Volume Fraction Of BCC Phase Research Articles

Microstructures and mechanical properties of the precipitation strengthened Al0.4Cr0.7FexNi2V0.2 high entropy alloys

In this study, a series of Al0.4Cr0.7FexNi2V0.2 (x: molar ratio, x = 0.5, 1, 2) high entropy alloys were cold-rolled and annealed. The microstructures and mechanical properties of the alloys were systematically investigated. The results revealed that all the solution-treated alloys with different Fe contents exhibited solo FCC phase. After annealing, the coherent L12 phases and hard BCC phases were formed in the Fe0.5 and Fe1 alloys, while the Fe2 alloy only contained the L12 phases. The precipitation of L12 and BCC phases increased the hardness of the alloys. The volume fraction of BCC phase was found to decrease as the Fe content increased, the excessive BCC phases led to the decrease of plasticity. The mechanical properties of alloys were mostly determined by the degree of recrystallization and the amount and type of precipitates. The precipitation of the second phase was regulated by tailoring the alloy composition, so that the AN Fe1 alloy can obtain excellent mechanical properties.

Corrosion behaviors related to the microstructural evolutions of as-cast Al0.3CoCrFeNi high entropy alloy with addition of Si and Ti elements

In this work, the electrochemical potentiodynamic polarization and impedance spectroscopy analysis were used to investigate the corrosion behaviors related to microstructural evolutions of Al0.3CoCrFeNiSix and Al0.3CoCrFeNiTix HEAs in the NaCl solution. The results presented that addition of Si promoted the formation of BCC phase, which was regarded as a micro-anode to prevent FCC phase as a micro-cathode from being corroded. While the volume fraction of BCC phase increased to enhance the corrosion resistance of Six alloys with increasing Si content. Furthermore, the reduction in the grain sizes of Six alloys with increasing Si content could also improve corrosion resistance of the alloys. Therefore, the corrosion resistance of Six alloys was increased with increasing Si content. Addition of Ti with a high corrosion resistance of Clˉ caused the reduction in the grain sizes of Tix alloys, which can improve the corrosion resistance of alloys. However, the high Ti content can destroy the corrosion resistance of the alloys due to the formation of a large amount of precipitated phases. Therefore, as Ti with atomic percentage be equal to that of Al can effectively eliminate the negative influence of precipitated phases and microstructure on the corrosion resistance of alloys, meaning the Ti0.3 alloy had the best corrosion resistance in Tix alloys. The analysis of X-ray photo-electron spectroscopy (XPS) identified that the contents of oxidized Cr3+ and Fe3+ in the passive film are the main contribution to improve the corrosion resistance of Six alloy. And the contents of oxidized Cr3+ and Ti4+ in the passive film are the main contribution to improve the corrosion resistance of Tix alloy.

Effect of high magnetic field assisted heat treatment on microstructure and properties of AlCoCrCuFeNi high-entropy alloy

High magnetic field assisted heat treatment process was used to regulate the microstructure and properties of AlCoCrCuFeNi high-entropy alloy. Results show that applying magnetic field can refine the FeCoCr-rich phase and suppress the large regional segregation of Cu-rich phase. The strength of the alloy increases greatly from 1482 MPa to 1795 MPa and the elongation also increases from 23% to 27%. The saturation magnetization is depressed after the magnetic field is applied. These variations are attributed to the decrease of Cu-rich phase segregation, grain refinement, and also the slightly decreased volume fraction of BCC phase upon applying high magnetic field.

Quantitative Phase Prediction in Dual‐Phase High‐Entropy Alloys: Computationally Aided Parametric Approach

Dual‐phase high‐entropy alloys (HEAs) have shown remarkable mechanical properties. However, type and fraction of the secondary phase play a significant role in determining their physical and mechanical properties. CALPHAD is generally used to predict the phases and their fraction in HEAs. Herein, a parameter‐based empirical model is used to predict the phase fraction in dual‐phase HEAs. Valence electron concentration and various measures of atomic size mismatch are utilized for that purpose. A new parameter, namely, critical mismatch factor (, is proposed in this work. Experimental verification is done on a series of AlxCoCrFeNi (x = 0.3, 0.5, 0.7) alloys synthesized by vacuum arc melting. Phase fraction is determined by X‐ray diffraction and electron backscatter diffraction analysis. The experimentally determined volume fraction of BCC phase in Al0.3, Al0.5, and Al0.7 is 0%, 6%, and 28–37%, respectively, which agrees closely with the predicted values proving the chosen approach useful.

