Study On Microstrucutre And Mechanical Properties Of Powder Metallurgy Iron-based Superalloy

Oxide dispersion strengthened (ODS) iron-based alloys are the most promising class of materials with a potential to be widely used in aerospace and nuclear industry owing to superior properties in tensile performance, creep property and neutron irradiation-resistance at high temperatures. In this investigation, Fe-14Cr-3W-0.4Ti-0.3Y (wt.%) ferrite alloy was fabricated by close-coupled gas atomized and ball milling powders via hot extrusion, hot rolling and annealing. Microstructure and mechanical properties of these powders and alloys were investigated by means of chemical analysis, laser particle sizing, metallographic analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical testing such as micro-hardness and tensile testing. The main results can be summarized as follows:(1) The close-coupled gas atomized and ball milling powders existed single ferrite phase, and no oxides existed.The alloys prepared by gas atomization existed single ferrite phase after hot rolling and annealing at different temperatures. The alloy prepared by ball milling powders existed new oxides, such as Cr2O3、(Fe,Cr)2O3、YTi2O6and Y2Fe4O9, except ferrite.(2) The slender grains in the two alloys fabricated by gas atomized powders changed to equiaxed grains after annealing. As annealing temperature increasing, the recrystallized grains coarsen. In the microstructure of alloy fabricated by ball milling powders existed larger grains with preferred orientation and small equiaxed grains. After annealing, the distribution of equiaxed grains became homogenization.(3) Tensile strength and total elongation at room temperature of alloys fabricated by gas atomized powders were410-470MPa and26%-39%, respectively. Tensile strength decreased at550℃and650℃. As annealing temperature increasing, the tensile strength showed W-type changes. The main fracture character was ductile fracture, some cleavage surfaces also existed.(4) Tensile strength of the alloy fabricated by ball milling powders was 2.6times as the tensile strength of the alloys fabricated by gas atomized powders. The tensile strength and total elongation at room temperature were1032.57～1601.18MPa and0.25%-2.5%, respectively. Tensile strength at550℃was similar as room temperature. Tensile strength at650℃decreased severely. As annealing temperature increasing, the tensile strength increased. The fracture character was cleavage fracture. Oxidation of the fracture existed as tensile temperature increased.