CoCrFeNiAl
x
Ti
y
high-entropy alloys were produced by the induction melting method and their oxidation behavior investigated when exposed to 1000°C for different durations. One or more body-centered ...cubic phases were found in all alloys, except CoCrFeNiTi
0.5
. In the CoCrFeNiTi
0.5
alloy, two different face-centered cubic phases and one tetragonal sigma phase were detected. Scanning electron microscopy elemental analysis showed that all the alloys exhibited homogeneous microstructure. Energy-dispersive x-ray spectroscopy analysis revealed that Cr and Fe elements were enriched in one phase and Al-Ni-Ti elements in another. The presence of Ti negatively affected the oxidation behavior. According to the oxidation test results, dominant Al
2
O
3
formation was observed in the CoCrFeNiAl
0.5
and CoCrFeNiAlTi
0.5
alloys. As a result, these two alloys exhibited the best performance among the five high-entropy alloys in terms of mass gain and oxide thickness.
In this study, microstructural and mechanical performance of AISI 1020 were investigated after severe vibratory peening (SVP) for emerging the potential and performance of this novel treatment among ...surface severe plastic deformation (SSPD) methods. The specimens were subjected to SVP treatment of V1, V2, and V3 conditions at 20, 40 and 60 min. durations, respectively. Optical microscope (OM) and SEM images demonstrated two layered gradient structure. XRD analysis showed the oxide layer was completely vanished besides surface nanocrystallization by severe plastic deformation (SPD). The microhardness test revealed an average improvement of 48% compared to the untreated specimen. SVP caused raising of hardness from surface to a depth of approximately 900 μm. In wear tests, the volume loss after SVP were less. The hardness improvement due to deformation overcame the negative effect caused by roughness increase. However, the friction coefficient of the unpeened specimen was the lowest at all loads.
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•SVP contributed eliminating oxide layer, besides formation of SPD and nanocrystallization.•SVP raised the wear performance effectively, conversely, the performance of SSP and SMAT.•SVP operation created two layered gradient structure beneath the surface.•The hardness depth influenced by the SVP reached 900 μm away from surface.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Boride layer characterization and dry sliding wear behaviors of borided H13 steel at different durations and temperatures with nanoboron powder have been investigated. A single phase boride layer was ...formed at 800 °C and a double phase boride layer was obtained at 900 °C and 1000 °C. According to the boriding process with Ekabor II, higher ratio FeB/FeB + Fe2B and total boride layer were formed when nanoboron was used in the boriding process. It has been observed that the increment in the boriding temperature and boriding duration has increased the boride layer thickness from 6,34 μm to 103.26 μm. Manganese boride and chromium boride phases were determined along with iron borides in the boride layer. The hardnesses of borides formed on the H13 steel reached 2028 HV0.1 and the change in hardness from the surface to the interior was slower at samples which were borided at higher temperatures and durations. Fracture toughness was found to be in the range of 1.32–5.23 MPa-m1/2 depending on boronizing time in samples which were borided at 1000 °C. The increase in the boriding temperature and boriding duration led to increased wear resistance. At high temperature, microcrack-induced plastic deformation and fatigue; at room temperature, microcrack formation were dominant wear mechanisms.
•High temperature dry sliding wear behavior of borided H13 steel was evaluated.•The increase in the boride layer led to increased wear resistance.•The sample borided at 1000 °C for 6 h showed the best wear properties.•The hardnesses of borides formed on the H13 steel were reached to 2028 HV0.1.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Iron-based superalloys are alloys produced for use in corrosive environments as an alternative to high-cost nickel-based superalloys. However, their average strength and hardness, attributed to their ...austenitic structures, limit their use in tribological applications. In an attempt to counter these drawbacks, boriding was applied to an iron-based A286 superalloy having an initial surface hardness of 320 HV. Boriding kinetics, some mechanical properties, and tribo-wear (ambient air and 3.5 NaCl environment) behaviors of the formed boride layers were investigated. Multicomponent boride layers (consist of FeB, Fe2B, CrB, NiB, Ni4B3) were formed on the surface of the alloy, with hardness and thickness values of 1498–1961 HV and 20–130 μm, respectively, depending on the boriding temperature and the treatment time. The integral diffusion model was adopted to deal with the kinetics of monoboride and hemiboride layers formed on the surface. The boron activation energies of FeB, Fe2B, and DZ layer were estimated as equal to 175.86, 198.7, and 205.73 kJ mol−1, respectively. As a result of increased surface hardness, all of the borided samples displayed reduced friction coefficients and higher wear resistance compared to the untreated alloy, in both ambient air and 3.5% NaCl. However, the increase in wear resistance was not proportional to the increase in hardness; while the best wear resistance was obtained in samples borided at 850–950 °C for 6 h, the lowest wear resistance was obtained in samples borided for 4–6 h at 1050 °C. This situation was caused by the Kirkendall effect and residual stresses in the structure of alloying elements with different diffusion rates due to the high-temperature effect of the boriding process.
