Abstract
An investigation has been made on the influences of pore filling with copper and the formation of alloy phase on the fatigue behavior of copper infiltrated sintered iron under completely reversed bending stress.
Iron skeletons with the density of 6.51 g/cm3 were prepared from electrolytic iron powder by means of compacting at 3.3 t/cm2 and sintering for 1 hr at 1150°C in hydrogen.
Subsequently they were infiltrated with copper powder compacts for holding time of 3 min (the short infiltrating time) and 123 min (the long infiltrating time) at 1130°C in hydrogen.
Results were summarized as follows:
(1) The fatigue strength of the iron skeleton infiltrated with copper powder compact remarkably increased with infiltrating time. This was considered to be caused by the effect of pore filling with copper and the strengthening effect due to the solid solution alloying of copper with iron.
(2) At the short infiltrating time, the fatigue cracks were initiated at the edges of the specimen, non-infiltrated pores and the multiple slip band in iron matrix, and then propagated at random through iron matrix and copper phase. While at the long infiltrating time, the main fatigue cracks preferencially propagated in linking of microcracks initiated at the iron-copper boundary.
(3) At the short infiltrating time, the remarkable pattern observed on fatigue fracture surface of specimen was striation, while at the long infiltrating time, was smooth fracture facet seemed to be fractured at the iron-copper boundary.
