Abstract: The high cycle fatigue fracture behavior of Al Al 3Ni in situ composites, with stress ratio R=-1, 0, ∞ respectively, was observed and investigated. It is shown in the fatigue specimens with R=-1 that microvoids are formed, linked up with each other and result in cracks growing along the interface zone in matrix preferentially, which is the controlling damage and failure mechanism. It is also found that the influence of stress ratio on the high cycle fatigue life and fracture process is very significant. For the fatigue specimens with R=0 ,the micro cracks are preferably growing in slip bands, and the fatigue life drops remarkably. For the fatigue specimens with R=∞ , however, the growth of micro cracks is concentrated in the deformation bands which are similar to those in compression, and the fatigue life is very high.

Key words: in-situcomposite fatigue, fracture stressratio, Al-Al3Ni