Tribological Behavior of DLC Film in Aqueous Environment Se-Jun Park, Kwang-Ryeol Lee, and Dae-Hong Ko Korea Institute of Science and Technology, P.O.Box 131, Cheongryang, Seoul, Korea ICMCTF 2004, San Diego, USA

Delamination of DLC Coating Film Deposition

Applications of DLC Coatings to Bio-medical Implants UHMWPE Femoral Head Ti or Co Alloy Artificial Hip Joint (DLC coated)

DLC Coated Head after Service Courtesy of Dr. R. Hauert

The Problem of the DLC Coating DLC coated Ti-6Al-4V Sapphire ball :  6 mm F N = 400gf, v =10cm/s Test in saline solution Catastrophic adhesive wear 100 ㎛

The Previous Investigations D. Drees et al, Surf. Coat. Technol (1996) 575. H. Ronkainen et al, Wear 222 (1998) 120. The vulnerable structure of hydrogenate structure of a- C:H in aqueous environment A rapid increasing wear process The influence of load and electrochemical environment The transmission of load to the coating-substrate interface

Purpose of the Present Work Characterize the tribological properties of DLC films in aqueous environment. –Pure DLC & Si-DLC of various structures with different adhesion enhancement Figure out the reason for the catastrophic failure of DLC film in aqueous environment. –Some model experiments

Deposition of DLC Film on Ti-6Al-4V Alloys RF PACVD (13.56 MHz) Precursor gas : C 6 H 6, C 6 H 6 +SiH 4 Deposition pressure : 1.33 Pa Bias voltage : - 400V, -800V Substrate : Ti-6Al-4V Film thickness : 1 ± 0.1 ㎛

Design of The Coatings Ti-6Al-4V Alloy Coupon DLC or Si-DLC film (1  m) Si buffer layer 0.4, 0.8, 1.6 nm

Adhesion by Tensile Test (a) (b) (c) Si Layer Thickness H. W. Choi et al, to be published (2004).

Design of The Coatings Ti-6Al-4V Alloy Coupon DLC or Si-DLC film (1  m) Si buffer layer 0.4, 0.8, 1.6 nm

Properties of the DLC Films Sample Residual Stress (GPa) Hardness (GPa) G-peak Position (cm -1 ) Pure DLC (-400V) 0.9 ± ± ± 0.3 Pure DLC (-800V) 1.8 ± ± ± 0.3 Si-DLC (-400V) 1.3 ± ± ± 0.3

Tribo-Test in Aqueous Environment Sapphire ball to exclude the effect of FeO x debris Normal load : 5.9N Sliding speed : 10 cm/s Temperature : Room temp. Test environment : 1. DI-water 2. Ambient air (RH : 30 %)

Friction Coefficient Against Sapphire Ball V b : -400V V b : -800V b

Wear Scar Surface -400V b Si : 0.4 nm, air 100 ㎛ Si : 0.4 nm, water 100 ㎛ Si : 16 nm, water Si : 0.8 nm, water 100 ㎛

Wear Track after Tribo-test Si : 0.4 nm, air -400V b 100 ㎛

Wear Track after Tribo-test Si : 0.4 nm, air Si : 0.4 nm, water Si : 0.8 nm, waterSi : 16 nm, water -400V b 100 ㎛

Interface of the Adhesive Wear 100 ㎛

Design of The Coatings Ti-6Al-4V Alloy Coupon DLC or Si-DLC film (1  m) Si buffer layer 0.4, 0.8, 1.6 nm

Photographs of Wear Track Si : 0.4 nm, airSi : 0.4 nm, water Si : 0.8 nm, waterSi : 16 nm, water -800V b 100 ㎛

Tribological Behavior of Si-DLC 100 ㎛ Si Layer Thickness : 0.4 nm In Aqueous Environment

Observations Sum-up Adhesive wear becomes significant in aqueous environment. = The adhesion of the DLC film was degraded in aqueous environment. The behavior is not sensitive to the film structure. Si incorporated DLC film shows the improved stability than pure DLC films

