Nature of Surface Microcracks on Phosphorus Micro-Alloyed Copper

The effect of plastic deformation and environment on the appearance of surface microcracks on phosphorus micro-alloyed copper (Cu-OFP) was studied by tensile test, scanning electron microscopy and focused ion beam milling (SEM-FIB). Specimens tested in ambient conditions under tensile loading showed several thousand microcracks per mm², with maximum length in the range of 15–20 µm and maximum depth of about 3 µm. Increasing plastic deformation resulted in a larger number of microcracks. While specimens tested in water with 80 mg/L sulfide showed a much smaller microcrack density, with no indication of growth due to the presence of sulfides. Tensile testing of three different batches of Cu-OFP material showed similar results, suggesting that the results are batch-independent. These results indicate that surface microcracks form on Cu-OFP due to plastic straining both in air and in sulfide-containing water. Furthermore, this study demonstrates that, under the tested conditions, sulfide exposure does not promote microcrack propagation through stress corrosion cracking.