Wear behaviour of gradient-multilayer diamond coatings deposited on cemented-carbide substrates

HFCVD method was used to prepare and characterize single and gradient multi-layered diamond coatings on tungsten carbide. The wear behaviour was evaluated in ambient air, against Si3N4 ceramic balls. The results demonstrated that with the increase of carbon-source concentration from 1% to 5%, the diamond surface grains gradually refined and formed crystal clusters, and the roughness (Ra) of diamond surface decreased from 62.3 to 32.54 nm. Concerning the 100, 300, and 600 nm gradient of multilayer diamond coatings, the roughness Ra was 31.3, 35.6, and 40.5 nm, respectively. The diamond film obtained with 1% CH4 concentration exhibited poor wear resistance. For higher CH4 concentration, the abrasion resistance increased gradually. The average friction coefficient of multilayer diamond coatings decreased from 0.052 to 0.023 as the modulated layer thickness increased from 100 to 600 nm. The gradient multilayer structure significantly improved the tribological behaviour.