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The effects of niobium and molybdenum additions on the microstructures, hardness and corrosion behaviors of CrFeCoNi(Nb,Mo) alloys were investigated. All of the CrFeCoNi(Nb,Mo) alloys displayed dendritic microstructures. The dendrites of CrFeCoNiNb and CrFeCoNiNb0.5Mo0.5 alloys were a hexagonal close packing (HCP) phase and the interdendrites were a eutectic structure of HCP and face-centered cubic (FCC) phases. Additionally, the dendrites of CrFeCoNiMo alloys were a simple cubic (SC) phase and the interdendrites were a eutectic structure of SC and FCC phases. The volume fraction of dendrites and interdendrites in these alloys were calculated. The influences of the volume fraction of dendrite in the alloys on the overall hardness were also discussed. The CrFeCoNiNb alloy had the larger volume fraction of dendrite and thus had the highest hardness among these alloys. The CrFeCoNi(Nb,Mo) alloys also showed better corrosion resistances in 1 M H2SO4 and 1 M NaCl solutions by comparing with commercial 304 stainless steel. The CrFeCoNiNb0.5Mo0.5 alloy possessed the best corrosion resistances in these solutions among the CrFeCoNi(Nb,Mo) alloys.
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The effects of the concentration of NaCl solutions on the corrosion resistance of granular CoCrFeNiV0.5 and dendritic CrFeCoNiV high-entropy alloys were studied. The polarization behavior of CoCrFeNiV0.5 and CrFeCoNiV alloys in deaerated 0.5 M and 1 M sodium chloride solution at different temperatures was measured by a constant galvanostatic/potentiometric. Electrochemical impedance spectroscopy (EIS) was used to examine CoCrFeNiV0.5 CrFeCoNiV alloys in 0.5 M and 1 M NaCl solutions. The results indicated that the CoCrFeNiV0.5 alloy showed a better corrosion resistance than that of CrFeCoNiV alloy because the dendritic structure of CrFeCoNiV had too many σ/FCC interfaces. The critical pitting temperatures (CPTs) of the alloys under different applied potentials were also analyzed. All of the results proved that CrFeCoNiV0.5 alloy had better corrosion resistance in 0.5 M and 1 M NaCl solutions.
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CrFeCoNiVx high-entropy alloys were prepared by arc-melting, and the microstructures and corrosion properties of these alloys were studied. The CrFeCoNiV0.5 alloy had a granular structure; the matrix was a face-centered cubic (FCC) structure, and the second phase was a σ phase with a tetragonal structure. The CrFeCoNiV alloy had a dendritic structure; the dendrites in this alloy showed an FCC phase, and the interdendrities had a eutectic structure of FCC and σ phases. Therefore, CrFeCoNiV was much harder than the CrFeCoNiV0.5 alloy due to the dendritic structures. The potentiodynamic polarization test and electrochemical impedance spectroscopy were used to evaluate the corrosion behavior of the CrFeCoNiVx high-entropy alloys in deaerated 1M sulfuric acid and 1M hydrochloric acid solutions. The results indicated that the CrFeCoNiV0.5 alloy had a better corrosion resistance because of the granular structure.
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The present work systematically investigated the effects of niobium and molybdenum on the microstructures and corrosion properties of high-entropy CrFeCoNiNbxMox and CrFeCoNiNbxMo1-x alloys, the maximum content of (Nb + Mo) was 20 at.%. All of the alloys were prepared by arc melting under an argon atmosphere. In CrFeCoNiNbxMox alloys (x = 0.15, 0.3 and 0.5), increasing Nb and Mo content would change the microstructure of the alloy from a hypoeutectic structure (x ≤ 0.3) to a hypereutectic one (x = 0.5). All of the CrFeCoNiNbxMo1-x alloys (x = 0.25, 0.5 and 0.75) had a hypereutectic microstructure. Only two phases were analyzed in these alloys, which were face-centered cubic (FCC) and hexagonal close packing (HCP). Increasing the content of Nb and Mo increases the hardness of the alloys by the effects of the solid solution strengthening and formation of the HCP phase. The potentiodynamic polarization curves of these alloys were also measured in 1 M sulfuric acid and 1 M sodium chloride solutions to evaluate the corrosion resistance of these alloys. The CrFeCoNiNb0.3Mo0.3 alloy had the smallest corrosion rate (0.0732 mm/yr) in 1 M deaerated H2SO4 solution, and the CrFeCoNiNb0.15Mo0.15 alloy had the smallest corrosion rate (0.0425 mm/yr) in 1 M deaerated NaCl solution. However, the CrFeCoNiNb0.5Mo0.5 alloy still had the best combination of corrosion resistance and hardness in the present study.
