Damage mechanisms of a nickel alloyed sintered steel during tensile tests

Microscopic damage mechanisms of a sintered steel submitted to tensile stresses were studied. Specimens were prepared from diffusion alloyed Distaloy AE™ (Fe-4wt%Ni-1.5wt%Cu-0.5wt%Mo) mixed with natural graphite (0,8 wt%). The material average density is about 7.40. The initial microstructure was characterised both from phases (nature, quantity…) and porosity (volume fraction, size, aspect ratio, shape factor…) point of views. Monotonic in-situ tensile tests were carried out. The details of damage initiation, crack propagation and specimen failure were surveyed by light or scanning electron microscopy during the tests. Those observations and the fractographic analysis show that damage mechanisms are strongly dependant on the microstructure. Namely, the pore characteristics and their localisation in the material microstructure appear to be critical parameters.