•Fe-based superalloy with average strengths and low hardness was successfully pack-borided.•Formed borides were examined using XRD, SEM-EDS, nanoindentation, microhardness, surface roughness and tribo-wear tests.•The hardness and elasticity modules of Fe-based superalloy were developed by boriding.•The friction and wear performance of A286 was improved with the boriding both in ambient air and 3.5% NaCl solutions.•Boriding open new possibilities for the use of Fe-based superalloys in tribo-corrosive environments.
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IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this study, CoCrFeNiTi
0.5
Al
x
high-entropy alloys were produced by induction melting and their dry sliding wear behavior was examined at different temperatures. In addition to face-centered ...cubic (FCC) phases, low amounts of a tetragonal phase were detected in the microstructures of alloys without Al and microscratches were formed by wear particles on the worn surfaces of the alloy specimens. Two body-centered cubic (BCC) phases were detected in the alloy with 0.5Al and a fatigue-related extrusion wear mechanism was detected on the worn surface. The alloy specimen with a high Al content exhibited the best wear characteristics. No wear tracks were formed in single-phase BCC intermetallic alloys at room temperature and they exhibited a higher wear strength at high temperatures when compared to other samples.
In this study, it was aimed to determine the effect of laser re-melting on the oxidation behavior of high entropy alloys produced with electric current assisted sintering (ECAS). CoCrFeNi, ...CoCrFeNiAl0.5 and CoCrFeNiAl0.5Ti0.5 high entropy alloys (HEAs) were produced using ECAS. After the production of HEAs, the laser re-melting (LR) process was applied to the surface of sintered samples. Then, isothermal oxidation tests were carried out to HEAs at 1000 °C for 5, 25 and 75 h. Before and after the oxidation tests, the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) mapping analysis. The obtained results show that the LR process significantly improved the microstructural properties of ECAS-HEAs. More homogeneous microstructure, lower porosity and single-phase formations were observed in HEAs after LR. This has enabled a more stable microstructure compared to ECAS samples. After the oxidation tests, lower oxide layer thickness, lower oxide growth rates and lower inner oxide formation were obtained in laser re-melted HEAs. The presence of Al-rich phases enables the formation of alumina layer on the surface of HEAs. The best oxidation performance was obtained with laser re-melted CoCrFeNiAl0.5.
•CoCrFeNiAlxTiy HEAs were produced as simple and fast by the combination of sintering and laser re-melting techniques.•Laser re-melting enabling more homogeneous and dense surface have enhanced the oxidation performance of HEAs.•Mixing enthalpy values were found to be effective in phase formations after both sintering and laser re-melting.•CoCrFeNiAl0.5-LR exhibited better oxidation resistance due to having continuous Al2O3 layer.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study is focused on a detailed investigation of high-temperature corrosion and oxidation behavior of borided CoCrFeNiAl0.5Nb0.5 HEAs, considering their use in advanced engineering applications. ...CoCrFeNiAl0.5Nb0.5 HEA was produced by arc melting. XRD and SEM-EDS analysis before boriding determined that the alloy consisted of four different phases with different chemical compositions. Powder-pack boriding of a CoCrFeNiAl0.5Nb0.5 HEA was performed at 1000 °C for 3 h in a boriding media containing 90 % boron carbide and 10 % sodium tetrafluoroborate. As a result of the boriding process, complex boride layers consisting of (CoFe)B2, CrFeB, CoNbB, FeB and NiB phases were obtained on the surface with a thickness of 40 μm and hardness of 3004 HV. it was determined that the microstructure with cauliflower appearance evolved towards a dense and non-porous appearance around 20 μm as the boron diffusing into the HEA microstructure filling the gaps of intermetallic compound in the single structure, HEA and borided HEAs were each subjected to a cyclic hot corrosion test at 900 °C in molten corrosion salts of Na2SO4 and V2O5. After hot corrosion tests, long rod-like structures were observed in both samples due to the excessive corrosion, while borided alloys were more resistant to hot corrosion damage. After oxidation tests, HEA consists of a compact protective alumina scale that provided better oxidation resistance, while non-protective mixed oxides with cracks were dominant in the borided HEA.
