TY - THES

T1 - Coating development for piston rings

AU - Bachmaier, Andrea

N1 - embargoed until null

PY - 2008

Y1 - 2008

N2 - Piston rings are currently coated to improve their performance. Nowadays, a multitude of coatings are used, where CrN coatings deposited by physical vapour deposition represent the state of the art for highly-stressed piston rings. The aim of this work was the development of new coating concepts for piston rings based on an optimisation of the CrN-coatings in use, where the primary object was the reduction of friction and wear at elevated temperatures. For this purpose, porosity of the coatings has to be reduced and resistance against oxidation as well as abrasive wear must be enhanced. To increase the oxidation resistance and reduce the porosity, Cr1-xAlxN coatings with Al contents x <0.25 were deposited by reactive sputtering using a laboratory-scale unbalanced DC magnetron sputtering system. Once the ideal coating composition of Cr75Al25N was determined, Ag, Nb or Re were additionally alloyed to the coatings, in order to obtain self-lubricating properties and further increase wear resistance. The content of these elements was varied and their influence on the properties of the Cr75Al25N coating was evaluated. Structure, composition, mechanical properties as well as residual stresses of these coatings were determined and ball on disc tribometer investigations were performed at room temperature and 200°C. The results show that all tested coating systems represent better alternatives to the presently used CrN coatings due to improved wear resistance and oxidation behaviour at elevated temperatures.

AB - Piston rings are currently coated to improve their performance. Nowadays, a multitude of coatings are used, where CrN coatings deposited by physical vapour deposition represent the state of the art for highly-stressed piston rings. The aim of this work was the development of new coating concepts for piston rings based on an optimisation of the CrN-coatings in use, where the primary object was the reduction of friction and wear at elevated temperatures. For this purpose, porosity of the coatings has to be reduced and resistance against oxidation as well as abrasive wear must be enhanced. To increase the oxidation resistance and reduce the porosity, Cr1-xAlxN coatings with Al contents x <0.25 were deposited by reactive sputtering using a laboratory-scale unbalanced DC magnetron sputtering system. Once the ideal coating composition of Cr75Al25N was determined, Ag, Nb or Re were additionally alloyed to the coatings, in order to obtain self-lubricating properties and further increase wear resistance. The content of these elements was varied and their influence on the properties of the Cr75Al25N coating was evaluated. Structure, composition, mechanical properties as well as residual stresses of these coatings were determined and ball on disc tribometer investigations were performed at room temperature and 200°C. The results show that all tested coating systems represent better alternatives to the presently used CrN coatings due to improved wear resistance and oxidation behaviour at elevated temperatures.

KW - Kolbenring Hartstoffschichten Tribologie Verschleiß

KW - piston ring tribology hard coatings wear

M3 - Diploma Thesis

ER -