Increasing the operating temperatures of gas-turbine engines in pursuit of greater efficiency has led to higher rates of hot corrosion of critical Ni-based superalloy components. However, the design and environmental factors that lead to this hot corrosion are not well-understood. Frequently, engines would be in for minor service only to have hot corrosion unexpectedly discovered. This seriously degrades the readiness of air platforms and increases operation and maintenance costs.
A team composed of researchers from Elder Research, Southwest Research Institute, the University of Virginia, and Rolls-Royce created HOTPITS: a modular, physics-based framework for predicting and simulating the hot corrosion of Ni-based superalloy components. The HOTPITS framework predicts:
- The “active state” required for hot corrosion based on engine design parameters and environmental factors
- The rate of pit incubation on Ni-based superalloy parts
- The rate of pit growth
- The transition of corrosion pits to fatigue cracks
Although initially developed for Ni-based superalloy systems, HOTPITS can be redefined for any material system and is being enhanced to model the effects of coating materials. A schematic of the hot corrosion prediction methodology is shown below:
HOTPITS was successfully validated against laboratory experiments at the University of Virginia. This Phase II success led to this team being awarded NASA’s first ever Sequential Phase II STTR. During this ongoing program, our team showed that the HOTPITS active state module successfully indicated when hot corrosion was observed in fielded engine performance data from across several historical and current engines at Rolls-Royce. This program is scheduled to end in August 2021, and the primary outcome will be an enhanced implementation of HOTPITS in the DARWIN probabilistic lifing tool for use by gas turbine engine OEMs.