Effect of Al additions on the microstructures and tensile properties of AlxCoCr3Fe5Ni high entropy alloys

AlxCoCr3Fe5Ni high entropy alloys with varying aluminum contents (x = 0, 0.1, 0.2 and 0.3) were synthesized by induction melting and casting method. The microstructures and tensile properties of the new HEAs were investigated. Different regions of CoCr3Fe5Ni matrix HEA have different microstructures. With the increase of Al content, the microstructure changes from dendrite to lamellar eutectic and dual-phase structure comprising FCC and BCC phases was found in all four samples with different ratios. The volume fraction of BCC phase increased. The ultimate tensile strength (UTS) of the alloy increased, with the highest UTS (1018.9 MPa) achieved at x = 0.3 in this work. On the other hand, increasing Al content further induced distortion of the crystalline lattice and enhanced the alloy strength.

A novel dual phase high entropy casting alloy with high damping capacity

The microstructure, phase structure, mechanical properties and damping capacity of Al x Fe2CrNiCu (x = 0.0, 0.5, 0.75, 1.0, 1.5) (x in molar ratio) HEAs were investigated. The results show that with the increase of x value, the volume fractions of BCC phase increase from 0 for x = 0.0 to 100% x = 1.5 for the as-cast Al x Fe2CrNiCu HEAs. Among them, a novel dual phase microstructure consisting of 51 vol.% FCC and 49 vol.% BCC with large interface area was obtained in Al0.5FeCrNiCu HEA. Especially the compressive yield strength of the alloy with BCC structure is more than 5 times larger than that of the alloy with FCC structure, indicating that a typical damping alloy with a soft second phase distributed on the hard matrix was successfully fabricated. Compared with other HEAs, the damping capacity (Q−1) of Al0.5 HEA is 0.1, which is the largest one obtained up to now. The foundational contribution of this paper is to show that the damping capacity of the HEAs can be adjusted by tuning the volume fraction of BCC and FCC phases.

The Effect of Remelting on Microstructure and Hydrogen Storage Properties of Ti–Mn–V Alloy

In this research, the effect of multiple remelting on microstructure and hydrogen storage properties of (TiZr)1(VFeCrMn)2.1 alloy was studied. The alloy was melted using a VIM furnace. This process was repeated three times. The microstructure was evaluated by SEM and XRD analysis, and the hydrogen storage properties were measured by Sieverts method. The results indicated that the microstructure contains predominant C14 Laves, BCC solid solution and titanium oxide phases. The homogenous microstructure and fine BCC phase distribution was obtained by remelting. The volume fraction of BCC phase was decreased from 26 to 18% during remelting. PCT curves revealed that increasing remelting times results in decreasing slope and hysteresis factors. The values of alloys slope factor for single, double and triple melting are 0.57, 0.26 and 0.21, respectively. Therefore, hydrogen storage properties of the alloy are improved as a result of homogenous microstructure and appropriate content of phases during the remelting process.

Fine-Grained FeCoNi(CuAl)x High Entropy Alloys: Phase Transformation, Microstructure Evolution and Mechanical Properties

