CoCrCuFeNi Alloy Research Articles

Recrystallization Behavior of CoCrCuFeNi High-Entropy Alloy

We investigated the recrystallization behavior of a cold-rolled CoCrCuFeNi high-entropy alloy (HEA). Two different face-centered cubic phases having different chemical compositions and lattice constants in the as-cast specimen have different chemical compositions: One phase was the Cu-lean matrix and the other was the Cu-rich second phase. The second phase remained even after a heat treatment at 1373 K (1100 °C) and Cu enriched more in the Cu-rich second phase. The calculated mixing enthalpies of both Cu-lean and Cu-rich phases in the as-cast and heat-treated specimens explained that Cu partitioning during the heat treatment decreased the mixing enthalpy in both phases. In the specimens 90 pct cold rolled and annealed at 923 K, 973 K, and 1073 K (650 °C, 700 °C, and 800 °C), recrystallization proceeded with increasing the annealing temperature, and ultrafine recrystallized grains with grain sizes around 1 μm could be obtained. The microhardness tended to decrease with increasing the fraction recrystallized, but it was found that the microhardness values of partially recrystallized specimens were much higher than those expected by a simple rule of mixture between the initial and cold-rolled specimens. The reason for the higher hardness was discussed based on the ultrafine grain size, sluggish diffusion expected in HEAs, and two-phase structure in the CoCrCuFeNi alloy.

Synthesis of Al0.5CoCrCuFeNi and Al0.5CoCrFeMnNi High-Entropy Alloys by Laser Melting

High-entropy alloys (HEAs) are a blend of 5+ metallic elements that can form solid solution disordered structures. Two HEAs were synthesized using laser melting in an argon atmosphere. The relatively well-studied Al0.5CoCrCuFeNi alloy was first produced to establish the feasibility of laser melting. Manganese was then substituted for copper to potentially lower both cost and density, producing a novel Al0.5CoCrFeMnNi alloy system. These samples were analyzed with XRD, SEM, EDS, and Vickers microhardness to determine the effects of the manganese substitution, as well as the effects of laser melting in comparison to the more traditional arc melting.

Novel cermet material of WC/multi-element alloy

Multi-element alloy “Al0.5CoCrCuFeNi” is a brand new novel metal material. It has high working hardness, high high-temperature strength, and anti-oxidation properties. Multi-element alloy powders can be prepared by blending various pure metal powders using a mechanical alloying method. Different ratios of WC and multi-element alloys can be sequentially mixed and alloyed using a mechanical alloying method. WC particles were dispersed homogeneously in ductile multi-element alloy without forming any second phase. After press forming, the admixed powders were debound at 500°C and then liquid-phase sintered at 1300–1450°C. The sintering process of WC/Al0.5CoCrCuFeNi multi-element alloy is similar to the traditional WC/Co. The hardness of the sintering body of WC/Al0.5CoCrCuFeNi alloy is Hv 200–300 higher than the traditional WC/Co sintering body measured at room temperature. Its high-temperature hardness is Hv 200 higher than the traditional WC/Co measured at 900°C. Substitution of multi-element alloy for Co as the base phase can enormously improve the material properties of WC super-hard composite material.

Alloying, thermal stability and strengthening in spark plasma sintered AlxCoCrCuFeNi high entropy alloys

Abstract Al x CoCrCuFeNi ( x = 0.45, 1, 2.5 and 5 mol) multi-component high entropy alloys synthesized by mechanical alloying were spark plasma sintered to produce high dense compacts. X-ray diffraction and scanning electron microscopy studies reveal that these sintered alloys exhibit varying microstructures from single phase to three phases depending on Al content. The thermal stability studies carried out in the temperature range of 400–600 °C for duration of 2–10 h in Ar atmosphere suggest that these alloys exhibit excellent thermal stability in terms of phases and crystallite size. Highest specific hardness of 160 (HV/g cm −3 ) is achieved in the sintered Al 5 CoCrCuFeNi alloy and there is no significant change in the hardness after heat treatment of Al 0.45 CoCrCuFeNi and AlCoCrCuFeNi alloys. Hall–Petch analysis based on hardness measurements carried out on sintered samples reveals that solid solution strengthening seems to increase with increase in Al content.

