Microstructure evaluations of A-286 super‌alloy under high strain rates

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: 1080-UFGNSM2021-FULL (R1)
School of Metallurgy and Materials Science, School of Engineering, University of Tehran, Tehran, Iran
A-286 is a nickel and iron-based, austenitic and age-hardenable superalloy that is useful for applications requiring high strength and corrosion and oxidation resistance up to 800°C, and for lower stress applications at higher temperatures. It is used in aircraft and industrial gas turbine components that are subject to high levels of heat and stress at service temperatures up to 800℃ such as turbine wheels and blades, frames, superchargers, and afterburner parts, also in fasteners of automotive engines. In this research, the mechanical properties and microstructure of iron-nickel base A-286 superalloy were investigated under different strain rates and temperatures. In this regard, the samples were subjected to forging operations in the temperature range of 1000 to 1100 ° C by drop hammer test equipment under a strain rate of 162 to 200 per second by 50% strain. The results obtained from the tests showed that grain nucleation was observed in the grain boundaries and new ultrafine grains were observed. It was observed that in forged samples the phenomenon of DDRX (Discontinuous Dynamic Recrystallization) occurred. Also, because the forging test was performed as an open die, dead zone, and shear band were created in samples, which in dead zones, nucleation is less and grain size has not changed much. However, in shear bands, the occurrence of DDRX in these areas is more noticeable. With increasing temperature from 1000 to 1100 ° C, the growth rate of new grains created by recrystallization increased, and microstructural changes from dead zone to shear band become more pronounced. Moreover, in general, the mechanical properties of forged samples such as hardness, yield strength, and the final strength of the samples before forging has increased by up to 50 percent.
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