A series of fine-grained FeCoNi(CuAl)x (x=0, 0.4, 0.6, 0.8, 1.0) medium-entropy alloy (MEA) and high-entropy alloys (HEAs) were fabricated by Mechanical Alloying (MA) and Spark Plasma Sintering (SPS). The effect of Al and Cu content (x) on phase composition, microstructure and mechanical properties of the alloys was investigated. Experimental results show that the crystal structure of FeCoNi(CuAl)x alloy transforms from single FCC phase for x=0 to FCC+BCC duplex phases for x=0.4~1.0, with the fraction of BCC phase gradually increasing with the increase of x. Adding a low content of Al and Cu elements to FeCoNi alloy can significantly hinder the grain growth during sintering process, the average grain size of FCC phase decreases from 0.95 to 0.30 µm at x=0.4. However, the grain sizes of FCC and BCC phases gradually grow up when x increases from 0.4 to 1.0. The variation in grain size indicates that the atomic diffusion rate of sintered alloy may be influenced by the sluggish diffusion effect in HEA as well as the content of Al and Cu with lower melting points. Mechanical properties of the HEAs are mainly affected by the volume fraction of BCC phase. The compressive yield strength and hardness of HEAs are improved at first and then slightly reduced, while the plasticity drops down continuously with the increase of x. The bulky HEA achieved excellent comprehensive mechanical properties with a compressive yield strength of 1467.7 MPa and plastic strain to failure of 24.9 % at x=0.6, due to the fine duplex microstructure.

Microstructures and Mechanical Properties of Multi-component AlxCrFe2Ni2Mo0.2 High-Entropy Alloys

A series of AlxCrFe2Ni2Mo0.2 alloy consisting of FCC + BCC phases have been designed, and their as-cast microstructures and mechanical properties were also investigated with x ranging from 0.6 to 0.9. It was found that with the addition of Al element, the solidified structures changed from dendrite to columnar crystal then back to dendrite again. Moreover, the increased amount of BCC phase resulted in finer and more uniform microstructures of FCC [FeCrNi(Mo)] and BCC (Al–Ni) phases. Tensile yield strength and hardness of alloys showed a similar increasing trend as the volume fraction of BCC phase increased. Both strain hardening rate and strain hardening exponent were calculated to assess the tensile properties of the alloys. It was shown that Al0.6CrFe2Ni2Mo0.2 exhibited the most excellent and comprehensive mechanical properties due to its high work hardening ability and stable strain hardening rate. The product of strength and elongation of Al0.6CrFe2Ni2Mo0.2 reached up to 38.6 GPa%, which was higher than most of the reported as-cast high-entropy alloys.

Effect of strong magnetic field on the microstructure and mechanical-magnetic properties of AlCoCrFeNi high-entropy alloy

While there have been multiple recent reports in the literature of exceptional mechanical properties in high-entropy alloys (HEAs) which tried to tackle the barrier of the “strength-ductility trade-off”, the research of how strong the magnetic field affects mechanical and magnetic properties of HEAs is still preliminary. This paper shows that applying strong magnetic field during heat treatment can tailor the microstructure and improve both mechanical and magnetic properties of AlCoCrFeNi HEAs compared with those without the magnetic field. After applying 6 T magnetic field, the magnetic difference between the product and parent phase would change the Gibbs free energy of phase transformation. The volume fraction of BCC phase would increase slightly and the volume fraction of FCC and σ phases would decrease subtly, leading to a slightly higher saturation magnetization, ultimate compressive strength and plastic strain. Therefore, an excellent combination of saturation magnetization (∼89 emu/g), electrical resistivity (∼188 μΩ/cm), yield strength (∼1231 MPa), ultimate compressive strength (∼2708 MPa) and compressive plastic strain (∼26%) was achieved when applying 6 T magnetic field at heat treatment temperature of 1200 °C. This work provides a potential approach for future development of soft magnetic materials, with more preferable mechanical, electrical and magnetic properties.

Phase evolution, microstructure, and mechanical behaviors of the CrFeNiAlxTiy medium-entropy alloys

