Fatigue and Microstructure of Iron Based Sintered Alloys

Direct metal laser sintering is a relatively new fabrication technique for near net shaped parts. It is for instance extensively used for die parts when making industrial forming tools. Another, yet more unexplored process is the starch consolidation method using environmentally friendly starch and water to shape components. A powder suspension is transformed into a green body by starch swelling and subsequent drying with sufficient strength to be handled and high vacuum liquid phase sintered. Here, it is used as a way to form high speed steels. Both methods are aiming to enable near net shaping of components subjected to wear, fatigue or thermal loads. Results presenting microstructure and mechanical properties are presented. In particular is fatigue strength and short crack growth in multiphase and low porosity sintered metal treated. The fatigue behaviour was shown to be related to the interaction of crack growth and complex layered structures, where crack initiation, growth and path are depending on porosity, microstructural barriers and crack linkage. Crack growth acceleration and retardation interacting with major barriers was a main feature in the bending fatigue tests.