Abstract: Using arc ion plating， CrAlN coatings were deposited on high speed steels. The effects of the negative bias voltage on microstructure and properties of the CrAlN coatings were investigated through analyzing surface morphologies， microstructure， microhardness， adhesion strength and tribological properties. The results showed that with the increase of the negative bias voltage， the surface macroparticles reduced gradually and the coating became denser. However， further increasing the negative bias voltage over -200V， the ion bombarding was so strong that many defects reappeared on the coating surface. Therefore， the grain size reached a minimum value and the coating was well crystallized at the bias voltage of -200V. Moreover， it was found that the microhardness and adhesion strength firstly increased and then decreased with the increase of the negative bias voltage. When the voltage was -200V， the microhardness reached the maximum value of 28.6GPa and the coating performed the best tribological properties.

Key words: negative bias voltage, surface morphology, microstructure, mechanical properties, tribological properties