J. Singh, N. Sonti, Penn State University, University Park, PA

Summary:

Carburizing and hardening has been successfully used for decades to provide the desired strength gradient on tooth surfaces of transmission gearing to resist the applied loads experienced in service such as in aerospace and automotive applications. With increasing demand for higher power density, improved reliability and longer life, hard tribological coatings have been considered to improve gear performance and life. However, most attempts of applying hard coatings as add-ons after conventional carburizing and hardening have not been successful due to constraints imposed by prior processing, metallurgical state and service environment. When subjected to high combined rolling and sliding conditions typical to above gear applications, coatings have failed prematurely, unable to survive the high surface and near-surface contact stresses. The high processing temperatures involved in commercial coating techniques also result in over-tempering of the substrate and/or improper mismatch of the coefficient of thermal expansion.

In this paper, ongoing research at ARL Penn State University will be presented describing the efforts to explore the application of nano-structured, single/multi-layered coatings to produce functionally graded gear tooth surfaces in order to improve the strength and durability of aerospace transmission gearing. Proposed functionally graded coatings under consideration include Ti-TiN graded systems with varying levels of vanadium or niobium. The functionally graded nano-composite coatings will be deposited using ion assisted EB-PVD technique. Other processes including cathodic arc and sputtering configuration are also being investigated.