A series of Co-free CrFeNiAlxTiy medium-entropy alloys (MEAs) were designed and prepared. The effect of Al and Ti addition on phase evolution, microstructure, nano- and marco-mechanical behaviors were systematically investigated and analyzed. The density of the CrFeNiAlxTiy MEAs was measured by the Archimedes method. With the content of Al and Ti increasing, the density of the CrFeNiAlxTiy system decreased. The density of the CrFeNiAl0.3Ti0.3 MEA is only 6.9294 g/cm3. The microstructural analysis indicated that the addition of Al element increased the volume fraction of BCC phase, while the Al and Ti addition increased the volume fraction of BCC and B2 phases. The mechanical tests suggested that the hardness, compressive yield strength, fracture strength, specific yield strength, and specific fracture strength all increased with the Al and Ti addition. The CrFeNiAl0.3Ti0.3 MEA possessed high Vickers hardness, compressive yield strength, fracture strength, specific yield strength, and specific fracture strength, whose values are 551 HV, 1712 MPa, 3700 MPa, 247.06 MP cm3/g, and 533.96 MP cm3/g, respectively. Furthermore, the compressive plasticity of the CrFeNiAl0.3Ti0.3 MEA is also very large (~39.8%). The CrFeNiAl0.4Ti0.2 MEA also displayed outstanding mechanical behaviors just as the CrFeNiAl0.3Ti0.3 MEA, whose Vickers hardness, yield strength, and compressive plasticity are 580 HV, 1600 MPa, and 45%, respectively. The good combination of strength and compressive plasticity of CrFeNiAl0.3Ti0.3 and CrFeNiAl0.4Ti0.2 MEAs could attribute to the peculiar microstructure. The phase formation criteria and strengthening mechanism were discussed. This study provides insights not only into the BCC/B2-containing MEAs but also into the future development of MEAs with high-performance, low-cost, and low-density for industrial applications.

Dynamic tensile deformation and microstructural evolution of AlxCrMnFeCoNi high-entropy alloys

The influence of microstructure and strain rate on tensile behavior of AlxCrMnFeCoNi (x = 0, 0.4 and 0.6 in molar ratio) high-entropy alloys was investigated. The alloys with lower Al content exhibited microstructures of simple fcc solid solution whereas the Al0.6CrMnFeCoNi alloy consisted of fcc + bcc mixed solutions after thermomechanical processing. Al0.6CrMnFeCoNi showed higher tensile strength at quasi-static condition due to the combinative contributions from solution strengthening, grain-boundary strengthening and precipitation hardening. Under dynamic loading conditions, both the yield strength and work hardening increased remarkably with increasing strain rate for the two Al-containing alloys. However, the Al0.4CrMnFeCoNi alloy showed a larger strain-rate sensitivity than Al0.6CrMnFeCoNi alloy owing to the existence of abundant bcc phase and interphase boundaries. Johnson-Cook constitutive model can be utilized to describe the effects of strain rate and strain on the dynamic flow stress. Compared to quasi-static condition, the higher density dislocations and interaction were the main characteristics of microstructures for dynamic deformation, leading to the increased flow stress. High volume fraction of bcc phase and strain rate led to a transition from ductile to quasi-cleavage fracture.

Enhancement of Mechanical Properties and Corrosion Resistance of Ultra-Fine Grain Al0.4FeCrCo1.5NiTi0.3 High-Entropy Alloy by MA and SPS Technologies

Al0.4FeCrCo1.5NiTi0.3 high-entropy alloy (HEA) was prepared by mechanical alloying (MA) and spark plasma sintering (SPS), which were evaluated in this study by XRD and TEM. After SPS, the bulk alloy exhibited a structure with a dominant fcc phase, a minor volume fraction of bcc phase, and the formation of TiAl3 intermetallic compound. Deformation twinning was observed in the fcc phase in the bulk HEA. The latter had a compressive strength, strain and Vickers hardness of 2225 ± 15 MPa, 17.52 ± 0.50 % and 515 ± 16 HV, respectively. The corrosion resistance studies indicated that Al0.4FeCrCo1.5NiTi0.3 with ultra-fine grained micro-structure was easier to passivate and possessed excellent corrosion resistance. DOI: http://dx.doi.org/10.5755/j01.ms.25.3.19452

Alloying, magnetic and corrosion behavior of AlCrFeMnNiTi high entropy alloy

The present report describes phase formation, magnetic and corrosion behavior of the AlCrFeMnNiTi high entropy alloy (HEA) synthesized through mechanical alloying. Simple solid solution of FCC and BCC phases are evolved after 25 h of MA. DSC analysis confirms that the synthesized phases of AlCrFeMnNiTi HEA are stable up to 550 °C and a re-crystallization is occurred at temperature greater than 550 °C. In order to investigate the effect of annealing on phase formation and magnetic characteristics, the synthesized HEA was annealed at 700 °C for 1 h and found that the volume fraction of BCC phase decreased. The synthesized HEA shows better ferromagnetic behavior with Ms = 17.55 emu/g and Hc = 153.8 Oe as compared to some of the recently reported HEAs and previously reported CrFeMnNiTi HEA by us. Moreover, corrosion behavior of the annealed AlCrFeMnNiTi high entropy alloy in 0.5 M and 1 M NaCl solution is also investigated. It is found that the annealed HEA shows good corrosion resistance in 0.5 M NaCl solution due to the presence of Al.