Entropy-driven phase stability and slow diffusion kinetics in an Al0.5CoCrCuFeNi high entropy alloy

Previous work on the stability of the solid solution phases in the high entropy alloys is inconclusive. We used a series of thermo-mechanical treatments to study the stability of the solid solution phases in a high-entropy Al0.5CoCrCuFeNi alloy. The solid solution phases were found to be stable, against the intermetallic compounds, at high temperatures >850 °C and at low temperatures <300 °C. At intermediate temperatures, however, the intermetallic σ-phase co-existed with the solid solution phases. The experimental observations were verified by the thermodynamic calculation results. The mechanisms for the phase stability, both at equilibrium and after quenching-equivalent annealing treatments, were discussed, and the roles of high entropy and slow diffusion kinetics were highlighted.

Effect of electromagnetic stirring on microstructure and properties of Al0.5CoCrCuFeNi alloy

The Al0.5CoCrCuFeNi high-entropy alloy was synthesized by the medium frequency induction melting furnace. The effect of electromagnetic stirring on the microstructure and mechanical property of the alloy was investigated. The results showed that the electromagnetic stirring was effective to refine the grains for Al0.5CoCrCuFeNi alloy. And the alloy exhibited excellent mechanical properties. The as-cast rod sample did not fracture even at a compressive engineering strain of above 50%. Besides, the compressive strength and the tensile strength of the alloy with electromagnetic stirring during solidification were higher than that without electromagnetic stirring. Due to the existence of microcracks, the tensile engineering strain of the alloy reduced a little with electromagnetic stirring, but was still higher than 25%.

Effect of temperature on mechanical properties of Al0.5CoCrCuFeNi wrought alloy

This work studies how temperature, from the ambient temperature to 900 °C, affects the mechanical properties of Al 0.5 CoCrCuFeNi alloys in different wrought states. The alloy displayed a good workability by rolling and an excellent combination of strength and elongation at ambient temperature in both the as-cold-rolled and the 900 °C-annealed states as compared to those of 304 steel and Ti–6Al–4V. However, both as-rolled and as-annealed samples displayed intermediate embrittlement between 300 °C and 600 °C. The investigation of fractography, precipitate phases and the aging hardening response of the samples revealed the embrittlement mechanism: the BCC phase particles that precipitated from the supersaturated matrix and Cu-rich phases between 300 °C and 600 °C rendered the alloy of interest harder but more brittle.

Effect of Aluminum Content on Plasma-Nitrided Al x CoCrCuFeNi High-Entropy Alloys

High-entropy alloys (HEAs) Al x CoCrCuFeNi with different aluminum contents (x = 0 to 1.8) were plasma nitrided at 525 °C for 45 hours with an aim to develop wear-resistant structural parts. The nitrided layer comprises a well-nitrided dendrite phase and an un-nitrided Cu-rich interdendrite phase. Surface hardening is a result of the formation of various nitrides in the nitrided dendrite: CrN, Fe4N, and AlN. With increasing aluminum content, the hardness of the nitrided layer increases due to the increased amount of hard AlN phase and the increased volume fraction of bcc phase being harder than the fcc one. The nitrided layer thickness shows an apparent decrease with the increasing aluminum content of the alloy. The present alloy system provides a wide range of substrate hardness from Hv 170 to 560 before nitriding, which even becomes harder by around Hv 30 after nitriding. For Al0.5CoCrCuFeNi alloy having the highest surface hardness of Hv 1300, a layer thickness of 23 μm, and a substrate hardness of Hv 300, an adhesive wear test confirms its superior wear resistance as being 17 times that of the un-nitrided samples.

Effect of vanadium addition on the microstructure, hardness, and wear resistance of Al0.5CoCrCuFeNi high-entropy alloy

