Microstructure and properties of CoCrNi medium-entropy alloy produced by gas atomization and spark plasma sintering
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Microstructure and properties of CoCrNi medium-entropy alloy produced by gas atomization and spark plasma sintering Jianying Wang1, Hailin Yang1,a)
, Jianming Ruan1, Yun Wang2, Shouxun Ji2
1
State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China Institute of Materials and Manufacturing, Brunel University London, Uxbridge, Middlesex UB8 3PH, U.K. a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 3 January 2019; accepted: 20 February 2019
A homogeneous structured CoCrNi medium-entropy alloy was synthesized by gas atomization and spark plasma sintering (SPS). The mechanical properties, corrosion resistance, and magnetic properties were reported in this study. The as-atomized CoCrNi MEA powder, with a spherical morphology in shape and a mean particle diameter of 61 lm, consisted of a single face-centered cubic (FCC) phase with homogeneous distributions of Co, Cr, and Ni elements. Also, the cross-sectional microstructure of powder particles gradually transformed from fully cellular structure into equiaxed-type structure with increasing particle size. After being sintered by SPS, the CoCrNi MEA consisted of a single FCC phase with a mean grain size of 20.8 lm. Meanwhile, the CoCrNi MEA can capable of offering an ultimate tensile strength of 799 MPa, yield strength of 352 MPa, elongation of 53.6%, and hardness of 195.3 HV. In addition, this MEA showed superior corrosion resistance to that of 304 SS (stainless steel) in both 0.5 mol/L HCl and 1 mol/L NaOH solutions. The magnetization loop indicated that this MEA has good soft magnetic properties.
Introduction High-entropy alloys (HEAs), consisting of at least five equiatomic or near-equiatomic elements crystalized as simple solid solution structures, have attracted significant interest owing to their unique phase structures and superior properties [1, 2, 3, 4, 5]. For example, the typical simple facecentered cubic (FCC) CoCrFeNiMn HEA generally exhibited excellent tensile strength (above 1 GPa) and fracture toughness (exceeding 200 MPa m1/2) [6]. The AlxCoCrFeNi HEAs exhibit superior corrosion resistance compared with that of conventional corrosion-resistant alloys, such as stainless steels and Al, Ni, Ti, and Cu alloys [5]. Nevertheless, the origin of the formation of simple solid solution structures and answer on whether more elements improve the mechanical properties of HEAs are still controversial. The explanation of development of simple solid solution structures rather than intermetallic phases by increasing the number of elements to obtain a higher entropy might be wrong, as demonstrated by related experimental and CALPHAD simulation results [2, 7]. On the other hand, Gail et al. reported that the introduction of Mn to
ª Materials Research Society 2019
the CoCrFeNi medium-entropy alloy (MEA) had a negligible effect on the degree of solid solution strengthening, as evidenced by their similar yield strength and ultimate tensile strength [8]. Therefore, there was no systematic correlation be
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