AlCrFeNiX (X = Cu, Si, Co) high entropy alloys (HEAs) were produced by mechanical alloying and sintering. The effects of the “X" additive on the microstructure, hardness, wear, and high-temperature ...oxidation behavior of HEAs were investigated. Different phases occurred in AlCrFeNiX HEAs depending on the “X" element. In addition to the BCC phase in all alloys, there are FCC phases in AlCrFeNiCu and AlCrFeNiCo alloys and two different intermetallic phases AlCrFeNiSi alloy. High negative mixing enthalpy values were found to be effective in phase and microstructure formation. In the alloy containing Si, 750 HV micro-hardness was seen as the highest hardness value. In the alloys containing Co and Cu, 450 and 420 HV micro-hardness values were determined, respectively. The best wear resistance and the lowest friction coefficient were seen in the AlCrFeNiSi alloy. In the wear tests performed at different loads, the increasing load increased the wear losses. The isothermal oxidation tests were conducted to HEAs at 1000 °C for 5, 25, and 75 h. Each HEAs exhibit very well oxidation resistance under the current conditions due to the selective alumina formation on the surface. It was not detected a dramatic difference in terms of oxidation behaviors of HEAs.
•High entropy alloys manufactured by mechanical alloying composed of FCC and BCC phases as well as intermetallic phases.•The highest hardness, highest wear resistance and lowest friction coefficient was obtained in AlCrFeNiSi.•The presence of Al in the alloys enables slow-growing and compact oxide scale.•Alloys in terms of oxidation kinetic and oxidation resistance are near to each other.
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The aim of this study is to enhance the magnetic and thermal properties of strontium hexaferrites by substituted with Al, Cr, and Mn ions instead of Fe, and to elucidate the changes in their ...structural, morphological, and thermal characteristics, in detail. SrFe12-xMxO19 (M: Al, Cr, Mn; x = 0.1, 0.3, and 0.5) powders were produced by the mechanochemical synthesis method from mill scale, which is a solid waste in steel production. While the Al3+ substitution did not cause any change in the phase structure, the Cr3+ and Mn3+ caused the formation of nanosized α-Fe2O3 and MnδFe2-δO4 phases in the structure, respectively. Increasing the Al substitution ratio led to a decrease in crystal size, from 176 nm to 32 nm. Similarly, the substitution of Cr resulted in a decrease in crystal size to 78 nm. However, Mn substitution had the opposite effect, increasing the crystal size of the powders. Al3+, Cr3+, and Mn3+ substitutions led to various effects on magnetic properties due to their placement in different lattice sites in the SrFe12O19 hexagonal crystal. The residual or remanent magnetization (Mr) and saturation magnetization (Ms) were lower than the initial values of Mr = 41.76 and Ms = 69.94 emu/g depending on the type and ratio of substitution ions. The highest coercivity was observed as 7116 Oe for SrFe11.5Al0.5O19. The Curie temperature increased to 515 °C with Cr3+ substitution but decreased to 431 °C and 426 °C with Al3+ and Mn3+, respectively.
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•Strontium hexaferrite powders are successfully produced using a mill scale wastes.•Mn3+ substation was caused to fomed MnδFe2-δO4 phase.•Powder shape and crystal properties of strontium hexaferrite powders was change depending on substutition rate.•The Curie temperature was cgange with substitution ion type and rate.
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In the current study, a CoCrFeNiAl0.5Nb0.5 high entropy alloy was manufactured via arc melting and exposed to laser surface remelting. The presence of Nb and Al was limited to the formation of single ...simple cubic phase formations. Both alloys are composed of four phases. Laser remelting did not change current phases, but it affected the microstructure. Hardness increased from 475 HV to 785 HV thanks to the change in phase ratios and grain refinement resulting from laser remelting. Wear resistance improved due to the increase in hardness, and volume losses decreased by 28 %. In short-term high-temperature oxidation, laser remelting enabled better oxidation resistance in alloy since it provided more paths for the diffusion of aluminum, which forms an alumina oxide scale. Interestingly, such a trend was not observed in the increased oxidation period. In the final oxidation stage, the depletion of B2 phases and the formation of inner oxides significantly worsened the oxidation resistance of LR alloy. Although Icorr, which expresses the corrosion resistance of the laser-melted alloy, was higher than before the laser-remelting process, the changes in the alloy's microstructure with rapid cooling caused a decrease in the passivation resistance of laser-remelted CoCrFeNiAl0.5Nb0.5 HEA.
