Multi-axial forging of Fe3Al-base intermetallic alloy and its mechanical properties

Tri-axial plane-strain forging was applied to the Fe–28Al–5Cr–0.8Zr–0.04B intermetallic alloy, in order to study its grain refinement and possible improvement in mechanical properties. The forging temperature range was from 20 to 600 °C. The maximum number of forging passes was 67. The deformed microstructure was investigated using electron backscatter diffraction in a scanning electron microscope. At forging temperatures <500 °C, the alloy was very prone to brittle cracking. At the temperature range of 500–600 °C, the overall plasticity of material increased and the cracking tendency was reduced but not completely eliminated. Extensive processes of dynamic recovery/recrystallization were observed during forging at 600 °C after 10–40 passes. Recrystallized areas with an average grain size of a few micrometers were observed. However, even after severe deformation at 600 °C, resulting from 40 forging passes ( ε ~ 11.3), dynamic recrystallization was incomplete and the fraction of low-angle boundaries was still high. The Vickers microhardness substantially increased from 280 HV0.1 to 450 HV0.1 at the center of the sample after both deformations at room temperature as well as after 20–40 cycles at 500–600 °C. However, a further increase of strain for a sample deformed at 600 °C after 67 passes ( ε ~ 28) led to quite a significant hardness decrease at the center of the sample. This phenomenon could be associated with the initiation of dynamic recrystallization. None of the samples forged at the 500–600 °C range exhibited any ductility improvement during subsequent tensile testing at room temperature, most likely, owing to the absence of a uniform ultrafine-grained structure developed during forging.