Interface substrate-coating

Optimised LPPS parameters were plasma power of 30 kW, argon gas flow rate of 30 slpm, hydrogen flow rate of 4 simp, powder feed rate of 12 g min-1, chamber pressure of 60 mbar and stand-off distance of 220 mm. Immediately adjacent to the interface substrate-coating an approximately 0.1 pm thick interdiffusion zone developed in the Ti6Al4V substrate with elevated Ca, P and O contents followed by a thin layer of ACP and then by a layer of oxyhydroxyapatite (Ca/P 1.67) as ascertained by Raman spectroscopy (absence of the stretching vibration of OH-... 

Recent studies performed with deactivated anodes show [55] that electroless or electrolytic platinum deposition on failed anodes, not only lowered the polarisation behaviour of these anodes (see Fig. 5.20), but also demonstrated an equivalent lifetime as that of a new anode in accelerated life tests in the sulphuric acid solution (see Fig. 5.21). These results unequivocally demonstrate that the deactivation of anodes, for which the Ru loading is still high, is a direct consequence of the depletion of Ru from the outer region of the anode coating. Note that this process of surface enrichment by conducting electroactive species will not lead to reactivating a failed anode, if there is a TiC>2 build-up at the Ti substrate/coating interface. 

The initial decrease in ionic film resistance and Increase in capacitance can be associated with either NaCl electrolyte or water entry into the film. From ER measurements this period is associated with a metal loss process at the substrate surface. However, between 9 to 23 days the ionic film resistance increases, which is associated with an arrest in metal loss at the substrate surface in ER measurements. It appears, therefore, that with the knowledge of an underfilm darkening phenomenon occurring at the substrate/coating interface, a film of a protective (ie passive or high ionic resistance) nature is produced during exposure. 

Coating-substrate decohesion and formation of a condensed electrolyte at the interface Substrate corrosion... 

Coating life in moist atmospheres is also influenced by the effects of moisture on the substrate-coating interface, and marked improvements in life have been claimed by the use of moisture-protective pre-treatments of the substrate. Niederhauser et al ° studied a wide range of metals and titanium nitride, titanium carbide and chromium carbide as pre-treatments. The material was sputter-deposited on a steel substrate, and then sulphided by introducing hydrogen sulphide into the sputtering chamber in order to improve molybdenum disulphide adhesion. They found a marked improvement in life, particularly with a rhodium or palladium interlayer, but the actual degree of improvement is confused because they also used co-sputtered PTFE, and this is discussed further in Section 10.6. 

Where a molybdenum disulphide film has been formed on a surface in air, the nature of the interface between coating and substrate is not fully established, but it is probable that the initial adhesion, either chemical or mechanical, is preferentially at edge sites. This will inevitably result in discontinuities, flaws and gaps in the film adjacent to the substrate surface. 

When considering a ductile substrate coated with a brittle film and subjected to a uniaxial strain during loading and before debond of the film (perfect adhesion), the displacement is assumed to be continuous at the interface. Then, the substrate deformation is entirely transmitted to the film through the interface. When exceeding the critical cracking strain of the film, a network of transverse cracks develops. At the interface, each crack tip will be surrounded by a... 

The corrosion protection of plasma interface-engineered coating systems relies on the tenacious water-insensitive adhesion and good barrier characteristics of the coatings [3]. DC cathodic polymerization and plasma treatment have been demonstrated as efficient in improving the primer adhesion to metallic substrates. 

Consider an ordinary substrate-ceramic coating combination. Such a composite system, prepared at elevated temperatures and subsequently cooled to room temperature, will be thermally stressed due to the usually large difference in thermal expansion and elastic moduli of the substrate and coating. These stresses often exceed the fracture strength of the ceramic component, particularly in regions close to free surface near the interface. This leads to either cracking of the ceramic part or to failure at the substrate-coating interface. 

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