Structure, mechanical and tribological properties of HfCx films deposited by reactive magnetron sputtering

Hafnium carbide (HfC) films have been deposited on Si (1 0 0) substrates by direct current reactive magnetron sputtering. The microstructure, compressive stress, hardness and tribological behaviors show great dependence on carbon (C) concentration and chemical bonding state. With C content in HfCx films rising, phase transforms from hexagonal-close-packed (HCP) Hf(C) to face-centered-cubic (FCC) HfC, and nanocomposite structure consisting of HfCx nanocrystalline grains encapsulated by amorphous carbon (a-C) matrix forms at moderate C content. The hardness of HfCx films increases significantly from 10.4 GPa (14 at.% C) to 34.4 GPa (58 at.% C) and then keeps dropping with further increasing C content. a-C appears in HfCx films with more than 32 at.% C and it obviously lowers coefficient of friction (COF). The wear resistance can be remarkably worsened by high compressive stress. The film with 76 at.% C exhibits relatively high hardness and low compressive stress, good fracture toughness and self-lubrication transfer layer, showing great combination of the lowest COF of 0.10 and lowest wear rate of 1.10 × 10−6 mm3/Nm.