Effect of Pore Size on the Precipitation of Iron-Rich Phase and Impact Toughness in Copper-Infiltrated Steel

The pore size plays a crucial role in both the copper infiltration behavior and mechanical properties of powder metallurgy sintered steel. Previous studies have explored this aspect, but accurately replicating pore size channels in real sintered steels using conventional micro-channeling methods remains challenging. This research utilized femtosecond laser technology to create single aperture channels with equivalent capillary radii ranging from 2.5 to 15.37 μm for copper infiltration. In conjunction with copper-infiltrated sintered steel prepared via powder metallurgy, the study examined the effect of iron-rich phase precipitation on impact toughness. The results indicate that copper infiltration enlarges the pore size in the single pore channel. No aggregation of iron-rich phase precipitation was observed in areas where the copper region size was below 6.20 μm in equivalent radius. Conversely, petal-like iron-rich precipitation was observed in areas with copper region sizes exceeding 6.20 μm in equivalent radius. For sintered steel prepared by powder metallurgy, after copper infiltration, the sample with a larger pore size (3.81 μm) showed a pronounced improvement, achieving 65.02% of the large copper region and significantly increased impact toughness from 11.71 J/cm² to 41.09 J/cm², attributed to significant precipitation of iron-rich phases that enhance material toughness. In contrast, the sample with a smaller pore size (2.87 μm) had an area of large copper region amounting to only 6.73%, showing a lesser increase in impact toughness, rising from 28.41 J/cm² to 38.21 J/cm², due to reduced precipitation of iron-rich phases and an increase in secondary cracks on the fracture surface, leading to lower impact toughness compared to the sample with a larger pore size.