NAME:- HARDIK HAPANISTUDENT ID: – 102866123UNIT: – SURFACE ENGINEERINGTOPIC: – MICROSTRUCTURAL AND MECHANICAL PROPERTIESANALYSIS OF TWO DIFFERENT HIGH ENTROPY ALLOYS (HEAS)COATED USING THERMAL SPRAY PROCESSThermal Spray ProcessThermal spray is process of coating of subjectwith the help of powder and material.Thermal spray creates mechanically bondedcoatings ranging from zinc to ceramics to hardmetals. It is used everywhere from frying pansto jet engines. There are four process that areassociated to thermal spray: –1) Plasma2) V-Gun3) Twin Wire4) HVOFFigure: – Thermal Spray Process1) https://www.griekspoorthermalcoatings.com/techniquesThermal Spray ProcessCoating methods in which molten or heated materialsare sprayed onto a surface are known as thermalspraying techniques. Electrical or chemical sources areused to heat the coating precursor (feedstock). Plasma orarc are examples of electrical phenomena, whilecombustion flames are examples of chemicalphenomena. Thermal spraying can create coatings withthicknesses varying from 20 micrometres to severalmicrometres. In comparison to other coating methods, itis dependent on the process and feedstock over a widearea at a high deposition rate. Metals, ceramics, plastics,and composites are among the coating materials used inthermal spraying. They are fed as powder or wire, heatedto a molten or semimolten state, and accelerated asmicrometer-sized particles towards substrates.Figure: – Thermal Spray Coating Processstepwise.1) https://www.thermalspray.org/what-it-is/Thermal Spray ProcessCoatings are formed as a result of the aggregation ofvarious sprayed particles. The surface may not heatup dramatically, allowing flammable substances to becoated. The porosity, oxide content, macro and microhardness, bond strength, and surface roughness of acoating are typically measured to determine itsconsistency. In general, as particle velocities increase,the coating consistency improves. This is the briefexplanation of thermal spray coating process.Figure: – Metallography of thermal spray coating.1) https://www.struers.com/en/Knowledge/Materials/Thermal-spray-coatingsHigh Entropy AlloysTo form an alloy base, high entropy alloys useconcentrated blends of five or more primary elements.High entropy alloys are a brand-new class of materials.The term “high-entropy alloys” was coined because theentropy increase of mixing is substantially higher whenthere are a larger number of elements in the mix and theirproportions are more or less equal.Figure: – Conventional and High EntropyAlloys Structures.Alloy 1 : – AlCoCrFeNiStudy Microstructure and Mechanical Properties ofAlCoCrFeNi1) Vicker’s Hardness2) Phase Volume Fraction3) Nanohardness4) Modulus5) Load displacement curves are used to get elasticand plastic behaviour of materials.6) Ductility7) TemperatureFrom observations, it shows that high temperaturepromotes the phase transition from BCC to FCC.Figure: – Angle v/s Intensity of structures1) Liangquan Wang, Fanyong Zhang, Shu Yan, Guangxing Yu, Jiawen Chen, Jining He, Fuxing Yin, Microstructureevolution and mechanical properties of atmosphere plasma sprayed AlCoCrFeNi high-entropy alloy coatings underpost annealing (2021) 1-12.Experimental Details: – As a feedstock, commercial AlCoCrFeNi powders prepared by gas atomization are used.As a bond sheet, Ni-10 wt% Al self-fluxing alloy powders are pre-deposited onto the substrate.The AlCoCrFeNi coating was sprayed with H2 and Ar as the carrier gas at temperatures ranging from 600 to 1000°C in an Ar atmosphere. In a tube furnace, samples were heated to the necessary temperature at a rate of 10°C/min for 4 hours, then naturally cooled to room temperature in the furnace.Results: –Microstructural Properties: –Herringbone matrix with divided A2 (Fe-Cr-rich, white rods)and B2 phase (Al-Ni, grey region), some A1 phase (Fe-Ni-Co-Cr,light region) and black oxide strips make up as-annealedcoatings (Al rich). Figure depicts these processes as well as theevolution of morphology during annealing treatments. Duringannealing, the size and shape of oxide strip defects appear toremain unchanged. Figure: – Overall microstructure evolution of plasmasprayed AlCoCrFeNi coatings under annealingMechanical Properties: –The Vicker’s hardness and phase volume fraction of HEA coatingsannealed at various temperatures are shown in the figures.Lowertemperature annealing (600–700 °C) increases the micro-hardness ofthe HEA coating, while high-temperature annealing (>800 °C) resultsin a marginal reduction in hardness.The nano-indentation test was used to evaluate the nanohardnessand modulus during annealing to better understand the mechanicalproperties of HEA coating.The plasticity factor p (p = Wp/Wt) is often used to keep the structurenearly stable as the temperature rises.As a result, it can achieve a strong strength-to-ductility performancebalance.Alloy 2: – Cr7Mn25Co9Ni23Cu36Study microstructural and mechanicalproperties of Cr7Mn25Co9Ni23Cu36Arc-melting was used to design and prepareCr7Mn25Co9Ni23Cu36 HEA. At roomtemperature in as-cast condition, this HEA withprimary FCC phase has a strong combination ofstrength and ductility (yield strength of 401MPa, ultimate tensile strength of 700 MPa, andelongation to fracture of 36%).1) Gang Qin, Ruirun Chen, Huahai Mao, Yan Yan, Xiaojie Li, Stephan Schönecker, Levente Vitos, Xiaoqing L,Experimental and theoretical investigations on the phase stability and mechanical properties ofCr7Mn25Co9Ni23Cu36 high-entropy alloy (2021) 1-8.Experimental Procedure: –The Cr7Mn25Co9Ni23Cu36 (at. percent, nominal composition) HEA samples were made by arc melting in a highpurity argon atmosphere on a water-cooled copper hearth. The samples were then quenched in water after beingheat treated for 2 hours at different temperatures (200, 400, 600, 800, and 1000 °C). The microstructure wasinvestigated using scanning electron microscopy (SEM) with an energy dispersive spectrometer (EDS) andtransmission electron microscopy with an EDS (Talos F200X).Results: –Microstructural Properties: –In the casting state and after heat treatment at 200, 400, and 600 °C,two FCC solid solution phases were observed.The composition of these two FCC phases has already beendetermined. The sigma phase vanished and Cu segregation zonesformed when the samples were heated to 1000 °C.The miscibility difference between the two FCC phases for thenominal alloy composition is due to the formation of Cu-rich FCC 2 at high temperatures (Cr7Mn25Co9Ni23Cu36).Figure: – Composition of FCC_1 and FCC_2 phases (at.%)in Cr7Mn25Co9Ni23Cu36 HEA in the casting state. Mechanical Properties: –Figures depict the HEA’s tensile mechanical properties.Theyield strength and ultimate tensile strength increasedfrom 401 to 581 MPa and 700 to 829 MPa, respectively,when the heat-treatment temperature was increasedfrom 200 to 600 °C.The elongation went down from 35% to 22%. Therefinement of nanoprecipitates caused by increasing theheat-treatment temperature to 600 °C was due to theseadjustments.Due to a decline in yield and ultimate tensile strengths to303 MPa and 530 MPa, respectively, and a decrease inductility to 15% strain to fracture, the 800 °C heattreatment resulted in a loss of fracture toughness.In conclusion, the sigma process has a negative impact onthe tensile mechanical properties ofCr7Mn25Co9Ni23Cu36 HEA.
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