Materials Science and Engineering A282 (2000) 38 – 48 Characterization and tribological evaluation of MW-PACVD diamond coatings deposited on pure titanium Yongqing Fu a, *, Bibo Yan a , Nee Lam Loh a , Chang Q.Sun b , Peter Hing b a Materials Laboratory, Schoolof Mechanical and Production Engineering, Nanyang Technological Uni6ersity, Singapore, 639798 , Singapore b Schoolof Applied Science, Nanyang Technological Uni6ersity, Singapore, 639798 , Singapore Received 31 May 1999; received in revised form 18 November 1999 Abstract Titanium alloys are widely used in aerospace and biomedical conditions, however, they are notorious for the poor tribolog properties. The deposition of a well adherent diamond coating is a promising way to solve this problem. In this study, diamond coatingsweredeposited on puretitanium usingmicrowaveplasmaassisted chemical vapour deposition (MW-PACVD). Characterisation of diamond coatings was performed using scanning electron microscopy (SEM), laser profilometry, Raman spectroscopy, grazing incidence X-ray diffraction (GIXD) and atomic force microscopy (AFM). Tribologicalpropertiesof diamond coatings were evaluated using a ball-on-disk wear tester (sliding with Al 2 O 3 balls)and a scratch tester (sliding with diamond pin). Results showed that the friction and wear properties of polycrystalline diamond coatings as well as the wear counterface were dependent significantly on the surface roughness, the morphology and crystalline structure of diamond c as wellas the counterface materials. For (111)-textured diamond coatings with rough surface and sharp asperities sliding with Al 2 O 3 balls,the coefficient of friction was much higher than that of (100)-textured coatings, and the wear ofthe counterface material was quite high. After polishing the diamond coating, the surface roughness, coefficient of friction and wear of coun decreased significantly. If sliding with diamond pins, the coefficient of friction of diamond coating shows a quite low and stable value.To improve the tribological properties, a three-step deposition method was proposed to obtain a smooth and nano-crys- talline diamond layer on bulk diamond coatings. The so-formed diamond coating showed the highest load bearing capacity, the lowest coefficient of friction and the lowest wear of the counterface. © 2000 Elsevier Science S.A. All rights reserved. Keywords : Diamond;MW-PACVD; Titanium;Tribology;Wear; Coefficient of friction www.elsevier.com/locate/msea 1.Introduction There are three main considerations for the selection of the biomaterials:(1) mechanicalproperties,i.e. Young’s modulus, fracture and fatigue strength, wear resistance and coefficient of friction,etc;(2) chemical properties,i.e. corrosion and fretting resistance; (3) biocompatibility with biological tissue and bone. Tita- nium alloys are widely used in biomedical area due to a good combination of mechanical properties, corrosion resistance and biocompability [1]. However,they are seldom used in tribological contactsituations,mainly because of their poor wear resistance [2]. The deposi- tion of a well adherent diamond coating is a promising way to solve this problem [3 – 6]. The extreme hardness and inertness, superior heat conductivity, good biocom- patibility,high abrasion, seizure and galling resistance of diamond coating may help to protect the titanium substrate [7,8]. However,there needs extensive work to be done before the successful application of diamond- coated titanium system. For example, the improvement of adhesion between diamond coating and Ti substrate [9,10]; the optimisation in the tribological performance of diamond coatings [11,12]; the need to sortoutthe controllingfactors determiningthe tribologicalbe- haviour of polycrystalline diamond coatings; the effects of the surfaceadsorbates; the reconstruction ofthe deactivated dangling bonds and the micro-graphitiza- tion on the friction and wear behaviour of the diamond coatings, etc. * Corresponding author. E-mail address : myqfu@ntu.edu.sg (Y. Fu) 0921-5093/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 9 9 ) 0 0 7 8 2 - 0