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FeCoNiMo and CrFeCoNiMo equimolar alloys were prepared by arc-melting. The microstructures of the as-cast alloys were examined by SEM, HREM and XRD; and a potentiodynamic polarization test of the as-cast alloys was undertaken to evaluate the corrosion resistance in the solutions. Results showed that both of FeCoNiMo and CrFeCoNiMo equimolar alloys had a dendritic structure. The dendrites of these two alloys were a single phase which was a simple cubic (SC) structure with large lattice constant; and the interdendrities of these two alloys had a dual-phased eutectic structure in which the phases were face-centered cubic (FCC) and simple cubic (SC). The hardness of CrFeCoNiMo alloy was higher than that of FeCoNiMo alloy. Additionally, the potentiodynamic polarization test showed that CrFeCoNiMo alloy was better than FeCoNiMo alloy in 1 M nitric acid and 1 M sodium chloride solutions. Adding chromium into FeCoNiMo alloy could increase corrosion resistance in these two solutions. All of the results indicated that the CrFeCoNiMo alloy surpassed FeCoNiMo alloy.
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The composition of the Cr27Fe24Co18Ni26Nb5 high-entropy alloy was selected from the FCC phase in a CrFeCoNiNb alloy. The alloy was melted in an argon atmosphere arc-furnace, followed by annealing in an air furnace. The dendrites of the alloy were in the FCC phase, and the eutectic interdendrites of the alloy comprised HCP and FCC phases. The microstructures and hardness of this alloy were examined; the results indicated that this alloy was very stable. This microstructure and hardness of the alloy almost remained the same after annealing at 1000 °C for 24 h. The polarization behaviors of Cr27Fe24Co18Ni26Nb5 alloy in 1 N sulfuric acid and 1 N hydrochloric acid solutions were measured. Both the corrosion potential and the corrosion current density of the Cr27Fe24Co18Ni26Nb5 alloy increased with increasing test temperatures. The activation energies of the Cr27Fe24Co18Ni26Nb5 alloy in these two solutions were also calculated.
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This paper investigates the effects of Ta content on the microstructures, hardness and corrosion behavior of as-cast CoCrFeNiTax alloys. The results indicate that the addition of Ta can change the microstructures of these alloys to dual-phased structures (FCC + HCP), as well as increasing their hardness. This study uses constant galvanostatic/potentiometric methods to measure the polarization curves of CoCrFeNiTa0.1, CoCrFeNiTa0.3 and CoCrFeNiTa0.5 alloys in deaerated 1 M sodium chloride solution at different temperatures. Electrochemical impedance spectroscopy is also used to analyze these alloys in sodium chloride solution. The results indicate that the CoCrFeNiTa0.5 alloy has a eutectic structure and the highest hardness. Furthermore, although the CoCrFeNiTa0.5 alloy has the best corrosion resistance, the CoCrFeNiTa0.3 alloy has the best pitting resistance among these alloys.
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This work studied the effect of niobium-content on the microstructures, hardness, and corrosion properties of CrFeCoNiNbx alloys. Results indicated that the microstructures of these alloys changed from granular structures (CrFeCoNi alloy) to the hypereutectic structures (CrFeCoNiNb0.2 and CrFeCoNi0.4 alloys), and then to the hypoeutectic microstructures (CrFeCoNiNb0.6 and CrFeCoNi alloys). The lattice constants of the major two phases in these alloys, fcc and Laves phases (hcp), increased with the increasing of Nb-content because of solid-solution strengthening. The hardness of CrFeCoNiNbx alloys also had the same tendency. Adding niobium would slightly lessen the corrosion resistance of CrFeCoNiNbx alloys in 1 M deaerated sulfuric acid and 1 M deaerated sodium chloride solutions, but the CrFeCoNiNbx alloys still had better corrosion resistance in comparison with commercial 304 stainless steel. In these dual-phased CrFeCoNiNbx alloys, the fcc phase was more severely corroded than the Laves phase after polarization tests in these two solutions.
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This study investigates the effects of niobium and molybdenum on FeCoNi alloy, including on the microstructures and hardness of FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys, and the polarization behaviors of these alloys in 1 M sulfuric acid and 1 M sodium chloride solutions. The results in this study indicate that both FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys had a dual-phased dendritic microstructure; all of the phases in these alloys were solid solution phases, and no ordering was observed. Therefore, the solid solution effect significantly increased the hardness of these two alloys; in particular, FeCoNiNb alloy had the highest hardness of the alloys of interest. The corrosion resistance of FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys was less than that of FeCoNi alloy because of their dual-phased dendritic microstructures. The corrosion resistance of the FeCoNiNb0.5Mo0.5 alloy exceeded that of the FeCoNiNb alloy in these solutions. However, FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys exhibited a favorable combination of corrosion resistance and hardness.
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This study investigated the effects of Ti content and vacuum annealing on the microstructure evolution of TixFeCoNi (x = 0, 0.5, and 1) thin films and the underlying mechanisms. The as-deposited thin film transformed from an FCC (face center cubic) structure at x = 0 into an amorphous structure at x = 1, which can be explained by determining topological instability and a hard ball model. After annealing was performed at 1000 °C for 30 min, the films presented a layered structure comprising metal solid solutions and oxygen-deficient oxides, which can be major attributed to oxygen traces in the vacuum furnace. Different Ti contents provided various phase separation and layered structures. The underlying mechanism is mainly related to the competition among possible oxides in terms of free energy production at 1000 °C.