Al0.2CrFeNiCo and Al0.2CrFeNiCu high entropy alloys were deposited with high velocity oxygen fuel (HVOF) on 316L substrate. Later, a laser re-melting (LR) process was applied to enhancing the coating ...microstructure. LR process effects on dry sliding wear and oxidation behaviors were investigated. The mixture of powders with free elements led to the formation of inner oxides in HVOF coatings. The oxide and porosity were eliminated using LR. After LR, FCC was the dominant phase in both alloys, while BCC, sigma and Cr2O3 phases were observed in Al0.2CrFeNiCo alloy. The hardnesses of the Al0.2CrFeNiCo and Al0.2CrFeNiCu coatings after HVOF were HV 591 and HV 361, respectively. After LR, the hardnesses decreased to HV 259 and HV 270, respectively. Although HVOF coatings were most affected by increased load, they showed the highest wear resistance compared to other samples. The lowest wear resistance could be seen in the substrate. After the oxidation tests, HVOF coating layer was completely oxidized and also, the coating layer was delaminated from the substrate after 50 h oxidation due to its porous structure. LR coatings exhibited better oxidation performance. Al0.2CrFeNiCo was dominantly composed of Cr2O3, exhibiting a slower-growing tendency at the end of the oxidation tests, while Al0.2CrFeNiCu was composed of spinel phases.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Nichrome (NiCr) coatings are widely used to provide resistance against oxidation and corrosion in many machine components. TBCs must include bond coatings that are resistant to oxidation resulting ...fromhigh-temperature operating conditions. In the present study, NiCr powders were sprayed on nickel-based superalloy Inconel 718 substrates using atmospheric plasma spray (APS) technique. Bond-coated substrates were coated with yittria stabilized zirconia (YSZ). As such, the TBC samples were kept at 1000°C for 8 h, 24 h and 50 h in high temperature furnace and their isothermal oxidation behavior was investigated. Microstructure and phase change properties of TBCs before and after isothermal oxidation were then studied and analyzed.
•CoNiCrAlY and ZrO2+Y2O3 powders were deposited on Inconel 718 superalloy using APS method.•Bond coats were shot peened to obtain a denser coating structure and lower porosity.•Oxidation tests were ...carried out on the samples at 1000°C in a time-dependent manner.•An increase in the oxidation resistance of shot-peened coatings was observed.
A conventional thermal barrier coating (TBC) system is made up of a multilayered coating system that comprises a metallic bond coat including oxidation-resistant MCrAlY and a thermally insulating ceramic top coat including yttria stabilized zirconia (YSZ). In this study, in order to improve the oxidation behavior in conventionally produced TBC systems, shot peening process is applied for modification of surface layer structure of atmospheric plasma spray (APS) bond coats. The oxidation behavior of TBCs, produced by the APS process and subjected to shot peening, was investigated. Oxidation tests were performed under isothermal conditions at 1000°C for different time periods. The coatings produced by the APS process include high porosity and oxide content due to atmospheric production conditions as well as exposure to very high temperature. In this study, the coatings, produced by the APS process, subsequently subjected to shot-peening, were compared with the ones which were not shot peened. Following the application of the shot peening process, a dense structure is obtained due to the plastic deformation effect in the metallic bond coating structure at a certain distance from the surface. To this end, the effects of the shot-peening on the high temperature oxidation behavior of the coatings are investigated and evaluated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In this study, an aluminide coating was applied to the surface of the Inconel 600 (IN600) superalloy to improve the high-temperature oxidation and wear resistance. The low-temperature aluminizing ...process was carried out for 3 and 5 h at 650 and 700 °C temperatures without using a protective atmosphere. A continuous and homogeneous coating has been created by providing aluminium diffusion inward in the cross-section of the alloy processed under low temperature and high activity conditions with the pack cementation method. It was observed that there was a super bonding between matrix and coating layers which are smooth, dense and porosity free. Dominant phases of Ni2Al3 and NiAl3 were detected by XRD analysis. The layer thickness was measured from the surface to the matrix and changed from 25 to 75 μm which was increased with increasing process duration and temperature. The aluminizing process positively affected the wear resistance with the durable layers formed on the surfaces. After the isothermal oxidation tests, IN600 and aluminized IN600 show a break-away oxidation trend. The formation of the alumina layer provided better protection for aluminized samples but the formation of pits led to spallation of oxide scale in the oxidation stages.
•The Inconel 600 was subjected to aluminization at different temperatures and times.•Effect of aluminization on microstructure, wear and oxidation properties of Inconel 600 were investigated.•The matrix hardness is 250 HV while the hardness of coating layer raised to 850 HV.•Aluminized surfaces are more resistant to dry sliding wear than substrate.•The aluminized samples exhibited break-away oxidation due to cavity formations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Rare-earth zirconates have a big potential as top coat material of TBCs due to their superior high-temperature properties. TBCs are usually produced by thermal spray methods or electron beam physical ...vapor deposition (EB-PVD) techniques. Cold gas dynamic spray (CGDS) is a promising deposition method for production of dense and non-oxide bond coat compared to other thermal spray processes, while EB-PVD process provides good adhesion and strain tolerance for top coating layers of TBCs. In this study, in order to observe the effect of Gd
2
Zr
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O
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on the oxidation behavior of TBCs, CoNiCrAlY was sprayed on substrate material using the CGDS method, afterward, yttria-stabilized zirconia (YSZ) and YSZ/Gd
2
Zr
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were deposited using EB-PVD technique. After deposition, specimens were isothermally oxidized in a high-temperature furnace at 1100 °C for 8, 24, 50, and 100 h. Microstructures of oxidized samples were examined and thermally grown oxide layer of TBCs were comparatively evaluated.
Atmospheric plasma spray (APS) process is commonly used in the production of TBCs due to low cost, and rapid and easy production. Cold gas dynamic spray (CGDS) method is an emerging coating ...technology which provides the desired properties such as low porosity, low oxide content, and dense structure for production of ideal metallic bond coat layer compared to APS and the other thermal spray processes. Within the context of this study, shot-peening process was applied to bond coats produced by APS technique in order to improve its microstructural properties like CGDS bond coats. TBCs having APS, CGDS, and shot-peened APS bond coats were isothermally exposed to 1100 °C for 8, 24, 50, and 100 h. Before and after oxidation tests, TBCs were examined and compared in terms of their microstructures and thermally grown oxide layer which forms at the interface of bond and top coats.
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