Acoustic emission in scratch processes of metals

A series of scratch tests were carried out on two metals: molybdenum (Mo) and tungsten (W). The scratch process described herein is defined as a mechanical deformation process: the diamond indenter moves across the surface of the specimen and a groove is formed. Different types of scratch damage are observed in different materials. The relationship between acoustic emission (AE) signals and scratch damage is examined. The results show that the typical AE signals from the scratch process of Mo are composed of continuous waveforms and bursts with high amplitude, but only AE bursts are observed in the scratch process of W. It is concluded that the detected bursts are generated due to the cracks and the continuous waveforms are generated due to the ductile tearing. In addition, the AE amplitude, RMS, kurtosis and mean frequency change with increasing applied load and scratch velocity in different ways. The results of the AE mechanism are also discussed, considering the stress, strain rate and temperature.