http://www.123seminarsonly.com/Seminar-Reports/2013-04/80827267-Coatings-tribology-contact.pdf

Coatings tribology—contact mechanisms and surface design

Analysis of coating fracture and substrate plasticity induced by spherical indentors: diamond and diamond-like carbon layers on steel substrates

Initial evidence showed that soft substrate materials (such as Ti–6Al–4V alloy) might not be able to provide adequate support for hard DLC films, adversely affecting their tribological performance and durability. An innovative concept in the development of advanced tribological systems involves coatings with a functionally-graded interface (FGI). This concept was experimentally studied in the present work by developing a model system involving DLC coatings with FGI based on theoretical finite element analysis (FEA) predictions. It was found that the durability of the DLC film is affected by the presence of the FGI and the loading level. Under low loading, FGI has a small effect due to the limited yielding occurring in the substrate. Under high loading conditions, the presence of FGI produced significant improvements (∼80% increase in coating lifetime). In view of the FEA predictions, these effects can be attributed to reduction of the plastic zone size and prevention of yielding at the coating/substrate interface.

Tribological behavior of DLC coatings with functionally gradient interfaces

The initial yielding behavior due to the indentation and friction process between an elastic cylindrical surface and hard coating/functionally graded substrate system is analyzed by finite element modeling. A thin hard DLC film deposited on a soft Ti-6Al-4V alloy substrate is considered as a model system. Two functional gradient substrate conditions are considered: (i) a gradient in yield strength and (ii) a gradient in elastic modulus. In both cases, appropriate gradients result in significant benefits to the reliability of the coated system compared to the case of an ungraded substrate. The results indicate that systems with an appropriate gradient in yield strength: (i) can withstand significantly higher applied contact stresses (3-12 times higher for the present model system), (ii) shift the location of the initial yield point deeper into the substrate (at least by a factor of 2 for the present model system), and (iii) can use coatings of greater thickness. Finally, the results indicate that an appropriate gradient in elastic modulus results in a dramatic reduction in equivalent stress on the contact surface and at the interface as compared to the ungraded case. The present results suggest distinct benefits to the durability of coated systems when using a substrate with functionally graded properties.

Finite element analysis of the initial yielding behavior of a hard coating/substrate system with functionally graded interface under indentation and friction

Diamond-like carbon (DLC) coatings have shown excellent tribological properties in laboratory tests The coatings have also been introduced to several practical applications However, the functional reliability of the coatings is often weakened by adhesion and load-carrying capacity related problems In this study the load-carrying capacity of the coating/substrate system has been evaluated The DLC coatings were deposited on stainless steel, alumina and cemented carbide with two different deposition techniques: the tetrahedral amorphous carbon (ta-C) coatings were deposited by a pulsed vacuum arc discharge deposition method and the hydrogenated carbon (a-C:H) films by radio frequency (rf) plasma deposition method The load-carrying capacity of the coated systems was evaluated using a scratch test, Rockwell C-indentation test and ball-on-disc test The effect of substrate material, substrate hardness, coating type and coating thickness was studied An increase in substrate hardness increased the load-carrying capacity for the coated systems, as expected The two coating types exhibited different performance under load due to their different physical and mechanical properties For the load-carrying capacity evaluations the ball-on-disc configuration was found to be most suitable

Kato Koji

Papers

Interface yield map of a hard coating under sliding contact

Spalling mechanism of Al2O3 ceramic coating coated WCCo substrate under sliding contact