•Borided HEA's surface degradation properties were investigated at high temperature.•Boriding process enhanced the hot corrosion resistance of alloy.•The presence of B2 phases provided alumina scale as oxidation product in the alloy.•The boriding process weakened the oxidation resistance as it caused the aluminum to migrate deeper.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
CoCrFeNiAlxTiy high entropy alloys were produced by electric current assistive sintering (ECAS) method and their surfaces were then subjected to laser re-melting. Microstructure, hardness, and wear ...behaviors were investigated using different parameters. While the CoCrFeNi alloy had FCC and oxide phases after ECAS treatment, only FCC phase was observed after laser re-melting. In addition to the FCC phase, also a BCC phase has been determined with the Al addition. FCC phases disappeared with the laser re-melting effect and the addition of Ti to the alloy. Mixing enthalpy values were found to be effective in microstructure and phase formation. Thanks to the rapid solidification provided by laser re-melting, the phases were distributed homogeneously and in much smaller particle size. Al and Ti elements have contributed positively to the hardness of the CoCrFeNi alloy. With additions of Al and Ti elements, a significant increase in the hardness of CoCrFeNi alloy was obtained. Significant increases in hardness values were observed after laser re-melting due to the smaller dispersion of the phases and the formation of hard phases (BCC/intermetallic). In the hardness values of all alloys, 1.5 times increase was observed by the effect of re-melting. The highest average hardness was determined as 859 Hv in laser re-melted CoCrFeNiAl0.5Ti0.5 alloy. The best wear resistance and the lowest friction coefficient was observed in the laser re-melted CoCrFeNiAl0.5Ti0.5 alloy. Laser re-melted alloys exhibited lower volume losses compared to only ECAS-alloys.
•Electric current assistive sintered CoCrFeNiAlxTiy high entropy alloys were subjected to laser re-melting.•Laser re-melting process has changed the phases occurring in alloys.•After laser re-melting, the hardness of the alloys increased by an average of 1.5 times.•Al and Ti provided an increase in hardness while replacing the phases occurring in alloys.•The LR has increased the wear resistance and the highest wear resistance has been seen in the CoCrFeNiAl0.5Ti0.5-LR alloy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Waste utilization is an important alternative to reduce disposal costs, potential environmental pollution problems, decrement of natural resources and production costs. In this study, it is aimed to ...create a different usage area for the slag wastes that cause problems to the environment and factories. For this purpose, the usability of slags (blast furnace, ferrochromium and converter) as a reinforcement material in epoxy composites were investigated for tribological applications. Epoxy matrix composites were produced by adding 30% of reinforcements with 61 μm size. The epoxy composites were tested against a stationary Al2O3 ball in a ball-on-disk tester under the loads of 10, 15 and 20 N, at a sliding distance of 300 m and a rotational speed of 300 rpm. Wear mechanisms were also investigated by Scanning Electron Microscopy. Mostly, the slag fillers showed higher wear resistance than the Al2O3 reinforced composites. Among the slag fillers, the blast furnace exhibited superior tribological performance. While Al2O3 and blast furnace slag reinforced composites showed plastic deformation due to fatigue, transverse cracks and displaced reinforcement particles were observed in ferrochromium slag and converter slag reinforced composites. Increasing the applied load caused acceleration in wear rate. Thermal conductivity was increased by particle addition, which contributed to the improvement of the wear performance. This study provided that industrial wastes can be used as reinforcement material in composites and thus a cleaner environment can be obtained.
•The usability of slag as a reinforcement in epoxy composites is investigated.•Use of blast furnace, ferrochromium and converter slags are compared with Al2O3.•Slag reinforcement offers better wear resistance compared to Al2O3.•The type of reinforcement significantly affects the wear behavior.•Use of industrial waste in the composite reduces its environmental impact.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Monel 400 was pack-borided in the temperature range of 1173–1273 K for exposure times of 2–6 h. The boride layers produced on the surface of the alloy were examined by scanning electron microscopy ...and phase identification was carried out by X-ray diffraction. The topmost layer on the borided Monel 400 was compact and contained the Ni
2
B phase while the diffusion zone contained grain boundary precipitates of borides. Boride layers of 35–290 µm thickness and 1002–1476 HV
0.025
hardness were obtained. SEM observations revealed a smooth interface between the boride layer and the diffusion zone. A kinetic model based on the integral method was applied to investigate the kinetics of Ni
2
B layer. The boron activation energy in the Ni
2
B layer was estimated as equal to 300.7 kJ mol
−1
. An experimental validation of the model was made by comparing the experimental layer thicknesses obtained, after boriding at 1198 K for 1 and 3 h, with predicted values.
Graphical Abstract
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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