The fatigue behavior of fine grained two-phase alloys

Abstract

The fatigue properties of a number of ultrafine grained two-phase alloys have been examined. Compositions and processing treatments were altered to produce volume fractions of the individual phases ranging from 0 to 100 pct along with changes in the grain sizes of the individual phases. In all two-phase alloys in this investigation, the second phase was distributed at grain boundaries rather than within the grains of the primary phase. The fatigue strengths of the two-phase microduplex alloys were generally higher than those of the corresponding single phase alloys. Tension-compression fatigue tests showed that a Coffin law type of fatigue relationship was obeyed in the low cycle fatigue tests. Fatigue crack growth rate studies in tension-tension on IN-744 sheet gave results very comparable to those reported for other steels. Fatigue cracks propagated through both phases without following any obvious crack paths and no indication of delamination or crack blunting was detected. The high cycle fatigue performance of microduplex alloys can be rationalized in terms of a critical crack opening displacement model for fatigue crack initiation.