Non-proportionally multiaxial fatigue behavior of A319 casting alloy: effects of strontium addition and hot isostatic pressing

Multiaxial fatigue behavior of A319 casting alloys has been studied with strontium addition and hot isostatic pressing (HIP). The tension-torsion fatigue tests were carried out by strain controlled under a circular loading path. Microstructure and fatigue damage was characterized and quantified using optical microscope and SEM together with image analysis. The experimental results indicated that the modified alloys with HIP treatment exhibited the best fatigue properties and the HIP-treated unmodified alloys were shown to have marginally lower performance. After HIP treatment, the areas of the torsional direction strain-stress hysteresis loops of both modified and unmodified alloys exhibited a significant decrease. Under non-proportional load conditions, different degrees of cyclic hardening occurred in all the alloys because of the influence of microstructures and casting defects. The degree of cyclic hardening in the torsional direction was more significant. Fractographic analyses revealed multiple crack initiations under multiaxial loading conditions. In general, HIP treatment presents more significant influence on crack initiate site while Sr modification of eutectic Si particles affects more on fatigue crack propagation. (paper)