Abstract
The possibility of microstructural refinement and improvement of mechanical properties by severe cold-rolling was investigated in an AlCoCrFeNi2.1 lamellar eutectic high entropy alloy (EHEA). The as-cast alloy revealed fine scale eutectic mixture of L12 (ordered FCC) and B2 (ordered BCC) phases. During severe cold-rolling up to 90% reduction in thickness the B2 phase maintained the ordered structure, while the L12 phase showed the evolution of a nanocrystalline structure and progressive disordering. Annealing of the severely cold-rolled material resulted in the formation of duplex microstructures composed of two different phases with equiaxed morphologies and significant resistance to grain growth up to 1200°C. Annealing at 1000°C resulted in an optimum strength-ductility balance with the tensile strength of 1175 MPa and the total elongation of 23%. The present results showed that severe cold-rolling and annealing can impart very attractive mechanical properties in complex EHEAs.
Highlights
High entropy alloys (HEAs) are originally proposed as a novel class of multicomponent alloys containing sufficiently large number of alloying elements (≥5) in equiatomic or near equiatomic proportions [1]
The AlCoCrFeNi2.1 Eutectic HEAs (EHEAs) (15mm x 90mm x 3mm) used in the present study was prepared by an optimized arc melting route starting from high purity elemental powders
The hardness of the constituent phases in the as-cast EHEA was analyzed by nanoindentation hardness mapping using a TI950 Triboindenter (Hysitron, USA) with the applied load linearly increasing from 1 μN to the maximum of 500 μN over a period of 0.25 s and unloaded to 1 μN over a period of 0.25 s before moving to the indent position
Summary
High entropy alloys (HEAs) are originally proposed as a novel class of multicomponent alloys containing sufficiently large number of alloying elements (≥5) in equiatomic or near equiatomic proportions [1]. Despite the presence of large number of constituents, the HEAs may show simple phases due to their large configurational entropy. In spite of their complex chemistry, the HEAs show several attractive and intriguing mechanical properties which have generated tremendous research interest [2]. 194 (2017) 012018 doi:10.1088/1757-899X/194/1/012018 microstructure and properties of these novel alloys significantly as observed in other HEAs [4] but needs to be clarified.
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