Potential of thermal sprayed Ti_nO_2n‐1‐coatings for substituting molybdenum‐based ring coatings

Abstract

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 Magnéli‐types phases Ti₄O₇ (∼17 per cent), Ti₅O₉ (∼66 per cent), Ti₆O₁₁ (∼17 per cent) deposited by plasma spraying, a vacuum sprayed TiO_1,93 and a plasma‐sprayed titanium‐molybdenum carbo‐nitride 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_nO_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.

Citation

Landa, J., Illarramendi, I., Kelling, N., Woydt, M., Skopp, A. and Hartelt, M. (2007), "Potential of thermal sprayed Ti_nO_2n‐1‐coatings for substituting molybdenum‐based ring coatings", Industrial Lubrication and Tribology, Vol. 59 No. 5, pp. 217-229. https://doi.org/10.1108/00368790710776801