抄録
The melt-sintered Al-Al2O3 dispersion-strengthened alloys have been fatigued in plane bending at strain amplitudes leading to fatigue life of about 106 cycles. Before testing, specimens were annealed at different temperatures in order to cause various states of microstructure. Optical, replication and transmission electron microscopy techniques were used to study the effects of microstructure on fatigue properties from a metallurgical point of view. It was found that the microstructure influenced the deformation mode and the nature of microcracking. In the specimens annealed at 373K subsequent to cold rolling, fatigue damage was characterized by microcracking along the boundaries of cells (less than 1μm in average diameter) introduced during the heat treatment. No dislocation cell structures produced by cyclic deformation were observed even in the vicinity of the fatigue crack. Only in some cells, many small dislocation loops were observed as a dislocation structure characteristic to cyclic stressing, although total dislocation density was not so high as those estimated for other metals. The fatigue deformation concentrated on the cell boundaries preferentially. In the specimens annealed at 773K, where recrystallization occurs, ill-defined cell structures were formed on a finer scale around fatigue cracks. Microcracking occurred in slip bands. The dispersed Al2O3 particles appear to improve fatigue strength due to the decrease in cell size and to their interaction with dislocations within cells.
These results are discussed in comparison with those of pure aluminium.
