Effect of Sample Tilt and Normal Load on Micro-Scratch Test of Copper with a Spherical Indenter

Micro-scratch experiments were performed on copper with a spherical indenter, and the effect of sample tilt on the scratch response of copper under different constant normal loads was studied. The results showed that the experimentally measured nominal friction coefficient was linearly related to the sample tilt angle, with their slope being unaffected by the normal load. The geometrical model considering the positional relationship between the spherical indenter and the tilted sample was established. It was found that the inclination of the sample had no effect on the adhesive component of the nominal friction coefficient, and the ploughing component of friction coefficient linearly changed with the tilt angle. The friction coefficients can be corrected by a sphere-to-flat contact mechanical model for tilted samples, so as to obtain the true friction coefficients corresponding to the condition without tilting. There was a non-linear relationship between the friction coefficient and the normal load with the ploughing component increasing linearly with the normal load, while the adhesive component increased non-linearly and then gradually stabilized. The residual scratch width measured by the scratch topography was hardly affected by the tilt of the sample, and had a linear relationship with the square root of the normal load. The change of scratch hardness with normal load was analyzed, and the scratch hardness calculated from the residual scratch width was found to be a constant value, while the scratch hardness calculated from the projected contact area increased with normal load, and then gradually stabilized.