Microstructure and magnetic properties of the FeCoNi(CuAl)0.8Ga0.06 high-entropy alloy during the phase transition

The FeCoNi(CuAl)0.8Ga0.06 high-entropy alloy (HEA) was prepared by the vacuum arc melt casting method, then annealed at different temperatures for 1 h. The microstructure, phase constitution, and magnetic and mechanical properties of the FeCoNi(CuAl)0.8Ga0.06 HEA during the phase transition were investigated. The experimental results showed that the as-cast alloy consisted of FCC and BCC duplex phases, and there were numerous nano-precipitates uniformly distributed in the BCC matrix. After annealing at different temperatures, the phase transformed from FCC to BCC. The relative volume fraction of the BCC phase increased, and the size of the nano-precipitates in the BCC matrix were larger after annealing than that of the as-cast sample. STEM-EDS images showed that there was a Cu-rich zone in the phase boundary region between FCC and BCC phases, and annealing may have significant influence on this region. Based on XRD, SEM, TEM and STEM-EDS results, a phase transition mechanism was proposed, which may have a close relationship with the Cu-rich nano-precipitates in the BCC matrix and the Cu-rich zone in the phase boundary region. In addition, it was found that the volume fraction of BCC (or FCC) phase can govern the magnetic properties. This study may help to deepen the fundamental understanding of the phase transition mechanism in HEAs.

Effect of annealing conditions and temperatures on phase formation and magnetic behaviour of CrFeMnNiTi high entropy alloy

An equiatomic CrFeMnNiTi high entropy alloy (HEA) was synthesized through mechanical alloying (MA) technique. The synthesized HEA consists of FCC, BCC and a minor σ-phase. In order to investigate the phase evolution and magnetic characteristics, the synthesized HEA was annealed under different conditions (vacuum and open air) at two different temperatures (500 and 700 °C). After vacuum annealing at 500 and 700 °C the volume fraction of FCC and BCC phases are changed. However, after open air annealing, the volume fraction of synthesized phases (FCC and BCC) is altered effectively along with the formation of an oxide (Mn2O3) and a spinel type (Fe,Ti)3O4 phase. The synthesized sample exhibits ferromagnetic characteristic and the value of saturation magnetization (Ms) and coercivity (Hc) are found to be 13.39 emu/g (A-m2/kg) and 162.2Oe (12.9 × 103 A/m) respectively. After annealing in vacuum and open air at 700 °C the value of Ms. is found to be 2.95 and 11.63 emu/g (A-m2/kg) respectively. Open air annealed sample at 500 °C shows better magnetic characteristics with Ms = 32.85 emu/g (A-m2/kg) and Hc = 159.34Oe (12.67 × 103 A/m) as compared to the synthesized and annealed samples. The enhanced value of Ms for open air annealed HEA at 500 °C corresponds to increase in the volume fraction of BCC phase and the formation of Mn2O3 and (Fe,Ti)3O4 spinel phase. The effect of annealing conditions on the phase formation and their correlation with magnetic characteristic are discussed and described in detail.

Correlation between the magnetic properties and phase constitution of FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) high-entropy alloys

The as-cast FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) high-entropy alloys (HEAs) were produced by vacuum arc melting. The correlation between the magnetic properties and phase constitution of the HEAs was thoroughly investigated. The results reveal that all samples contain BCC plus FCC duplex phases and the addition of Ga can promote the formation of BCC phases. Energy dispersive spectroscopy (EDS) results revealed that Cu and Ga elements are enriched in the BCC phases and they are more seriously in the phase boundary regions. Furthermore, the magnetic properties are closely related to the phase constitution of the as-cast FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) HEAs. The values of saturated magnetization (Ms), maximum magnetic flux density (Bm), remanence (Br), coercivity (Hc) and hysteresis losses (Pu) increase with the increase of the volume fraction of BCC phases, while the values of initial permeability (μi) and maximum permeability (μmax) increase with the increase of the volume fraction of FCC phases. In addition, the mechanical property of FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) HEAs was also discussed in the work.

