Potential of thermal sprayed Ti{sub}nO{sub}(2n-1)-coatings for substituting molybdenum-based ring coatings

摘要

Purpose - This paper aims to focus on the potential for substituting molybdenum-based piston ring coatings, which are recognized as "allrounder" by other candidate metallurgies. Another purpose is the tribological interaction of molybdenum-based and new triboactive/reactive piston ring coatings with low SAP, polymer- and metal-free as well as bionotox engine oils with high-viscosity indices. Design/methodology/approach - Substoichiometric titanium dioxide composed of the Magneli-types phases Ti{sub}4O{sub}7 (～17 per cent), Ti{sub}5O{sub}9 (,66 per cent), Ti{sub}6O{sub}11 (～17 per cent) deposited by plasma spraying, a vacuum sprayed TiO{sub}1,93 and a plasma-sprayed titanium-molybdenum carbonitride coated piston rings were compared to a state-of-the-art molybdenum-based piston ring. They were tribologically characterized by means of BAM and SRV tests lubed under mixed/boundary lubrication by factory fill engine oils, engine oils as blends of hydro-carbons with esters as well as prototype engine oils based on esters and polyglycols. Findings - Overall, the molybdenum- and titanium-based ring coatings wore in the same order of magnitude. The ranking depends on the test used. The BAM test favours MKP81A (PL72) more, whereas the SRV methods favour the Ti{sub}nO{sub}(2n-1) more. The different bionotox and low-ash prototype engine oils with reduced additive contents displayed isoperformance regarding the tribological behaviour of common and triboreactive materials. They presented no visible weakness in wear resistance, coefficient of friction and extreme pressure properties. Research limitations/implications - The next steps have to confirm functional properties by different engine and endurance tests. Practical implications - Titanium-based piston ring coatings are overall more attractive, as they are primarily refined from titania, which is cheap and not rated at stock exchanges, and they present at least an isoperformance when compared with molybdenum-based ring coatings. Originality/value - This supplier report displays the complete methodology in order to substitute molybdenum- by titanium-based piston ring coatings as well as illuminating the beneficial interaction with alternative engine oils in existing engine architectures.