Investigation of the microstructural properties and oxidation behavior of Fe-Ti-Cr based alloy

Ferritic alloys are potential materials for structural applications at high temperatures such as fossil fuel power plants due to their outstanding thermal conductivity, lower thermal expansion coefficient, moderate oxidation resistance and low material cost compared to Ni-based superalloys and austenitic stainless steels. However, their inadequate creep resistance at temperatures above 600 °C strongly hinders their potential applications. Several attempts such as alloy design and development have been performed in order to improve insufficient properties and service temperatures. In this study, the microstructures, phase relationships, hardness and oxidation behavior of model ternary Fe-10Ti-nCr (n= 4, 7 and 10 at. %) alloys were investigated in detail for as-cast and heat-treated states. The cast specimens were subjected to quenching after solutionizing (1000 °C for 1 h) and aging treatments (800 °C for 8, 16 and 24 h), respectively. The microstructures and phase relationships were investigated with scanning electron microscopy (SEM) and x-ray diffraction (XRD) techniques. The oxidation behavior were examined with cyclic oxidation tests carried out at 500 °C in laboratory air. The microstructures of the investigated alloys were composed of α-Fe matrix phase and Fe2Ti particles. For Fe-10Ti-4Cr and Fe-10Ti-7Cr alloys, fine Fe2Ti particles were distributed uniformly along the grain boundaries and within the grains of equiaxed and coarse α-Fe grains after aging treatments. The mean microhardness values were increased with increasing Cr amount and aging time. With increasing Cr amount, the oxide scale thickness and mass gain were decreased which implies the improved oxidation resistance. The surface oxide layer was Fe2O3 for investigated alloys. In addition, mixed Fe-Cr-Ti oxides were formed beneath the surface layer of Fe-10Ti-10Cr, containing the highest amount of Cr among investigated alloys.