Cylindrical billets are cut lengthwise on a 100 mm diameter billet and processed into equal-section samples with a working section diameter of 6 mm (see figure).
Thermomechanical fatigue and low cycle fatigue (LCF) tests were carried out on MTS 810 hydraulic servo fatigue tester.The precision of temperature control and strain control can reach 0.5% and 0.05% respectively.
The thermomechanical fatigue test is controlled by total strain with a strain ratio of R epsilon=-1.The temperature cycle ranges from 400 ~800 C and the cycle time is 100 s.Both load and temperature waveforms are triangular.Thermo-mechanical fatigue tests are in phase, i.e. when the load reaches its maximum, the temperature reaches its maximum (see figure).The compressed air is cooled by electromagnetic induction heating.
Before the test, three thermocouples are welded in the working section of the sample to measure the temperature. The specific method is as follows: using vanadium as solder, first melt the 0.3 mm diameter solder into three points on the surface of the standard distance section of the sample which is distributed in a straight line along the axis, with two 5 mm intervals between the three points.Three thermocouples are spot-welded to the vanadium spot welded with special clamps.The test was carried out in accordance with GJB6213-2008 Thermomechanical Fatigue Test Method for Metal Materials.
The low cycle fatigue test is controlled by total strain, the strain ratio R E=-1, the load waveform is triangular wave and the strain rate is 10-3s-1.The resistance furnace is heated and the test temperatures are 400 ~C and 800 ~C, respectively.The tests were carried out in accordance with GB/T15248-2008 Method for Axial Equal Amplitude Low Cyclic Fatigue Testing of Metal Materials.
After the test, the fracture surfaces of the samples under different test conditions were observed and analyzed by FEI Quanta 600 scanning electron microscope (SEM) to study the fatigue damage and failure mechanism of the alloy.