Effect of heat treatment on adhesion in the Cr/Al₂O₃ system

Continuous microscratch experiments have been carried out to investigate the effect of various heat treatments on adhesion in the Cr/Al₂O₃ system. After samples were prepared by vapor depositing 0.32 μm thick Cr films on (1102) surfaces of single crystal sapphire substrates, they were annealed at different temperatures at controlled oxygen partial pressures. In the subsequent continuous microscratch tests, a conical diamond indenter with a 1 μm tip radius was driven simultaneously into and across the sample until a load drop occurred. Optical and scanning electron microscopy observations demonstrate that a portion of the Cr film delaminated from the Al₂O₃ substrate at that point. The interfacial strain energy release rate was calculated from the load at failure combined with the size and geometry of the delaminated region. The work of adhesion was found to decrease dramatically on annealing in an H₂-Ar mixture at 250°C.