•The produced HEA composed of BCC/B2, FCC and Laves phases.•Laser remelting (LR) homogenized microstructure and enhanced the hardness of HEA.•LR alloy improved the hardness, wear resistance and friction coefficient of HEA.•LR process negatively affected the corrosion of HEA due to decreasing of passivation resistance.•LR-HEA exhibited slightly better oxidation in short term but longer time exposure led to worse oxidation.
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The motivation for the present work is to explain the ferromagnetic properties of Cantor high entropy alloy by adding an alternative metal atom instead of Cr, which decomposes at high temperatures. ...With this motivation, MnTix and AlTix (x=0.0, 0.1, 0.3 and 0.5) were added to FeCoCuNi alloy to investigate the change in magnetic properties related to structural properties. The FeCoCuNiMn HEA showed similarities with the Cantor alloy, including an FCC phase. Replacing Mn with Al introduced B2 and BCC phases alongside FCC. Adding Ti to the FeCoCuNiMn alloy did not affect the phase structure but refined the microstructure. In contrast, Ti induced a transition from FCC to BCC in the FeCuCoNiAl alloy. For magnetic properties, FeCoCuNiMn had a saturation magnetization of 40.64 emu/g and a coercivity of 346 Oe, while FeCoCuNiAl exhibited 21.60 emu/g saturation magnetization and 38 Oe coercivity. The addition of Ti led to altered magnetic characteristics, converting FeCoCuNiAl from a soft magnetic alloy to a hard magnetic alloy. However, it negatively affected the saturation magnetization, with values of 17.11, 10.66, and 10.93 emu/g at Ti ratios of 0.1, 0.3, and 0.5, respectively.
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•FeCoCuNiMn and FeCoCuNiAl high entropy alloys exhibit ferromagnetic properties at room temperature.•FeCoCuNiAl with a coercivity of 38 Oe, is an important candidate for soft ferromagnetic materials.•Titanium has a negative effect on the saturation magnetization of both FeCoCuNiMn and FeCoCuNiAl.•Titanium imparted hard magnetic properties to FeCoCuNiAl alloy with soft magnetic properties.
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FeB-based alloys were successfully produced by the vacuum arc melting method. FeB-based alloys with various compositions were obtained by the gradual addition of different elements with Cu, Co, and ...Mo. The structural, magnetic, and electrochemical properties of the produced alloys were investigated. It was determined that there was a significant change in the structure with the addition of Mo. It was observed that the Fe3B phase was formed instead of Fe2B depending on the solidification rate. No changes were detected in the phase structure or microstructure, morphology of the other alloys. The hardness changed from 41.88 HRC to 64.24 HRC due to the phase change. All FeB-based alloys demonstrated soft magnetic properties. The lowest coercivity was 13 Oe for the Fe85B15 alloy, and the highest saturation magnetization was 173 emu/g for the Fe63Co21Cu1B15 alloy. While the lowest corrosion resistance was in the Fe85B15 alloy with 6.47 × 10-5 A.cm-2, the highest corrosion resistance was observed in the Fe38Co38Mo8Cu1B15 alloy with 8.21 × 10-6 A.cm-2.
•The produced Fe-B based alloys composed of dominant α-Fe and hard phases like Fe2B and CoMoB phases.•Mo element affected the hardness and corrosion properties.•Co, Mo and B elements positively affected the corrosion of HEA due to decreasing of passivation resistance.•Magnetic properties of the different Fe-B based alloys are investigated.
