Investigation of PVD DLC Thin Films Manufactured using HIPIMS Etch/Unbalanced Magnetron Sputter (UBM) Deposition and Secondary Mechano-Chemical Modification

摘要

PVD Diamond-like-carbon (DLC) coatings find increasing industrial acceptance in automotive, aerospace and medical applications due to reduced friction and low wear coefficient. Very recently, High Power Impulse Magnetron Sputter (HIPIMS) sources have been shown to produce fluxes with very high metal ion fraction similar to that produced by arc evaporation sources, without showing excessive heating and droplet formation characteristics. These new source properties now enable industrial scale low temperature, low roughness and high efficiency etching of the substrate prior to deposition to deliver enhanced adhesion. We report on the properties and performance of HIPIMS etched titanium containing DLC (Me-DLC) and metal free (graphite based) C-DLC films deposited at temperature below 160°C. Prior to deposition, the coating-substrate interface was engineered using high substrate bias voltage closed field unbalanced magnetron enhanced Ar etch followed by metal ion etch using a single Cr HIPIMS source. The mechanical, tribological and physical properties of the coatings have been investigated using XTEM, dynamic micro-hardness, Scratch and Rockwell-C Adhesion, Raman microscopy and pin-on-disc tribological testing. 3.5μm as-deposited Me-DLC films showed hardness around 1000 HV, friction coefficient 0.15 and excellent adhesion (LC1～60N, LC2>140N). 2.5μm thick as-deposited C-DLC coatings exhibited significantly increased hardness to 3400 HV, extremely low friction coefficient (0.06), a shift in phase composition to high sp3 percentage, whilst maintaining very good adhesion following HIPIMS etch. XSTEM & EDX analysis across the coating-substrate interface showed distinct modification of the substrate through the use of a HIPIMS source. After deposition, selected Me-DLC coatings have been treated by secondary surface modification using a novel mechano-chemical method. SEM and nano-indentation investigations established that by applying mechano-chemical processing it is possible to change the microstructure of Me-DLC coating, increases hardness and decrease surface roughness without compromising friction or adhesion behavior. In particular a significant change in the film morphology has been observed and as a result the hardness of the films may be increased by up to 40%.