Cooling rate effect on microstructure and mechanical properties of AlxCoCrFeNi high entropy alloys

The AlxCoCrFeNi alloys were prepared by arc-melting (AMx) and suction-casting (SCx) method. Their microstructure and phase constituents were characterized by scanning electron microscope, X-ray diffractometer and electron backscattered diffraction, and the compressive properties were tested as well. It is found that higher cooling rate during suction-casting process could not only refine microstructure but also change the phase morphology and strengthening mechanism. Microstructure refinement should enhance the strength of SCx alloys, but the strength difference between SCx and AMx alloys increases first when the Al content increase from 0.15 to 0.75 and then decreases. For Al0.15CoCrFeNi alloy, the density of 60°〈111〉 deformation twins in the compressive samples prepared by arc-melting is higher than suction-casting. This will offset the strength contribution of microstructure refinement caused by higher cooling rate. For Al0.75CoCrFeNi alloy, the high strength for SC0.75 alloy can be attributed to not only microstructure refinement but also increase in volume fraction of BCC phase with high strength and lattice strain in FCC phase.

Microstructures and mechanical properties of Co2MoxNi2VWx eutectic high entropy alloys

In this paper, Co2MoxNi2VWx (x=0.5, 0.6, 0.8, 1.0, 1.5, and 1.75 in molar ratio) eutectic high entropy alloys (EHEAs) were designed to achieve a combination of strength and ductility. The effects of Mo and W elements on the microstructures and mechanical properties of the alloys were investigated, and results showed that by decreasing the Mo and W contents to 0.8 in Co2MoxNi2VWx alloy, a fully eutectic microstructure was obtained. By increasing the Mo and W contents to 1.75, a primary BCC solid solution phase plus eutectic microstructure were obtained. The eutectic microstructure consisted of a mixture of FCC solid solution phase and μ phase. The Co2Mo0·8Ni2VW0.8 alloy with the largest volume fraction of eutectic microstructure exhibited the highest compression strength of 2364MPa, while the Co2Mo1·75Ni2VW1.75 alloy with the largest volume fraction of BCC phase exhibited the highest yield strength of 1607MPa.

V–Ni–Ti multi-phase alloy membranes for hydrogen purification

Hydrogen-selective membranes formed from body centred cubic alloys can exhibit very high hydrogen permeability, but are prone to brittle failure due to excessive hydrogen absorption. Until issues associated with this are overcome, these materials will not provide a viable alternative to Pd-based membranes. Multi-phase V–Ni–Ti alloys which contain a significant proportion of a BCC component show promise for this application. In order to examine this system in greater detail, alloys of the general form V 85− x Ti x Ni 15, in which x was varied between 0 and 30 (at.%), were fabricated via arc melting and electrical-discharge wire cutting. Hydrogen permeation measurements of Pd-coated samples at 400 °C showed a monotonic increase in permeability with increasing Ti, reaching a maximum of 1.0 × 10 −7 mol H 2 m −1 s −1 Pa −0.5 for the V 55Ti 30Ni 15 alloy at 400 °C. The driving force for hydrogen transport is provided by hydrogen absorption, which varies non-linearly with Ti content, and is dependent on the volume fraction of BCC phase, and levels of Ti and Ni solution in the BCC phase. Diffusion coefficients of atomic H through the bulk alloys alloys are dependent largely on microstructure. Whereas the V 85Ni 15 alloy forms a single phase microstructure, progressive substitution of V with Ti introduced several minor phases; a NiTi-type phase (formed when x ≥ 5), and a NiTi 2-type phase (formed when x ≥ 10), both as V-containing solid solutions. These minor phases act as barriers to hydrogen diffusion, resulting in a significantly reduced diffusion coefficient compared to single-phase BCC alloys. Importantly, the mechanical stability of these alloys appears to be enhanced by the multi-phase microstructure. These alloys therefore show great promise for meeting future flux, cost and durability targets.