Abstract
High entropy alloys (HEAs) are usually fabricated using arc melting which has the disadvantages of diseconomy, and the limitations in the shape and size of final products. However, recently, quite a large amount of research has been carried out to find the fabrication techniques for HEAs with better properties such as mechanical alloying and rapid solidification. In this paper, an AlCoCrFeNi high entropy alloy was successfully fabricated by the shock consolidation technique. In this method, the starting powders were mixed by mechanical alloying and then the shock wave was imposed to the compacted powders by explosion. High levels of residual stress existed in samples fabricated by the shock consolidation method. Due to this, after fabrication of the sample, heat treatment was used to eliminate the residual stress and improve the mechanical properties. The microstructure of the samples before and after heat treatment were examined by XRD, SEM and electron backscatter diffraction (EBSD). The shock consolidated sample and sample with heat treatment both showed the nano-structure. After heat treatment the hardness of the sample was decreased from 715 HV to the 624 HV, however the failure strength increased, and as expected the ductility of the sample was improved after heat treatment.
Highlights
Alloys have been developed according to the base element model
The nearly full dense AlCoCrFeNi high entropy alloys (HEAs) with nanocrystalline was successfully fabricated by mechanical alloying and subsequent shock consolidation of Mechanical alloying (MA) powders
HEA consist of nano-sized grains, with the number fraction of ultra-fine grains (UFGs) < 500 nm reaching 80%
Summary
Alloys have been developed according to the base element model. This strategy begins with one and rarely two principal elements. Body-centered cubic (BCC) phase with crystallite size less than 10 nm They consolidate the powder using vacuum hot press (at 800 ◦ C) and achieve high hardness (7.55 GPa) and compressive strength (2.3 GPa). Fabricate nanocrystalline Al20 Li20 Mg10 Sc20 Ti30 HEA powder by mechanical alloying, and they observe the phase change (FCC to hexagonal close-packed (HCP)) after annealing. They achieve super-low density (3 gr/cm3 ) and high hardness (6.1 GPa) by this method. Due to the rapid cooling rate of 109 K/s, the high temperature is limited to the surface while the interior of particle remains relatively cool These inherent properties make the shock consolidation a promising method to fabricate nanocrystalline materials. X-ray spectroscopy (EDS), Scanning Electron Microscopy (SEM) and electron backscatter diffraction (EBSD), and the mechanical properties were investigated by hardness measurement and quasi-static compressive test
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