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

Hafnium carbide (HfC) films have been deposited on Si (100) 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 x 10(-6) mm(3)/Nm. (C) 2014 Elsevier B.V. All rights reserved.