Impact fracture toughness of porous alloys between room temperature and −60°C

A study has been made of the impact deformation and fracture behaviour between room temperature and −60°C of porous iron and a porous heterogeneous Fe-Ni-Cu-Mo-C alloy, both produced by powder metallurgy. Unnotched as well as sharp notched specimens (in order to obtain impact fracture toughness data) were tested. In the case of porous iron, the main contribution to the total absorbed energy for the unnotched specimens arose from the energy for plastic bending and the total absorbed energy was found to decrease as the testing temperature was decreased. On the other hand, the impact fracture toughness was found to increase as the testing temperature was decreased. The heterogeneous Fe-Ni-Cu-Mo-C alloys showed a decrease, as testing temperature was decreased, both in the total absorbed impact energy, in the case of unnotched specimens, and in the impact fracture toughness. All these results were interpreted on the basis of a process zone model, making reference to the particular deformation and fracture mechanisms.