MICROSTRUCTURAL EVOLUTION AND MECHANICAL BEHAVIOR OF ADVANCED ALLOYS UNDER EXTREME CONDITIONS
Keywords:
Microstructural evolution, advanced alloys, high-entropy alloys, creep behavior, thermal stability, mechanical degradation, extreme conditionsAbstract
Background: High-performance alloys such as aerospace, nuclear, and power generation applications are using advanced alloys in their operations extensively since they have great thermal resistance and mechanical strength. Nevertheless, high temperature as well as mechanical loads, when exposure is prolonged, cause microstructural degradation hence long term reliability and safety of both Initial failure, as well as further reloading.
Aim: The objective of the present study is discovering the microstructural evolution and mechanical properties of three advanced alloys, of which are Ni-based alloy, CoCrFeMnNi high-entropy alloy, and a refractory high-entropy alloy, under severe temperatures and deformations.
Method: Thermal exposure of 50 hrs at 1000 Degree C combined with mechanical creep loading of 150 MPa was carried out on the alloys. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD) and X ray diffraction (XRD) was used in characterization. Tensile strength, hardness and creep resistance analyses were done mechanically. Thermo-Calc and DICTRA were used to determine phase transformations and grain growth by thermodynamic and kinetics simulations.
Results: The refractory high-entropy alloy had the least grain growth of 14%, lowest creep rate of 4.4 x 10 -6 s -1 and its tensile strength and ductility was retained by more than 95 percent. Conversely, Ni-based alloy portrayed severe microstructural damage, i.e., 45 percent grains development and decreased YS (dropping 485 MPa YS to 330 MPa). As fractographic examination proved, the refractory alloy fractured ductilely, but the Ni-based alloy fractured brittle inter-granularly.
Conclusion, refractory high-entropy alloys have comparable microstructural stability and excellent mechanical properties over severe conditions; therefore, they make good prospects of future high-temperature structural applications