The authors studied the effect of vanadium addition on the microstructure and properties of Al0.5CoCrCuFeNi high-entropy alloy. The microstructure of Al0.5CoCrCuFeNiV x (x=0 to 2.0 in molar ratio) alloys was investigated by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. With little vanadium addition, the alloys are composed of a simple fcc solid-solution structure. As the vanadium content reaches 0.4, a BCC structure appears with spinodal decomposition and envelops the FCC dendrites. From x=0.4 to 1.0, the volume fraction of bcc structure phase increases with the vanadium content increase. When x=1.0, fcc dendrites become completely replaced by bcc dendrites. Needle-like σ-phase forms in bcc spinodal structure and increases from x=0.6 to 1.0 but disappears from x=1.2 to 2.0. The hardness and wear resistance of the alloys were measured and explained with the evolution of the microstructure. The hardness values of the alloys increase when the vanadium content increases from 0.4 to 1.0 and peak (640 HV) at a vanadium content of 1.0. The wear resistance increases by around 20 pct as the content of vanadium increases from x=0.6 to 1.2 and levels off beyond x=1.2. The optimal vanadium addition is between x=1.0 and 1.2. Compared with the previous investigation of Al0.5CoCrCuFeNi alloy, the vanadium addition to the alloy promotes the alloy properties.

Adhesive wear behavior of Al xCoCrCuFeNi high-entropy alloys as a function of aluminum content

The Al x CoCrCuFeNi alloys with different aluminum contents prepared by arc melting were investigated on their adhesive wear behaviors. With increasing aluminum content, both the volume fraction of BCC phase and the hardness value increase, and thus the wear coefficient decreases. Moreover, the wear mechanism changes from delamination wear to oxidative wear. For low aluminum content, x = 0.5, the microstructure is of simple ductile FCC phase and the worn surface is deeply grooved and undergoes a periodic delamination which produces big debris. For medium aluminum content, x = 1.0, the microstructure is a mixture of FCC and BCC phases, and the worn surface is deeply grooved in FCC region but smooth in BCC region. Delamination wear is still dominant although oxidative wear occurs in the smooth region. For high aluminum content, x = 2.0, the microstructure is of BCC phase and the worn surface is smooth and yields fine debris with high oxygen content. The high aluminum content gives a large improvement in wear resistance. This improvement is attributed to its high hardness, which not only resists plastic deformation and delamination, but also brings about the oxidative wear in which oxide film could assist the wear resistance.

Nanostructured nitride films of multi-element high-entropy alloys by reactive DC sputtering

Multi-element high-entropy alloys (HE alloys) are new alloys with over five principal elements each having an atomic percentage no more than 35%. Using the alloys, e.g. Al 0.5CoCrCuFeNi, Al 2CoCrCuFeNi, and AlCrNiSiTi, as target materials in reactive sputtering, nanostructured metallic and nitride films were deposited. XRD patterns show that the alloy films of Al x CoCrCuFeNi are crystalline with structures of simple fcc or mixed bcc + fcc solid solution, and the crystallinity decreases and approaches an amorphous structure with increasing nitrogen flow rate into the processing chamber. Unlike the Al x CoCrCuFeNi HE alloys, the metallic film of AlCrNiSiTi is amorphous and its hardness is much higher than the hardest nitride films of Al x CoCrCuFeNi alloy. TEM, FESEM and AFM observations show that the films morphology and structure evolution with N 2/Ar fraction is different between Al x CoCrCuFeNi and AlCrNiSiTi HE alloys. The slope of films resistivity versus N 2/Ar ratio is much steeper in AlCrNiSiTi than in Al x CoCrCuFeNi HE alloy. The hardness enhancement in nitrides is less significant in AlCrNiSiTi than in Al x CoCrCuFeNi HE alloys.

Mechanical performance of the Al x CoCrCuFeNi high-entropy alloy system with multiprincipal elements

The AlxCoCrCuFeNi alloys with multiprincipal elements (x=the aluminum content in molar ratio, from 0 to 3.0) were synthesized using a well-developed arc-melting and casting method, and their mechanical properties were investigated. These alloys exhibited promising mechanical properties, including excellent elevated-temperature strength and good wear resistance. With the addition of aluminum from x=0 to 3.0, the hardness of the alloys increased from HV 133 to 655, mainly attributed to the increased portion of strong bcc phase to ductile fcc phase, both of which were strengthened by the solid solution of aluminum atoms and the precipitation of nanophases. The alloys exhibited superior high-temperature strengths up to 800 °C, among which the Al0.5CoCrCuFeNi alloy, especially, had enhanced plasticity and a large strain-hardening capacity. Moreover, the wear resistance of these alloys was similar to that of ferrous alloys at the same hardness level, while the alloys with lower hardness exhibited relatively higher resistance because of their large strain-hardening capacity.