Rolls-Royce extends partnership
This Rolls-Royce North American Technologies USA sponsored research on "Microstructural Investigation of Environmentally Assisted Crack Growth" focuses on developing a fundamental understanding of the role of the structural and compositional instabilities that occur during microstructural evolution, and how they influence the environmentally accelerated damage processes in nickel-based superalloys.
As jet engine manufacturers intensify their efforts to increase the operating temperature of turbine alloys above 700°C, concerns about the corrosion caused by oxygen and sulfur are moving to the forefront. Improving the operating temperature of disk alloys by only 25°C would translate into approximately a 10% increase in aircraft engine efficiency, resulting in cost savings of billions of dollars and reduction of CO2 emissions for a fleet of aircraft during their service life.
“The reduction in fatigue life at these punishing high temperatures is primarily caused by the absorption of oxygen into the materials, making them fail prematurely,” Viswanathan added. The oxygen-induced damage is often also accentuated by the deformation caused by the creep-fatigue processes occurring simultaneously with the environmental damage. “This damage can only be mitigated if we understand where it causes changes to the local microstructure, in places such as grain boundaries, and at the relevant length scale.”
The kind of state-of-the-art instrumentation needed for this research is available at CEMAS.
“The aberration corrected Titan 60-300 kV (S)TEM microscopes, for example, are equipped with image Cs correctors, a monochromator and ChemiSTEM technology, and an ultrahigh resolution EELS spectrometer, and provide unparalleled capabilities for materials characterization down to sub-Ångstrom levels,” Viswanathan said. “It is the objective of this of research program to use these state-of-the art capabilities in CEMAS and other testing facilities in Ohio State’s Department of Materials Science and Engineering and to capture, assess and develop accurate descriptions of the early stages of environmentally induced damage buildup in Ni based superalloys, and so develop solutions for mitigating or minimizing damage accumulation. The mechanisms that will be investigated in detail are expected to have far-reaching implications for the understanding of the creep-fatigue-environment effects on fatigue life in aero engine alloys, and consequently are expected to impact alloy development and thermo-mechanical processing of the next generation of alloys.
Joining Viswanathan on the project will be Materials Science and Engineering Professor Mike Mills. Based on efforts in the last two years, Rolls-Royce has also added support for computational modeling work to complement experimental results. Maryam Ghazisaeidi, an assistant professor in materials science and engineering, will spearhead the modeling efforts on the project.