Compaction and development of green strength of powdered iron under severe shear deformation
摘要
The consolidation of iron powder was investigated using conventional methods (pressing and forging) and advanced processing routes involving a high shear component of severe plastic deformation, namely, asymmetric rolling and high-pressure sliding. A comparative analysis of the “green” strength of specimens produced by different techniques demonstrated the significant strengthening effect of shear deformation during densification. At room temperature, the “green” strength increased from 32 MPa for pressing and 48 MPa for forging to 82 MPa after asymmetric rolling. Additional roll pressing during asymmetric rolling further enhanced the strength to 218 MPa. High-pressure sliding yielded the highest green strength, strongly dependent on the initial porosity: 443.5 MPa at 27% porosity and 330 MPa at 13%. The influence of deformation temperature was studied for forging and asymmetric rolling specimens. Forged specimens exhibited strength growth with temperature, attributed to reduced yield stress of iron. In contrast, asymmetric rolling specimens showed non-monotonic behavior, with anomalous strengthening up to 1054 MPa at 100 °C, decreasing to 250–300 MPa at 200–300 °C, and rising again to 1200 MPa at 400 °C, linked to dynamic strain aging. TEM analysis confirmed nanocrystalline structures (0.3–0.5 μm) formed near boundaries under shear deformation, accompanied by partial loss of segregation films and nearly ring-shaped diffraction patterns, evidencing nanostructural states.
Graphical Abstract