Thermo-mechanical Deformation of Al319 - T7B with Small Secondary Dendrite Arm Spacing

Abstract

Thermomechanical fatigue and isothermal deformation experiments were conducted on cast Al 319 alloys with small secondary arm spacings (SDAS) in the range of 25 to 35μm. The alloy was studied in the overaged state designated as T7B. In the case of the T7B treatment the material possesses dimensional stability, but incurs considerable loss of strength with time and cyclic deformation at temperatures exceeding 250°C. A two-state variable unified constitutive model was developed to characterize the stress-strain response for the material. The model handles temperature and strain rate effects and captures the microstructurally induced changes on the stress-strain response. The thermomechanical fatigue response under in-phase (TMF IP) and out-of-phase (TMF OP) conditions was simulated and the material exhibited a decrease in the stress range by as much as 50% with continued cycling. The decrease in strength was attributed to the significant coarsening of the precipitates at high temperatures and was confirmed by transmission electron microscopy.

Interaction of thermally induced and mechanical fatigue

“…To predict the cyclic deformation behavior under thermomechanical fatigue conditions, models considering the microstructure, e.g. [26][27][28], as well as phenomenological approaches based on continuum mechanics [29][30][31][32] are used. The cyclic deformation behavior at critical locations of the component calculated by these methods is then used to predict a crack initiation lifetime.…”

Lifing the thermo-mechanical fatigue (TMF) behaviour of the polycrystalline nickel-based superalloy RR1000

“…Previous attempts to model TMF behaviour in the literature [1][2][3][4], especially in nickel based superalloys for disc applications, are quite limited. They do however, fall broadly into two categories; the first assumes that under strain controlled loading a significant fraction of the TMF life is spent in crack initiation and as such traditional approaches such as strain-energy partitioning, MansonCoffin [5] etc., can be applied [6,7].…”

An Empirical Approach to Correlating Thermo-Mechanical Fatigue Behaviour of a Polycrystalline Ni-Base Superalloy

“…Previous attempts to model TMF behaviour in the literature [ 1 , 2 , 3 , 4 , 5 ], especially in nickel based superalloys for disc applications, are quite limited. They do however, fall broadly into two categories; the first assumes that under strain control loading a significant fraction of the TMF life is spent in crack initiation and as such traditional approaches such as strain–energy partitioning, Manson-Coffin [ 6 ] etc ., can be applied [ 7 , 8 , 9 , 10 ].…”