Abstract
En este trabajo se estudia la posibilidad de preparar aleaciones de alta entropía del sistema Al-Sc-Ti-V-Cr. Para ello se han seleccionado los elementos y la composición utilizando los criterios conocidos y disponibles en la literatura y se han preparado mediante fusión por arco tres aleaciones con contenidos que varían entre el 10 y 35 at.%. Las tres aleaciones tienen una microestructura dendrítica bifásica similar, siendo las dendritas una solución sólida bcc enriquecida en Ti, V o Cr. El escandio aparece únicamente en el espacio interdendrítico formando el intermetálico Al2Sc. La dureza de las dendritas crece con el contenido en Ti y se hace menor a medida que es mayor el contenido en Cr. Además, la tenacidad de las aleaciones depende de la dureza de las dendritas siendo ésta mayor cuanto más blandas son las dendritas. Los resultados obtenidos demuestran que ni los criterios empíricos utilizados ni los cálculos mediante THERMOCALC permiten predecir la formación de una única solución sólida ni la naturaleza de las fases observadas experimentalmente.
Highlights
The high-entropy alloys (HEA) are receiving great scientific attention over the last decade in view of the good balance of properties (Cantor et al, 2004; Cantor, 2011; Zhang et al, 2014)
One of the most accepted definition is that HEAs alloys are not based around a single major element but rather contain several (≥5) major elements, present each in concentrations between about 5 and 35 at.%, that are expected to stabilize a solid solution with simple crystal structure in view of the high mixing entropy
22.6 10.8 11.5 42.7 12.5 re-melted five times turning over the button each time, to ensure homogeneous composition which was confirmed by Energy Dispersive X-ray (EDX) microanalysis at several areas
Summary
Three Al-Sc-Ti-V-Cr alloys, whose nominal compositions are listed in Table 1, were prepared from pure elements in an arc furnace under argon atmosphere. 22.6 10.8 11.5 42.7 12.5 re-melted five times turning over the button each time, to ensure homogeneous composition which was confirmed by Energy Dispersive X-ray (EDX) microanalysis at several areas. Phase and microstructural characterization was carried out by X-ray diffraction, Scanning Electron Microscopy (SEM) and EDS microanalysis, and by electron backscattering diffraction (EBSD) carried out in a SEM. Observations of samples by backscattered electron images were conducted at 10 and 15 kV but EDS microanalysis was always carried out at 15 kV. Thermal characterization of the alloys, especially to determine the temperature where melting started, was done by differential thermal analysis (DTA) in argon atmosphere using a heating rate of 10 K min−1. The macrohardness of the alloys, as well as the microhardness of different phases and an estimate of fracture toughness, were determined from Vickers hardness imprints on polished samples. KQ, was estimated from the length of cracks generated at the corners of indentations at progressively higher loads, ranging from 200 g to 2 kg, noting the load when c racking began, and using standard relationships (Anstis et al, 1981; Morris et al, 1998) to determine toughness from the crack length at an applied load of 2 kg
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