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High entropy alloys have promising wear, oxidation, and corrosion properties compared to conventional alloys and superalloys. In the present study, CrCuFeNiAl0.5 and CrCuFeNiAl0.5Si0.5 alloys were ...prepared using a traditional powder metallurgy process and then remelted the surfaces via laser. The laser remelting (LR) process gains a denser and more homogeneous surface to alloys. Pressureless consolidated and laser-remelted specimens were subjected to wear, corrosion, and oxidation tests. In the wear tests, it was observed that the wear resistance of Si-containing samples was better due to higher hardness. However, the laser remelting process has mostly increased rather than reduced wear losses. The less volume loss of laser-melted samples was attributed to the almost pure Cu in its content. There is little difference among all samples in electrochemical corrosion measurements. The formation of a fragile passivation layer was observed in potentiodynamic polarization curves of CrCuFeNiAl0.5Si0.5 and LR-CrCuFeNiAl0.5Si0.5 alloys. The alloy with the best corrosion resistance is CrCuFeNiAl0.5Si0.5, whose icorr value is 0.936 × 10−6 A/cm2. After high-temperature oxidation tests, the CrCuFeNiAl0.5 alloy exhibited the worst oxidation performance due to not forming a protective oxide layer on the surface, while LR enabled the protective oxide scale in a short oxidation time. The presence of Si in this alloy relatively enhances the oxidation resistance. The best oxidation performance was observed in LR-CrCuFeNiAl0.5Si0.5 due to the forming of a protective Al2O3 layer during the oxidation tests.
•Laser remelting significantly enhanced the microstructure and phase distribution.•Si addition increased hardness, wear, corrosion and oxidation resistance.•Cu-rich regions caused wear losses to be different than expected.•The addition of Si affects the electrochemical properties and passive film formation•The laser remelting process and Si addition provide alumina scale after oxidation.
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This study is dedicated to the detailed investigation of boronization kinetic, microstructural, mechanical, and wear properties of high entropy alloys (HEAs) considering their sluggish diffusion ...effect properties. A CoCrFeNiAl0.5Nb0.5 HEA was powder-pack boronized in the interval of 850–1050 °C for 2, 4, and 6 h in the boronizing medium containing 90 wt% of boron carbide and 10 wt% of sodium tetrafluoroborate. Boronizing of CoCrFeNiAl0.5Nb0.5 HEA was successfully produced. The obtained multi-phase boronized layers were characterized by compactness and flatness showing up inside its typical dendritic zones. The X-Ray Diffraction (XRD) studies showed the presence of ternary phases inside the boronized layers having a thickness of 4.38–92.16 µm. The nano and microhardness values were also determined and the adhesion force was analyzed through the Rockwell indentation tests. In addition, the Vickers fracture toughness values (0.46–1.83 MPa m−1/2) of the treated samples were found to be very dependent on the boronizing temperature. The wear losses have decreased due to the increase in hardness and an improvement of up to 99% has been achieved. The average diffusion coefficient model was implemented to deduce the boron activation energy in the CoCrFeNiAl0.5Nb0.5 HEAs. Finally, the predicted layers’ thicknesses were coincident with the experimental data.
•(CoFe)B2, Fe0.88C0.12B, NbNiB, CoNiB and Cr2Ni3B6 phases were formed.•Thicknesses and micro-hardnesses of the boride layers were in 4.38–92.16 µm and between 2520 and 2736 HV.•Fracture toughness was parallel with the adhesion tests and an improvement occurred due to increasing coating thickness.•Activation energy was found to be 211.07 kJmol−1 and the simulated layers’ thicknesses matched well the experimental data.•Boronizing and increasing boronizing temperature provided to have higher wear resistance.
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The formation of the Ti substituted Mg2Ni alloys, a promising hydrogen storage material for various applications is studied in detail. Mg1.95Ti0.05Ni alloy and ribbons are successfully prepared by ...vacuum arc melting and melt spinning methods. The phases, microstructures, and thermal behavior of the alloys and ribbons are characterized by XRD, SEM, TEM, DTA/TG. Sievert-type apparatus is used to study hydrogen sorption properties. Apart from the dominant Mg2Ni phase, the formation of MgNi2, Mg, and Ni3Ti phases is seen in both Mg1·95Ti0·05Ni alloy and ribbons. During the initial three cycles, Mg1·95Ti0·05Ni ribbons showed 2 wt % hydrogen storage capacity. To explain the atomic-scale influence of Ti dopant in the studied alloys and hydrides, FP(L)APW + lo method based on Density Functional Theory (DFT) is applied to Mg2-xTixNi (x = 0.25 and 0.5) alloys and Mg2-xTixNiH4 (x = 0.25 and 0.5) hydrides. An increase in the Ti dopant on the Mg site leads to the hydrides destabilization. Bader's charge density topology analysis provides insight into the charge transfer and bonding between the constituent atoms.
