Fatigue properties of tungsten from two different processing routes

Fatigue failure is a distinct possibility in spallation targets like tungsten, subjected to cyclic thermo-mechanical loading caused by beam trips and beam pulses. In this study, the tensile and fatigue properties of pure tungsten from two different processing routes have been determined at room temperature. The specimens tested were sintered, rolled and annealed (RA), as well as sintered and HIPed tungsten (SH). Tensile tests showed low total strain (∼0.25%) and negligible plastic strain for both specimens. However, the UTS for rolled specimens (∼1 GPa) was much higher relative to the HIPed material (567 MPa). As tungsten is very brittle, fatigue testing was done primarily under stress-control, using the staircase method and a near zero stress ratio. For the rolled and HIPed materials, fatigue limits (no specimen failure up to 2⋅10⁶ load cycles) were determined to be 350 MPa and 180 MPa, respectively. In addition, results from strain-controlled multiple-step testing (strain ratio ∼0) indicated a slight relaxation in stress for the HIPed material while the rolled specimens showed a purely elastic response. The implication of fatigue test results for spallation target design is discussed.