys

Al–Cu–Ni alloys are of scientific and technological interest due to high strength/high temperature applications, based on the reinforcement originated from the interaction between the Al-rich phase and intermetallic composites. The nature, morphology, size, volume fraction and dispersion of IMCs particles throughout the Al-rich matrix are important factors determining the resulting mechanical and chemical properties. The present work aims to evaluate the effect of the addition of 1wt%Ni into Al–5wt%Cu and Al–15wt%Cu alloys on the solidification rate, macrosegregation, microstructure features and the interrelations of such characteristics on tensile and corrosion properties. A directional solidification technique is used permitting a wide range of microstructural scales to be examined. Experimental growth laws relating the primary and secondary dendritic spacings to growth rate and solidification cooling rate are proposed, and Hall–Petch type equations are derived relating the ultimate tensile strength and elongation to the primary dendritic spacing. Considering a compromise between ultimate tensile strength and corrosion resistance of the examined alloys samples from both alloys castings it is shown that the samples having more refined microstructures are associated with the highest values of such properties.