Observations Sum-up Si : 0.4 nm, air Si : 0.4 nm, water 100 ㎛ -400V b

Observations Sum-up Si : 0.4 nm, air Si : 0.4 nm, water 100 ㎛ -400V b Si : 0.4 nm, airSi : 0.4 nm, water -800V b 100 ㎛

Why adhesive wear is accelerated in aqueous environment? Ti-6Al-4V Ti-6Al-4V Alloy Coupon DLC or Si-DLC film (1  m) Si buffer layer 0.4, 0.8, 1.6 nm

Why adhesive wear is accelerated in aqueous environment? Ti-6Al-4V Ti-6Al-4V Alloy Coupon DLC or Si-DLC film (1  m) Si buffer layer 0.4, 0.8, 1.6 nm Can residual stress vary in aqueous environment?

Why adhesive wear is accelerated in aqueous environment? Attack of water molecules through the pinhole or mico-pores in the film Ti-6Al-4V Ti-6Al-4V Alloy Coupon DLC or Si-DLC film (1  m) Si buffer layer 0.4, 0.8, 1.6 nm

Interfacial Damage via the Pinholes of the Film Courtesy of Dr. R. Hauert, EPMA

AES Depth Profile Soaking in water for 24 hours Ti-6Al-4V Alloy Coupon Auger analysis here ! Before Soaking After Soaking

Effect of Pinhole in the Film Patterned DLC film - Masking the substrate - Si-buffer layer : 1.6 nm - DLC coating : 1 mm - Remove Mask

Effect of Pinhole in the Film Patterned DLC film - Masking the substrate - Si-buffer layer : 1.6 nm - DLC coating : 1 mm - Remove Mask

Effect of Pinhole in the Film Patterned DLC film - Masking the substrate - Si-buffer layer : 1.6 nm - DLC coating : 1  m - Remove Mask Patternd DLC Coating Unpatterned DLC 100 ㎛

Defect-add a-C:H Patterned DLC 100 ㎛ Unpatterned DLC 100 ㎛

Effect of Pinhole in the Film Pinhole-free DLC film - Si-buffer layer deposition : 0.4 nm - DLC coating : 350nm - Ultra sonic cleaning - DLC coating : 350nm - Ultra sonic cleaning - DLC coating : 350nm DLC 100 ㎛

Effect of Pinhole in the Film Pinhole-free DLC film - Si-buffer layer deposition : 0.4 nm - DLC coating : 350nm - Ultra sonic cleaning - DLC coating : 350nm - Ultra sonic cleaning - DLC coating : 350nm

Effect of Pinhole in the Film Pinhole-free DLC film - Si-buffer layer deposition : 0.4 nm - DLC coating : 350nm - Ultra sonic cleaning - DLC coating : 350nm - Ultra sonic cleaning - DLC coating : 350nm Pinhole-free DLC

100 ㎛ DLC 100 ㎛

Electrochemical Properties E corr (mV) I corr (nA/cm2) B a (V/decade) B c (V/decade) R p (kohm/cm2 ) Porosity Protective Efficiency(%) Substrate a-C:H Pinhole-free a-C:H Si-DLC

Tribological Behavior of Si-DLC 100 ㎛ Si Layer Thickness : 0.4 nm

Which pinhole is significant? The same behavior in the DLC films of different structure  The pinholes are not attributed to the structure of the film.  a kind of macro-pinhole presumable due to the dust on the substrate Improved behavior in Si-DLC films  The pinhole is closely related to the deposition environment.  Dust formation during the initial stage of the plasma ignition.

Conclusions Defects or pinholes in the film is the main reason for the adhesive wear of DLC film in aqueous environment. –Water molecule seems to attack the interface between Si and Ti alloy substrate via the defects. Si-DLC film had better resistance in aqueous environment than DLC films. –Extremely low porosity of Si-DLC films Friction coefficient of DLC film was very low and stable in aqueous environment. –Lubricant effect of water.