Effects of pre-deformation and annealing on the mechanical properties and microstructure of miniaturized FeCrAl-Y-Si alloys

Abstract

The evolution of mechanical properties and microstructure in FeCrAl alloys with added Y and Si was investigated using miniaturized specimens. The FeCrAl alloys underwent warm rolling, resulting in thicknesses of 1 mm and 2 mm, followed by annealing at temperatures ranging from 600 °C to 1050 °C. Mechanical properties were determined through three distinct methods: conventional uniaxial tensile testing (UTT), micron indentation hardness testing (MIHT), and small punch testing (SPT). Microstructure evolutions were characterized using various techniques, primarily focusing on electron backscatter diffraction (EBSD). Two types of precipitates containing Y, Si, and Al were observed during annealing. Fracture morphologies revealed that as the annealing temperature (AT) exceeded 900 °C, size effect and brittle failures became prominent in SPT specimens. Brittle failures in SPT can be attributed to the segregation of Y, Si, and Al along the grain boundaries, the size effect, and the dispersed distribution of grain sizes. The optimum inter-pass annealing temperature was identified as 700 °C based on grain orientation spread (GOS) maps. SPT and MIHT results were correlated with UTT results when conducted at room temperature (RT, 25 ℃), and a Hall-Petch equation was derived. It was observed that the correlation equations for SPT were significantly influenced by brittle failures, resulting in relatively larger fitting errors. However, these SPT correlation equations proved effective in predicting total elongation compared to MIHT correlation equations and the Hall-Petch equation. The Hall-Petch equation exhibited the lowest average fitting error though limited by deformed grains. MIHT exhibited the strongest correlation with UTT, particularly in terms of yield strength and ultimate tensile strength. The three fitting methods have distinct advantages and shortcomings in characterizing the mechanical properties of Y and Si-added FeCrAl alloys.