Microstructure and Properties of WB2/Cr Multilayer Films with Different Bilayer Numbers Deposited by Magnetron Sputtering

The influence of the bilayer number on the microstructure, mechanical properties, adhesion strength and tribological behaviors of the WB2/Cr multilayer films was systematically investigated in the present study. Five groups of WB2/Cr films with the same modulation ratio were synthesized by magnetron sputtering technique. The crystalline structure of the films was determined by X-ray diffraction. The morphologies and the microstructure of the films were observed by scanning electron microscopy, atomic force microscopy and transmission electron microscopy. Furthermore, Nano indenter, scratch tester and ball-on-disc tribometer were used to evaluate the mechanical and tribological properties. As bilayer numbers varied from 5 to 40, the hardness increased first and then decreased with the maximum hardness of 33.9 GPa when the bilayer number is 30. The H/E* and H3/E*2 values calculated to evaluate the fracture toughness showed the similar changing trend with hardness. The adhesion strength reached the maximum of 67 N when the bilayer number is 30. The surface roughness and friction coefficient decreased with increasing bilayer number. The wear mechanism was also investigated, and the results suggested that the multilayer film with bilayer number of 30 exhibited the best wear resistance (1.78 × 10–7 mm3/Nm), benefiting from the contribution of high hardness, fracture toughness and adhesion strength.