•Partial substitution of a low amount of Ti was carried out in Mg2Ni intermetallic alloy.•The melting temperatures of the intermetallic Mg2Ni phases in Mg1·95Ti0·05Ni alloy and ribbons are about 725 °C.•Hydrogen storage capacity of Mg1·95Ti0·05Ni ribbons reaches 2 wt% at 350 °C.•Ti reduces the stability of the hydride by weakening the binding energy.
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This study investigated the microstructure and mechanical properties of the recycled Ti6Al4V alloy produced using the waste chips vacuum arc melting (VAM) process. The waste chips were cleaned to ...remove machining residues before VAM and dried in the oven. The dried and compressed chip compacts are vacuum arc melted and hot rolled. Microstructural characterization was performed by using an optical microscope, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analysis. Mechanical properties were determined by tensile and hardness tests. The microstructures of recycled Ti6Al4V alloy, which produced the VAM process, consist of acicular structures due to rapid solidification. After hot rolling from 950 °C, the elongated α grains and transformed β grains consisting of fine acicular α phase were observed. The recycled Ti6Al4V alloy by hot rolling after VAM exhibited very low total elongation compared to the as-received Ti6Al4V alloy. While a micro dimples ductile fracture was observed on the fracture surfaces of the as-received Ti6Al4V alloy after the tensile test, a brittle fracture surface was observed in the recycled Ti6Al4V alloy samples after VAM + hot rolling due to the coarse α and β grain structure after cooling in the air after hot rolling.
In this study, the effect of Ti addition on microstructure and corrosion properties of high entropy CoCuFeNiMnTix (x = 0.0–0.5) produced by the vacuum arc melting method was investigated. According ...to X-ray diffraction analysis, it has been found that Ti-free CoCuFeNiMn and CoCuFeNiMnTix HEAs had FCC crystal structures. It was understood from the SEM images that the CoCuFeNiMn and CoCuFeNiMnTix alloys were dendritically solidified. While the CoCuFeNiMn alloy had a homogeneous chemical composition in dendritic and interdendritic regions, Ti-rich regions were formed in the interdendritic regions with the Ti addition to the CoCuFeNiMn. The ratio of the Ti-rich region formed in the interdendritic region increased with the increase of Ti in the CoCuFeNiMnTix alloy. The corrosion resistance of the CoCuFeNiMnTix alloy decreased with the increase of Ti addition. The Ecorr and icorr values for CoCuFeNiMn alloy were found to be as −0.322 V (vs. Ag/AgCl) and 6.30 × 10−7 A.cm−2, and these values were measured as −0.982 V and 1.16 × 10−3 A.cm−2 for CoCuFeNiMnTi0.5 alloy, respectively. From the Nyquist and phase angle plots, it was understood that the 0.3% Ti ratio was the critical value for the formation of the passive TiO2 layer on the alloy surface. Ti addition's most important effect on the CoCuFeNiMn alloy's corrosion properties was determined as the transformation of pitting corrosion type to galvanic corrosion.
•The Ti-dopped CoCuFeMnNiTix high entropy alloys were successfully produced by vacuum arc melting in the FCC structure.•Additional Ti in CoCuFeMnNiTix caused micro-level segregation in the interdendritic regions in the microstructure.•Pitting corrosion in the titanium-free alloy turned into galvanic corrosion in the titanium-free HEAs.•The corrosion resistance of the Ti-free high entropy alloy was equal to Cantor alloy.•The additional Ti decreased the corrosion resistance of the CoCuFeMnNiTix.
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