J.W. Yeh

The effect of boron on the corrosion resistance of the high entropy alloys Al0.5CoCrCuFeNiBx

High entropy alloys are a newly developed family of multicomponent alloys that consist of various major alloying elements, including copper, nickel, aluminum, cobalt, chromium, iron, and others. Each element in the alloy system is present at between 5 and 35 atom %. A high entropy alloy has numerous beneficial mechanical, magnetic, and electrochemical characteristics. This investigation discusses the corrosion resistance of the Al 0.5 CoCrCuFeNiB x alloys with various amounts of added boron. Surface morphological and chemical analyses verified that the addition of boron produced Cr, Fe, and Co borides. Therefore, the fraction of Cr outside borides precipitates was scant. The anodic polarization curves and electrochemical impedance spectra of the Al 0.5 CoCrCUFeNiB x alloys, obtained in 1 N H 2 SO 4 aqueous solution, clearly reveal that the general corrosion resistance decreases as the concentration of boron increases.

Microstructures and mechanical behaviors of Ni–Al–Fe intermetallic compounds

Abstract A series of Ni25Al− x Fe ( x = 20–40 at.%) intermetallic compounds were prepared for mechanical property measurements by means of hardness and tensile testing. The microstructural evolution of these alloys was examined by X-ray diffraction, high temperature differential calorimetry, optical microscopy, scanning electron microscopy and transmission electron microscopy. The results reveal that two phases, γ′ and β′, exist in the alloys with low iron content, and the microstructure changes from the mixture of γ′ and β′ phases to a nearly single β′ phase when the iron content reaches 40 at.%. An increasing iron content, which substitutes for nickel in this alloy, results in an increased melting point, hardness, yield stress and ultimate stress, but a decreased elongation.

Microstructure and aging behaviour of Al5Cr32Fe35Ni22Ti6 high entropy alloy

Abstract The Al5Cr32Fe35Ni22Ti6 high entropy alloy was designed, and its microstructure, mechanical properties, corrosion resistance and aging behaviour were investigated. The as cast and as homogenised alloys were composed of three phases: body centred cubic, face centred cubic and Ni2AlTi Heusler phases. Aging at 700–900°C triggers the formation of various phases including sigma-CrFe, eta-Ni3Ti and Ni2AlTi Heusler phase and leads to significant age hardening and a maximum hardness of 900 HV. Additionally, the corrosion resistance of the Al5Cr32Fe35Ni22Ti6 alloy is found better than that of 316L stainless steel in 0.5M H2SO4 solution.

Microstructure and tensile properties of Al0.5CoCrCuFeNi alloys produced by simple rolling and annealing

Abstract This study demonstrates that simply by rolling at ambient temperature, FCC type high entropy alloy Al0.5CoCrCuFeNi can be refined to have nanocrystalline structure and exhibits outstanding combination of strength and ductility. The yield strength and ultimate tensile strength are 1284 and 1344 MPa, respectively, in combination with an elongation of 7.6%. After a short annealing at 900°C for 10 min, the elongation is doubled to 15.3% with a trade-off around 20% in strength. This excellent combination of strength and ductility is attributable to the activation of quasi-dynamic recrystallisation during cold work and the limited grain growth during 900°C annealing.

Evolution of microstructure and crystallographic texture in severely cold rolled high entropy equiatomic CoCrFeMnNi alloy during annealing

An equiatomic FCC CoCrFeMnNi high entropy alloy (HEA) was heavily cold rolled up to 90% reduction in thickness followed by isochronal annealing for 1 hour at temperatures ranging between 700°C to 1100°C. A strong brass texture was observed in the cold-rolled condition indicating the low stacking fault energy of the material. A fine stable microstructure was observed during annealing at low temperatures. The recrystallization texture was characterized by the presence of deformation texture components, in particular, the α-fiber (ND// ), S ({123} ) and the typical brass recrystallization texture component ({236} ). Annealing twins were shown to have important effect on the formation of annealing texture.

The microstructures and mechanical properties of niobium-modified Ni-25Al-27.5Fe intermetallics

Abstract The Ni-25Al-27.5Fe alloy was selected from the Ni-25Al- x Fe alloy system (x is from 20–40 at%) and macroalloyed with niobium to further improve the mechanical properties. The results reveal that three phases, fcc (γ); ordered fcc (γ′): and ordered bcc (β′) phases, exist in these alloys. The alloys show dendritic microstructures, and the interdendritic regions get thinner and fewer after adding niobium. After annealing at 1000 °C for 4 h a large amount of fcc-structured particles (γ-Fe) was precipitated within the matrix of β′-phased dendrite. This γ-Fe contained higher iron- and niobium-concentration when compared to the β′ phase. In addition, increasing the niobium content to 1 at% results in increasing all the room-temperature tensile properties. However, the tensile properties will decrease sharply with the addition of niobium beyond 1 at%. This phenomenon could be caused by decreasing the interdendritic regions after adding niobium of more than 1 at%. Moreover, the temperature effect on the tensile properties is very significant. Both the yield strength and ultimate tensile strength decrease with increasing temperature, and the elongation increases sharply when the temperature is beyond 600 °C.

Microstructure investigation in B2-phased Ni-25Al-40Fe intermetallic compound

To change the microstructures and improve the room-temperature ductility of B2-structured ({beta}{prime} phase) NiAl intermetallic compound, macroalloying with iron was reported by referring previous literature. In the previous investigation on the Ni-25Al-xFe alloys (x is from 20 to 40 at.%), the alloy was prepared by bulk-processing because of convenience for structural application. Therefore, the significant segregation could not be avoided due to the cooling rate. In the Ni-25Al-xFe alloy system, the alloys exhibited two-phased dendritic microstructures when x was lower than 40 at.%. The as-cast morphologies changed to a single-phased granular structure after the Fe-content reached to 40 at.%. This single phase existing in the as-cast Ni-25Al-40Fe alloy was identified as an ordered bcc {beta}{prime} phase like {beta}{prime}-NiAl by TEM and XRD analysis. The B2-phased compounds show a typical CsCl structure which is 3/2 Hume-Rothery electron compound (1.5 electrons/atom), order at high temperatures and has many interesting properties, as described by some literature. This B2 phase also revealed unusual diffraction patterns and images when examined in the transmission electron microscope. In this paper, the authors will show the behavior similarity of this bulk-processed Ni-25Al-40Fe alloy, moreover report the effect of segregation and the precipitates in the alloy during annealing.