New understanding of the initiation of material transfer and transfer layer build-up in metal forming-In situ studies in the SEM

► A new in situ observation method for galling initiation studies was utilised. ► The test comprised a sharp aluminium tip sliding against a tool steel flat. ► Aluminium was immediately transferred onto fine polished tool steel. ► It was localised to the surface irregularities and slightly protruding carbonitrides. ► Intentional scratches resulted in large-scale transfer and high friction coefficient.