Application of full-surface view in situ thermography measurements during ultrasonic fatigue of cast steel G42CrMo4

• Full-surface view in situ thermography investigations were performed on cylindrical fatigue specimens at ultrasonic loading conditions.
• The results from full-surface view in situ thermography measurements were correlated to fractography using the scanning electron microscope.
• Full-surface view in situ thermography measurements were combined with the in situ analysis of the resonant frequency and the non-linearity parameter.
• Crack initiation due to single and clustered non-metallic inclusions in cast steel G42CrMo4 was studied.
• The functionality of a novel spinel-coated metal melt filter was investigated by ultrasonic fatigue testing and subsequent scanning electron microscopy.

In the present investigation a full-surface view in situ thermography method is adapted to an ultrasonic fatigue testing system. Full-surface view in situ thermography measurements were successfully performed in the high cycle fatigue and in the very high cycle fatigue regime on cast steel G42CrMo4 in the quenched and tempered state. The method enables the monitoring of the entire cylindrical specimen circumference during fatigue testing by infrared temperature field measurements with one thermocamera and two mirrors. Moreover, by correlating fractography and thermography the precise determination of the location of the crack initiation site and the time of final crack growth is possible. The technique is applied to study crack initiation at non-metallic inclusions in the investigated cast steel specimens. Moreover, the effect of a novel carbon-bonded metal melt filter coated with a functionalized spinel (MgAl2O4) coating is evaluated by ultrasonic fatigue testing in combination with the full-surface view in situ thermography technique and subsequent scanning electron microscopy.