Effect of Structural Refinement on the Mechanical Properties of Fe–28 Al Intermetallic Alloy Produced by Direct Powder Forging III. Development of High-temperature Consolidation Route for Fe–28 Al Iron Aluminide for Dynamic Recrystallization Conditions
摘要
A high-temperature consolidation route based on direct powder forging under dynamic recrystallization conditions was developed. An original die design was proposed to enable plastic deformation in a closed die cavity through controlled displacement of a flash layer. Using the DEFORM 2D/3D software package, the optimal conditions for the dynamic recrystallization mechanism were identified as three deformation steps at a temperature of 1150–1200°C. After each forging step, the cross-sectional density, strain intensity, and distribution of radial strains were calculated. Under the optimal process conditions for dynamic recrystallization, iron aluminide samples produced from powders with different initial morphologies were forged. For unground iron and aluminum powders, recrystallization resulted in clean grain boundaries, locally decorated with fine particles. Fracture proceeded via a transcrystalline mechanism. The bending strength reached 1220 MPa. For ground iron and aluminum powders subjected to deformation processing, anisotropic grains with an average transverse size of ~2 μm were observed. No continuous segregation layers were present at the grain boundaries, and a large number of fine particles (<0.3 μm) were found. In this structural state, the bending strength increased to σb = 1835 MPa. For composites with a presynthesized Fe3Al matrix reinforced with boride particles, triple forging at 1150°C produced a superfine structure. The grain size was estimated at 2–3 μm, and the average boride particle size was 50–100 nm. In the samples doped with 0.6 vol.% chromium boride, the room-temperature strength reached 2029 MPa with nearly 3% ductility and a fracture toughness of 48.6 MPa · m1/2, which was higher than in all the above cases.