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This paper reports the microstructural evolution and mechanical properties of a low-density Al0.3NbTa0.8Ti1.5V0.2Zr refractory high-entropy alloy (RHEA) prepared by means of a combination of mechanical alloying and spark plasma sintering (SPS). Prior to sintering, the morphology, chemical homogeneity and crystal structures of the powders were thoroughly investigated by varying the milling times to find optimal conditions for densification. The sintered bulk RHEAs were produced with diverse feedstock powder conditions. The microstructural development of the materials was analyzed in terms of phase composition and constitution, chemical homogeneity, and crystallographic properties. Hardness and elastic constants also were measured. The calculation of phase diagrams (CALPHAD) was performed to predict the phase changes in the alloy, and the results were compared with the experiments. Milling time seems to play a significant role in the contamination level of the sintered materials. Even though a protective atmosphere was used in the entire manufacturing process, carbide formation was detected in the sintered bulks as early as after 3 h of powder milling. Oxides were observed after 30 h due to wear of the high-carbon steel milling media and SPS consolidation. Ten hours of milling seems sufficient for achieving an optimal equilibrium between microstructural homogeneity and refinement, high hardness and minimal contamination. [ABSTRACT FROM AUTHOR]

The present study is focused on synthesis and mechanical properties characterization of equiatomic CoCrNi medium entropy alloy (MEA). Powder metallurgy processes of mechanical alloying (MA) with subsequent spark plasma sintering (SPS) for bulk alloy densification have been utilized. As opposed to the single-phase alloys of identical composition fabricated via casting routes, the alloy after SPS compaction consisted of a major FCC solid solution phase (94.4%), minor fraction of secondary BCC phase (5.6%, precipitated at the FCC grains boundaries), and negligible amount of oxide inclusions. The alloy exhibited high ultimate tensile strength of 1024 MPa and a elongation to fracture of 26%. Elastic modulus of the alloy reached 222 GPa and the thermal expansion coefficient (CTE) was measured as 17.4 × 10 −6 K −1 The plastic deformation in the alloy is carried out by a combination of dislocation glide and mechanical nano-twinning at room temperature. [ABSTRACT FROM AUTHOR]

Abstract The present work deals with the synthesis and evaluation of the microstructural and mechanical properties of face-centred cubic Ni 1.5 Co 1.5 CrFeTi 0.5 high-entropy alloy strengthened by nano-sized titanium oxide dispersion and coherent precipitates of Ni 3 Ti intermetallic phase produced by powder metallurgy. The alloy's properties are well tuneable by the use of proper heat treatment. The alloy exhibits an excellent combination of tensile strength and ductility, reaching an ultimate tensile strength of 1460 MPa and elongation of 14.5% in solution annealed state and 1660 MPa and 4.8% in the aged condition. Most of the strengthening contribution was attributed to Orowan-type strengthening mechanism. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

The present work is focused on synthesis and mechanical properties evaluation of non-equiatomic Ni 1,5 Co 1,5 CrFeTi 0,5, ductile single phase high entropy alloy (HEA) with excellent mechanical properties (bend strength R mb = 2593 MPa, tensile strength R m = 1384 MPa, tensile elongation to fracture of 4.01%, and elastic modulus of 216 GPa) surpassing those of traditional as-cast HEA. For the alloy production, a combination of mechanical alloying (MA) process in a planetary ball mill and spark plasma sintering (SPS) for powder densification was utilized. The tensile properties of a bulk material produced by a combination of MA + SPS are characterized for the first time. The feedstock powder and corresponding bulk material microstructure, elemental and phase composition, and mechanical properties were investigated by scanning (SEM) and transmission (TEM) electron microscopy, energy-dispersive X-ray spectroscopy (EDX), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), as well as impulse excitation of vibration, Vickers microhardness and tensile and bend strength tests, respectively. The structure of the samples consisted of single-phase FCC high entropy solid solution of extremely fine-twinned grains and oxide inclusions inherited from the original powder feedstock. Dimple-like morphology corresponding to ductile fracture mode has been observed on the fracture surfaces, with crack initiation sites on the inclusions phases. [ABSTRACT FROM AUTHOR]