Ultra-high frequency vibration fatigue of DD6 single crystal superalloy simulating thin-walled specimens

Abstract

The effect of specimen thickness on the very high cycle fatigue （VHCF） properties of DD6 nickel-based single crystal superalloys for turbine blades with hollow air-cooled structure was investigated. Based on the finite element method （FEM）, a thin-walled vibration fatigue specimen with a thickness of 0.5 mm was designed with a natural frequency of 1425 Hz, which was a suitable test efficiency for VHCF test. The VHCF test was carried out by electrodynamic shaker at room temperature, and a VHCF S-N curve up to 109 cycles was obtained. Comparing with the rotational bending fatigue and vibration fatigue test data of conventional size specimens, the results show that the fatigue strength of DD6 single crystal superalloy continues to decrease after 107 cycles and the fatigue strength is decreased about 25%，from 107 to 109 cycles; The high cycle fatigue strength of the thin-walled specimen is basically the same as the standard rotary bending fatigue strength of the same material, and slightly lower than the conventional vibration fatigue strength. The cracks in the thin-walled specimen initiate on the surface of the dangerous section, showing the characteristics of line source. There are two propagation planes in the fatigue growth zone, showing the characteristics of cleavage like.

Keywords

• dd6 single crystal superalloy
• thin-walled specimen
• uhf vibration fatigue
• very high cycle fatigue s-n curve
• fracture mechanism